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Solar Powered Iphone

06/27/2011 7:37 PM

Hello dear electrical engineers community! I am a mechanical engineer with basic knowledge in electricity. I think starting here for my small project is a good idea.

I want to build myself a small Iphone charger with 2x 12V-125mA solar panel. Actual Iphone charger is rated 5V-0.5A. I would like to drop the voltage without losing any power because the output of both panel is only a little higher than the needed input of the Iphone.

I do not have any specific questions and I do not expect CR4 to realise the project for me... I would only like to hear some advice about the way to obtain right voltage and current output out of these panels. Perhaps an amplifier? This is my first "solar power project", so I would like to receive some relevant infos/links/documents from you guys.

Thanks a lot, have a good day!

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#1

Re: Solar Powered Iphone

06/27/2011 9:52 PM

Your panel puts out 125ma. Your phone takes .5 amps, AKA 500ma. Your panels only produce 1/4 of the power. How do you see your panels as putting out more power?

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#2

Re: Solar Powered Iphone

06/27/2011 10:43 PM

Your 12 volts solar panel has already cells in series. Check if you can "split" the voltage eg. in 4 times 6 volts. That is way closer and if you can connect in parrallel then, you'll have your 0.5 amps when the sun shines. Do you call permanently? I suppose you don't need to charge permanently either. If you look around, you will find solar panels in different voltages too.

Now as far as the charger, you can try to hack into the regulator of the existing one, so that battery and charger are a match.

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#3

Re: Solar Powered Iphone

06/28/2011 4:15 PM

There are NiMH battery charger chips available that will take a 12V solar panel input and provide a regulated 5V 0.5A output. Try an internet search of "NiMH battery charger controller".

As for the solar panels, they should work, however they will need to be in direct sunlight to provide the necessary minimum power to charge the cellphone battery, if the output current falls below the minimum required for charging the battery (for example the solar panels are in the shade or a cloud pass in front of the sun) then the battery will (likely) stop charging until the current rises again. This may result in a very long recharge time and potential reduction in battery life.

You may need more or larger solar panels for this particular project.

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#4
In reply to #3

Re: Solar Powered Iphone

06/28/2011 4:22 PM

or...he could just get an old USB cable and sever it in the middle somewhere. Strip the shielding back. Locate the red and black wires (+ -). Reconnect those together and he will get the 5V he needs and not worry about azimuth or clouds.

But that sounds too easy and it's cooler to walk around with solar panels you set up while you're eating lunch.

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#7
In reply to #4

Re: Solar Powered Iphone

06/28/2011 8:47 PM

It is do-able with a USB connection, however it wouldn't really be a project, or portable for that matter. You would be better off using the phones battery charger.

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#13
In reply to #7

Re: Solar Powered Iphone

06/29/2011 6:21 AM

I know. I was just showing off my vast knowledge of ways to get 5 volts

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#5

Re: Solar Powered Iphone

06/28/2011 4:51 PM

You know that they make these already right? So we can assume then that you want to "roll your own" just for fun or to prove you can?

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#6

Re: Solar Powered Iphone

06/28/2011 6:15 PM

Fredski, 2 panels 12V x 0.125A = 3 W, while 5V x 0.5A =2.5W. You probably misread the info.

Panels are riveted so I wouldn't open them to split them. They also seem to be single pieces so splitting them or changing the included regulator would be last resort's plan.

I like the idea of having a battery charger controller. This way, panels' 12V could be used to fill a battery, and if this battery's output isn't 5V, I could use a DC-DC regulator to charge the phone with the right output.

This project is for fun and I know buying an already made device would the best solution for someone who really needs that, but I don't. I just want to work on something to be proud of it at the end. I'll be fishing for a week with some friends, and their cellphones will run out of power... Taunting them with my solar powered phone will satisfy myself deeply hehe. In this optic, it would be stupid to ruin my Iphone's battery for some little "geek funny project".

It will be important that I test the device to know if the output is right before plugging the Iphone on it, but how could I simulate the load on that experimental circuit? I know theory about electric circuit - kirchkoff laws and stuff, but didn't have the opportunity to get some practical experience in various situation.

thanks.

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#9
In reply to #6

Re: Solar Powered Iphone

06/28/2011 11:49 PM

Nice project but take your time to plan and learn. You should use batteries to be charged by the solar panels, serving as buffers when the sun aint so bright. Look at DigiKey for DC-DC converters, I got a small board ($25) that can step up and down (called buck-boost) something like 2V to 20V and bring it to 5V 1A with 90% or so efficiency. Just need to buy a USB a receptacle (at DK) and solder properly. Surge current when connecting your phone may be higher than 500mA, fully discharged. I got this board to build an AA battery pack to use while traveling, some bought packs state 5V at 1A but just dont deliver if the phone is below 85%, even with fresh batteries...

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#8

Re: Solar Powered Iphone

06/28/2011 11:30 PM

Do you have the car charger for your iPhone, it will convert 12 volts to the 5 volts you need. Either solder it directly to the solar panel leads or buy a cigarette lighter receptacle from an automotive parts store to connect to the solar panel leads.

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#10

Re: Solar Powered Iphone

06/29/2011 12:15 AM

You need to understand the basics of Solar panels, then it all makes sense. A 12v oc solar panel will only charge a 6 volt battery. It is 12 volts OPEN CIRCUIT voltage, (That means at ZERO current). 125mA refers to the MAXIMUM current at SHORT circuit, (That means at ZERO voltage), in a Laboratory, at maximum Sunlight conditions, at 25C surface temperature. To charge a 12v battery the panel would need to be 22Volts open circuit. If the phone battery is 4.5 volts you need a 9Voc PV panel.

So the watts is NOT the Voc X Isc. Solar panel watts peak are not the output watts.

If you connect your panel direct to your battery, the panel voltage will drop to the battery voltage. In direct Sunlight, perpendicular to the Sun the panel will heat above 25C and output will be around 80mA (if it is a Thin Film PV panel it will be 110mA) at battery voltage. As the battery begins to charge the voltage will rise. You MUST stop the charging when the voltage reaches maximum for your battery or the battery indicates full charge.

An MPPT unit is a gadget that drops the voltage and increases the current. It has no advantage on charging a battery with the correct size solar panel but if you have the wrong size panel then the MPPT can save loss of energy from too high a voltage panel.

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#11

Re: Solar Powered Iphone

06/29/2011 4:10 AM

Your phone needs 2.5watts

You have available 3 watts from the panels (when working at full pitch, a third panel may be a good idea!).

That's a bit tight I feel with 2 panels, but you could buy a DC to DC converter that takes the available power and drops it to 5 volts.......if its efficient it should be OK.

Here are a couple of links that may help you further:-

http://www.mornsun-power.com/de/index.html?gclid=COilwYbU2qkCFYEo3wodmRYyZw

and a reasonable explanation is here:-

http://en.wikipedia.org/wiki/DC-to-DC_converter

Best of luck.

PS. I just read that PatNV basically said the same thing first!! But without the links!!

