Charge controller question

azrc

Is there any reason for going with any larger charge controller than the minimum? (Beyond future expansion of course).

Ie, if I have a single string of T-105 225Ah batteries, their nominal max charge rate would be ~15A, correct? So would there be any reason for going with a charger > 40A? I'm assuming that you would want to limit the maximum rate to 15A anyway correct?

Aside from being cheap, I noticed that some of the smaller chargers have a slightly better efficiency spec.

Thanks

niel

Re: Charge controller question

normally we recommend between 5% and 13% of ah capacity for the charge rate in amps, but trojan prefers around 10% which translates to around 22a or 23a. i suspect a 20a charge would suffice, but you don't want to feed your 225ah batteries with 40a as this would be too much for them. 15a will give about a 6.67% charge rate btw.

mikeo

Re: Charge controller question

but you don't want to feed your 225ah batteries with 40a as this would be too much for them

The charge controller should handle topping and floating the batteries no matter what size charge controller you have. With a 40 amp charge controller you should be able to charge the batteries and use any excess solar to run your loads while the sun is shining provided you have panels enough to supply 40 amps. If you can't use that extra power, then you have wasted money on your system.

Cariboocoot

Re: Charge controller question

If you only have enough panels to produce 20 Amps at the output, the charge controller will not put out more than 20 Amps - regardless of its maximum current rating.
Some charge controllers, such as the MX60, work best at about 75% capacity - their efficiency going down a bit as they near their maximum (heat production).
So no, there's no real advantage to having an over-capacity charge controller unless you are going to expand.