Jumping a 6v with a 12v

[Guest Blkcloud1]

I'm trying to jump my 6v car with a 12v jump box.. I googled it and apparently it's a common practice.. I tried it  and when I hooked up the cable I got a lot of sparking from the 6v ground.. which was what I hooked up last.. is this normal? I had all my lights off on the car and it doesn't have a radio. Thanks 

[MCHinson]

It is not a good idea, but I admit it can be done. I might have even done it myself before. You can probably get away with it if you make the connection only briefly.

 

What kind of car? For instance, a Model A Ford should be Positive Ground. If you were to connect the negative cable of the jump box to the grounded battery terminal of a Model A Ford, you would see a lot more sparks than if you connected the positive cable to the grounded terminal.

[Guest Blkcloud1]

It's a 52 mainline 

[MCHinson]

I think that would also have a positive ground. If you are going to use a 12 volt jump box, be sure to only connect it momentarily and be sure to connect the positive cable to the positive battery terminal, which I think you will find to be the grounded terminal.

[Rusty_OToole]

There are 2 ways to do this. One is to disconnect the ground cable then connect the 12V battery, positive to positive and negative to negative. If the car is positive ground, you will connect the ground cable (+) to the engine or to the ground cable and the (-) to the battery -. This cuts the 6v battery out of the system as one side is disconnected. Be sure all lights radio etc are turned off. Start engine then quickly disconnect the booster ground and stick the battery ground back on. You have to be quick so the car does not stall.

 

The other way takes 2 people. One to start the car, the other to man the jumper cables. The cable guy connects the power cable, waits for the starter guy to turn the key, and sticks the ground cable on, ready to take it off as soon as the car starts.

 

I have done both methods. #1 is preferred, #2 is quicker and easier. The thing to keep in mind is not to have the 12v connected to the 6v battery any longer than you have to.

[cahartley]

When boosting with a 12 volt battery on a 6 volt system jump directly to the starter and ONLY when the starter is doing its thing.......it's a two person operation but it's also safe.

In fact we did just that when we started my '32 Confederate for the first time.

[viv w]

I agree with MCHinson, it can be done but not recommended. Jumping 6V with a 12V battery can cause a 6V battery to explode, showering both the car and anyone nearby with sulphuric acid.

i worked in a collision repair shop and we had a battery specifically used for jump starting cars. The battery was left to charge overnight. One morning we came into the shop and there were pieces of battery and acid everywhere, up to 30ft away. Fortunately the battery was in an area where there were no cars, so damage was minimal. The cause of the explosion, a build up of hydrogen from charging and an internal spark inside the battery.

 If you are going to jump start a car, be advised, it is in your own interest to wear safety glasses, to protect your eyes should an explosion occur.

Viv.

[kgreen]

I would also presume that you could heat up the coil sufficiently that it could be damaged.  

[Rusty_OToole]

The coil will heat up but it takes a long time. I have run 6v cars on 12v for 10 - 15 minutes with no damage. One coil did overheat and quit working after 1/2 hour but once it cooled down it was fine.

[Willie Wurke]

12 hours ago, cahartley said:

When boosting with a 12 volt battery on a 6 volt system jump directly to the starter and ONLY when the starter is doing its thing.......it's a two person operation but it's also safe.

In fact we did just that when we started my '32 Confederate for the first time.

Thanks for this post. This is the only safe way to do it. The only danger is if the 6V battery happens to have an internal open it could explode.

Old man---been there--done that!   But you still get the cigar!!

 

BTW: I never saw a car title with mainline or confederate on it!  Those words only apply to body parts, not mechanical parts .

[keiser31]

I did it on my 1928 Model A truck. It fried the coil.

[mcdarrunt]

(1)  Disconnect 6v Battery cable and main feed wire from solenoid. Now everything is dead: lights, instruments, horn, EVERYTHING.

(2) Hook 12v battery cable to solenoid where 6v cable was and a 12v  ground to the engine.

(3) Tie the 6v battery cable that was on the solenoid to the main feed wire with a short bolt.

  You now have a car that is all on 6v except for the starter. You can start it as many times as you want and leave it running for as long as needed with no harm. Sometimes a 6v solenoid will stick on 12v so we use a 12v solenoid and activate it with a short 12v jumper.