Charge controller not charging battery

[salmirabile]

Hi everyone,

This is my first post so apologies for any noob questions.

I have a very simple setup of 1x 100w solar panel with a pwm charge controller which came with it.

The panel works just fine and outputs 20v when I measure it but once the controller is connected and the battery is connected to the controller, I only get 12.2v from the battery terminals of the CC. Is that normal? Surely it should be more than 13v for it to be able to charge the battery? Currently, the battery is at 70% charge.

Many thanks for any help

[SunEagle]

Hello salmirabile and welcome to Solar Panel Talk

First off that panel should be sending about 5 amps and 17 volts to the CC measured at the CC input terminals. So check that out.

If the panel is working then I would say something is either wrong with the CC or battery. It seems the battery is pulling down the voltage when at 70% a good battery will be looking for a higher voltage which the panel should be able to provide thru the CC.

So again either the CC is bad or the battery is bad or worst case both are bad.

[salmirabile]

Thanks for your reply.

Ok, I'll check out the reading from panel to CC in the morning.
The battery is brand new and charges fine with a normal 4a home charger and charges to 12.75v so can only assume it's the CC at this point in time.

[Mike90250]

Hook the panel directly to the battery, and in full sunlight. Measure battery voltage. Wait 10 min and measure battery voltage again . Did it increase ?

[salmirabile]

Wouldn't that destroy the battery? The panel would charge it at 20v?

[littleharbor]

Wouldn't that destroy the battery? The panel would charge it at 20v?

20 volts is the, no load, open circuit, voltage from the panel. Once you connect to a battery the voltage will be pulled down to the battery voltage but should rise as the battery charges. If there is a data label on the back of the panel is should show Voc. and Vmp. voltage numbers. The Vmp. is the highest voltage you will see under load. Temperature does affect output somewhat but when charging, the controller should hold the absorb voltage at approx. 14.6 - 14.8 max.

[salmirabile]

20 volts is the, no load, open circuit, voltage from the panel. Once you connect to a battery the voltage will be pulled down to the battery voltage but should rise as the battery charges. If there is a data label on the back of the panel is should show Voc. and Vmp. voltage numbers. The Vmp. is the highest voltage you will see under load. Temperature does affect output somewhat but when charging, the controller should hold the absorb voltage at approx. 14.6 - 14.8 max.

ok thanks for the info. I'll give it a go.


just a small update before I do. I tested the current output of the panel this morning and it read 25ma! It's a very cloudy and cold day but is that still too low or normal? When I first installed this system, I was certainly getting much more power from an equally cold and cloudy day.
I did the test by connecting the multimeter between the panel and controller. I then did the same test putting the multimeter between the controller and battery. both had the same result.

1 more thing....Last night my battery was at 70% as i stated and my system came on at 8pm for 12hrs. My system should not take more than 0.6a total so for 12hrs it should have drain around 7.2ah. the capacity of the battery is 40ah. After taking into account the 70% capacity left in the battery, the level should've been at approx 20-21ah. or around 12v.
I went into the garage 30 mins ago and to my shock, the battery was at 10v! i have no idea what on earth has happened here but something clearly drained the battery!

Could a bad controller drain the battery in any way?

This is my first endeavor into solar power so apologies for anything that may seem obvious to anyone.

[Mike90250]

With your small panel, a 10 min test won't hurt a thing.
Don't leave a panel direct connected at night, it usually does not contain a Blocking Diode. That function is provided (nearly always) by the charge controller.