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12 volt battery to start


Frank Blackstone

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Can a 12 volt battery be used to jump start an engine with a 6 volt system? Can the 12 volt then be disconnected and the engine will operate on the less than 2 volt charge in the 6 volt battery.. Seems to me running the 12 volt battery continuously  would cause a fire hazard in the 6 volt system wiring.

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The biggest risk in jumping a six volt system with a 12 volt battery  is the possibility of reversing the polarity making an 18 volt dead short of up to 200 amperes.

If your six volt battery  is down to 2 volts then it is not going to react well.  It could explode because of the hydrogen gas created.   When I start a six volt car with a 12 volt battery, I put the battery  in the car and connect it with the polarity the same as the car's system.  Before making any connections, I remove the armature lead from the generator and the wire (s) from the fuel tank sender.  Then I make sure all lights and accessories are off.    The starter is quite capable of handling the extra voltage in short bursts.  So is the ignition coil.

None of the above is recommended..........so the short answer to your question is Yes.   But it is never a good idea.

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I have used a 12V battery to start my 6V, positive ground car like this:

Disconnet 6V battery negative cable from battery post.  Turn off everything in the car that uses any 6V.  No heater no, radio, lights, wipers, nothing.

Use battery booster cables off a remote 12V battery. Wear safety glasses...Seriously. Do not install 12V battery in the car. Hook 12V positive post from remote battery to ground on the car. Hood hinge works well.  Have a friend in the car ready to turn the key. Touch battery booster cable from negative post on remote 12V battery to starter solenoid hook lug where battery cable normally attached. Turn key immediately and start engine. Remove 12V negative cable from starter solenoid right away.  Remove other cable, positive, from the ground spot you chose. Hook back up the original 6V battery to car and go.

Edited by keithb7
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25 minutes ago, Frank Blackstone said:

Can a 12 volt battery be used to jump start an engine with a 6 volt system? Can the 12 volt then be disconnected and the engine will operate on the less than 2 volt charge in the 6 volt battery.. Seems to me running the 12 volt battery continuously  would cause a fire hazard in the 6 volt system wiring.

Yes,and yes. Not a fire hazard,though. The old 6 volt systems handed more amps,but fewer volts. Which means the wires are thicker.

Your 12 volt battery won't fully charge,though.

No  big deal since if the charging system is working properly,all you need a battery for is to start the engine.

Don't turn on anything electrical while the 12 volt battery is hooked up,though. 6 volt light bulbs and radios don't play well with 12 volts.

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  • 2 months later...

Yes, I successfully jumped my 54 Plymouth with my 65 Mustang back in the 1970's . First I connected positive to positive (ply pos ground) Connected the negative to 12 volt mustang, then BRIEFLY  touched the neg 12 volt cable to the far side of the Plymouth solenoid, directly to the 6 volt starter cable. Fired right up, pulled the neg 12 volt cable away from the 6 volt starter. Then i sat down as my heart was going faster than the mustang ever went. It worked, no problem afterwards. 

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Does anyone know if a 1954 Windsor came stock as 12v?   I purchased a 265 engine out of a 54 Winsor and I was assuming it was still 6 volt.  The started has a 12v small stamp on the side.  Heres whats interesting;

When I put a 12v battery to a 6v starter (another engine) It spins fast and engages effectively.  When I used a 12v battery on the 264 starter tagged with 12v, it smokes when I engage it.  What can cause  a starter to smoke

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32 minutes ago, 40desoto said:

 When I used a 12v battery on the 264 starter tagged with 12v, it smokes when I engage it.  What can cause  a starter to smoke

It's shorted out.  You are going to have to remove it to take it apart and physically inspect it to see if there are any obvious shorts,or if the armature itself is bad.

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31 minutes ago, Pauls_Plymouth said:

54 wa still 6 volt. It looks like the starter that smokes was defective (internal short) before you got it. You say it smokes, did it spin?

Yes, it spins.  I will take it into the shop.

 

Thank you

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