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#12
In reply to #11

Re: Solar Powered Iphone

06/29/2011 4:47 AM

Watts is not relevant when charging a battery. AMPERES will charge the battery. Also note that the panels will probably never give full output outside its laboratory conditions.

Example: if you have a 35 watts peak PV panel, giving 18watts panel output at mid day, (1 amp at 18 volts), charging a 12v battery. If this is constant for 1 hour, then you have 1 amp hour, charged into your battery from a 35wp solar panel. You get back 12v 1 amp, (12 watts) minus battery losses.

If the 35wp PV panel is giving the same 18 watts out at 36 volts 0.5 amperes then you only get HALF the charge into the battery. 36v goes IN but only 12v comes out of a 12v battery. 12v 0.5 amps (6 watts) out.

Don't calculate in watts. Use the amp hours in your calculation.

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#14
In reply to #12

Re: Solar Powered Iphone

06/29/2011 9:48 AM

Paulmil,

I tried to cancel your "off topic" vote, but I'm not sure it worked. I also tried to give you a "Good Answer" vote, and I'm not sure that worked either. Oh, well!

I have done extensive research on solar power installations and you are "right on." No one else comes close. Always use the amp hours when doing calculations for your battery charging.

You must have experience in this field?? I'll look for you when I have questions.

VM

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#16
In reply to #14

Re: Solar Powered Iphone

06/29/2011 10:30 AM

Actually, its very easy to "convert" the power values into useful units of AMPs etc., the panels are usually (as far as I am aware always, but that may not be 100% true) quoted as a power and a voltage. I am open to good proof of the reverse if true....

Here is a web link showing exactly that:-

http://www.affordable-solar.com/store/solar-panels

As I mentioned above, its exceedingly easy to convert to amps if needed. Just divide the watts by the voltage and you have amps......so you only have to understand how to convert and the relationship between the different units...

Anyone who is dabbling in solar charging (any charging) MUST be able to work in all these values, without thinking or blinking.

Looking at what Paul posted to try and understand what the problems are my thoughts are that it would appear that he put himself out on a limb with a slightly rash and partially incorrect/misleading statement, but as far as I can tell, nobody has given him an Off Topic, or at least, none is shown at this time.

The sentence in question was:-

Watts is not relevant when charging a battery. AMPERES will charge the battery.

It is perfectly feasible for anyone used to working in the various units, to understand battery charging and probably put something together to allow the IPhone to be safely charged.....don't forget the original charger will have to handle any possible "worst case condition" and probably a slightly lower powered supply will charge just fine usually, it might just take a bit longer that is all......that might still be fully acceptable.

We must not forget that most batteries are current charged and a few are voltage charged. Most phone batteries are current charged and have a complicated charge algorithm, to properly charge such a battery without damage, whereas a voltage charged battery, on a correctly designed (relatively simple) charger will charge correctly and safely.

His post was a bit like saying "never-ever".

The only time to use never is always as in "never say never".....

Proper/real Engineers can work well from other units and are not forced into using the units that Paul appears to rely on for his own working, if I understood his post correctly.....as they can quickly and easily recalculate 9into any needed units...

I hope this settles the matter for all concerned......I wish everyone a good day......to those from Oz G'Day.

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#20
In reply to #16

Re: Solar Powered Iphone

06/29/2011 10:52 PM

Andy,

You completely misunderstood Solar Panels. You can NOT divide the watts by the current to get the voltage. Look at the IV-curve of the solar panel. A Solar panel does NOT work like a battery charger. The Voltage given as open circuit voltage is say 24 volts. That is at ZERO amps, open circuit voltage. 24v X 0amps = ZERO power output at that voltage. 1 amp is given as the Short circuit current. Short circuit means at zero volts. 1 amp X 0v = ZERO power out. Power output is best at a voltage and current somewhere in the middle of the IV curve at a lower voltage of the battery.

If you like, you can consider the Solar panel as a current limited device. If 1 amp is its short circuit output, it does not matter how you connect to it, you will NEVER get more than 1 amp from the panel directly. (And I mean NEVER. You can divide it by as many amps as you like and short circuit it all day long BUT its short circuit current will NEVER be more than 1 amp).

If you have a 36 volt oc, 1 amp sc, solar panel, (That would be a 15wp solar panel) and connect a wire between the panel and the 12v battery, what is the voltage in that wire? Only 12v. It can not be 12v at one end of the wire and 36v at the other end. So the battery is charging at 12v 1 amp, (1 amp is the maximum, short circuit current available) from a 36v 15wp, solar panel. 12 watts from a 36 watt peak solar panel is all you get. Your calculation of watts is lost. You will not get 36 watts charge. You can not convert watts into amps and volts because you are NOT using the open circuit voltage of the solar panel, as this will drop to the voltage of the battery and as the battery charges, the voltage will rise.

Now if you have a DC to DC converter, then you can use the watts and your formula will work. You can take 36v at 0.5 amps IN and get 12v at 1.5 amps OUT, if it was 100% efficient. But such a circuit is NOT 100% efficient so you lose power in the conversion. A 22V oc Solar panel will charge a 12v solar panel more efficiently than a DC to DC converter. But if you have a 36v solar panel then you would have to use a DC to DC converter to get the same charge into the battery, probably less after converter losses.

Note: the voltage rises as the battery charges, up to the Voc voltage, if you let it. This is why you must have a solar controller to protect the battery. This cuts off the charging at 14v on a typical 12v battery.

I hope I have made more sense this time. You can get Solar Power training which will explain all of this in a few weeks training program. Can't explain here in 1 box of writing.

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#21
In reply to #20

Re: Solar Powered Iphone

06/29/2011 11:20 PM

Small note:

If you buy a solar panel for 12 volts, the no load (open) voltage is supposed to be minimal 17 volts. Why bringing up your open voltage? Solar panels are available for all kind of "practical" voltages. You can get the amperage by dividing the Power rating by the voltage. The voltage however will be determined by the state of the charger, or the battery.

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#26
In reply to #20

Re: Solar Powered Iphone

06/30/2011 12:45 PM

I understand that you are new to this forum, so you may not fathom that being immediately insulting to long-standing members is unwise, if you want to remain here and be taken seriously.

Your comment "You completely misunderstood Solar Panels" is incorrect. I can assure you that Andy understands solar panels, and clearly has a much better understanding than your own re dc/dc converters, wattage, efficiency, conservation of energy, etc.

This makes you come across as both abrasive and poorly informed. In some forums people thrive on this kind of thing (insult for the sake of insult), but here, you will find that this is not rewarded.

You can get Solar Power training which will explain all of this in a few weeks training program.

The above comment applies here too.

Now if you have a DC to DC converter, then you can use the watts and your formula will work. You can take 36v at 0.5 amps IN and get 12v at 1.5 amps OUT, if it was 100% efficient. But such a circuit is NOT 100% efficient so you lose power in the conversion.

