Forum Discussion

Johno02's avatar
Johno02
Explorer
Jun 16, 2013

Battery charging, Again!!

We have just had an opportunity to boondock for a few days, and it raised a question for me. I use a CPAP machine, running from the coach battery with no problem. However, I did need to charge the batteries some each day after a full nights use. I can charge the batteries either with the generator, or from the alternator on the main gas engine. With the generator, 110v power goes to the converter, which then provides 12(?)v to the batteries. using the main engine, 12v charging is direct from the 12v alternator on the engine. For a quick charge top-up, which is best??
Class A
  • rvten's avatar
    rvten
    Explorer
    Jun 16, 2013
    Guess depends if you want a quick charge from MH engine.
    Or One that takes several hours to charge everything up.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Jun 16, 2013
    By far the generator, You may well get a faster charge, but for sure you will use less fuel.
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 16, 2013
    SeaDog/BRR wrote:
    The engines 12V alternator will provide the fastest charging rate.
    Please explain.
  • Johno02's avatar
    Johno02
    Explorer
    Jun 16, 2013
    My thought exactly. The MH has a 60+ amp generator, and although the convertor is quite large, I am not sure what kind of charging current goes to the battery. In this case, we used the generator which worked well. I was thinking that if we had needed some AC, I might have used the coach AC at the same time. That thought passed quickly as I realized that alternator output is dependent on engine speed, whereas the generator is speed regulated depending on load. If I was going to be driving, then yes, the alternator charge is probably faster.
  • hmknightnc's avatar
    hmknightnc
    Explorer
    Jun 16, 2013
    2oldman wrote:
    SeaDog/BRR wrote:
    The engines 12V alternator will provide the fastest charging rate.
    Please explain.


    Hi 2oldman. Assuming he has a standard converter with standard wiring then the alternator will have greater Amp capacity feeding with larger wires and operating at nominally the converters boost voltage (14+)

    Now if the OP has an upgraded converter and upgraded converter to battery wiring the above my not be true
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 16, 2013
    hmknightnc wrote:
    the alternator will have greater Amp capacity feeding with larger wires
    and where are these larger wires?
  • hmknightnc's avatar
    hmknightnc
    Explorer
    Jun 16, 2013
    2oldman wrote:
    hmknightnc wrote:
    the alternator will have greater Amp capacity feeding with larger wires
    and where are these larger wires?


    It really depends on the OPs actual setup but assumming standard configeration. Every alternator charging system I have ever seen on an RV uses standard battery cable (like 4ga or larger) versus a standard converter wiring of 8 or 10 gauge.
  • Lobstah's avatar
    Lobstah
    Explorer
    Jun 16, 2013
    Also, most alternators I've seen on later model motorhomes are 100 amp or better.
    Most converters I've seen are 60-75amp range.

    Jim

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