DC to DC three-stage charger for RV

ShadowcatcherShadowcatcher Solar Expert Posts: 228 ✭✭✭
One of the threads on an RV forum is the voltage regulation, or lack of, from the tow vehicle/motor home alternator. The suggestions range from using a Balmar marine alternator charger (expensive) to some sort of DC to DC three-stage charger. Balmar makes a charger/regulator which and it is unclear if you need an externally controlled alternator.
I do not know the value of trying to regulate voltage coming from our Subaru to the Lifeline AGM battery in our teardrop trailer. I used a 10Ga wire from the battery to the 7 prong connector.
It would be a fairly easy task to add some sort of regulator before the Vectron monitor shunt. Part of this equation is the 185W panel feeding a Morningstar Sun Saver MPPT controller.


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: DC to DC three-stage charger for RV

    Only my opinion but ...
    Don't use the tow vehicle to charge the deep cycle house battery. Even with a big alternator needed for the extra current demand, the charging profile is not suitable. Since the main problem is that vehicle charging does not go up to high enough Voltage and then stay there (Absorb cycle) they are inherently unsuitable for the task. Add in 20' of wire resistance and you have even lower available charge Voltage. If you up the output on the alternator to overcome this you cook the starting battery. Putting any form of charge regulator between the vehicle and the house battery will only use up power.

    It's the same old story we repeat here often: you can not recharge two different batteries from one source; one, the other, or most often both will suffer.

    The best thing you can expect from this sort of set-up is to help Bulk the house battery or keep it from falling below the 13.8 Volts that a vehicle normally operates at.

    Now will come all the opposing POV's from others. :roll:
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: DC to DC three-stage charger for RV

    lifeline agms may work off the alternater/regulator of some automotive systems depending upon the actual charge voltage setpoint of it. it would not ever go into a float stage as it would only allow the bulk and absorb stage with no temp compensation. the nominal range for charging at 77 degrees f +/-10 degrees is 14.2v to 14.4v. i would not advise a charge to continue for very long after full charge is attained though. this means if you are driving 300 miles to your next destination and that battery is still being charged off of the alternator and started out as charged that this should be avoided and the power from the alternator should be killed to that battery if no load is upon it during the trip.

    many other batteries need higher voltages to reach a full charge and some electrical systems in cars may not go high enough for the full charge. they may do a good portion of the bulk charge enen if too low and supplemental power from another source can finish the job. if you are in doubt as to what yours goes to then use a dvm or dmm to accurately measure the battery voltage with the engine running. note that paralleling batteries like that of the starter battery and the lifeline opens up a new set of gotchas.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: DC to DC three-stage charger for RV

    The newer Chevy trucks do active voltage/charge management. Not saying its perfect but better than the old dumb voltage regulators.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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