Forum Discussion

Cheyenps's avatar
Cheyenps
Explorer
Jan 02, 2015

Charging question

Years ago I remember checking the voltage at my truck battery to see if the charging system system was working correctly. The instructions were to check the voltage at the battery with the engine running and then check the voltage with the headlights turned on. IIRC, the voltage was supposed to jump up to about 15 volts with the lights on, indicating that the charging system was working.

Do modern charging systems work this way? If so, would I get faster charging back to my TT batteries if I ran with the headlights on as a matter of course?
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Jan 02, 2015
    I've seen my float voltage maintained at 13.1V/110F and 13.9V/25F for GC2 batteries.
  • ScottG's avatar
    ScottG
    Nomad
    Jan 02, 2015
    pnichols wrote:
    ScottG wrote:
    Modern charging systems are temperature compensating and will allow higher voltages.


    Modern charging systems will also put out only 12.9 to 13.1 volts under certain temperature conditions.

    I've seen my RV's 130 amp Ford alternator put out only this much in 100 degree outside temperatures. It was probably REALLY HOT under the hood in these outside temperatures, too. The good thing is that in these temperatures, I wouldn't want my batteries to be seeing voltages any higher than this, either.


    Exactly, the temperature adjusted voltages are probably why batteries last as long as they do.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jan 02, 2015
    THE problem with charging a TT with a tow vehicle is the disheateningly long distance and vulnerable connections. 20 amps of trailer solar panels works beteer than a thousand dollars worth of charging line modifications. It isn't even a fair comparison.
  • pnichols's avatar
    pnichols
    Explorer II
    Jan 02, 2015
    ScottG wrote:
    Modern charging systems are temperature compensating and will allow higher voltages.


    Modern charging systems will also put out only 12.9 to 13.1 volts under certain temperature conditions.

    I've seen my RV's 130 amp Ford alternator put out only this much in 100 degree outside temperatures. It was probably REALLY HOT under the hood in these outside temperatures, too. The good thing is that in these temperatures, I wouldn't want my batteries to be seeing voltages any higher than this, either.
  • ScottG's avatar
    ScottG
    Nomad
    Jan 02, 2015
    Modern charging systems are temperature compensating and will allow higher voltages. In the cold weather it would not surprise me to see 15V or so.
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Jan 02, 2015
    Plus you'll get more charging to the TT batteries with the headlights off and bigger cable. Most TT/5 ers/trucks have relative small wiring from the alternator to the house batteries. Larger wire and less TV loads means more amps to the battery.
  • sch911's avatar
    sch911
    Explorer
    Jan 02, 2015
    Check the voltage with the engine off, then with it running. If it's higher with the engine running then it's charging. Headlights on or off shouldn't matter....

    Voltage engine off 13.4-13.6
    Voltage engine on 13.7-14.5

    Actual numbers depend on battery and alternator condition so it's give or take a few tenths of a volt.
  • tvman44's avatar
    tvman44
    Explorer
    Jan 02, 2015
    The alternator should charge between 13.6 and 14.6 volts regardless of the headlights. :)

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,211 PostsLatest Activity: Mar 08, 2025