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Old 11-18-2020, 09:04 PM   #1
Mister Moose
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Default 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?
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Old 11-18-2020, 09:09 PM   #2
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Default Re: Jumping a 6 volt battery

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Originally Posted by Mister Moose View Post
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?
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
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Old 11-18-2020, 09:28 PM   #3
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Default Re: Jumping a 6 volt battery

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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
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?
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Old 11-18-2020, 09:52 PM   #4
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Default 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.

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Old 11-18-2020, 10:15 PM   #5
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Default Re: Jumping a 6 volt battery

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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
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.
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Old 11-18-2020, 10:21 PM   #6
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Default Re: Jumping a 6 volt battery

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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!
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Old 11-18-2020, 10:51 PM   #7
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Default Re: Jumping a 6 volt battery

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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!
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!)
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Old 11-18-2020, 11:10 PM   #8
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Default Re: Jumping a 6 volt battery

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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?
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.

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Old 11-18-2020, 11:23 PM   #9
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Default 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.
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Old 11-18-2020, 11:46 PM   #10
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Default 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.
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Old 11-19-2020, 12:28 AM   #11
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Default Re: Jumping a 6 volt battery

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Originally Posted by Mister Moose View Post
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?
Put a 1⅜" socket on the ratchet nut, feed an extension thru the crank hole and hit it with an impact to loosen it.

As for jump starting with 12 volts, just make sure your lights are turned off, polarity is correct and start it up. Not going to hurt anything if you disconnect right away.
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Old 11-19-2020, 05:17 AM   #12
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Default Re: Jumping a 6 volt battery

I would keep a spare batt in the trunk.
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Old 11-19-2020, 06:53 AM   #13
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Default Re: Jumping a 6 volt battery

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Put a 1⅜" socket on the ratchet nut, feed an extension thru the crank hole and hit it with an impact to loosen it.

As for jump starting with 12 volts, just make sure your lights are turned off, polarity is correct and start it up. Not going to hurt anything if you disconnect right away.
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!!!
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Old 11-19-2020, 07:39 AM   #14
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Default 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.
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Old 11-19-2020, 10:02 AM   #15
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Default Re: Jumping a 6 volt battery

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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.
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.
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Old 11-19-2020, 10:14 AM   #16
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Default Re: Jumping a 6 volt battery

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Originally Posted by Mister Moose View Post
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?



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.
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Old 11-19-2020, 10:28 AM   #17
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Default 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.
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Old 11-19-2020, 10:47 AM   #18
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Default 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.
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Old 11-19-2020, 10:53 AM   #19
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Default Re: Jumping a 6 volt battery

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If you do it, make sure your accessories/lights are off, including foot off the brake. 12v on 6v bulbs/accessories - not good.
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.
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Old 11-19-2020, 11:04 AM   #20
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Default Re: Jumping a 6 volt battery

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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.



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?
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