My original email to the company:
We have a GoPower 95 watt solar panel and GP-PWM-30 solar regulator which was installed in our trailer by Escape Trailer Industries.
I have noticed that the GP-PWM-30 seems to read 100% state of charge when it is charging during the day, but this number drops to a much lower number when it is not charging in the evening even if there is no load. Can you tell me how the solar regulator determines state of charge? Is it based just on the voltage? Won't this give erroneous information if the battery is under charge or load? Would it make sense to take a reading of state of charge early in the morning before charging starts and in the evening when it is dark, making sure that there are no loads?
The response which I received today:
Yes the GP-PWM-30 reads the state of charge based on Voltage. And yes this number will change due to voltage drop due to no charge coming in from the solar module. To get the most accurate reading of battery state of charge you would need to use a shunt style measurement device like an E-meter or a Link 10. These devices look at every item that brings power in and every item that pull power from the battery. unfortunately we do not offer this measurement style in our regulator as this would drastically increase the cost of the Solar Controller.
Carmanah Technologies Corp.
Yesterday I installed a Trimetric TM-2025-RV
in our trailer. It is nice to be able to see the net amps going in or coming out of the battery and a more accurate estimate of state of charge. The Trimetric does use a shunt to measure amperage. The installation was easy, the documentation was excellent. I bought the unit from a Canadian distributor, WeGo Solar. Their prices are competitive and their service was great. Highly recommended!