This is the first thing you have written that makes sense in light of the original post, and show that you have a basic understanding of the painfully obvious. A dc/dc converter is precisely what the OP has in mind, as you can infer from his reply to Fredski's first post (re Fredski's early misconception re wattage and amperage). Always read the other posts before you comment, to avoid coming across as an idiot.

Finally, you are getting to the OP's question after all the insults and pedantry. While you are correct that these converters are not 100% efficient, you will note that Gigaconcept suggested this approach long ago, and that his converter is about 90% efficient. Using this approach is far better than driving a solar sell to its short circuit amperage and wasting its potential wattage output.

While you are correct that simply running a 12 volt (typically 16-17 open circuit, 14 volt at rated operating amperage) solar panel into a low impedance low voltage device does not produce the rated wattage output of the solar cell, you miss the OP's point entirely -- that being that he wants to use the full output of the solar cell, which he can only do with a dc/dc converter. The output of a 12 v nominal solar cell straight into an iPhone will do nothing: the iPhone's input is not so stupid as to allow the connection.

I hope this smooths out your future posts here:

1. Don't be be insulting.

2. Read all the posts in the thread before posting.

3. Think first, then post.

3. Don't assume that you know more than others.

4. If you claim to know more than others, be prepared to provide authoritative links to support your claims.

I'm looking forward to more meaningful posts in the future.

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#35
In reply to #26

Re: Solar Powered Iphone

07/01/2011 3:43 AM

Fry, thank you for your advice. I will try to explain better in future. In my defense, I was referring to how the solar panel output works differently, with absolutely no increase in max amps out, with voltage changes in the PV output and did mention that DC to DC converters work differently from solar panels. And I am afraid that Andy did not understand how to get the best output out of the PV panels themselves. The actual solar panel output is determined, before it goes into a DC to DC converter, relative to the insolation it receives, although he was correct about the DC to DC converter side. Also ALL batteries are measured in amp hours, coulombic and not calculated in watt hours charging. So the comment You can get Solar Power training which will explain all of this in a few weeks training program, was serious. It was not an insult. It would indeed take at least 2 weeks to fully explain the details of measuring and sizing Solar panels, which is very different from using DC to DC converters and I could not explain it in this space.

The original question was how to get the most out of the solar panel. The correct size solar panel gives the best charging and can not be increased in output using DC to DC converters, which is what I was trying to explain. Only the wrong size panel can be increased in output, by the converters, so losses are higher with converters. Converters MPPT are used when putting power into the grid and not charging a battery. MPPT is not any more efficient than using the correct size panel, when charging a battery. In this case it would be less cost to buy a panel sized to the correct voltage (RM100) than to buy a DC to DC converter RM250). Using a higher voltage panel will also give more power over the whole day, so offsets some losses. So connecting directly to the phone may actually give more charge, in amps, over the whole day, than using DC to DC converters. This you would have to calculate but need a lot more information to do the calculation. As someone said, they do sell solar panels that you can connect directly to the phone. Voltage will drop to battery voltage upon connection. The units from Germany are 9V oc which is just right for the 4.5v battery range.

I am an ISPQ certified, PV system designer and certified PV installer. I do these calculations all the time. But these days we have computer programs that work out all this for us.

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#38
In reply to #35

Re: Solar Powered Iphone

07/01/2011 6:47 AM

LOL!

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#30
In reply to #20

Re: Solar Powered Iphone

06/30/2011 3:28 PM

You should not have posted, you are only demonstrating your flawed knowledge and thinking in many areas, mixed with some knowledge... sorry.

Did you read Mr K Fry's comments, he was on the money (as I was!!) He agreed with me, not you.....I hope you unstand now "WHY"...

If you really want to post well here, you must first brush up on basic electrical knowledge.

Also you ought to re-read what I wrote, slowly too..

A Solar panel is sold to work at a nominal voltage and a certain power in watts. What I said was that you can work out the max current simply by dividing the watts by the voltage, you got it the wrong way round in the first sentence.

You wrote:-

You can NOT divide the watts by the current to get the voltage.

Do you see the difference?

What I wrote was:-

Actually, its very easy to "convert" the power values into useful units of AMPs etc., the panels are usually (as far as I am aware always, but that may not be 100% true) quoted as a power and a voltage. I am open to good proof of the reverse if true....

Did you now understand that what you said I wrote, I did not write!!!!

Solar panels are easy to work with if fully understood, you appear to be the one having the problems in understanding.

Why did you not go onto the website I posted and you would have seen how they are described and sold? Simple....

Furthermore, another of your comments:-

Note: the voltage rises as the battery charges, up to the Voc voltage, if you let it. This is why you must have a solar controller to protect the battery. This cuts off the charging at 14v on a typical 12v battery.

Should be qualified as to what type of battery. I know you mean lead acid, but does everybody? Of course not. You must also learn to write correctly for all readers of our blogs.....

Sorry to be a bit rough, but leaving you with so many errors in your knowledge, might cause you to have an unfortunate accident sometime in the future.....

For example, Lead acid batteries alone account for many people to be blinded and or burnt each year.......

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#36
In reply to #30

Re: Solar Powered Iphone

07/01/2011 5:27 AM

Andy, Sorry about the typing error. You did say, about a PV panel, "you can work out the max current simply by dividing the watts by the voltage", which is NOT correct on a solar panel. You would not get the maximum current outside the testing laboratory. You would need to look at the IV-curve which shows the current at a given voltage and temperature. Then at the angle of inclination, then at the surface temperature, then at the manufacturers rated value, then at shading during part of the day, then at dust build up in the area, then at the PSH and then you can work out the current expected. Which is no longer the rated watts divided by the voltage. For the panel maximum power rating there is a laboratory rated power at laboratory conditions and 3 voltages and currents."(as far as I am aware always, but that may not be 100% true) quoted as a power and a voltage)" The open circuit voltage, the maximum power point voltage and nominal voltage. You didn't state which one will you divide the watts by? All are laboratory voltages not operating voltages. You would need to work out the operating voltage. There is a Current at maximum power point, a current at short circuit, in laboratory conditions. Again you would need to work out the actual current in the working conditions. It is not as simple as you stated.

This cuts off the charging at 14v on a typical 12v battery. A typical battery in a PV system is lead acid. You are correct, I should not have assumed you would know a typical system. Batteries are measured in amp hours. They are charged in amp hours, so the calculations for charging are in amps over time and state of charge is amp hours and depth of discharge? Are we on the same page now? Sorry if my explanations are not clear.

Paul

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#39
In reply to #36

Re: Solar Powered Iphone

07/01/2011 6:49 AM

LOL!!

Its not worth me wasting any further time on answering your mixtures of fact and fiction.

If I knew who you worked for, that would be a strong reason NOT to use their services.......ever.

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#17
In reply to #14

Re: Solar Powered Iphone

06/29/2011 7:11 PM

I charge my 12V batteries from 120 volts. The amperage at the 120 volt side is not much more than 1/10 that at the 12 volt side.

I charge my 50 V battery pack in my electric car from 120 volt supply. The amperage on the 120 V side is about half that on the 50 V side. If that were not the case, the charger would be smoking hot.

