Will my alternator damage my controller or panels?

neuroneuro Registered Users Posts: 8
I am working on installing two solar panels with total max power of 330w at 12v on my motorhome. The battery bank is in a typical configuration such that it is also connected to and charged by the engine alternator. Of course, a battery isolator is in place to prevent the house battery bank from depleting the engine battery.

Will there be any problems between the battery bank, solar panels and the alternator when I connect the charge controller? There will then be two sources charging the battery bank (solar and alternator) and I don't know whether they will play well together.

Will the alternator, which puts out much higher amperage current than the solar panels, damage either the controller or the panels?


  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Will my alternator damage my controller or panels?

    Properly connected, there should be no problem at all. When the alternator drives up the battery voltage, the charge controller should just "assume" that the batteries are charged, and back off, reducing or stopping the charge from the solar panels until the voltage falls again.
  • mike95490mike95490 Solar Expert Posts: 9,401 ✭✭✭✭✭
    Re: Will my alternator damage my controller or panels?

    Beware of "Battery Isolators". The cheap ones will undercharge your house battery.
    Some ideas


    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • RCinFLARCinFLA Solar Expert Posts: 1,407 ✭✭✭✭
    Re: Will my alternator damage my controller or panels?

    The vehicle alternator will not harm the PV charge controller.

    I don't like the idea of rewiring the vehicle alternator to give it direct path to house batteries then have a controller to pass it through to vehicle starter battery. It says if house battery is below 13 vdc it opens path to starter battery. So if house battery goes low or goes bad, like developes a shorted cell, you get no charging on vehicle electrical system. I think vehicle battery should have first priority on charging. If someone does something dumb with excessive loads on the house side you get no vehicle starter battery charging.

    It is hard to tell what the Balmar controller has in it but it looks like a simple PWM MOSFET passthru. This would seem logical based on vehicle starter battery charging being lighter load on alternator then house battery, "most of the time". A PWM controller can rake havac on the vehicle system when vehicle batteries are low or heavy load on vehicle (headlight, etc), much worse ripple then alternator noise.

    A better way would be to have a low ratio buck converter that limits house battery charging from alternator to some percentage of alternator capability or fixed max rate of current. Vehicle alternators do not regulate current. They will put out full rated current to recharge battery (unless the alternator temp gets too high). This type of controller would just tack in parallel to vehicle battery so no rewiring of vehicle alternator. Vehicle starter battery gets charging priority.
  • cptdondocptdondo Solar Expert Posts: 99 ✭✭✭
    Re: Will my alternator damage my controller or panels?

    My experience with diode-based isolators is less than positive.

    Look up the Blue Sea ACR. If you want to isolate battery banks, that's the way to go. They work, and there is no voltage drop.
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