Jump-starting a 12V vehicle from my 24V one - Procedure

[markthemenace]

I felt really bad the other day when I came across a fellow Merc driver who had a flat battery. This was because I was driving my 24V HJ at the time, and for the life of me couldn't remember how to hook up the thing so that I could safely jump his battery without ruining mine.

The other guy was no help either, as he said it should be no problem hooking up 24v to his 12v system...more power right? It should start really strongly for sure! Sorry, but I had to walk away from that.

I do recall someone saying that there's a diagramme or something floating around that shows the many different connections one could make without worrying too much about damaging either the host or guest vehicle.

Does anyone have any idea how to do this? I almost feel I would like to hardwire it to my batteries with one of those forklift charger type plugs and the next time someone needs a jump I could just plug cables into that and away we go.

 

[Squash]

Disconnect the easiest post of one battery thereby rendering 12 volts.

 

[9180ltd]

For a simple jump start I would not hesitate to " Center tap" or in other words just hook up as normal on the LOW side battery. That would be the one with its neg terminal going to chassis ground. I know there is an insane fobia out there about doing this but I work in the heavy equipment world which is all 24v and have seen OEM's taging a Center tap on low side battery for 12v power point plugs in the cabs.... So if komatsu can do that and have there batteries last 2-3000 hours a jump start here and there is not going to hurt.

 

[amaurer]

Choose either battery and just hook up the cables. Match the +'s and the -'s, of course... there is no voodoo here.

 

[kim]

You can safely jump from the low side battery...grab ground and +12v from the low side battery and feel good helping someone out.

I have had an incident where I wouldn't recommend jumping from the high side battery, +24v and +12v.

 

[John Galt]

My truck has a pair of marine starter batteries and uses the built-in wing-nut posts to connect the two in series with a short battery cable. It's easy to isolate the low battery by disconnecting the short cable. It makes jump starts from the low battery to a 12v vehicle easy and safe.

 

[crushers]

either battery will work ... think 2 - 12V batteries and you get the idea.
just don't ground to the frame and use the 24V positive.
yes, i have done the 24V to 12V jump in the past at the request of the owner of the car. it toasted his starter but it sure did spin FAST and it did start ... when he went to start the vehicle to go home after work the starter was pooched. with todays electronics i would never recommend a 24V - 12V boost.

either battery by itself is 12V, if you plan on doing this often then wire up a set of quick connects from one battery to the front of the vehicle then wire up a set of jumpers with the quick connect. this way you can boost with no concerns.

note, if it is a long crank to get him started then when you get home recharge the boosting battery to make sure it is back up to snuff. 24V systems don't read each battery.

 

[blis]

Just remember that if you use the high-side battery for jumping dont ground in the frame but use the neg-post for ground...

 

[markthemenace]

Thanks guys. I just thought that there might be some voodoo involved, seeing as to how paranoid we all are abou the centre tap. No worries I'll just tap off the low-side battery then...easy enough to do.