Solar panels do not work by magic, but obey all the same physical laws as other electric devices. I wonder if Paulmil has noticed that a typical small home welder puts out 100 amps, but is fed from a 20 amp socket. Magic?

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#22
In reply to #17

Re: Solar Powered Iphone

06/30/2011 3:42 AM

If you can get 10 amps out from a 120 watt peak solar panel at 12 volts, it WILL be magic! You will be a millionaire.

Try it and let me know. If you can't, then let me know your revised calculations to show why 120 watts divided by 12 volts doesn't give you 10 amps from a solar panel.

If it is a 36Volt oc panel it will give you 5 amps. (Let me see your calculation for this)? Solar panels DO follow the laws of physics, so must your calculations. Electricity produced is proportional to the Sunlight hitting the panel. So trying to draw more amps from the panel is useless, unless you can increase the Size of the Sun. Note that SHORT CIRCUIT current is given. That is the MAXIMUM current the panel will give, if it is a dead short circuit, positive wire connected to negative wire. (Check the difference in the short circuit current of a transformer)

Power = volts X amps. If amps is maximum of 5 amps, a 120 watt panel will give 5 amps and no more. 5 amps at 36v, 5 amps at 12v, 5amps at 24v. The Sun can not move more than 5 amps worth of electrons. See the IV-curve of the Solar panel.

If you have a transformer then it is very different. If you short circuit this, you will draw much more current than 5 amps, more than 50 amps if you let it. But the solar panel only had 5 amps to give, so only 5 amps will come out at short circuit. Do you understand the difference?

So did your car battery charge at the amps on the 120v side or the amps going into the 50v battery side? Only the amps on the battery side go into the battery. You need at least 50v to charge a 48v battery. So if 50v, 10 amps goes IN, (500w), how much comes out. Remember the OUT voltage is 48v, not 50v, so only 480w would come out if it was 100% efficient. It is 80% efficient so only 340w comes out. Does it make sense yet?

Solar panels act like a current limiting transformer, if that helps with the calculations. You need to learn more about this electrickery stuff.

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#25
In reply to #22

Re: Solar Powered Iphone

06/30/2011 11:58 AM

You need to learn more about this electrickery stuff.

I am afraid it is much less tricky, but more complicated than you think. The physical laws are never violated. Understanding the practical and efficient operation of solar cells requires a grounding in physics and basic electrical/electronic laws.

Solar cells are always specified and sold by power output. Everywhere in the world the cost-per-watt is a key factor in determining the economic viability of solar panels. Power is the only reasonable yardstick, because solar cells convert energy (power x time) from one form to another. A 120 v 350 watt solar array and a 12 volt 350 watt solar array both can do the same amount of work in the same increment of time. To accomplish a particular bit of work, the voltage may need to be stepped up or down, and the amperage will do the inverse. Typically buck or boost converters are used.

The OP would be foolish to connect the 12 volt panels directly to the 3.7 v battery he will be charging. Profoundly foolish. He correctly understands that he needs to make a converter which will allow the panels to operate at a voltage near their maximum operating point voltage (not at their open circuit voltage, and not at their short circuit amperage). To be able to use the iPhone's built-in charge regulation, he should provide a 5 volt output to the iPhone's input. If less than .5 amps can be supplied by his converter, that's OK -- the charge time will simply increase. As long as the iPhone sees 5V, it's charge controller will operate correctly. If it sees 12 or more open circuit volts from the panels, (the iPhone input initially being very high impedance, while voltage checking goes on) the charge input will not connect -- the panels will then be doing nothing useful at all.

Only an idiot would connect solar panels directly to the iPhone's input. The OP is clearly not in that category. Fortunately, he will disregard your advice, and build a proper dc/dc converter to take advantage of the solar panels' wattage.

The OP is far ahead of you in understanding this stuff, I gather. He appears to understand that he can either parallel his panels for 12 V(nominal) .25 A, or put them in series for 24 V(nominal), .125 A. In either case, the power is the same. In one case he will build a 12v to 5 v dc/dc converter, in the other he will build a 24 to 5 v dc/dc converter. Either of these will be about 85% efficient, if he is very careful in design. His panels will be rated for an operating amperage and for a short circuit amperage. He will not be so stupid as to select the short circuit amperage for his power input calculations. He will likely find in the spec sheet, that the panels operate (with optimum load) at a voltage higher than 12 V. He will pay attention to open circuit voltage mainly to ensure that the input side of his converter has adequate headroom. He will use the maximum operating voltage as a guide for circuit design, because it is likely that he can hand orient the unit (and can therefore drive to cells to full spec), and because it would be fun to make the device as efficient as possible.

So if 50v, 10 amps goes IN, (500w), how much comes out. Remember the OUT voltage is 48v, not 50v, so only 480w would come out if it was 100% efficient. It is 80% efficient so only 340w comes out. Does it make sense yet?

No, not one bit of this makes any sense at all. It is complete nonsense.

I gather you are unfamiliar with lithium ion batteries, so let's assume, as you have, that my battery pack is lead acid, nominally 48 volts. These will charge at 14 volts, and will be maintained at 13.8 volts, after the bulk (regulated amperage) and finishing (regulated voltage) charges have completed. 10 amps at 56 volts would be a reasonable spec for the bulk charge current. This would be a 560 watt power input. The batteries, in use, can output 50, 100, 200, or any value up to 300 amps. (Up to 15 kilowatts, for the lead acid batteries that use to be in my vehicle.) The ratio of input power to output power of a battery system has nothing at all to do with battery or charging efficiency. Given that I have seen 300 A outputs from my old batteries (at 44 volts) output power was 13,200 watts. Efficiency, as you have operationally defined it here, would be 13,200/560 or 2357%. A nonsensical number. Meaningless.

Solar panels act like a current limiting transformer,

If you are using them in this mode you are making a costly device even costlier.

Andy's original post, and his second post, which has justifiably accumulated several good answer votes, are correct. Your "correction" to his post, ("Watts is not relevant when charging a battery.") is flat wrong. Andy correctly understands that the power input is a little too close to the desired output for comfort, but if the OP is willing to charge a just slightly lower rate than the wall wart supports, it should work fine. (With careful design and construction, however, getting 2.5 watts out from a 3 watt input in a dc/dc converter is a realistic goal.)

Perhaps there is something that you have written that makes sense, but I'd have to reread your posts carefully to find it.

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#33
In reply to #25

Re: Solar Powered Iphone

06/30/2011 4:09 PM

You deserve the GA I have just given you, simply for not giving up.

Leaving him at his level of ignorance is tantamount to murder sorry suicide!On his part I mean.

Sadly I have little hope that you, I or anyone else can correct his flawed knowledge, but I haven't quite given up yet!!!

But it is a bit like shooting fish in a barrel!!!!

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#18
In reply to #14

Re: Solar Powered Iphone

06/29/2011 8:55 PM

I have done extensive research on solar power installations and you are "right on."
Perhaps you've never actually used them, however?


In every electrical device power = volts x amps.


