question

The temperature at the controller is in the low 60s at night so the controller should be compensating based on that temperature from what I understand.

The mppt will use the temperature it measures when the PV array starts producing power at the start of the day.

But if I enter a -16.66mv/°F it reduces the voltage instead of increasing it like it should.

Very odd. You are using the - (minus) sign before the number?

Hi @SteveCT

That upper limit you mention is a conversion from the metric equivalent of 5mV/degC/cell. I've never seen battery makers quote higher than this, and the function is very coarse, so they usually quote in full numbers, like 3, 4 or 5, etc. Convert that to degF and you get something that looks precise, but it isn't really.

I use GC pattern fla batts, which may be like yours. My maker said 4mV/degC/cell, and over my 48V that's 96mV/degC. I just rounded that off to an even 100, cos it's rough anyway.

As already mentioned, the entries must be negative, so charge V increases as Temp drops. And if you don't have a realtime T reading, you may need to compensate your charger V targets to allow for a T rise over the day.

So I figured out the limit issue. The .0028 volts is a rounded number from interstate. The actual value is .00277 which equates to 16.66mv. So that problem is solved.

I am still seeing what appears to be a reversed compensation. The temperature this morning was in the low to mid 50s at the controller. When I enter the temperature compensation as a - value the charge voltage is decreased which is the exact opposite of what it should do. When I input the temperature compensation number as a + value the charge voltage rises which is what I would expect with temperatures in the 50s.

I have the float voltage set to 13.4 volts and it's holding it at 13.3 if I input a - temperature compensation number and at 13.5 if I input a + temperature compensation number.