Solar Control

Hi John,

I hope you don't do this with your new batteries :>

Seriously, even a 15W panel can over-charge a VRLA battery, gels are particularly sensitive to this. One amp can push up the battery voltage beyond 15V easily. I estimate that up to 1 gram of electrolyte is lost that way on a daily basis. On a VRLA battery of this size you can affort to lose just 200~300 grams of electrolyte over the course of its useful life....

A solar regulator is mandatory to preserve battey life.
It should be set to the float voltage level of 13.8V in Winter and 13.6V in Summer.

cheers, Peter

Peter,

I'll bow to your greater experience. In my experience a small panel capable of less than an amp doesn't manage to push the voltage up enough on a 100Ah battery to cause a drama. Admittedly my experience doesn't stretch to gels and brand new batteries (until now!)

The two I got from you are great and will get all possible TLC.

Cheers

John

Hi John,

reasons why you haven't seen this high voltage at small charging currents are:
Ageing AGM batteries have a higher steady state current compared to new ones.
Battery temperature has a similar effect.
And last but not least, the battery probably wasn't really fully charged when you thought it was when observing the voltage rise.
As long as there's some lead sulphate to be converted back to lead and acid, the terminal voltage won't rise much. Only if all of it has been converted (battery 100% charged), then you can observe this effect.
I've run tests on a number of different brand new AGM batteries, and the terminal voltage can be pushed up to 17V with relatively low charging currents (3~5A).
You can hear it gassing :)

cheers, Peter

Ray,

Your 10W panel will supply a maximum of about 0.6 amps from strong sunlight when optimally aligned with the sun. While I respect Peter's judgement, I think the the need for a controller is pretty borderline with your big battery.

Suggest charge the battery fully, then connect the panel directly and monitor the voltage at the terminals. After everything has stabilised, if the voltage rises above the limits suggested by Peter, then you DO need a controller.

Cheers

John