To change the voltage of a set of solar panels to something useful for charging batteries (or other low voltage uses) a DC/DC converter is used. Here is one with a 96 volt, 5.5 amp input. Its output is 12 volts 29.2 amps. Obviously, it would be a shame to limit its use to 12 volt circuits with no more than 5.5 amps (by, as Paulmil suggests "Don't calculate in watts.") This converter is typically 80% efficient, they say, so that in typical operation, the input might be 120 volts at 3 amps, and the output would be 15 volts at 19.2 amps. (120 x 3 x .8 = 15 x 19.2)


Input watts * efficiency = output watts.


Talking about this stuff in terms of amps when the voltages are different (as will be the case in the OP's charger) is nearly nonsensical. At very best using amps or amp hours alone can be an extremely crude rule of thumb, if the voltages are not too far apart. But as you can see from this DC/DC converter, the amperages are often not close at all: 5.5 is not equal to 29.2 -- because the voltages are not close. In any moderately efficient such device, power in roughly equals power out. Amperages in and out can vary dramatically.


So for any reasonable situation in which you want to charge a battery with a solar panel of higher than the battery's voltage, you must take wattage into account. You must also be certain that the voltage cannot exceed the maximum voltage for the battery. In Paulmil's example of 18 volts at 1 amp, a lead acid battery will gas. It is essential that the charge voltage never goes above 14.5 v. To accomplish that, you need a DC/DC converter, a voltage regulator, and a means of providing different charging rates at different states of charge -- in effect, you need a battery charger, which has these features combined.


So, Andy's comments make complete sense. Paulmil's comments make limited sense only under limited conditions in which no voltage regulation is used. Many sailors have destroyed expensive batteries by charging them with solar cells without proper regulation and DC/DC conversion. Solar panels are usually (and should always be) rated for maximum power point voltage and amperage. So these panels have an open circuit voltage of 33.7 and a maximum power point voltage of 27.4, at which point the amperage is 6.37 amps. One would be foolish to hook these directly to a 12 volt battery, because you'd be wasting power (only 6.8 short circuit amps are available). A dc/dc converter is necessary, and then (as the OP and Andy both understand) available amperage can be around 12 at 12 volts (with the precise value depending upon the efficiency of the DC DC converter. One could not know the available amperage at 12 volts without calculating using power (watts) in the calculation. In this case the amp hours into the battery roughly doubles by using a good DC/DC converter, as one is prompted to do by doing the math correctly.


The OP can use these same sorts of calculations to find out what the actual charging currents can be at the reduced voltage his batteries require. By doing the math correctly, he can find, as he suspects that the amperage into his battery will be somewhat more than double that from the cells, provided he builds or buys a good dc/dc converter.

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#23
In reply to #18

Re: Solar Powered Iphone

06/30/2011 8:28 AM

This is exactly the information the OP needs to understand, and all other who think laws of physics dont fully apply...

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#31
In reply to #23

Re: Solar Powered Iphone

06/30/2011 3:32 PM

Fully Correct.

But sadly several other people don't understand them hardly at all.....or modern electronics!! DC to DC converters for example.......or efficiency.

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#29
In reply to #18

Re: Solar Powered Iphone

06/30/2011 3:06 PM

GA

Agree entirely.

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#15
In reply to #12

Re: Solar Powered Iphone

06/29/2011 10:28 AM

I liked your answer. I know you can make a voltage divider in electronics that will step a voltage down to any voltage you like. The issue is once you tap into that divided voltage it can really drop if you use it for more than just a signal. A real load like a lamp or motor will pull it down and usually will fry something. So to my question..

On a solar panel how do you calculate for an allowable load? Do you know a formula, NOT a general rule of thumb. I'm trying to get my arms around the math. Thanks

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#19
In reply to #15

Re: Solar Powered Iphone

06/29/2011 9:16 PM

I liked your answer. I know you can make a voltage divider in electronics that will step a voltage down to any voltage you like. The issue is once you tap into that divided voltage it can really drop if you use it for more than just a signal.

A voltage divider is not used for things like charging batteries (or anywhere you care about power and efficiency). A DC/DC converter is used, and these work on the "power out = power in minus losses" principle. Most of these are 80-90% efficient. The one in my electric trike converts the 50 volt battery pack voltage to 13.5 for charging the starter battery and running the lights and accessories. When I turn on the night lighting, the 12 volt system sees 4 amps, but the 50 volt battery sees about 1.

So the formula used is the same as for any other electric device: power in x efficiency = power out. You need to find the maximum power point voltages and amperages from the solar panel spec. sheet, and use the appropriate dc/dc converters to keep them operating at that level (the converters are rated for voltage and wattage.) Putting a 12 v battery across a 24v solar panel would be nearly the equivalent of a dead short -- creating heat and wasting the panel's power.

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#28
In reply to #19

Re: Solar Powered Iphone

06/30/2011 3:03 PM

GA

Agree entirely.

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#34
In reply to #15

Re: Solar Powered Iphone

06/30/2011 11:42 PM

Fredski, Here is the basic formula for sizing a solar panel. It is wrong according to Andy but I hope it makes more sense to you. It is the international standard for calculating PV array size. Determining the Size of Array_ To determine the output from the PV array we need to know under what conditions the output will be determined. i.e. Will it be wet or dry season conditions? We also need to know what the inclination of the array will be. Available solar energy is expressed in Peak Sun Hours (1PSH =1000W/m²) and information should be established for peak sun hours based on latitude, season and inclination of the array. Tables of PSH for different locations are available from meteorological departments. PV modules are rated under Standard Test Conditions [STC] (irradiance of 1000 Watts/m2, 25° cell temperature and 1.5 Air Mass) which means that, for example, if they receive 5PSH per day, then the maximum output of the module per day, in the laboratory conditions, will be 5 times their rating. For example if a 100W module was exposed to 5 PSH at laboratory STC, then it would produce 500Wh of energy (remember this is not taking into account the losses in real operating conditions). Choose the Sharp NE080T1J modules. Rated Power 80w Nominal Voltage 12v Maximum Power Voltage, 17.3Vmp Maximum Power Current, 4.63Imp Open Circuit Voltage, 21.6Voc Short Circuit Current, 5.15AIsc. Temp coefficient of power -0.5%/C (You DO need a 21.6Voc panel to charge a 12v battery). Because the modules are used for 12v battery charging, we are more interested in the current at 14 Volts at the effective cell surface temperature, generally about 4.8A at 14V. @25C surface temperature of the PV, in laboratory conditions. You must derate power output by -0.5% per degree centigrade for each degree surface temperature above 25C. Note surface temperature is air temp + 25C. Manufacturer's power tolerance, typically + - 5%. Therefore the guaranteed output, in a laboratory, is 95% of the maximum output (100% - 5%), and the guaranteed current will be 95% of the current at 14V at Imp at 25C. Example: output current = 0.95 × 4.63A = 4.4A. At Air temp 30C surface temp = 55C - 0.5% X 25C means you X 0.85. 4.4A X .85 = 3.74A You need to also consider the effect of the modules getting dirty. So derate another 5% X 0.95 = 3.55A. The average daily charge output of the array can be calculated as follows: Q a r r a y = I m o d X H t i l lt X N (Q = Average daily charge output of the PV array in Ampere -hours (Ah). Imod = The de-rated current output of the module in Amperes (3.55A). N = number of modules in the array. Htilt = daily irradiation, in PSH for tilt angle of your panel. This indicates the size of Solar panel you need to charge the battery. So your 80w rated panel will give you 3.55A X the Sun hours. You see the output is in AMP Hours NEVER in watts, as I said earlier and got shot down. Note also that batteries are measured in AMP hours and rating is all in AMPS, never in watts. Remember the output is NOT the rated output but in reality it varies constantly from zero to the maximum derated value. If you have no battery, the output varies so much you could only drive a motor at times when the Sun was strong enough, so a battery allows you to store the energy at times when the Sun is too weak to drive the motor. This is a very basic way and as I said to Andy, you WOULD need to go for a proper training course to learn the full details.

