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Seamutt's avatar
Seamutt
Explorer
Sep 07, 2015

External battery charger

Now and again I use an external three stage battery charger on my two 6 volts without disconnecting the batteries from the trailer. I have not had any issues so far but was recently told not a good idea, that I should disconnect first before using the external charger.

Any thoughts on this?

31 Replies

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  • pnichols's avatar
    pnichols
    Explorer II
    Sep 09, 2015
    MEXICOWANDERER wrote:
    # T900XHD - Extra Heavy Duty Voltage Regulator Brush Holder Assembly for 6G Series Alternators - I-D-A Connection, 14.8 Volt Set Point

    Time to become knowledgeable about ALL systems that can affect your storage battery. This particular alternator is used on ALL NEWER FORD TRUCKS but it does have three variant voltage regulators. Do you know which one your newer Ford chassis has?


    I'm not quite sure what "voltage regulation" has to do with my Ford's V10 alternator. I watch what it's output voltage is all the time with a voltmeter sitting right on the cab dash.

    The alternator's voltage is all over the map - around 14.4 volts or so, briefly, when starting up cold, as low as 12.90-13.10 volts when going down the road in scorching hot weather, and everywhere in between - depending upon the outside air temperature at the time and depending upon the charging/maintaining load that the engine starting battery in parallel with the coach batteries are placing on it simultaneously. The alternator seems to "magically know" the float-voltage-versus-temperature table for our RV's coach batteries and applies the proper voltage accordingly. Somebody at Ford did their homework in specifying how our particular alternator model should and shouldn't act.

    Kindof like the OP, I often use an external battery charger on the RV batteries ... but use it in parallel with the coach's stock converter that is also powered up and connected to the batteries at the same time. The resultant voltage winding up on the coach batteries is a mix (depending upon internal battery and charger impedances all in parallel with each other) of the higher voltage of the external charger and the lower voltage of the RV's stock converter. Due to the stock converter's nominal 13.6 volt output "dragging down" the external chargers output a bit, the internal 12 volt items in the RV never see over-voltage when both the converter and external charger are charging the coach batteries while the coach batteries are still switched into the RV's system.
  • MNtundraRet's avatar
    MNtundraRet
    Navigator
    Sep 07, 2015
    MNtundraRet wrote:
    BFL13 wrote:
    Some here with those Schumacher brand chargers have said they will go to 16 volts in a sort of unpredictable way. In that case you should disconnect the rig's batteries first. The fridge controls have a 15.4v upper limit EG.

    You have to know the charging profile of the OP's charger to answer the question.


    You are correct. I have the largest Schumacher SC-12000A multi-stage charger which was dropped from their catalog about two years ago.

    I mainly use it for a separate Trojan 12v battery used with a inverter to power my television and recharge a Kindle Fire when not on shore-power. I leave my Trojan 6v batteries on "disconnect" when charging with Schumacher every once in a while. The Schumacher would run de-sulfation mode when needed on my previous pair. Not required yet on the newer pair. There are no items getting power when my house-batteries are on "Disconnect".

    I have used the charger many times to start vehicles at campgrounds when the owner misused and depleted their starting battery. It should be noted that the charger only hits the high voltage when finish charging at low amps and high voltage. It does not happen in the early charging up to around 85 to 90%soc.

    If one does not have a "disconnect" switch the refrigerator should be turned "off" to protect it's CPU. Don't mess with using a laptop, or charging smart-phones, etc., (using an inverter) while the charger is finishing the final 10% of charging to be on the safe side.
  • MNtundraRet's avatar
    MNtundraRet
    Navigator
    Sep 07, 2015
    BFL13 wrote:
    Some here with those Schumacher brand chargers have said they will go to 16 volts in a sort of unpredictable way. In that case you should disconnect the rig's batteries first. The fridge controls have a 15.4v upper limit EG.

    You have to know the charging profile of the OP's charger to answer the question.


    You are correct. I have the largest Schumacher SC-12000A multi-stage charger which was dropped from their catalog about two years ago.

    I mainly use it for a separate Trojan 12v battery used with a inverter to power my television and recharge a Kindle Fire when not on shore-power. I leave my Trojan 6v batteries on "disconnect" when charging with Schumacher every once in a while. The Schumacher would run de-sulfation mode when needed on my previous pair. Not required yet on the newer pair. There are no items getting power when batteries are on "Disconnect".

