battery question

Discussion in 'Motorhome Chat' started by Terry, Apr 10, 2011.

  1. Terry

    Terry Funster

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    Following on from johnp10 post about gennys - MORE CURIOUS THAN ANYTHING - how long would you have to run the van to charge a (just for figures) 100 amp hr battery depleted to a 50 % charge-say 50 amps charging only from the engine alternator ?
    terry
     
  2. pappajohn

    pappajohn Funster Life Member

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    do you mean engine or leisure battery ?
     
  3. barryd

    barryd Read Only Funster

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    Dont know but ours seems to charge up quite quick. We often go weeks without hookup and just by moving every couple of days we seem to survive without genny or solar panels. I would like a solar panel though as with the price of diesel I intend to stay put more.

    Interesting question, now I will wait for someone who knows what they are talking about to answer it.
     
  4. Terry

    Terry Funster

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    I have a split relay so both :thumb::Wink:

    Same for us :thumb: never needed a genny or panels :thumb: but like you we move around nearly every day :Rofl1:
    terry
     
  5. aba

    aba

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    it is cheaper to run a genie than the van engine as at newark our leisure battery got quite low as it is only a small battery and consumption is quite high so i ran the van for a couple of hours just to keep it going saturday and sunday and used i would estimate in the region of 2 gallons of diesel in doing so. a genie on the other hand i would expect at least 16 hours run time for same amount of fuel.
     
  6. Terry

    Terry Funster

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    Hi I understand what you are saying and never doubted it for a moment,but I just wondered how much time it would take to stick the very aprox 50 amps required :BigGrin: By far the cheapest option would be just to fit another batery (which if I needed to I would) but thenagain the alternator would then have 3 batterys to charge :Rofl1: another question in itself
    terry
     
  7. aba

    aba

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    hi you obviously understand the principle of the more battery power you have the more you have to replace which takes longer the more you have.
    our battery was very low at around 11.4v before we left newark largely due to swmbo leaving the outside light on all night and around 10 minutes with the fridge on battery (as i forgot to switch it to aes).
    on our return home a trip of around 100 miles the battery was showing 12.6v so still not fully charged.
    as the fridge takes around 20amp on battery the alternator has a lot of work to do to even get a small amount into the batteries with i presume engine battery being priority leisure battery second but with the draw from the fridge i guess it don't get much.

    a solar panel and maybe a wind turbine also should help no end.
     
  8. barryd

    barryd Read Only Funster

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    Again I dont really understand engines but I am sure I read on here or one of the forums that running a diesel engine on idle for long periods of time can damage it. Might be worth looking into.
     
  9. pappajohn

    pappajohn Funster Life Member

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    i believe once the engine battery is fully charged it merely trickle charges the leisure battery via the split charge relay.

    connect both batteries together (hard wired) and both will charge at the same rate until the strongest is fully charged.

    in other words it could take many hours to charge the leisure battery via split charge....unless its a battery master type.
     
  10. Terry

    Terry Funster

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    Last time I put a tester on (long time ago) I got a reading of 13.7v ( i think) coming from the alternator to the engine battery and the same at the L/battery hence the original question of how long to charge.One (in my mind :Rofl1:) would asume once the engine battery is fully charged it would switch more to the L/B until that is charged ?
    Just to spice things up a bit does the alternator chuck 13.7v no matter what the load is?Also in the mix after thinking about it is the fridge that is also on the split relay but at the time I do not think the fridge was on 12v :Doh::Eeek::Rofl1::thumb::BigGrin:Also being an ex ambulance it has a heavy duty alternator on ? what that does comparired to a normal one is anyones guess :Rofl1:
    terry
     
  11. pappajohn

    pappajohn Funster Life Member

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    that sounds about right for alternator output volts.
    the current (amps) will vary depending on how much current is needed into the battery.

    flat battery = high current

    charged battery = low current

    but it will output around 13.7v regardless of how flat or charged the battery is.

    i put a flat (11.9v)car battery on charge this afternoon.
    within 5 mins the chargers LCD showed 13.7 and the bar graph showed fully charged......not physically possible with a 3.7amp charger and i know it will take at least 24hours to fully charge.

    standard alternator may be 65/75amps...heavy duty may be 100amps or more.
     
