Jumping a 6 volt battery
 

The dead battery thread got me thinking about this...

I did a search and saw a few comments, but they were about running a 12V battery permanently on the same starter and 12V coil.

Who here has had a dead battery, and got a jump start from a passerby 12V good Samaritan? Did anything smoke or fail?

If you keep the 6V battery in the circuit, it will act as a bit of a buffer on the 12 volts I'd think.

My car has a messed up crank pulley, the crank just won't engage without slipping. I can't start the car by hand. I didn't find this out until the car was together, and the engine rebuilder didn't catch it either. (!)

So I haven't needed to yet, but what say you if I'm on the road and need a jump start and there's no downhill in sight?

Re: Jumping a 6 volt battery
 

Pertaining to your "messed up crank pulley". The ratchet nut is what the hand crank engages into and can be replaced easily if needed. https://www.snydersantiqueauto.com/P...earchByKeyword

Re: Jumping a 6 volt battery
 

Without removing the radiator? What stops the crankshaft from turning? Must be pretty well torqued.

Edit
I see they also have a $35 tool to remove the nut without removing the radiator. Is it true?

Re: Jumping a 6 volt battery
 

The original question regards jumping a 6 volt battery with a 12 volt battery.

I have done that with my 1933 Chev. This was a negative ground system and when I connected the two together it was a very brief connection. Its somewhat risky because the jumper cables will act as a resister that changes the 12 volts to 6 volts.

I did the "jump" when I was 18 years old and was "indestructible". Today I would use a battery charger made for 6 volts.

Marc

Re: Jumping a 6 volt battery
 

Yes on the cables, it might make sense to intentionally carry cheap smaller gauge jumper cables to add some resistance.

But I'm asking in the context of being on the road, not the garage. I drive my Model A to the hardware store, it's a little balky starting,or maybe I left those oh so bright headlights on by mistake, and I run the battery down. Do I jump it to get going again? I'm leaning towards yes.

Re: Jumping a 6 volt battery
 

When using a jumper box (12 volts) let the box drain down completely then start your 6 volt A. With jumper cables from a 12 volt car, just let the electrons flow a few minutes and remove cables and start your A. Or just push your car hop in grind 2nd gear pop the clutch, when I was 16 yrs old that's what I did way to much!

Re: Jumping a 6 volt battery
 

That's an interesting idea I hadn't thought of, 12V charging but disconnecting to crank. I like it.

I've popped plenty of clutches, so yes if you have the smooth flat straightish spot to do it. (I've been hand propped too!)

Re: Jumping a 6 volt battery
 

How do you stop the crank from turning? Put the car in gear and set the brake.

You may know more than I do but I wouldn't think the torque requirement was that high as you are turning it clockwise when you start the car.

Charlie Stephens

Re: Jumping a 6 volt battery
 

I’ve had to get a 12v jump. I did it very quickly, no problems. I also asked three girls one night if they could give me a push. It was a flat parking lot, and I popped the clutch in third. It only took about 12 feet and less than a minute. The girls laughed and had a fun moment with an old guy helping with his old car.

Re: Jumping a 6 volt battery
 

There are a few things to be aware of. First your 6v system is positive ground so make sure that you hook positive of the jumper to positive of the jumped car (and negative to negative). Most people will naturally want to put the negative cable from the jumper car to ground of the A. DO NOT DO THAT! Do not let the vehicles touch each other either while the cables are hooked up.
Make sure all the lights are off, putting 12v to 6v lights can burn the bulbs out.
I like the idea of letting your battery charge and then unhooking the cables before trying to start the car. I don't think leaving them hooked up would be a problem on a stock A but if you have upgraded to electronic ignition it could be damaged by the 12v.
Zoom

Re: Jumping a 6 volt battery
 

Re: Jumping a 6 volt battery
 

I would keep a spare batt in the trunk.

Re: Jumping a 6 volt battery
 

Of course! I have the air impact wrench and a big air compressor, so all set there. Just need to be sure the socket has room to get on the nut. Eliminates the need to worry about brakes slipping from torque. Guess I need to get busy shopping for a 1-3/8 1/2" drive socket.

That's why these forums are so great, someone frequently solves your problem. Thanks!!!

Re: Jumping a 6 volt battery
 

Two things:



First, if you put the car in gear and set the brake to keep the engine from turning while removing the nut, use high gear. There is less chance that the engine will turn.



Second, the automotive stores, and Amazon, sell a jumper battery that you can charge with an AC power and carry in your trunk. It is a lot smaller than a regular battery and a lot lighter. It will allow you to start the car up to 30 times between charges. They are 12 volts so use the advice of others regarding starting a 6 volt car with a jump from a 12 volt battery. You can use it on your modern car or truck too. See https://www.amazon.com/TACKLIFE-T8-C...s%2C187&sr=8-3.

Re: Jumping a 6 volt battery
 

I've seen these but never used one. Clearly lithium has higher energy density and better self discharge rates. I don't know and haven't looked into the discharge curves for various current rates. In other words, with a battery like this rated for 18AH, you aren't going to get all that rated current when drawing at 250 amps. AH ratings are based on a standard 20A discharge rate. Even if it's a magic battery, that gives you max 4 minutes of cranking, which under any normal circumstances should be plenty. I'd be wary of the claim for 30 real world starts off a single charge though. Also performance drops off dramatically in the cold.

Right now my engine starts in a 1/4 turn, but there are days after it sat when it gets moody and cranks for many many turns before I can get a start. (In the past I had a sticky fuel float valve) That's why I'm asking about a jump start should it ever arise.

Thanks all.

I don't have a trunk, but wouldn't mind getting one some day. In the meantime.... getting my crank nut replaced would be a good idea too.

Re: Jumping a 6 volt battery
 

An alternate method of removing the ratchet nut. Once you have a wrench on the ratchet nut, Jam the handle against the frame or ground/floor - you may have to use a length of pipe for an extension, parking brake on, out of gear, ignition off, bump the starter. I could not get mine off and struggled for a while till the Barn told me this tip.

Re: Jumping a 6 volt battery
 

I jump-started my stock Model A with a 12 volt battery frequently when I was 16. I couldn’t afford a new 6 volt battery and never considered the potential hazard. That was many years ago - I wouldn’t do it now.

Re: Jumping a 6 volt battery
 

If you do it, make sure your accessories/lights are off, including foot off the brake. 12v on 6v bulbs/accessories - not good.

Re: Jumping a 6 volt battery
 

Right.

I'd think you could also jump from a 12V car that wasn't running. The current draw would drag the 12V surface charge off and lower the voltage across the 6V battery to 9-10 volts depending on the strength of the 12V host battery. Of course you don't want to do this very long, or you'll have 2 dead cars.

This is better than from a running car where the alternator is trying to keep it at 13.8-14 volts.

Re: Jumping a 6 volt battery
 

A little off subject.


Not sure I would want to do this. Would think you would get some arcing at the battery posts and a voltage drop on the 12v battery. Even with the 12v car not running, key off, not sure what this could do to the electronics/alternator/sensors of a modern car?


Do not know what would happen if you removed the battery lead on the 12 v car, do you take the chance of losing settings when the battery is disconnected for a length of time?