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#37
In reply to #34

Re: Solar Powered Iphone

07/01/2011 6:45 AM

Even if there is really any value in your post, most of us will never find out as it lacks proper English (American? we, or at least I don't know whether you are Malaysian by birth or moved there,or if English is your primary language or not) punctuation and paragraphing, as when done properly, it makes reading it a far more rewarding experience.....

Never forget, presentation is EVERYTHING!

Bad presentation probably drops your "viewer" count to a tiny percentage of the possible audience.

These comments I make here are primarily intended to help you in the future with any posts you might make on CR4 and to improve your usage of the English language, nothing more, nothing less.

Sad to say, other than you "trying" (very! ) always to find some hidden fault in what I write each time I post, which of course was never written to indicate what you somehow managed to read into it.

The rest of what you posted the last time, was not only tedious to read through, it also appears to be a composition taken from various websites, that was at least my personal impression after I searched using parts of your post as keywords in Google. I could not tell if it was by accident or design....

The word in English is "plagiarism" I do believe, if it was a composition, without mentioning the web-links used!!

By the way, I would be most interested to learn from which of my posts and what sentence or paragraph you managed to squeeze out that:-

It is wrong according to Andy but I hope it makes more sense to you.

As it proves to me and others, that you simply do not (or want to) fully comprehend the English language, even when correctly written, if it does not fit your take on the subject....

I do believe that I have asked for such explanations in a similar way before from you, but as these "thoughts" are apparently only in your head, therefore each time you deigned not to answer.....

But really I do not expect an answer to any of my question(s) this time either, but do please try and surprise me and prove me completely wrong!! I do like nice surprises!

By the way, one of the persons (amongst many others here) you could possibly ask about the validity of some of your comments, is your friend and mine from Atlanta (Hotlanta), Georgia, Mr K.Fry. He REALLY knows this subject (but is certainly not alone either).

Now you may notice that I often start a new paragraph within a post, I use upper case only to emphasize a word, not to shout, so do please try and make your posts look as similar as possible please. Then I (and many others) will read them gladly, each time you post.

Have a great day and stay well.

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#40
In reply to #37

Re: Solar Powered Iphone

07/02/2011 1:56 AM

Andy, All the posts were taken from the same training manual and copied to help you understand solar power.

The last post on calculating output from a solar panel is taken directly from the Australian PV installer training manual, chapter 15 on sizing the PV array. I was hoping you would understand your own language version better but alas I failed again. I guess you didn't get a pass this course. (I got 95%) The original section is 8 pages long and the whole chapter is 32 pages, so it was too big. I used copy and paste, so the result was all the words were in line instead of paragraphed but the words remain the same as original. I removed big chunks of it that were not relevant to the calculation, so you are right it was a bit disjointed but I thought it still made sense, but I know and understand it, so it would make sense to me, even if it is not enough information to make sense to you.

As I read faults into your post you read faults into mine. You know the DC to DC converter stuff very well but failed completely to understand the Solar power stuff. I probably did not understand what you meant on some parts, just as you didn't understand some of my comments. I will try harder to work out what you are saying next time.

Paul to Fredsky: It is wrong according to Andy but I hope it makes more sense to you.

All the previous posts were from the same training manual and your response to the information quoted was:-

Andy: a slightly rash and partially incorrect/misleading statement...

Andy: You should not have posted, you are only demonstrating your flawed knowledge and thinking in many areas, mixed with some knowledge...

Andy: Actually, its very easy to "convert" the power values into useful units of AMPs etc., the panels are usually (as far as I am aware always, but that may not be 100% true) quoted as a power and a voltage

It certainly isn't as simple as that and and you were very wrong, the 32 pages of the PV installer manual indicate how complicated it really is. So I get chance to say you were wrong again. See the correct way to find the amps of a solar panel from the little bit of information I sent to Fredsky.

Andy: Its not worth me wasting any further time on answering your mixtures of fact and fiction. If I knew who you worked for, that would be a strong reason NOT to use their services.......ever.

I am a full time PV system designer and installer. We do not advertise and rely on word of mouth to get customers. As our systems are always producing more energy than any of the competitors, we survive. I design the circuits for solar controllers, MPPT, Inverters and all the control electronics and build them under our own brand name.As you are the expert in Photovoltaic system design I would not claim to be as good as you are.

Andy: Leaving him at his level of ignorance is tantamount to murder sorry suicide!On his part I mean. Sadly I have little hope that you, I or anyone else can correct his flawed knowledge, but I haven't quite given up yet!!!But it is a bit like shooting fish in a barrel!!!

Andy: Even if there is really any value in your post, most of us will never find out as it lacks proper English

Andy: As it proves to me and others, that you simply do not (or want to) fully comprehend the English language, even when correctly written, if it does not fit your take on the subject....

The language was taken, copy and paste, from the Australian Photovoltaic training Manual. Sorry if you don't understand Australian. Some words in between, were my attempt at explaining the information as you obviously could not understand it, as you would agree, judging by your responses above.

By the way the manual is not my take on the subject. It is the international take on the subject, accepted by the rest of the World, except for Andy. I just copied the formula in shortened format, to Fredsky because he asked if anyone knew the calculations and I did. You very obviously did not. I apologise to Fredsky if the extract from the manual confused him as much as it confused you. It is very difficult to explain in short form and like I said, you need 2 weeks to go through the training manual to get it. This is not an insult, you really would need 2 weeks to go through and understand the training manual. If I wanted to insult you I would have said you were too stupid to understand it in 2 weeks but if I think you can understand it in just 2 weeks, that is a compliment. I did try to answer the misconceptions you have on PV panels but you didn't understand the basic physics involved, despite the training manual explanations. Possibly my poor explanation of the information copied or you just plain can't understand it! (OK that one was an insult but just joking).

So, like my Solar panels, get plenty of Sunshine and work hard.

Paul.

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#41
In reply to #40

Re: Solar Powered Iphone

07/02/2011 5:48 AM

So I was right, you DO copy from other sources without naming them at the time, that is considered to be a very poor showing on CR4 (and in exams!). It also leaves a bad impression of subterfuge. The rest of your posts are just a cover up.

