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Thread: Jump-starting 24V vehicles

  1. #1
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    Default Jump-starting 24V vehicles

    Bedford was flat the other day (someone left the isolator on, not me!) - we ended up taking the batteries out and charging them individually, but what's the correct procedure for jump starting a 24V veh from a pair of 12V vehicles?

    If you just parallel each battery with a car battery (still in a car) using two sets of jump leads, if an electrical connection is made between one car and the truck chassis or both cars, at least two batteries are shorted! Could remove chassis earth connections from the cars but then why bother with jump leads, might as well remove the batteries.

    So, have I missed something?

    Stone

  2. #2
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    Default Re: Jump-starting 24V vehicles

    Ive jumped a 24v from a 12 no problems, why do you need 2?

    Christian

  3. #3

    Default Re: Jump-starting 24V vehicles

    Suppose you could use 1 x car and jump leads to parallel whichever truck battery is flat. If both flat and you want to use 2 car batteries and jump leads -

    Neg. post car 1 to pos. post car 2 - neg. post car 2 to neg. post truck (earth lead) - pos. post truck (24V ouput) to pos. post car 1.

    Only need to remove neg lead on car 1 battery as car 2 and truck (the one with earth lead) neg.s are both to earth.

    Always get a grownup to check my advice - the usual disclaimers apply

  4. #4

    Default Re: Jump-starting 24V vehicles

    I need a slave start in my Foden wrecker once and had no other military vehicles around, a bloke stopped in his Golf and I took the opportunity to throw my slave lead onto his battery, 12v to 24v nearly sucked the life out of his battery but started my wagon, no dramas with his vehicle after that.

    Edited to add this is not something I would recommend but it got me out of a spot of bother.
    Last edited by recymech66; 11-11-2009 at 18:06.

  5. #5
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    Default Re: Jump-starting 24V vehicles

    Quote Originally Posted by recymech66 View Post
    I need a slave start in my Foden wrecker once and had no other military vehicles around, a bloke stopped in his Golf and I took the opportunity to throw my slave lead onto his battery, 12v to 24v nearly sucked the life out of his battery but started my wagon, no dramas with his vehicle after that.

    Edited to add this is not something I would recommend but it got me out of a spot of bother.
    Erm! don't think that is a good idea!

    Quote Originally Posted by N.O.S. View Post
    Suppose you could use 1 x car and jump leads to parallel whichever truck battery is flat. If both flat and you want to use 2 car batteries and jump leads -

    Neg. post car 1 to pos. post car 2 - neg. post car 2 to neg. post truck (earth lead) - pos. post truck (24V ouput) to pos. post car 1.

    Only need to remove neg lead on car 1 battery as car 2 and truck (the one with earth lead) neg.s are both to earth.

    Always get a grownup to check my advice - the usual disclaimers apply
    Totally Agree you need to connect to one battery only, if only one 12volt source is available. Then it must be Positive to Positive and Negative to Negative.

    If you are trying to jump start a 24V motor from a 12V motor, then connect the jump leads across one battery only on the 24 vehicle. (if you have a voltmeter, try and find which of the two 12V batteries, used on the 24V vehicle, has the lowest voltage and jumper the helping battery across this one). The 12 V battery on the helping vehicle will raise the voltage of one of the assisted vehicles bateries, and may be enough to get it started.

    On no account concider connecting 12V across 24V. The 24V battery will try to discharge itself into the 12V, possibly raising its voltage to a point where equipment is damaged on the 12V vehicle. Remember the 12V battery will still be connected to the 24V system if and when when the engine starts, and if using any revs the Alternator on the 24V vehicle will cut in and will be pushing 28V (or more) around the system.

    If you wouldn't put a 24 Volt battery charger across a 12Volt battery in a car, because of the obvious risk of damage, why are you allowing a 24V alternator to run its output into a 12 Volt battery?
    Last edited by antarmike; 11-11-2009 at 18:21.

  6. #6
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    Default Re: Jump-starting 24V vehicles

    I forgot to add when I do jump starts which is often, the Renault Master has a big battery and the Pajero is 2 x12volt heavy duty batteries(not 24v)
    I wouldnt like to try using a Golf too often lucky he was passing by and never to be seen again

    Christian

  7. #7
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    Default Re: Jump-starting 24V vehicles

    This thread has reminded me of a time when I was at the Rotunda Museum in Woolwich, working on vehicles for them, a Tracked Rapier was parked in the driveway, when an Esso tanker arrived. The Rapier was in the way so I went to start it only to find the batteries flat, the tanker driver, to my surprise, offered to jump start it off his tanker. He must have noticed my concern and said it was reasonably safe he was delivering heating oil ! Anyway we did it and he was able to continue his delivery.
    Richard Farrant

    1943 Bedford QLD - 1941 BSA WM20 - 1943 Daimler Scout Car Mk.2
    MVT no. 1087 - IMPS no. 57 - AMVCS hon. member
    KVE Committee member and Newsletter editor
    KVE Facebook page: https://www.facebook.com/corowaswimin

  8. #8
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    Default Re: Jump-starting 24V vehicles

    Quote Originally Posted by N.O.S. View Post
    Only need to remove neg lead on car 1 battery as car 2 and truck (the one with earth lead) neg.s are both to earth.
    Hadn't thought of only removing one lead

    Quote Originally Posted by antarmike View Post
    Erm! don't think that is a good idea!
    Well, so long as the jump leads are thick enough for double the current, you just have to worry about setting their battery and radio on fire when the alternator kicks in


    Quote Originally Posted by N.O.S. View Post
    If you are trying to jump start a 24V motor from a 12V motor, then connect the jump leads across one battery only on the 24 vehicle. (if you have a voltmeter, try and find which of the two 12V batteries, used on the 24V vehicle, has the lowest voltage and jumper the helping battery across this one).
    Makes sense to me. Probably easiest if we just carry a single spare battery around then - we can swap it over to get it started and then recharge the duff one on the generator, and not too much extra stuff to be carrying. Not a bad idea having some jump leads in the back, though!

    Quote Originally Posted by Richard Farrant View Post
    He must have noticed my concern and said it was reasonably safe he was delivering heating oil ! Anyway we did it and he was able to continue his delivery.
    Rather you than me!

    Stone

  9. #9
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    Default Re: Jump-starting 24V vehicles

    Quote Originally Posted by Stone View Post


    Makes sense to me. Probably easiest if we just carry a single spare battery around then - we can swap it over to get it started and then recharge the duff one on the generator, and not too much extra stuff to be carrying. Not a bad idea having some jump leads in the back, though!


    Rather you than me!
    If you have one duff battery and are carrying a spare, then it would be a better idea to make sure that you are using a pair of good batteries of equal voltage, rather than carrying on like that, because it will drag the other battery down eventually.

    Regarding the tanker, not a problem, no worse than the proximity of a 100 gall. fuel tank on a truck.
    Richard Farrant

    1943 Bedford QLD - 1941 BSA WM20 - 1943 Daimler Scout Car Mk.2
    MVT no. 1087 - IMPS no. 57 - AMVCS hon. member
    KVE Committee member and Newsletter editor
    KVE Facebook page: https://www.facebook.com/corowaswimin

  10. #10

    Default Re: Jump-starting 24V vehicles

    Quote Originally Posted by honeileen View Post
    I forgot to add when I do jump starts which is often, the Renault Master has a big battery and the Pajero is 2 x12volt heavy duty batteries(not 24v)
    I wouldnt like to try using a Golf too often lucky he was passing by and never to be seen again

    Christian
    As I said earlier, not something I would recommend, and it got me out of a spot of bother, no problem with his Golf after the slave start either.

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