  12. Terry

    Terry Funster

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    Hi John, so if my thinking is right (probably not:Rofl1:)half hours running @ 100 amps would in theory put the 50 amps back into the battery? (original Q) OR on a normal 50/65 amp alternator aprox 1 hr ?---How long would a small genny take and at what rate do they charge? Sorry about all the questions but my mate who could answer them all is not avaiable to ask at the moment :BigGrin::Wink:
    terry
     
  13. pappajohn

    pappajohn Funster Life Member

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    in theory yes, but it depends what else is being used at the same time....heater, radio etc.
    probably need a couple of hours to ensure a full charge rather than a residual 'surface' charge.....the battery needs to absorb the charge.

    genny...depends on whether you mean from the 230v output or direct from the gennies 12v output.

    most 12v outputs are only 8amps so will take a long time.
    230v will obvioulsy run your onboard charger but it may only be rated at 12amps or 15amps...so again, a long time

     
  14. jonandshell

    jonandshell Funster

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    Sterling Battery to Battery charger.
    -Most efficient way to recharge your habitation battery when wilding it.
    We have one, it works!:BigGrin:

    http://www.sterling-power.com/products-battbatt.htm

    Charges at 50A (measured with a clamp-ammeter) at just above tickover!
     
  15. Terry

    Terry Funster

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    Hi John and Shell, I don't think I will be paying 200 quid plus for that one :Rofl1::Wink:I already have a 22 amphr charger for hook up and the relay is working fine keeping the L/B topped up- never ran out of power yet:thumb:-
    terry
     
  16. Terry

    Terry Funster

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    So again John in theory, if you run a genny for 6 hrs it will put the req 50 amps into the battery using about a gallon of fuel - ish or I can run my engine to the shops etc, for one hour and get the same result :thumb: without the need for a genny :Rofl1:It may use a bit more fuel but I get the shopping at the same time :Rofl1::thumb::Wink::Smile:
    terry
     
  17. scotjimland

    scotjimland Funster Life Member

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    Hi Terry .. remember there is no such thing as a 'free lunch'...

    as you say, you will use extra fuel charging the leisure battery while driving ... this is not efficient!!

    a genny with a decent multistage charger will be more efficient and cheaper than using the alternator..
    also, an alternator is a poor charger, it's primary function is to power on board electrics.. not charge batteries from flat..
     
  18. Terry

    Terry Funster

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    Theory again -It would be better to couple up a genny to my onboard 22amp charger and run that :thumb: than run the genny stright to the battery @ say 8 amps then ?
    All this was to satisfy my curiosity :BigGrin: I am not intending to change anything or buy a genny or panels :Rofl1: if I find myself running out of power at least I can run the engine :Wink: or add another battery to give me the extra un needed power :Doh:
    terry
     
  19. scotjimland

    scotjimland Funster Life Member

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    a most empathic YES Terry ..

    genny 12vdc outputs are not good chargers .. they are primarily designed to power 12v appliances .. not charge batteries.
     
  20. jonandshell

    jonandshell Funster

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    Hi Terry

    The Sterling unit not only charges faster, but more efficiently and prolongs battery life.
    Due to my personal intolerance of poor batteries, I am running 115Ah 12V open lead acid traction monoblocs. I need to protect my investment in those batteries. A 14.2V or so charge from the vehicle's alternator would not complety raise the specific gravities sufficiently, be akin to opportune charging and would lead to suphation over time.
    I am not exaggerating when I say we can run the van off hookup, at below freezing, 4hours of telly a night, Webasto dualtop running constantly at 21 degrees C, lighting as required, for three days and nights for an 80% discharge of the battery.
    Four hour's running brings the battery up to 100% and it will perform again and again.
    I take your point about the price or the unit though, I think they might be over £300 now! We got ours on Ebay for £160 so were very lucky.:Smile:
    The unit is overkill for most applications I agree, but we like to be self sufficient and I can't remember the last time we used our hookup lead whilst out and about!:BigGrin:
     
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