Forum Discussion

dshinnick's avatar
dshinnick
Explorer
Jul 07, 2013

Wattage and ohms and amps.....Oh My!

Sorry about that....

Anyway, I have a diesel Motorhome with 4, 12-volt deep cycle batteries (Energizer GC2's, to be specific).

We're used to running the generator during movie time, but I'm beginning to wonder if the house batteries/inverter can handle it. I turned on the inverter this morning while dry camping, and turned on our entertainment center, and started a movie. Our power mgmt system told me I was drawing 40 amps.
Now, given that, and my batteries, how do I figure out how long I can maintain a draw like that without taking the batteries too low?

Thanks-
Dave
Class A
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jul 08, 2013
    Hi,

    Since there are 4 six volt batteries without going below 50% state of charge there are about 232 amp-hours available. 232/30 =~7 hours.

    How will recharging be done?
  • SCVJeff's avatar
    SCVJeff
    Explorer
    Jul 08, 2013
    Look at what he's running. That's competition with Regal :)
  • Daveinet's avatar
    Daveinet
    Explorer
    Jul 08, 2013
    I agree with SCVJeff, 40 amps seems like a lot. Are you sure your fridge is not automatically switching over to electric?? Second question, is the inverter an OEM install, or did you do it. Or really what I am asking is if the inverter is just wired to shore power? If it is, it may also be running converter, which would waste a lot of power as well.
  • dshinnick's avatar
    dshinnick
    Explorer
    Jul 08, 2013
    During the movie I checked, and it was 30 amps.
    And, we have:
    - 47" TV
    - home-theater receiver
    - movie server
    - Directv DVR

    ....and mumerous other items drawing less power.
    Yeah, I think 30 amps is about right....
  • SCVJeff's avatar
    SCVJeff
    Explorer
    Jul 08, 2013
    40A is a LOT of power for a DVD player and TV to consume. I have a 32" LCD, DirecTV, DVD player, my i7 PC, and a couple of CF lights, and I just clear 20A, and run at that level for 5+ hours a night. Are you sure you're not also measuring the 110vac heater element on the fridge?
  • dshinnick's avatar
    dshinnick
    Explorer
    Jul 08, 2013
    Whew! Thanks Mr. Wizard. I took a screen shot of that and I'll study it later when it's not happy hour. :0)
    Thanks much.
    Dave
  • MrWizard's avatar
    MrWizard
    Moderator
    Jul 08, 2013
    40 amps at 12.3v into the inverter inverter output approx 4 amps at 120vac

    six volts go in series to make 12v
    4 6v make (2) 12v batteries

    total amps hrs is approx 212 amps per (pair of 6v)
    meaning 424 amphrs total capacity at 12v .... NOT 880
    50% means 212 ampHrs,
    40 ampHr draw = 5hrs run time
    this not include power used by lights, fans, fridge, water pump etc..

    anyway yes you can watch a Movie with out the generator
    just be shore to run the generator the next day to recharge the batteries
  • dshinnick's avatar
    dshinnick
    Explorer
    Jul 07, 2013
    OK, yes, 6 volt golf cart batteries.
    And, that 40 amp draw was all 120 volt devices.
    And, how can I tell if the house batteries are fully charged? What voltage readout should I see on power my mgmt display?
  • hmknightnc's avatar
    hmknightnc
    Explorer
    Jul 07, 2013
    Your battery bank is roughly 440 AmpHours (it is 4 6volt batteries BTW) and you should not use more than 50% of that on a frequent basis. So assumming your batteries were fully charged (big assumption) then you have 220 Amp hours available before needing to recharge. At a 40 amp load you can go about 5 hours.
  • Mainship's avatar
    Mainship
    Explorer
    Jul 07, 2013
    220 X 4 880 amps fully charged down to 50 percent = 440 or 10 hrs run time, if the batteries are new, and not running anything else. if the 40 you quoted was 12v and not 120 v. which would only last an hour.

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