    I have used the charger many times to start vehicles at campgrounds when the owner misused and depleted their starting battery. It should be noted that the charger only hits the high voltage when finish charging at low amps and high voltage. It does not happen in the early charging up to around 85 to 90%soc.

    If one does not have a "disconnect" switch the refrigerator should be turned "off" to protect it's CPU. Don't mess with using a laptop, or charging smart-phones, etc., (using an inverter) while the charger is finishing the final 10% of charging to be on the safe side.
  • landyacht318's avatar
    landyacht318
    Explorer
    Sep 07, 2015
    My Schumacher sc2500a would regularly goto 16.4v, even on the AGM setting, and just blow past the mid 14's pumping out 12 or 25 amps.

    Abusive. Also the included voltmeter reads 0.2 to 0.3v low, so that was really 16.7v.

    Too high and too abusive for even an EQ charge. I could never leave unattended on anything but the 2 amp setting, and even then I could not trust it.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Sep 07, 2015
    I constantly make this point and it seems it enters ears, gets on a 4-lane highway and zooms out the other ear. This is the voltage regulator setting for some Ford 6-G regulators. Do six hours of driving one day, eight hours the next day, and yet some folks worry themselves to death over a tenth of a volt "quandary" of a converter voltage setting...



    # T900XHD - Extra Heavy Duty Voltage Regulator Brush Holder Assembly for 6G Series Alternators - I-D-A Connection, 14.8 Volt Set Point
    Price: $49.95
    # T900XHD - Extra Heavy Duty Voltage Regulator Brush Holder Assembly for 6G Series Alternators - I-D-A Connection, 14.8 Volt Set Point

    Extra Heavy Duty Voltage Regulator Brush Holder Assembly for 6G Series Alternators - I-D-A Connection, 14.8 Volt Set Point


    Time to become knowledgeable about ALL systems that can affect your storage battery. This particular alternator is used on ALL NEWER FORD TRUCKS but it does have three variant voltage regulators. Do you know which one your newer Ford chassis has?
  • BFL13's avatar
    BFL13
    Explorer II
    Sep 07, 2015
    Some here with those Schumacher brand chargers have said they will go to 16 volts in a sort of unpredictable way. In that case you should disconnect the rig's batteries first. The fridge controls have a 15.4v upper limit EG.

    You have to know the charging profile of the OP's charger to answer the question.
  • red31's avatar
    red31
    Explorer
    Sep 07, 2015
    Bad to leave the batteries connected and let the parasite loads drain the battery too deeply, good to properly charge batteries.

    Proper charging may exceed fridge control board voltage limit.
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    Sep 07, 2015
    There is the possibility that if there is not a isolation transformer, that there could be a problem. But as you stated, nothing wrong so far.

    So likely you have the proper equipment to charge the battery safely, or it would have tripped the 20 amp input circuit breaker soon after plugging in the second charger.

    The 'risk' would be that overcharging the battery will boil away more water. However a controlled overcharging to say 14.4 volts is 'good' for a battery perhaps twice a year. This will break up any excess battery plate build up, and restore the battery to near new condition for a while.

    So why are they telling you that it is bad? Well it can be bad, if you do not check the battery water level before and after a controlled overcharge. Also smoking during the controlled overcharge or any sparks around the additional hydrogen going out of the boiling water of the battery can explode. Leave it vented, and not over 13.8 volts, and everything is safe. Enclose the battery, or something, and it can become a danger. . .

    Personally? I use a solar charger to keep my battery full on a daily basis. I do not need to use a second charger, in fact my built in 70 amp charger is rarely used.

    If I did not have the solar, I would use the built in charger that came with the RV (normally 45+ amps) and a second charger is not normally needed. My friend with a 1987 class C had to use a portable charger to keep generator run time to a minimum. Before about 1995, most RV's had 'converters' and not good electronic voltage regulated high amperage chargers. That has changed, and if your RV is newer than 1995, then the built in charger is enough to charge the battery quickly, and no need for the portable one. Yet the portable one is safe, if you are not going over 13.8 volts, or if at 14.4 volts for a short time is only safe if you know that the battery plates are not dry, and excess hydrogen is well vented!

    Fred.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Sep 07, 2015
    You need to audit every single battery powered device in your rig and see if any one of them demands voltage lower than the highest voltage the charger can develop. I have LED light chips that are un-regulated. When I do a top charge or equalization, I make dog-bone* sure that no LED lights are switched to on.

    *Censor Resistant Expletive

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