Small solar power system questions.

nobody928 Solar Expert Posts: 62 ✭✭✭✭
Hello everyone. First off I just wanted to thank all of you for all your help. I live 100% off-grid full time. I now have a working system that powers: My direct TV box, 32in LED tv, flojet on demand water pump and lighting throughout the trailer.

I have 3x140 watt UL solar panels. I have a c40 xantrex pwm charge controler, 4x 105 a.h a.g.m. batteries. And a 1500 watt sine wave inverter.

I built this system myself with help from this forum and a few youtube videos. It powers my small mobile home and is a great alternative to the $15000 dollars that the power company wanted to charge me.

Now for my problems. I seem to be going in to float mode in the afternoon most the time on good sunny days. My charge controller is set to bulk @ 14.2 v and float is set to 13.2 v. How come once the sun goes down my voltage is droping to 12.8 volts or less? Shouldnt it be all the way full if its floating???

Thanks in advance for any advice.


  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Small solar power system questions.

    Welcome to the forum.

    The Float Voltage is actually higher than the batteries' normal Voltage. It is maintained at Float level by the solar panels. When there's no longer enough sun to keep the Voltage up, it slides down to battery Voltage. An "at rest" 12 Volt battery (fully charged, no current going in or out for several hours) would normally measure about 12.75 Volts +/-. So what you are experiencing is perfectly normal.

    You might want to turn your 'Bulk' Voltage up to 14.4 on those AGM's, and possibly increase the Float Voltage too. This could help make certain the batteries are more fully charged with each cycle and lead to greater battery life.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Small solar power system questions.

    i concur with coot's advice and will add for you to watch your batteries do not get too far drained down. with a bank of 4 at 105ah the usable ah is half of that or 210ah. at 12v this is 2520wh and it'll go faster than you think. some use a battery monitor for this, but is only a relative indication.