Originally Posted by Burgeogull
Ok so I have mine up and running! 4 six volt batteries and 220 watts of solar panels. The panels have no problem getting the batteries up to over 14 volts on a sunny day.
Now I have a question...how long should I expect to be able to use a small tv, my Satelite reciever and the trailer stereo. Right now the batteries drop fairly quickly in the evening to about 12.5 volts and remain all night.
Is this right or should I expect better?
There are a couple of points of confusion here. Using battery voltage to determine battery SOC (state of charge) has many limitations.
- when the battery is being charged, you are reading the charging voltage which has nothing to do with SOC. It does tell you if the charging system is working, but not the battery SOC or even how many AH (amp hours) are being put in
- it takes nearly 24 hours after disconnecting the charger for the battery voltage to be an accurate reading of the SOC. The voltage will read higher than actual SOC, gradually declining to the real value. And that's with no load attached during the period.
- reading battery voltage with a load attached, but not under charge, will under-read the SOC. The bigger the load, the more the battery voltage droops.
Amp hours are the measure of a battery's capacity. You need something like a Trimetric to monitor AH in and AH out to really understand how your batteries are doing. Calculating your AH load per day can be a good approximation, but it's very hard to know how many AH the solar panels are actually putting in.
A very rough approximation would be battery voltage at the same time each morning (before the solar panels kick in). If the voltage is holding steady, the solar panels are providing enough to cover the load. If the voltage is declining day-to-day, the solar panels aren't providing enough.
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan