Charging while towing

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  • #46103
    Lorne
    Participant

    2 questions:
    1) how fast do your batteries charge while you are towing?  I have 2 brand new Trojan T105 batteries and when we finished dry camping this weekend they were at 12.2v (60%?).  I hooked up (Ford F250) and drove 30 minutes back home and was surprised to see them at 12.5v (90%?).  Note: I only have a volt meter hooked up to the batteries for displaying voltage, not a proper trimetric meter.  Not sure if that makes a difference.  I did wait overnight to see the 12.5v reading when I got home.  Anyway, if my voltage readings are accurate I was a little surprised to see that much charging in such a short drive.   Does this jive with how fast other’s batteries charge when towing?  Or am I missing something here.

    2)Similar to Ray’s setup, I have my stock converter/charger turned off at the panel and a progressive industries charger plugged into the 110v system and hooked to the batteries.  Am I correct in assuming that neither of these has anything to do with charging while towing?  I’m assuming that the truck’s alternator does the charging.  Or would the truck provide power to the converter/charger and that does the charging?

    #46107
    Ray
    Keymaster

    I’m surprised too, I get now where near that good of charging. I think my trucks tow package puts out around 5-7 amps max for charging.

    I just drove 5 hours in mostly cloudy weather bu a bit solar charging going on as well and only but back around 40 amp hours into the bank.

    #46114
    Stephen C Keller
    Participant

    Is it possible to charge house batteries while driving? Yes depending on the amp hour of your alternator in the tow vehicle and how well it is wired. Of course you will lose some charging by the length of the wire going to the back but if it is a larger wire then there is a chance it did work. There are many variables to this question but feel lucky that it did work. Usually you only get a partial charge not a complete charge. I am speaking from experience as a auto/ truck tech from way back and what has worked for me and what hasn’t. I should add that it may have worked this time and you may never match this happening again but maybe you will.

    #46117
    Lorne
    Participant

    I’m not sure I believe it.  Seems excessive for such a short drive.  I wonder how accurate a simple volt meter is on assessing the state of charge?

    #46119
    Lorne
    Participant

    I read that to get a meaningful voltage reading your batteries have to be idle (no loads or charging) for at least 6 hours preferably 24 hours.  Maybe the 12.2 reading at the end of camping was bogus (not idle long enough) and the 12.5 reading after idle was real.  Argggg, I’m beginning to see why people install those trimetric battery monitors.

    #46141
    J J
    Member

    Lorne,  you are absolutely correct in your assessment. The only way to assertain the exact state of charge without prolonged and presise electronic monitoring is to let the batteries sit for at least 6 hours with no load and then do a specific gravity test on each cell. It’s easily ✅

     

     

    • This reply was modified 5 years, 7 months ago by J J.
    #46146
    Lorne
    Participant

    I’m done guessing.  I’m buying a TriMetric monitor tomorrow and installing it.

    #46286
    Michael M
    Participant

    Stephen C Keller said is absolutely true as what he advised.

    Static voltage measurements are almost meaningless after a burst of high amp charging as you got to put a load on the battery for a few seconds then measure it with the voltage meter to get a more accurate rating. As from my experience testing batteries for over 20 years most batteries generally show atleast .2-.5 volts of increase static voltage charged when recently charged.

    As to take it further the charging system from your engine is apparently getting good voltage and amperage to your rear house batteries. So your wiring cable must be of an appropriate gauge plus your system might be using a relay type isolator with a low voltage drop.

    When the batteries are very low in voltage at 12.2v or 80% of its usable life is depleted the alternator will sense this and may provide maximum amperage based on a few variables. As if driving highway speeds you will get a higher amperage charge and higher voltage.

    Now in a short period you can get a good boost of amps back inside the battery at 30 minutes of 50-100 amps per hour. So after 3o minutes it could provide 50 amps back in them as that would be a 25% increase in a 200 amp hour battery bank. Which means to your battery bank of .25 volts increased or 50 amps. So your battery was at 12.2 and add .25v and now you got 12.45 volts. Calculations are based off battery percentages 50% at 12.2 volts and 100% at 12.7. Just a guide as some batteries such as AGM can sit around 13.1 at 100% charge. As my battery bank sits at 13.1 fully charged.

     

    • This reply was modified 5 years, 7 months ago by Michael M.
    • This reply was modified 5 years, 7 months ago by Michael M.
    #46289
    Michael M
    Participant

    #2. The battery chargers you got are only operational when plugged in. Both chargers will do the job however the progressive will take about half the time to fully charge the batteries 100%. As the progressive will take 6-9 hours to fully charge the batteries and the stock charger 9-18 hours on a set of fully depleted batteries for two trojan 105’s.  As if you use your 120v progressive charger then assume 3 hours at 90% charged and 6-9 hours at 100% or close to it.

    • This reply was modified 5 years, 7 months ago by Michael M.
    #46296
    Stephen C Keller
    Participant

    Thing is charging house batteries off the TV while driving may do the trick but I would not necessarily count on it to do the job. But there is always a chance it will work if everything is aligned. A external charger while parked would be best bet. External meaning a camper type built in charger or specific type charger. I always carry a external battery charger so I can use it on TV or camper if needed. That way I know the batteries will be charged when needed. Sounds like your connection from your vehicle to camper is a really good one. Congrats  :yahoo:

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