Small 12v Project Needs Help

Del gives you a solution that is worth a good answer. (got the hint?)

Here another possibility: with some switches and you can create:

A.

A battery charging sequence (timed) and only use 6 Volts during that time, you can charge your 2 batteries in parallel to 6 Volts (it will take a while with 1.5 Watt)

Eventually you can use Dell's idea to step it up to 12 volts from here or you switch to:

B.

A 12 volts "use sequence" where you change the parallel circuit of the batteries to a series connection and disconnect the solar panel.

Or:

Buy a next identical panel and make a series setup. A 12 volts 1,5 Watt panel is dirt cheap.

The choice is yours of course.

What capacity and type are the batteries - in amp hours?

A 1.5 watt panel used with a battery system will provide maybe 0.75 watts per hour of good insolation (meaning good summer direct sun). If you get 6 hours of somewhat good sun you will have maybe 4 to 5 watts available from the batteries.

You don't have adequate panel to charge lead acid batteries.

The batteries are like this ones

http://www.amazon.com/Wheels-Toddler-Rechargeable-Replacement-Battery/dp/B002IPGW4S

You'll need 60 - 80 Avg.depending on how deep they are discharged of bright sunlight to charge both. ( I read 4 ah and your panel produces roughly 100 mA)

If you have just one solar panel, then charging the batteries in parallel would make more sense than in series. Then when you use them, you would put them in series to supply 12 v. Occasionally charge them separately to balance them.

Given the very low output of the panel, I assume the batteries are small, and simply re-cabling them with spring clamps could work. Or you could use some switches, being careful to arrange them so it is impossible to short the batteries.

The battery shown is a 4 amp hour battery.You will charge that with a 1.5 watt panel?

Sure, you only have to top up the battery to replenish the small amount used by charging a cell phone, etc. So if his cell phone used up 3Wh in a day, his charger would have to produce let's say 4.5Wh (3 hours worth) per day to do the cell phone charging and account for losses.

The 4 watts will operate the toy for how many seconds?

It depends on the device. If its wattage is less than 4, it will run indefinitely.

From the Fisher Price site -

Short run time(Less than 1 - 3 hours per charge) Charge the battery for at least 14 hours after each use of the vehicle (that is for the charger plugged into a wall socket)

No other specs there

Kids really love that! Sorry, no more car today, it has to charge for 14 hours.

An impossible question to answer. A 4 watt source will operate a 4 watt load forever, if nobody turns off the switch.

The key issue is voltage from the solar panel under typical conditions...
All the watts in the world are no damn good if the voltage is below that of the batteries.
That's why you need to step up, you can then add some fancy charging regulation if you want.
Or as a minimum you need to check the volts out under typical conditions.
Del

I don't know the required voltage to charge a 6 volt battery though a 12 volt battery requires 17 so I suppose this would require 8.5 volts.

Actually this is an area where typically one needs to be very good with electronics or it gets far more expensive than is practical.

Still 4 to 5 watts daily ( even 10) from the panel isn't going to do anything worthwhile.

However, "6v" solar panels put out 8.5v open circuit and 7.25v or so when loaded to the rated output. That's because they are made to charge 6v batteries, just as "12v" panels are made to charge 12 volt batteries, (and therefore put out 17v open circuit and 14.5v loaded).

Loads of people have used such things to charge batteries without any fancy-schmancy circuitry at all, beyond the diodes that are often part of the panels (and if you can hang around to disconnect things when the big cheese turns the sun off, you don't even need the diode)

But you're right, it would make great sense to check the actual output voltage and current of the panel. It would also make sense to do the math, which would seem to indicate that it would take several days (29 hours of good sunlight) to charge each 6v battery... but that assumes that the battery is completely dead -- probably never the case for his planned usage.