By the way, this is most common in modern teenagers, "borrowing" information for their exams. There is even software around nowadays to find out whether they have done just that, but when you have been around as long as I have in both industry and teaching, you don't need software....

You are also still definitely having problems in correctly understanding my comments and still continuing the error by "finding" so called imagined "faults" in my posts, but I have no problem in reading from yours that you have a poor grasp on the whole subject and you are building a smoke screen to cover it up. But VERY badly!

Others here have correctly criticized your statements, you simply ignore them, why?

Please remember that pass marks in exams can sometimes be taken as an indication of subject knowledge, but learning "Parrot Fashion" and still not understanding the background properly will often give even better exam results. Well known fact.

Answering from a position of proper knowledge and full understanding does not always bring top marks. I would therefore guess that you are a "Parrot Fashion" student.

This attitude similarly demonstrates a relatively young mentality, not yet fully formed, probably you are physically under/around 25, but mentally not yet 18 years old.

But don't worry, usually time will improve the situation and by 35, your mental age will have caught up with your physical. This is not uncommon.

With regard to your exam results, we only have your word about your studies and marks, proof is just about impossible online, which is why I do not see a reason to make a big "song & dance" about my qualifications (I don't know any of the "real" CR4 people who do), I know that is simply not needed nor required on CR4. You obviously feel otherwise.....

My opinion is that you probably still need some 5 to 10 years of active experience in your chosen field to make you better.

Most people showing your type of online aggressive, irrational qualities are in real life a meek person, trying to change. This is a so called "Walter Mitty" complex.

I suspect that in your "real" life you may have real problems relating to other people around you and "live" online to try and achieve some sort of balance. Your parents, older siblings may bear the brunt of your frustrations in many of these cases....

Do though please enjoy your youth, gain experience and knowledge as well, its a great time to enjoy and you only get one bite of the apple (many forget that!).

You can keep posting your imaginary findings about me (and anyone else) if you wish, but I have now stopped reading them as they are simply a waste of my time (What I have left!), but DO continue to post for the sake of other CR4 members. It will keep you off the streets!

If you are juvenile enough to believe you have won a fight, so be it!!! I can live with that, but can you?

But your "war" has still to run.......as life will show you further as it progresses......

Your complete CR4 Bio gives no accurate representation of your age, but I think it sums up your age, experience & knowledge in it's one short and simple sentence that I took from your CR4 log-on details:-

Mad scientist and part time Drummer in a Heavy metal Band.

You may want to consider changing it sometime soon as it rather sums up the whole of this post rather well I think and I will checkup regularly to see if the new Bio is any better!! So think longer and harder before changing it!!

Have a good day.

PS In the many months (over several years in the '60s) that I lived in Malaysia and Singapore (before you were born I believe), I met many really great people, who often beat me at both table tennis (I was/still am awful at it) and badminton (reasonably good at RN levels), but they were never ill mannered or uncouth......don't times change?

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#42
In reply to #40

Re: Solar Powered Iphone

07/02/2011 9:30 AM

The best thing to do is to quote your books and give their names, then interrested parties and the OP could source them and get to learn from them.

The actual project of charging a cell phone using solar power is somewhat removed from a PV installation. Even if components used may have the same name, such as battery, DC-DC converter, wire, etc, they are not identical in their performance and applicable specifications.

This link came up as I googled "DIY solar cell phone charger":. "I found this quote in the article quite facinating:his current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce."

This is scientifically true even if it is not the way you are used to in your calculations. This happens often when training is given on a specific field of application. The knowlege you are using is derived and simplified from science (not the other way around), many installers would not grasp University level science and to follow a recipe suits them.

Following recipes does not work in this case, as the application and components are not standard. In such case, one has to fall back on fundamental science to design a specific recipe for the application.

Remembering all this should relativate your self expertise certitudes. Understanding all this will allow you to learn and truly understand your trade and tools, allowing succesful departure from the usual applications you have learned to manage so far.

This is Engineering science for you, what makes us Chiefs not Cooks

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#43
In reply to #42

Re: Solar Powered Iphone

07/02/2011 10:12 AM

GA

Many thanks for adding some good common sense, good manners, principles and expert knowledge to this blog.

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#44
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Re: Solar Powered Iphone

07/02/2011 11:33 AM

Same to you, tks for preserving Mr Watt, Ohm, Ampere and Volta legacies undisturbed!

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#46
In reply to #44

Re: Solar Powered Iphone

07/02/2011 12:48 PM

Many thanks, it wasn't easy, but we achieved it in the end.....

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#45
In reply to #42

Re: Solar Powered Iphone

07/02/2011 12:24 PM

Guru, Yours was a very good post. All of us use text books and training manuals as well as experience to learn what we know. After we have learned it, we know it. It is upon this experience that our calculations should be based and not on fixed, rule of thumb ideas from other areas, as given by Andy and engineers inexperienced in the field.

I noticed that Andy and the others did not state which text books they used in their training or where they got their information from, when they gave their comments. After over 25 years in the Solar power business I don't use only 1 text book but keep up to date with many modern text books and training manuals. The training manual referred to is not available to the public. It is the industry training manual used in the certified PV training centers, so I am not able to refer you to it. It is one of the many sources of the knowledge that I have.The information I know very well but it is easier for me to copy and paste it, in order to correct wrong information in other posts, than it would be to re-right it. Because I copied it from the manual in the last post, does not mean it is different from what I know or what I wrote earlier and the information is just the same.

"This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce."

May I add to this without reprise or further insult, to assist others who might be interested? It is correct but it is only part of the answer. At night the solar cell produces zero current and zero voltage. It would therefore appear that other factors are important in order to define the power that the Solar cell will produce. The amount of Sunlight reaching the surface of the cell, cell temperature and all the other factors affecting the power produced, must be accounted for. As you indicated, each application is different and each application requires a great many calculations based upon its own set of requirements. In a typical day we may be asked to give quotations for over 100 different systems. Calculating this by hand would take the whole day so, those of us who are able, usually write programs that will take in all the parameters and calculate the size of Solar Panel, battery and controller. This does not mean that we forget how to do the calculations. The program is a tool to assist us but we must still know its roots and be able to see if there are any errors.

Charging a phone, BIPV, powering a street light, running a factory on PV all need to be calculated. If you know the calculations they will apply to all these systems. The calculations again with an example relative to the Iphone. My own writing based on my own knowledge and that given in the Australian PV installers training manual 2010 but not copied this time.

For the application to the Iphone you will need to know the following parameters

1) What is the input voltage window of the phone? (That is the maximum and minimum voltages you can put into it)

2) What is the maximum and minimum current it will work with?

3) What is the IV_Curve of the solar panel? ( This shows the current that will be available at different voltages). Example at 20v the current will be 0.001 amp. At 1 volt the current will be 0.185 amp. at 12v the current will be 0.184 amp

4) what is the battery voltage?

