5 amp charge controller debugging

soylentgreen

A friend who owns my old camper van was trying to debug the house battery not charging. We fixed a major problem (battery combiner relay mis wired). The van also has an el cheapo 15w panel with the small plastic box 5a charge controller.

The panel was showing 20v open circuit in semi overcast skies so we concluded it's probably ok.
However the charge controller was showing only 5v open circuit. We were expecting 13 ish.

Question: was that a reasonable test of the charge controller? Or does testing it open circuit not give a valid voltage?

(This was debugged over the phone and he said it was "kind of sunny" so an alternative explanation is that it simply wasn't enough insolation)

Cariboocoot

Re: 5 amp charge controller debugging

What do you mean 5 Volt open circuit on the charge controller? If you mean on the output leads with no battery connected this would be because the controller doesn't work without a battery connected. Otherwise there really is no open circuit Voltage on a controller.

The only way to check a controller is to measure input current compared to output current.

A 15 Watt panel will not produce even 1 Amp of current. It isn't going to charge anything. It can keep a battery up, but it won't charge it (unless it's like 10 Amp hours).

soylentgreen

Re: 5 amp charge controller debugging

Correct: measured voltage at output leads with no battery connected.

I agree the panel is way under sized but this is a camper van that's rarely camped in for more than a few days so the major charging comes from the alternator.

Cariboocoot

Re: 5 amp charge controller debugging

If he's got a 5 Amp charge controller he ought to at least have an 80 Watt panel to make it worthwhile. That would be around 5% charge rate for a typical 90-100 Amp hour 12 Volt battery. As it is he may as well have no controller and just let the daily trickle from the panel keep the battery topped up.

BB.

Re: 5 amp charge controller debugging

Some (most) charge controllers need >9 volts on their Battery Output connections to work correctly. If unconnected, you may get zero or random voltage on the charge controller's output.

If you can justify it--Get a DC Current Clamp type DMM (Sears make a "good enough" for our use meter) and measure the actual current flow when the circuit is connected and the sun is shining.

-Bill

soylentgreen

Re: 5 amp charge controller debugging

Thanks to all the replies - it sounds like the method used (open circuit testing of the charge controller output) was not a valid one. I'll advise my friend to make sure the battery is OK, and then to reconnect the charge controller and see what happens.