Assume he is only using the battery to charge a cell phone or an iPod. His panel could generate that in 2 hours. Thus, if he kept the panel connected to one of his batteries for several hours per day, he could charge his cell phone every night, even if the cell phone were completely dead -- very unlikely. (The battery just lets him time shift, so that he can charge the cell phone when the sun is down for maintenance.) Lots of cell phones are good for several days between charges -- unless the user is a teenager.

Many cell phones nowadays accept the 5v dc from a usb port. Many, I'd wager, would also accept 6v directly from his battery -- the charging circuits in cell phones are pretty robust and well-protected against things like over voltage and overcurrent.

FINALLY!!!

The answer I was looking for (and yes for some reason I put the parallel and serial the other way arround, sorry)

and that's exacly what Im trying to do when I said that I want to charge small devices (like and ipod, iphone or other cell phone, even a psp) with a car charger

So Mr K Fry, can you be a little more specific on how can I do that?

Thans in advance

Initially, I'd just wire it up with spring clips. Check that the batteries are close in voltage first. If they are not, charge them individually until they are within .1 volt. (If one battery is low the other will charge it, possibly at a too-high rate: heat and explosions, etc are things to worry about).

Put the batteries in parallel, (+ to +, - to -). Connect the panel (positive output lead to +, - to -). Put the panel in the sun, and check that the battery voltage has come up slightly (by .1 volt or so), indicating that charging is occurring. If there is no change, check that the output of the panel is greater than 6 volts, when it is disconnected (8v would be good). Assuming the voltage is good, then reconnect to the batteries, and check the battery voltage again in 1 hour. Monitor voltage until the battery voltage is about 7.0 - 7.2, then disconnect the panel.

Check the batteries after they have been sitting (attached to nothing) for four or five hours. The voltage should be about 6.3 (fully charged). You can then hook them in series (one lead from negative to positive between them, with the car charger/adapter going to the remaining + and - terminals.)

A charge controller seems like overkill with such a tiny solar panel. They are cheap for 12 volts, but might be hard to find for 6 volts. If you were going to use a charge controller, then you might want another panel, hooked in series, to provide 12v nominal. Then the project is really simple: just hook the batteries in series all the time, and charge them through the charge controller.

Once the system works right, then make more durable connections, mechanically mount things so that there can be no shorts, etc. Rather than hard-wiring the car adapter to your batteries, you'd want to use a cigarette lighter socket (from Radio Shack, etc.)

Thanks again for the reply Mr K_fry (You're the only one that seems knows what he's talking about) but one more question

What if I just want to use 1 battery with the solar panel?

Can I use one battery with the cigarette lighter socket?

because I think that for using one of those cell phone car chargers you need a 12v output, is that correct?

The short answer: yes, some car adapters will probably work with 6 volts. In general, they are regulated power supplies, (not a simple voltage divider that would give you half the voltage on 6v input as it would on 12) and if the circuitry is fairly simple, 6 volts could give the same output voltage (say 4.5v) as with a 12 v input, and adequate output current.

Longer answer:

Many car adapters have mass-produced, cheap but moderately sophisticated circuits that prevent them from working on low voltage (undervoltage protection), and most are protected from high voltage as well.

Less sophisticated car adapters can have circuits like shown in this diagram*. This one uses a zener diode to regulate voltage, and is powered by 6 volts. (Slight changes in the circuit could optimize it for 12v.) It has no undervoltage protection, so if a car adapter had a circuit like this, then that adapter would work on 6 volts. Some car adapters probably do... there would be no harm in trying -- there are no car adapters that will go up in smoke from too-low voltage.

I'm guessing here, but I'd think that at least half of the car chargers would work with a 6 volt battery supplying them (assuming the phone in question can be charged by a USB cable).

Many cell phones, GPS units, etc, have a proprietary version of a usb connector, so that they will only work with the original equipment charger. (The unit being charged must "see" a particular resistance across certain USB pins [that would otherwise be unused] before the charged unit's charge regulation circuits turn on. (As far as I know, this is only a ploy to generate more revenue by locking you into the original equipment vendors stuff... but one could argue that some devices would overtax a standard usb supply, but the manufacturer wanted to use the USB connector, because the device had to communicate with a computer.) Now, many phones (and mp3 players, etc) will work with any USB charge source.

