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BillHoughton's avatar
BillHoughton
Explorer II
Jul 04, 2019

House battery charging issue

We can normally run 4-5 days on the house batteries (two six-volt "golf cart" batteries in series, for 12 volts) on our 2006 Itasca Navion. We're just back from a week and a half trip (total mileage probably did not exceed 500), and encountered a problem. On the second to last stop, after three days, the battery indicator (this is just about house batteries; motor battery was fine) was showing that the batteries were flat. They turned out to be nearly flat, although they had enough grunt to bring the slide in when we left camp (thank goodness; I really don't need to learn how to bring it in manually any earlier than I must). We then drove about five hours to the next stop, at which point the battery indicator showed just 2/3 charge. The motor's alternator charges the house batteries when the van is running, and a drive of that distance should have had them fully charged. We were at the last stop only overnight, and used the battery as little as possible. After a two-and-a-half hour drive home, the battery continued showing 2/3 charge.

I also note that the electrolyte, which I always top up before a trip, is down. Normally, I've found one or two cells below full, to a minor degree, and fine at the end of the trip.

I'll be starting by pulling the batteries, manually charging them individually, and getting them tested. My hypothesis is that a cell fried on one of them, and the alternator, diligently trying to bring them up to full charge, was overcharging the battery combination, leading to evaporation of electrolyte.

If that's correct, should I replace both batteries, in case of damage to the good one?

I presume that the house battery charging current is controlled by a separate voltage regulator from the voltage regulator controlling charge for the motor battery (otherwise, one or the other could be getting overcharged at any given time). Should I be testing that charging circuit, and is this something a good automotive electrical shop can test, or will I need to make an appointment with an RV shop (and wait and wait - the good one in this area is booked out for months)?
Class C

16 Replies

  • pianotuna's avatar
    pianotuna
    Nomad III
    Jul 06, 2019
    Hi Phil,

    Clearly there is something else going on. My charging paths are twin #8 wire with automatic breakers at 50 amps each. Since I changed to the telecom jars, I get almost no charging from the engine--and the voltage quite quickly tapers to 13.2 volt. One wire is OEM from the under the hood fuse box, and the other, which I added, comes directly from the starter battery. I do have manual control of each of the solenoids.

    I may have damaged my alternator over the 105,000 miles and 9 years of ownership as I did often run the water heater. This was with the 875 amp-hour battery bank of 7 Walmart Marine jars. I would do 20 minutes on which would knock the voltage down to 12.5, and then 40 minutes off. Actually that is how I came up with the 20 minute duty cycle--I did not want to run the starter battery down.
  • pnichols's avatar
    pnichols
    Explorer II
    Jul 06, 2019
    pianotuna wrote:
    No, once the starter battery is full charging rates go down to more or less a trickle charge. That is just what the 'brains' of the charging system do. That is, unless the starter battery is in bad shape.


    Don ... above is a clip from an earlier post of yours in this thread.

    My (Winnebago) Itasca 24V's coach and chassis battery systems do not act this way: The engine battery can be charged right up to full, but if the coach batteries are low the alternator will still dump large charging currrents into the coach batteries. I've seen up to ~71 amps so far going into the coach batteries when they started out being about 50% discharged and I had the V10 engine idling.

    I'm not sure how this is being accomplished, but I "think" that all 3 batteries (one engine 12V, plus two coach 12V) are all connected together in direct parallel by the solenoid whenever the ignition switch is on. This solenoid is probably the same one that is also switched on by the boost rocker switch on the cab's dash.
  • Bordercollie's avatar
    Bordercollie
    Explorer
    Jul 05, 2019
    I previously bought "US" brand 6 volt batteries that were supposedly equivalent to T-105 golf cart batteries from a local Powertron store. They were cheaper than T-105's.

    PS: I also check batteries with a hygrometer that shows specific gravity of electrolyte acid in each battery cell group and health of each, after charging. It has needle that shows good, marginal or poor. I think I ordered it from Sears.
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Jul 05, 2019
    Bill,

    If you killed a pair of GC2s and expected them to be better than 80% after five hours of driving, the only thing wrong here may be your expectations.

