Solar panels generating 21 volts (1 Viewer)

[Mace]

So I picked up a couple Hecho in china Solar panels for cheap. They had been set up previously for charging batteries from the looks of it with alligator clips and an on/off switch. The panels are about 3x1 ft (glass) and there are two of them. No major markings on the backside to indicate the amps.

Question, I see that a lot of the folding controllers have a built in charge controller. What is the easiest way to identify if these panels do? Also, if there isn't one, the internets say that the 21 volts is not a big deal. And that hooking it up to a battery will reduce the voltage to the 12V range.

Or, should I pick up some sort of small charge controller and try to stick it to the back of one of the panels?

I'm just trying to figure out if I can use these to keep a battery charged up and running well or not..

 

[e9999]

You should be able to see a distinct box attached to the panel back if it has a built-in controller. Otherwise, they'd just be a couple of wires coming out.

As to the need for a controller, I have seen very small panels attached directly to the battery for trickle charging but I would not do that with a sizeable panel. You don't want to put an excessive voltage/current on it for very long after it's fully charged and a large panel (as in 50W) will charge a typical battery pretty fast. Plus a good (MPPT) controller will give you a better charging efficiency.

 

[george_tlc]

Charge controller unless you want to boil your batteries.

PWM to save money, MPPT otherwise.

Most any solar panel for 12V use will be in the 18V or higher range. The tiny dash top ones can't produce much charge so not a big deal to run without some controller, but get into the 20W+ range and you really don't want the panel connected to your battery long term without a controller.

cheers,
george.

 

[Mace]

Bout what I thought. Scary that they have alligator clips mounted directly.. lol

What charge controller do most people use on the smaller folding solar panels?
This one looks small and cheap

http://www.amazon.com/Charge-Contro...&sr=8-18&keywords=pwm+solar+charge+controller

 

[george_tlc]

The amazon unit is a typical cheap PWM controller from China. Ebay abounds with them. They come on all the cheap folding panels (at least in oz). They work 'ok' if you're cheap

cheers,
george.

 

[Cruiserdrew]

Morningstar SunGuard is a good and cheap (but well made) charge controller-max 4.5 amps I think.

http://www.amazon.com/SunGuard-Char...43477926&sr=8-1&keywords=morningstar+sunguard

Or to allow for a better future panel, a Morningstar SunSaver 10 is also well made and about $50.

 

[alia176]

If you have a DC amp clamp or another means of measuring the current using a shunt, do this: aim the panel at the sun, connect the pos and neg together and short circuit the panel. This is how you get the Isc (short circuit current) and see if the panel(s) produces enough current for your needs.