But definitely try your adapter on 6 volts. I'd think there would be a 50/50 chance that it would work OK. (This would, of course, not work to charge anything that requires over six volts at the input to the charged device, such as a laptop.)

Certainly, the simplest arrangement is 12 volts, because everything is built for that market.

* This circuit, by the way, would work directly from your 6v battery, and would eliminate the need for the car adapter. You could make this for a few dollars. If the output were wired to a USB cord, you would just plug the usb cable into whatever would accept it -- which these days is a lot of stuff.

If you think that these batteries will never be discharged, this contraption will never be used. 29 hours will encompass 6-8 days. 100% efficiency in wiring, cell production, etc is pretty tough to get. That PV cell is like the one you get on a two dollar calculator. (I believe this has to be academic, to answer your question, Lyn)

If you think that these batteries will never be discharged, this contraption will never be used.

Yes, discharging a battery is how we use a battery, so if he is not discharging the battery, he is not using the contraption. But we don't have to discharge a battery until it is flat.

My UPS has had a full battery for years, and only occasionally have I used 10% of the battery's capacity. I use it even though I do not fully discharge its battery. Maybe I'm missing your point, but I don't think I said that he would not partially discharge the SLA battery in the course of charging his cell phone.

One need only replace (by charging) the energy used from the relatively larger battery (plus a tiny amount to counter self-discharge). The energy used is that to charge a cell phone, i.e about 2 Wh, depending upon cell phone usage. Three hours of sunlight each day, on average, is a pretty reasonable expectation, for 4.5 Wh. So, he could charge his cell phone and another small device each day.

If he charged the large batteries until full, (2 x 6v x 4Ah = 48Wh) then he could charge his cell phone roughly 20 times. But of course, he would be very unlikely to do do that. It is unlikely to be dark for 20 days.

His setup would have more than twice (48/18) the storage capacity of this backpack. His smaller solar cell (1.5 watt vs 2.7 watt) would mean that he could not quickly charge a cell phone directly from sunlight. But given several hours in the sun each day, his unit could quickly charge stuff at night.

I think we can assume that the OP is not so dim-witted that he would run the large battery all the way down before he recharges it.

yes you are missing the point. Your UPS had a charger that could supply 100% of the maximum charge rate at any time, and your demand (when the grid failed) occurred very infrequently. The key is that your recharge cycle was powerful.

This poster is charging frequently, if not daily. His charging source is miniscule, and intermittant, and he will not find it is anything close to sufficient by the time he factors in PV, wire and battery losses. He needs a much larger charging source. Remember, he has 1.5 at 6V rated solar production, which is.75W at 12V, or actually about .6 at 14.2, which is what he needs. I'm not being a wet blanket, I'm just telling you how it works, because I've been part of m,any an experiment that seemed reasonable on paper, but was far shy of really working. This is not even reasonable on paper.

You make many assumptions about my UPS and the OP.

My UPS does not come remotely close to supporting "100% of the maximum charge rate." You can find articles about adding an additional battery to a UPS, and they will say that, before doing so, one should check that the charge rate is at least 2% of the batteries C figure (i.e 2 amps per 100 Ah of battery capacity). Some UPS chargers are not capable of this figure... that's why you need to check. My UPS is not capable of charging at even 1C, let alone the 5C "maximum charge rate" the battery can accept.*

The poster's charging source for his cell pone is the 12v SLA battery pack, which is not "miniscule": it has many times the capacity of his cell phone (and more capacity than a $100+ solar backpack). Then, the question is "Can the solar cell supply (to the battery pack, during sunlight hours) the 2 watts-hours per day required by the cell phone?" The answer lies in the solar cell's output: 3 watt-hours in two hours. So the answer is yes, (but that perhaps on a bad day it will take 4 hours of sunlight, or even 6.) The advantage of having a relatively huge (as compared to the cell phone) battery pack is that every single day need not be sunny, and (more obviously) it is easier to charge your cell phone or ipod at night, when you are not using it.