    Try charging them from shore power before you do anything rash.

    Matt
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jul 05, 2019
    No, once the starter battery is full charging rates go down to more or less a trickle charge. That is just what the 'brains' of the charging system do. That is, unless the starter battery is in bad shape.

    In my class C the solar panels send current to the engine.

    If I turn on a large load, such as the electric water heater, I can see up to 70 amps from the alternator. But that doesn't charge up the house batteries as they are providing about the same amount of power to the load.

    DrewE wrote:


    Whether it's a trickle charge or not depends on the way the motorhome is wired up, and how well done it is. On mine, it's far more than just a trickle charge, and I think it's probably typical of not a few class C's. There is a heavy (2 gauge or so, I think) wire between the chassis battery and the hose batteries, and a continuous-duty solenoid to connect the two together when the engine is running or the emergency start switch on the dash is pressed. I've happened to see 20+ A charge even when the house battery isn't extremely low, and would not be the least surprised if it's higher at times as the ammeter isn't really visible from the driver's seat.
  • D_E_Bishop's avatar
    D_E_Bishop
    Explorer
    Jul 05, 2019
    Bill, how are we suppose to help if you keep secrete the year, make and model of your RV?

    How can anyone tell what the charge rate should be with out some basic information.

    Do You have a Winnie.

    Does your rig have a B.I.R.D., do you know what a B.I.R.D. is? How old are the batteries?

    All this is important.

    My rig charges the house and chassis at the same 14.8 Volts. Not a trickle charge.

    More Info Please.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Jul 04, 2019
    BillHoughton wrote:
    If I do have a bad battery, I'll have to search the recent battery-related posts: I bought Costco batteries when I replaced the previous ones, but I recall a recent conversation in which someone recommended a particular brand.

    Costco sells Interstate batteries. Sams Club sell Duracell (made by East Penn) batteries. Both are good.

    The "premier" brand is probably Trojan. They are much more expensive and I don't know if the will last longer.
  • Gjac's avatar
    Gjac
    Explorer III
    Jul 04, 2019
    Bill, how old are the batteries? I would rather trust a volt meter reading than the lights saying 2/3 full. Start by checking the voltage on the battery posts with the engine running you should see about 14 volts. If not check the battery isolator/relay, it may be bad. If you don't see alternator voltage there check the starting battery. Your thinking may be right about your batteries but I would do these simple checks first then try to equalize them to see if they will come back. What kind off battery charger do you have and how many amps will it charge at?
  • DrewE's avatar
    DrewE
    Explorer II
    Jul 04, 2019
    pianotuna wrote:
    Hi Bill,

    Charging from the alternator is mostly just a trickle charge.

    It is possible to add an external diode to the alternator and then some serious charging is possible.

    Now a days DC to DC converters are an excellent, if some what expensive, way to get excellent results.


    Whether it's a trickle charge or not depends on the way the motorhome is wired up, and how well done it is. On mine, it's far more than just a trickle charge, and I think it's probably typical of not a few class C's. There is a heavy (2 gauge or so, I think) wire between the chassis battery and the hose batteries, and a continuous-duty solenoid to connect the two together when the engine is running or the emergency start switch on the dash is pressed. I've happened to see 20+ A charge even when the house battery isn't extremely low, and would not be the least surprised if it's higher at times as the ammeter isn't really visible from the driver's seat.

    Diode-based isolators tend to have poorer charging performance due to the voltage drop across the diode. Systems installed with smaller wires also tend to perform less well due to the voltage drop in the wire. In ones with a solenoid of some sort (or a BIRD, which is a solenoid plus some fancy control electronics), the house battery charging won't work if the solenoid isn't functioning properly, and they are somewhat prone to wearing out--perhaps because they're often somewhat underspecified, and sometimes more or less exposed to the elements.

    For a trailer, charging from the tow vehicle is indeed more like a trickle charge in the majority of cases, and especially via the standard 7 pin trailer connector; but motorhomes are different.

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