Solar Panel Voltage

The charging voltage can vary according the charge being held by the battery...On some systems the lower the charge held by the battery the higher the charging voltage...

What is the voltage at the output of the charge controller?

Look at a spec sheet of any 12volt solar charger - what does that tell you?

http://www.streakwave.com/mmSWAVE1/Video/TPS_Solar_Panels_Spec_Sheet.pdf

How and why does a charge controller do what it does?

Gav

the DIFFERENCE in voltage between the charger, regardless of the type of charger, and the battery's voltage (what is present when the charger is temporarily removed) determines the charge rate. Your assertion is incorrect. The CHARGE RATE should increase as the battery's voltage drops. Too great of a charge rate is going to ruin the batteries, so having the charging voltage increase as the battery becomes more depleted is not a good thing.

Your answer is incomplete/misleading and as such could lead to basic misunderstandings by others.....

Now if you posted a complete and correct answer, I would be prepared to give a GA.....

I disagree, maybe 18 volts is allowed, but most likely is that the voltage is simply dropped by the load of the battery when charging to a lower value.....it goes with the internal resistance of the solar cell and the battery.....both are variable with load/charge.

I am not impressed by the electrical knowledge of the OP and I would assume that he has not made his voltage checks in the correct manner....an open circuit for example might easily give such a voltage on the charger. You have to have the battery connected/charging and also simultaneously measure the charging current = need for two meters.

I would assume (hopefully true!), that the charge controller would set the charge voltage to a correct level, therefore the charging current, to a safe level that will recharge the battery at a rate for which it is designed for......see manufacturer's infos....

I also believe that solar panels of 18 volts nominal are quite normal (I am not a "solar" person!) and are regularly connected to 12 volt (nominal) lead acid batteries via charge controllers, as that is their job....

If you accept the gassing, the shortened battery life and the safety rules, charging with a voltage of around max 14.4 volts will give a 100% fully charged 12 volt battery. Almost every modern 12 volt car does this every day.....= normal business....

In some cases, even higher voltages (producing higher charge currents) can be used provided:-

a) the battery is so designed.

b) The safety rules are followed with regards to the gas produced.

I personally stop charging on my caravan battery at between 13 - 13.2 volts to extend the battery life and to not gas it, but this does mean that the battery is only around 70% charged. But as I bought a battery far larger than I ever need, it works well for me....It is now over 8 years old......

Well then I challenge you to attempt to get a reading of 18 volts between the battery terminals of a lead acid battery (with an ammeter hooked up), get back to us, and relate what that reading is (charge rate). I can guarantee it will be a value WAY higher than what is reasonable for that particular battery. I have used batteries ranging in size from golf cart size up to about 400 pounds PER CELL. I charged the batteries at a safe rate designed to get maximum life out of the batteries. I NEVER had 18 volts at the battery terminals.

I built a generator out of a 1600 cc subaru engine and two high-output alternators and spent quite a bit of fuel and time putting well over 100 amps continuously into large lead acid batteries that had been left idle long enough that they sulfated. The reading was over 15 volts. Eventually the batteries broke out of reversion and began performing like normal batteries again (accepting a charge) and, with the same current reading on the ammeter, the voltage dropped. The pertinent point is that the battery pack WILL load down the solar panels and the resultant voltage reading at the battery terminals will not be 18 volts UNLESS the battery is much too small for the application. I have built and used solar systems. I know how it works. I learned by trial and error that for a usable household solar system, even to run just a few household items, you need a lot of battery power. A large battery bank is going to drop that 18 volts from the panels down to about a volt (maybe less) over the batteries voltage. Even when I'm using a high output generator putting out way more current than the solar panels, I never get anything even close to 18 volts. You are just flat out wrong.

Charge controllers are not necessary unless the battery pack is small. There is a safe "float" charge that can be applied. I use a battery pack big enough that the solar panels cannot overcharge them, period. Anyone who has any experience with a solar and battery arrangement knows it takes a LOT of battery power to run a household. PERIOD. The first solar system I had was about 2 tons in battery weight. The last one I used weighed about one ton. As I work from home using computers (so I'm home all the time) it was not enough battery power. The first system had enough battery power to (generally) last all day.

You obviously read or understood (I do not know which) only a tiny part of my last post........

If you want you can tell me which it was (not reading or not understanding, tip, go for not reading it all), please do....as you will find out that I covered the point with the thought that probably no battery was connected.....then it would be quite possible, no load = no voltage drop......