Getting actual sunlight requirements requires knowing the efficiency of his car charger, but many of these are switch mode and 80% efficient. SLA batteries are 75% round trip efficient at these low charge and discharge rates. So if he needs to replace 2 watt-hours of cell phone consumption, then he needs 2/(.75x.8) = 3.33 watt hours solar cell output. Although in your belief system this is an unreasonable daily output for a 1.5 watt solar cell, in the beliefs of those who work with solar cells every day, it is not.

Remember, he has 1.5 at 6V rated solar production, which is.75W at 12V,

I can see why your experiments do not work out. For those unacquainted with the most basic electricity, a 1.5 watt 12 volt solar cell might seem seem to output twice as much as a 1.5 watt 6 volt solar cell. This is, of course, completely wrong. Those unaquainted with electricity might think that a 120v 100 watt light bulb would be half as bright as a 100 watt 240 v lightbulb. This is obviously wrong too.

The key is that your recharge cycle was powerful.

That is not "the key" at all. If there is a "key" it is that a ups can supply relatively high wattage for a very short time. One reason they are so cheap is that they have chargers that are very weak, not powerful. Thus if you have a power failure, and run the UPS down completely, it takes quite a while before it can deal with another long outage.

yes of course its watts, I read amps. You are correct.

Your UPS has a charger, whatever the rating, that operates at 100% of it's capacity at the request of the battery bank voltage sensor, converting AC to DC, with no time parameters.

The battery in this scenario is no more the ultimate energy source than the batteries in your UPS. It's the 120V grid and the PV cell, respectively.

A PV cell operates at the pleasure of insolation levels that occur with no relationship to demand cycles.

These two operating schemes are fundamentally different. But just build it yourself and see. Battery charge/discharge cycles are notoriously inefficient, and at this scale, You will not be able to maintain, much less charge the batteries even in optimal conditions, with a 1.5 watt PV cell. This is a public forum. Don't tell someone it will work when it won't.

Of course the reference to power (which is relative compared to the solar system you are contrasting) refers to the potential charge current delivered in the two systems. Your UPS has an unlimited supply of AC Grid power to recharge with, your PV cell has an unreliable infrequent source of energy.

Here is a solar calculator which might help to eliminate your confusion. It takes into account battery losses, etc.

The OP (or you, if so inclined) can input his daily need: 1 hour at 2 watts to charge his cell phone one day, (or I pod, etc.... none of which require daily charging, and some of which require only weekly charging) But, for a worst case, we'll say 2 watt-hours every day. (In operation, this is likely to be 4 hours at .5watts)

His battery (when wired in series) is 12v, 4Ah.

Your own figure (see your post above) is for 5 effective hours of sun per day.

He can plug these figures in and find that his system will work fine.

I wonder if your confusion stems from the fact that you think (as you stated above) that his panel is the size of that on a calculator. I have such a calculator, and its panel is 3/8 sq in. This 1.8 watt panel is 18" x 6.5", or 117 sq in. Multiplying that by 1.5/1.8 gives us an estimated panel size of 97.5 sq in for 1.5 watts. This is 260 times as big as a calculator panel. (People are pleased with these battery maintainers, which counter the large parasitic loads [which consume more watt-hours per day than a cell phone requires] in modern cars.)

No reply needed, I just wanted to balance your naysaying with a realistic view of things. I am sure the OP can make his own decisions re whether he wants to take a couple minutes to hook this up for an experiment. Unlike you, I see no downside in encouraging him.

a 6V 1.5 watt Pv Panel that is 117 square inches?

