Jumping a 6 volt battery from a 12 volt car

[Chuck51631]

What would be the proper way to hook up jumper cables. The 6 volt car is a positive ground and the 12 volt car is a negative ground car. Is it still negative to negative and positive to positive? I have never had to jump start a car under these circumstances. I thought it would be good to know in an emergency. I don't want to blow up a battery or short out an electrical system.

Thanks in advance for your replies.

[TodFitch]

Aways negative to negative and positive to positive.

 

It is not very kind to the electrical system of either car to jump from 12v to 6v but I've done it. Or rather have done it in the distant past. Nowadays I'm wealthy enough to fix the underlying problem I might have with starting and can afford new batteries from time to time.

 

Anyway, make your last connection as far from both batteries as possible as you don't want sparks near the hydrogen outgassing. Only have it connected for the shortest possible time (need two people: One to be in the driver seat ready to hit the starter and the other on the cables). Don't have the cars (bumpers) touching as that would connect positive to negative. Have all non-esential electrical devices off (all lights, radios, etc.) as you might damage them.

 

My experience with this was back in the 1970s when the new 12v cars I jumped from had pretty bullet proof points type ignition and no fancy computerized engine controllers. Current new cars might not take so kindly to this type of electrical abuse as the older 12v cars.

[ptwothree]

I would also disconnect the 12 volt battery from the car that battery lives in. 

[Chuck51631]

Thanks for the reply's. I have no intention of doing this. You never know when you go someplace and get a dead battery. I usually replace my 6 volt every 4 years to be on the safe side. Then again I have had a battery fail after 2 weeks. It was the battery. I had the charging system checked when it was installed.

[Silverdome]

As stated above NEG. to NEG. and POS. to POS. and have someone with you to disconnect quickly or be real fast about it yourself.

 

One other note you can do this without disconnecting the 12V battery but make sure you don't have the 12V car running and have accessories and ignition switch off.

[greg g]

You can easily bypass the 6 V bat in the car to avoid passing 12 V through it.  Rather that connecting jumpers or charge pac to the battery connect the ground to a cylinder head bolt or similar, and with the ignition on, connect the negative to the starter side solenoid pole.  that will crank the starter without involving the battery.  hopefully your 6v bat will have enough juice to power the ignition.

[wallytoo]

exactly as greg says above, that is the correct way to jump start a 6-volt vehicle from a 12-volt source. hook the cables to the 12-volt battery, and the other end to a ground on the dead vehicle, and to the starter post (i'm pretty certain it makes no difference which goes to which, and that i've hooked them up both ways and been able to jump my 6-v pos-grnd tractor using my 12-v neg-grnd car). make certain that the "dead" vehicle is in neutral, and that the ignition switch is "on".

not a good idea at all to connect directly to each battery with the difference in voltage.

[BigDaddyO]

The ground cable to the frame or engine block of the 6v vehicle should be the last connection in the sequence and the first to be disconnected to keep arcing damage to a minimum and away from either battery. You can do a little bit of arc welding if you are not careful.

[ebraysmith]

i just bought a spare battery, batt box, and trickle charger that I keep in the trunk with some cables.  

After a couple years--could cycle them through or time for new one, but seemed safest and reliable.

[rb1949]

If this is ever necessary, the tip about bypassing the battery is one I hope to remember. That advice has been given several times in posts about jump starting.

[FlashBuddy]

On 4/26/2016 at 10:58 PM, ebraysmith said:

i just bought a spare battery, batt box, and trickle charger that I keep in the trunk with some cables.  

After a couple years--could cycle them through or time for new one, but seemed safest and reliable.

Thanks for this. Here I was stressing about getting 'er jumped when what I really need is a spare battery, charged and ready to go. I'm off shopping for a battery and charger.

[wagoneer]

Won't the 12v affect the electric shifting solenoids/governer in the m5/m6 transmissions? I'm worried about burning out other items? Maybe if I pull the 30 amp fuse, that woudl be a good precaution?

[greg g]

If you connect bypassing the battery, you are only powering the starter.  The solenoid isolates the 12v as long as you hook up momentarily to the starter side terminal when crankin as most of the electrical feeds for the rest of the car come from the battery side terminal, so as long as the solenoid is not energized the 12v can't pass through it.

Edited September 11, 2020 by greg g

[Plymouthy Adams]

last time I was prepared to jump a 6 volt battery I hid behind the door for an hour or better before I realized the battery was already dead.......!

 

 

 

 

 

 

 

Lighten up folks....laugh a little....

[maok]

Have by standers push start the car...in my experience, they don't mind pushing a vintage, actually, they volunteer freely...?