Voltage drop

[Sheogorath]

What would be a typical voltage drop across a charge controller? The system will be used to charge a single 12v battery at a constant current of about half an amp.

[Sheogorath]

ok let me add a bit actually, the deal is, I need to ge 450mA at about 16.5v minimum into this battery. Most solar panels I see have an Voc of about 21-22 volts, given that, and given whatever voltage drop the controller causes, is it possible? I mean, most of these panels claim to be designed for charging 12v batteries, but looking at IV curves it seems kinda strange, most of them cant keep the voltage high enough, current isnt my problem at all really. Basically im asking, can a 21-22 10-30 watt panel deliver 16.5 volts at 450mA constant current load to a 12v 20AH battery through a charge controller?

[joelhacker]

Remember that when you look at IV curves, that the most important

thing is the current going into the battery.  As long as you can

keep your voltage anywhere above the static voltage of the battery,

your battery will charge.

The current into the battery will depend upon the internal resistance

of the battery and the difference in voltage from the open voltage

of the battery and the open voltage of the solar panel.

Put a meter on the battery, connect the solar panel, and if the

voltage rises on the battery (even slightly), the battery is charging.

[Sheogorath]

Thanks for the comment

But I have to think of this in a much more technical way, I HAVE to get 16.5 volts at least, at the constant current of 450mA. Its a conceptual design scheme for an alternate power system for 3rd world countries. Taking into consideration the effects of a charge controller, I have to find out if a 21-22 Voc panel can put 16.5 volts into a battery at that much current.

[ghurd]

I will say no.  Just because of your defined terms and state of operation of the system.

Apples and oranges don't make strawberries.

If you have a 12V battery, and a panel able to put out 450ma at 16.5V...

the battery will determine what the voltage of the system is running at.

Pump 450ma into a 12V battery and it will still be a 12V battery.

To get a 12V battery up to 16.5V means it is probably already damaged.

Or it soon will be!

Many panels are able to maintain 450ma at 16.5V. As long as the sun is bright enough. A 10W panel should do it.

But the controller's whole point is too keep the voltage and current low enough to keep from damaging the battery.

If you HAVE to have a constant currant of 450ma at 16.5V,

you must redefine the system.

And pray a cloud doesn't happen past.

G-

[Experimental]

       As stated by others, what you are trying to do, can,t be done with a single 12 volt battery -- as 16.5 volts will destroy the battery in time -- a very short time !!

       If you use two batts producing 24 volts ( actually, more) then regulate the output voltage at 16.5 -- you can accomplish your goal -- and both batts can be charged by a 12 volt panel !!

       However, if your 16.5 volts are critical, it is going to take a pretty sufisticated regulator -- most swing obove or below the preset voltage -- but it can be done -- others here, more versed at electronics than I , can tell you how to do that..

       The amperage is easy, what ever you are operating will determine that rateing, and I would recommend two sealed, lead acid batteries of about 16 amp hours, as they are available and easy to maintain --- the load requirement in milliamps make that an easy choice !!

      Much luck to you, Bill H.....

[wpowokal]

Me thinks he/she is a little confused about battery charging and needs to Google on subject.

If otherwise please explain so we may best advise.

Allan down under

[finnsawyer]

O.K. Assuming you really have a 16.5 volt battery (hey, it's possible), you need to put about 7.5 watts into the battery.  For the 10 watt panel that leaves 2.5 watts left over.  This translates to 5.7 volts, which should be enough to operate the regulator.  Of course, this probably will occur only under bright direct sun light.  The situation will be better for the thirty watt panel, namely because it can provide more current at any level of illumination.  

What you really need to know is what voltage the panels provide at 450mA at various levels of illumination, not Voc.  Then you can pick the one that works best for you.  I also think you need to consider the daily drain on the battery to properly size the system.  What you are really doing here is asking for an easy answer to a fairly complex engineering problem.  You may just have to buy some panels, build a prototype system, and get some data.  There's a reason why engineers are paid the big bucks.

If you're planning to make a million or so of these units contact the panel manufacturers and request the engineering data that would be useful to you, namely the voltage-current curves for different levels of illumination.

As always, "The devil is in the details!"

[Sheogorath]

Ok, I misunderstood other members of the project when asking my original question. Basically, we need 16.5 volts to power our box, which then internally charges the battery with of course a lower voltage. I do not want to put 16.5 volts into a battery.   The project is lead by the Engineering Dept at Columbia U, where I am working for this summer.

We have already designed and built prototypes of our original charging/discharging system and have working units. Now, we are considering the possibility that individuals, (those using the system, not us) may want to plug their own solar panel into our box instead of using our institutionalized village charging station setup. So, this now comes down to a few main questions, which maybe you can help me with.

what algorithm does a basic solar charge controller use? What are typical set points for overcharge, float, LVD etc?

we have a 3 stage charging system that charges to 14.4 overcharge voltage and 13.8 float voltage?

Sorry for the confusion earlier, and sorry for all the questions, your help is greatly appreciated.

[Sheogorath]

arg sorry, the sentence regarding the 3 stage charging system is NOT a question.

[wpowokal]

http://www.homepower.com/files/battvoltandsoc.pdf

[ghurd]

I believe the algorithm varies by brand.

See wpowokal's link for battery voltages.

To get a higher working voltage from a solar panel, you may want to look at panels with more than the standard 36 cells.

At least BP and GE, maybe others, make at least some panels with 40 cells, which will increase the operational voltage "sweet spot".

Smaller GE 40 cell panels are sold out almost everywhere I know of, and no more will be arriving from China for about 2 months at best. (I still have 3 50W )

Smaller BP 40 cell panels should be easier to find right now.

For testing and prototyping, 3.2W VW panels have 42 cells and put out over 200ma in good sun. I saw 225ma in decent conditions, so 2 would be right at the 450ma.

They have a built in 13.8V regulator in the plug that could be removed.  

The VW dealership may just give you a couple for a school project.  Or they are all over ebay.

G-