Jumping a 6 volt positive ground?

[Carla]

Jumping a 6V battery with 12V was a standard everyday practise in automotive shops, years ago.......I've done it myself, dozens......if not hundreds.....of times.

A common arrangement was to have a large 12V 'shop battery' mounted on a little hand truck frame, normally kept in a convenient corner with a trickle-charger on it. A set of jumper cables was bolted to the terminals of the jump battery and kept wound around improvised brackets on the hand truck frame.

Obviously, the first step in jumping a dead 6v vehicle with the 12V battery was to identify whether it was a negative (most all Chevrolet,  GMC, and other GM cars/trucks, some other makes with Delco electricals) or positive (Dodge, Ford, and some other makes with Autolite electricals) ground vehicle. (for that matter, some of the '50's and '60's 12V systems were positive ground.....check this carefully and be certain)

The appropriate polarity of jump cable from the 12V battery would then be clamped to the grounded terminal of the 6V vehicle battery.

This was indeed a 'two person job', as there was one very important thing to remember about this procedure.......

The person handling the jump cable must never apply it to the non-grounded or 'hot' battery terminal until the other person was actually operating the starter, so the 12V was never applied to the system until the starter load was present.

In practise, this is easy enough......you just keep the 12V cable 'poised' over the hot side of the 6V battery until you hear the starter trying to turn, then quickly grip the 6V terminal with the jump cable, keep it on whilst the engine cranks, and very quickly remove it when the engine fires, or, if the engine doesn't fire, after 20 seconds or so, no more than half a minute at the very most.

You must never allow the 12V to remain connected when the starter load isn't applied to the 6V battery. There is a little bit of a 'trick' to quickly grabbing the terminal with the jumper to avoid any sparking, but its obvious and easily learned.

cheers

Carla

[TodFitch]

Been there, done that. It is not recommended but it has worked for me.

1) Connect positive to positive, negative to negative: Since your old Plymouth is a positive ground and the new car is a negative ground you want to make sure that the bumpers, etc. are not touching.

2) The 12v system will be trying to bring the 6v system up to its voltage. This is not very good for either car and a lot of current will be flowing through the jumper cables. So have the? wires connected for only the few seconds that you need to spin the starter. This is definitely a two person job as you don't want to leave the cables on long enough to allow you to get in the car to start it after you connect them yourself.

3) With all that current going into the 6v battery it is very likely to out gas hydrogen and get very hot. Sparks near that could be very bad. I have heard of batteries exploding when jump starting. This has never happened to me but if it were to happen this would be the time. So make your last connection somewhere away from both batteries. On my 1933 this happens to be at the power input to the starter. It might be on the frame on your car.

4) Turn off all accessories in both vehicles before trying this. They will probably be okay but why take the chance of frying them?

Caveat: The last time I had to do this was before most of the modern electronics in new cars. There might be more things to go wrong now. But it did work for me back in the 1970s when I had a worn out engine, an old battery and lived in a climate that got cold (so starting was a problem) and had no money or time to fix them.

[Bill James]

 Can't you jump a 6 volt pos. ground? I should know the answer, I'm sure I've done it before in my 60+ years of messing with old cars. back in the day we just push started em. Would you hook the pos. lead to ground on the car, and the neg. lead to the starter?? Hmmmm ???