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fotodog's avatar
fotodog
Explorer
Dec 30, 2013

Overnight battery drain

I'm trying to determine if the overnight drain on my batteries seems reasonable. My 2008 Tiffen Class A coach came with 2 house batteries and an Onan generator. I want to dry camp at times, so I had 2 additional Interstate 6 volt batteries and a Prosine inverter with 3 stage charger professionally installed. I check the electrolyte level often.

On my recent trip to Death Valley with no hookups, I would charge the batteries with the generator during the day to a reading of about 12.7 amps. My heater would come on 6 to 8 times a night, with the fan running for about 5 or 6 minutes. When I got up each morning, the reading on my inverter panel would read 11.6 to 11.7 amps. From what I have read, this seems too low.

I left my DVR plugged in to avoid having to reset it, and didn't notice until the last day that the draw at night was 6 amps. If I unplugged it, the draw as 2 -3 amps with no house lights on. Since I had the fridge set to gas, I'm not sure where that was coming from, unless it was a couple of phones charging.

For those that understand electrical issues, does this seem normal? Thanks for your help!

21 Replies

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  • westend's avatar
    westend
    Explorer
    Dec 30, 2013
    If you've only charged the batteries at intervals of two months to six moths apart and haven't used a disconnect switch to separate the batteries from the parasitic draws, your batteries are probably toast. In between charges, the batteries are drawn down to nothing. There aren't too many FLA batteries that will endure more than a few of those cycles.

    Your easiest, hands off option is to install some solar. You won't have to disconnect or connect anything, the solar will provide some power and charging during the day when in use, and will allow your batteries to become fully charged when stored.
  • fotodog's avatar
    fotodog
    Explorer
    Dec 30, 2013
    Thanks for all the quick responses. On this trip, I ran my generator for 2 - 2 1/2 hours per day. Being a former tent camper, I still try to limit the amount of time I run it. I will definitely turn off the inverter from now on when not in use.

    We normally camp with electrical hookups, so I would think the batteries have been fully charged before. But it sounds like I may not be charging the batteries enough between trips, which are sometimes 4 to 5 months apart. I normally try to take the coach out for an hour drive with the generator running under load every month, but I admit that when work is busy, it might be 2 months between charges. My storage facility doesn't have electricity to keep the batteries charged.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Dec 30, 2013
    Hi,

    If you plan to boondock in the desert get a solar system.

    12.7 is clearly not enough. Likely the battery bank has never ever been fully charged. It can take 168 hours of shore power to get the job done, depending on the converter that is in use.

    The load of 6 amps in twenty-four hours = 144 amp-hours. Add in some lighting plus an hour of run time for the furnace probably adds another 26 amp hours. So the bank is down 170 amp-hours by morning.

    Recharge time on batteries is fairly quick until 85% state of charge is reached. Then it drops off fairly dramatically.

    Since you probably have 464 amp-hours of storage that means the last 15% of recharge time starts at about 70 amp-hours. To replace the first one hundred amp-hours would take my system about 2.5 hours (assuming night time with no solar help). To replace the remaining 70 amp-hours would take about 5 additional hours.
  • MrWizard's avatar
    MrWizard
    Moderator
    Dec 30, 2013
    heater/furnace fan runs on 12v and can pull 8-10 amps when running

    the fridge control board and fans use 12v
    these and other items like the propane control valve, the CO detector etc..

    constitute parasitic loads that are always on when the batteries are connected

    2-3 amps constant is NORMAL for a late model coach

    many inverters can draw that much at idle with no loads turned on

    how many hours did you run the generator ?
  • eb145's avatar
    eb145
    Explorer II
    Dec 30, 2013
    Tim,

    concerning your question about "parasitic loads" on your batteries, here are some possibilities where they are coming from:

    - your Fridge might have a 12V heater around the magnetic gasket on the door to eliminate condensation. This can be a big load. Some fridges include a switch to turn off this heater.

    - Antenna booster can draw lots of current. There is a little push button toggle switch with a LED light on/off indicator that boosts the signal from antenna to television.

    - Inverter left on even with no load can consume lots of power.

    1 Amp of parasitic load is more typical - it is what I see in my TT. This is from the fridge circuit board and the propane leak detector.

    For charging phones I have some 12V USB chargers that I plug into cigarette lighter plug to charge phones - more efficient than converting to AC and back to DC again.

    I hope this helps you figure out your high current draw.

    Ed
  • BFL13's avatar
    BFL13
    Explorer II
    Dec 30, 2013
    Yes that 11.7v for your morning voltage is way too low for your size of battery bank and the time spent charging them, even allowing for a 6amp draw all night. That is only 60AH.

    Usual thing there is the batteries being sulfated so they have way less capacity than you think, so they run down quickly. You can spot sulfation by using an hydrometer to see what the SG is when they are fully charged. Might be 1.250 instead of 1.275

    Your prosine has a desulfation program to do 16volts for however many hours. You must disconnect the rig from the batts first so you don't hit the fridge control board with 16v (15.4v limit on that) and any other delicate items. Read the prosine manual instructions before doing it :)

    Next, review how they got that way--undercharging and being left below full charge overly long. Follow this guide:

    http://www.wholesalesolar.com/pdf.folder/battery-folder/charging_instruction_2011_2.pdf
  • time2roll's avatar
    time2roll
    Nomad
    Dec 30, 2013
    How many hours did you run the generator? Expect to run 3 to 4 hours and still get to just 85%/90%.
    Inverter may idle at 2 amps when not in use. May not seem like much but it adds up. I would turn off when not in use. Other 12v controls could easily be the rest of the normal draw.

    LED lighting and/or 200 watts of solar would make a huge difference.
  • rvten's avatar
    rvten
    Explorer
    Dec 30, 2013
    Your propane heater runs off 12 volt so does the fan.
    An Inverter converted 12 volt to 110 volt. Usually fir entertainment center.
    The Converter takes The 110 volt shore power and makes 12 volt to charge your coach batts. And run 12 volt items like lights.
  • fotodog's avatar
    fotodog
    Explorer
    Dec 30, 2013
    Yes, sorry, I meant volts. As far as I know, there is nothing else running off the inverter other than the heater fan, phone chargers, and dvr. I use a portable satellite dish.

    When I mentioned a charge of 12.7 volts, that was the reading after the generator had been turned off for a few minutes. I'm not sure about the reading when the generator was running.
  • BFL13's avatar
    BFL13
    Explorer II
    Dec 30, 2013
    Your charger has a voltage of at least 13.6, probably 14.4 volts. Batteries are charged when they get to the charger's voltage and then stay there while being charged for even longer. Wait at least an hour after the batts get to 14.4 before shutting off the charger.

    Stopping the charge when the batts are only up to 12.7 from whatever they were down to, is nowhere near getting them "charged"

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