Back up charging question... possible damage to system?

DailypixDailypix Registered Users Posts: 11 ✭✭
I have an off grid cabin with Renogy Panels and their MPPT charge controllers. It will be my first winter and I will not be up every weekend. I have the panels at the right angle for winter which is pretty steep but I am in a snow belt and there was about 5 feet of snow on the ground last year. I was wondering if I get there and the panels are covered and the batteries too discharged can I just connect a good quality automobile battery charger to the same terminals that come out of the charge controller and crank up the back up gas generator or should I disconnect the charge controller first when attempting to charge the batteries at night or poor sunlight?


  • westbranchwestbranch Solar Expert Posts: 5,123 ✭✭✭✭
    That will work but you should be using the battery terminals or buss bar or as close to them as you can get,
     a shunt connection works too if you have one , then you can monitor the charge...

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  • DailypixDailypix Registered Users Posts: 11 ✭✭

    Westbranch, thank you for your quick response. I will be attaching the battery charger directly to the buss bar at the same location that the wires from the charge controllers connect. I was just worried that the automotive battery charger might damage either the charge controllers or somehow burn out the solar panels. I suppose a high quality automotive charger has the same safeguards as a good charge controller so as not to overcharge and the current going in from this source is little different from the current coming in from multiple charge controllers. This is all new to me.


  • BB.BB. Super Moderators, Administrators Posts: 28,325 admin
    edited October 2015 #4
    The automotive battery charger should not damage the solar charge controller or the panels.

    However, if the automotive battery charger is of the typical (low cost/fast charge) type--It could easily over charge the battery and damage it (and eventually over voltage the battery bus--damaging and attached DC devices, including possibly the solar charger).

    Watch how it behaves during charging. Since you are charging from a genset, you will not have to worry about the charger being "on" 24x7. However, you may need to disconnect it from the DC bus--The battery charger may draw some DC current when there is no AC power in its input (not good during winter/dark weather when you are not there).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DailypixDailypix Registered Users Posts: 11 ✭✭
    Thank you Bill. I thought about the electric charger possibly draining power when the generator was turned off so I disconnected it when I left after the weekend. So far we have plenty of power from the panels alone but it was good to know I have a back up in case we have a week of clouds and two feet of snow on the panels.
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