To refresh your memory, here are the first two sentences again with some significant underlinings for you, remember "never say never" especially on CR4!!!!:-

I disagree, maybe 18 volts is allowed, but most likely is that the voltage is simply dropped by the load of the battery when charging to a lower value.....it goes with the internal resistance of the solar cell and the battery.....both are variable with load/charge.

I am not impressed by the electrical knowledge of the OP and I would assume that he has not made his voltage checks in the correct manner....an open circuit for example might easily give such a voltage on the charger. You have to have the battery connected/charging and also simultaneously measure the charging current = need for two meters.

I covered all points in a (I thought easily understood manner) simple manner and nobody here (except you yourself) thought that there was a 12 volt battery with 18 volts across it....but being a careful person, I never say "never".......as theoretically with some sort of heavy duty battery and temperature control, it could be possible, but probably only for a short time. I have never tried it myself.....

In the early 60's, we used to not put the CHARGER temp sensor in a badly sulfated battery and we would charge it till it was hot and some batteries would then accept a charge again (as you have done)....I was a school kid and never checked the voltage achieved.....not my job....

Have a great day anyway.....

People are reading way too much into all of this. We do not know if the battery is a lead acid battery. For all we know the battery is an 18V lithium ion battery pack for a hand held power tool or that the controller has a mode for charging these batteries. With switching supplies being so inexpensive today, the solar array voltage can be easily converted to any desired voltage to charge a battery. So knowing the voltage rating of solar array is meaningless.

Initially, if the battery condition is good and just in a discharge state, the battery normal tendency is to pull the charging potential down to its terminal voltage. A good lead acid battery will be acting like a zener diode, clamping the charging voltage down to its original battery terminal voltage. This condition will continue with heat developing during the charging process. After a certain time and this charging process condition is not terminated by either manually or electronic means, one or both component will be destroyed.

If the output voltage of your controller is exactly the same as the input voltage of your controller, then your controller is shorted! (Unless your controller has boost capabilities...)

I was thinking it might be an equalization charging voltage but that is normally around 15.5V for nominally 12V lead acid batteries. 18V is a bit high.

What is suspicious is that the charge controller's output is identical to the input. It's either buggered or not connected to a battery.

If it is connected to the batteries and not buggered then the temp compensating sensor might be playing up, that's if the controller has temp compensating feedback.

Make and model would be nice to have.

It would be better if you gave the make/model of the controller so we could find specs on the controller so an accurate assessment can be made.

That being said I believe that it may be a faulty controller, as the charge voltage for a 12 volt lead acid battery should not go up to 18 volts, it would normally not go over 14 to 15 volt.

Some controllers I have used have a 3 stage charging system that has a fast charge in the 1st stage up to 15 volts & reducing for the following stages

Are you measuring the output of your charge controller with it connected to or disconnected from the batteries?

Thats a good question wal I didn't think of that. They can go high when disconnected with no load

To add to what has been said you need to do an equalizing charge from time to time to get all the batteries to the same voltage and amp's storage capabilities. From time to you need to desulfate your batteries to clear the scale from the plates, this causes a battery to not hold a charge and sometimes to short out a cell. to get back to the original question you need a charge differential/additional voltage to give the batteries a charge. The voltage must be higher to give up the charge to the batteries.

I think in this case the word "controller" is slightly misconstrued. I don't believe it is designed to regulate voltage, but to monitor it on the battery side. And when a predetermined voltage is reached, it shuts off, to prevent overcharging the batteries. Great marketing. Buy my CONTROLLER!

The solar panel is 18 volts in a full solar load. The system should be 50% more than the charging voltages of the charging system in chase the solar load change and make the voltage low in this case the system in a cloudy day will still charging full. The battery should be charge a top charge voltage that is in the rage of 12.5 to 13.8 volts depending on the system and a especial Amp. rate The controller is the one bringing the voltage from the solar panel down. Depending if the day is cloudy or not and giving a good current and voltage to the batteries to be charge in the best way.

This is the facts for you to understand how the system work. and if you want to change something on it is better to consult with the company that installed o build the system for technical information.

Thanks Javier

What you need is a DC-DC converter/battery charger designed for the battery chemistry and voltage you have.

These are commercially available or you can design your own to your specific requirements using one of the battery charger chips from TI, Linear Tech, or a variety of other chip manufacturers ...... but you do need to understand what you are doing before undertaking such an exercise, as stated elsewhere it is easy to ruin your batteries by under or over charging......