Keep digging.

a 6V 1.5 watt Pv Panel that is 117 square inches?

Are you intentionally being a belligerent jerk? I wrote that a 12v 1.8 watt panel measures 117 sq inches. You can verify that area with the link I supplied. Do you understand this much? Are you calling Amazon.com a liar?

A 1.8 watt 6 volt panel would be expected to be the same area, if the cell tech is the same: you need to produce twice the current, so the series strings of cells in the panel would be shorter and the parallel strings would be longer. Any third grader can understand this. Do you get this much?

Here's where the tricky math comes in. The OP's panel is not 1.8 watts; it is 1.5 watts. So we can expect that its area is about 1.5/1.8 times that of a 1.8 watt panel. That comes out to 97.5 sq in. So far so good? This might be where I lost you with the math. If so, this might help.

So if your question fragment (a 6V 1.5 watt Pv Panel that is 117 square inches?) is to mean "Do you mean that a 1.5 watt PV panel would measure 117 square inches?" my answer would be "No. You are simply showing that you are incapable ore reading." What I wrote was that a 1.5 watt panel would be expected to be 97.5 square inches. That is based on the fact (not your half-baked brand of conjecture and exaggeration) that a 1.8 watt panel has 117 square inches.

Keep digging.

I don't know WTF you mean by "Keep digging". No digging required. This all has been the simplest application of 4th grade math and 5th grade physics, tempered with 40 years experience using solar panels on sailboats and in other applications.

You have demonstrated clearly that you have not even the foggiest understanding of the difference between watt and watt-hour, amps and watts, or the relative areas of a calculator solar panel and a 1.5 watt solar panel. You're off by more than two orders of magnitude on the last!

When you write using the wrong terms, your writing becomes nonsense -- one can only guess at what you might have meant, or if you simply have no clue at all. I assume the latter. The fact that you took the time to write (and presumably thought about what you wrote) "Remember, he has 1.5 at 6V rated solar production, which is.75W at 12V, shows that you are simply really unfamiliar with electricity or simply belligerent just to be belligerent. I assume the latter, because you are here at CR4, where people generally get at least the basics.

Perhaps this is sport to you. It is not to me.

So, I've added you to my very small list of people to whom I do not respond (so small that it now has only 1 CR4 member.) I am not a fan of belligerence for the sake of belligerence.

Yup it's a fair cop Guv'.
I was harking back to the days of 'cells' rather than panels.
I shall go into the corner of shame, pile all my GAs together, set fire to them and throw myself onto the inferno.
Or maybe I'll just have some tea and toast.
Of course we all spotted the series parallel thing but thought it was just a typo.
Just goes to show the pitfalls of language and feline intelligence.
Del

You don't want to connect the batteries in parallelto get 12v; they need to be in series. But they could be charged in parallel. A bit of switching could make both situations workable.

The answer is that you could, but it would be a very poor and expensive design.

first, determine load, or the amount of watts you want to be able to consume each day.

second, determine storage capacity, or the size of the battery bank. This number is not relevant to voltage or amps. Those details will have to be addressed, but the question to be answered is this. How many days worth of energy (question 1) do I want to be able to store, while keeping my batteries above 50% charge capacity?

third, if you have two 4 amp hour batteries at 6 volts, you have 24 watts of usable power. (4x6=24 watts, 2 batteries x 24 = 48 watts 48 x 50% minimum charge level maintenance.) If you can get 5 hours of full sun equivalent (or sun hours, google insolation at your address), a minimum PV panel would need to produce 24watts/5 hours, or a 5 watt panel at a bare minimum. Voltage issues can be resolved. Most would at least triple that solar PV, because the reliability of sun exposure is only very good over long periods of time, and you sound like you are thinking this could be a charging station.

Bottom line, buy a 10 or 20 watt 12 V panel (which is really 17V), serial your batteries to 12V), and then ask about configuration. Sounds like a cool project.

Is this just for grins, or what?