From this information you can look at the effect of putting the solar panel directly to the phone. (I do not advise this until after you make the calculations).

An example using figures I have made up until you get the real figures. (I can take some examples from the manual but this causes too many problems, so I will wright my own example to save the hassle. It is the same information)

The voltage window is 24v to 5V

Current drawn by the phone battery is 0 to 500mA.

Solar panel gives 0.185 amps at zero volts and 0.155 at 5v and 0.184 at 12v in this climate at the tilt angle we are using. Values taken from the IV-curve.

Battery is 4.5v

The result of connecting this panel directly to this battery, which is 4.5 volts, would be to short out the panel output. Connecting the panel would short the panel voltage to 5v. At this voltage the panel can only give 0.155 amps maximum but the battery can accept much more, so no damage would occur. The battery would begin to charge. The phone would charge at only 0.155amps so it is not efficient to do this. Power is 0.155A X 5v Maximum

Now if you calculate using a DC to DC converter for comparison, you would need to know the converter losses and the input voltage of the converter. If the converter has an input voltage of 20 volts then the solar panel will provide 20v at 0.001 amps minus losses, so no use to us as this is less than charging directly from the panel. Power is 0.001A X 20v

If the DC converter has an input of 12 volts then the solar panel will provide 12v at 0.184A. 2.22w. This is more power so it is useful to us. The converter can now take 2.22w and deliver it to the battery at 5v, increasing the amps to deliver 2.22w, minus losses into the battery. The battery can take 0.5 amps maximum. At these values the DC converter will increase the power to the battery from this panel. But the correct size panel would have been more efficient.

Because the input voltage is at 12v, the maximum output of the panel, we get a good result. So MPPT trackers are units that keep the input voltage at the maximum output voltage of a solar panel.

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#47
In reply to #45

Re: Solar Powered Iphone

07/02/2011 1:39 PM

An almost completely laughable post. Seems you'd have changed your mind about many points recently?

You have certainly made a terrible, miserable name for yourself Buddy here on this blog after only a few months or so on CR4!!

Andy G. did a clean, respectable job, and has the Good Answer posts to prove it.

How many did you manage to get on this subject? Does that not tell you something?

Ken Fry managed 6 GAs on this blog alone. Clever and modest Guy.

Such scores, are reasonably reliable most times due to the sheer amount of expertise available here.

QUICK! you can go and give them all some more OTs if you wish:-

Ken Fry 6 GAs 0 OTs

Gigaconcept 3 GAs 0 OT

Andy G. 4 GAs 0 OTs

Paulmil 0 GAs 1 OT

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Comments rated to be "almost" Good Answers: Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!

OH! MUCH TOO LATE!!

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#48
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Re: Solar Powered Iphone

07/02/2011 1:49 PM

We are not just fighting for GAs here, at least I am not.....

Its very nice if they come, but that should not be the main aim.

Helping someone in a fully correct technical manner and correcting ANY errors.....

But I would also like to thank all of you most kindly for giving me some GAs (and not giving me any OTs too)

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#49
In reply to #48

Re: Solar Powered Iphone

07/02/2011 11:00 PM

OT can be fun too... Better to self proclaim OT!

The luck we have to help solve problems in a peer reviewed manner, and get a little credit from time to time for a inspired post, is what makes CR4 great.

Too bad for the occasional agravation, GA stats and guru status seem to be worth more to people who have none of it...

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#50
In reply to #49

Re: Solar Powered Iphone

07/03/2011 5:40 AM

Nicely put Sir, thanks.

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#24

Re: Solar Powered Iphone

06/30/2011 11:00 AM

thanks all for your discussions. I'm learning a lot reading your debates. I realise that I didnt give correct specs about panels. Those are made to charge a 12 V battery at a rate of 0.125Ah... (forgot the h on my original post). Rated 1.8W...

I would then like to use a 12 V battery before the DC/DC converter, but 12 V batteries are usually heavy lead acid battery and I would like to have something easily portable in a backpack. I could probably try to look for a voltage regulator without using an intermediate battery... Problem with this is that charge won't be available at night, but this would be great for camping. At home, I could easily use a car battery with a converter. I'll try both...

Another question: I know that some electric device such as motor will burn if their input is too low... do such phenomenon occurs with a battery if input is lower than needed? I would be very surprise to hear so because it wouldn't make any sense to me. Charging will only take more time. Am I right?

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#27
In reply to #24

Re: Solar Powered Iphone

06/30/2011 1:09 PM

rate of 0.125Ah...

Oh no, it's contagious! Paulmils posts have made you crazy too!

AH is not a rate. It is a quantity of charge, (and, for a given voltage, is a measure of energy stored).

Another question: I know that some electric device such as motor will burn if their input is too low... do such phenomenon occurs with a battery if input is lower than needed? I would be very surprise to hear so because it wouldn't make any sense to me. Charging will only take more time. Am I right?

Essentially, yes. But as it happens, the iPhone will do nothing if the input voltage is not within range. (It is an expensive device and is well-protected.) The battery is roughly 3.7 v, and could be charged at 4 volts. However, the iPhone's input is not likely to accept a 4V input -- although I have not checked the specs. The input is set to be compatible with USB sources. (If the input v is too high or too low, the phone just sits there, without doing any charging.)

Batteries (of all chemistries) benefit from being charged at something close to the "right" amperage: not too fast, not too slow. If you can supply .3 to .5 amps at 5 volts to your phone, you will be fine. The converter will maintain constant voltage as as amperage fluctuates (if you build it correctly).

But the basic answer is that charging your iPhone battery at a somewhat low rate will not measurable hurt it. It's not like a motor. A reasonable analogy is in charging a car battery, As you probably know, there are car battery chargers that output amperages from about 2 to 30 or more. They all work OK -- although routinely charging your car battery at 30 amps might shorten its life. (However, these rates, and higher are often seen in the car itself.)

You could put together a pack of NiMH or lithium ion cells and charge them to 12v nominal (and even for this you would need at very least diodes between solar cells and battery, but better a real charge controller). Then, a simple car converter would work as the input to the iPhone. This would be less educational than building from scratch, however.

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#32
In reply to #24

Re: Solar Powered Iphone

06/30/2011 3:56 PM

There are some quite tiny sealed LA batteries for sale, which react in a similar manner to a big LA battery of course, but nowhere as powerful or as heavy.....

If you want to use non-LA batteries (which are generally current charged and not voltage charged. LA batteries for example are voltage charged and quite easy to to design a charger for because of that), may I suggest that you find a ready made charger (for 12-18 volts input) for the chemistry you finally decide on. Try and match the "power" as well if you can noting any efficiency losses as closely as possible.....

Non LA battery chargers are quite complicated devices if charging is to be fast and correct.

Cheap/badly designed chargers just ruin batteries no matter what the chemistry used is!!

I hope this helps....

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#51
In reply to #32

Re: Solar Powered Iphone

07/04/2011 8:48 AM

Of course it helps. I'll give you some feedback when the project will be completed. I'll update here. Thanks again.

Sorry for misusing the word "rate" ;)

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