Jumping 6V with 12V battery

O

Oldgearz

Senior Member
Has anyone set up their 6 volt A so they can use a 12 volt jump battery? I can do this on all my 8N tractors because there is a solenoid which separates the ignition system from the 6V starter. In other words the ignition system stands on its own. On an A this is not so. The starter voltage is connected to the ignition circuit, and while the 6V starter will work fine on 12Vs, I don't want to put the 12 volts through my ammeter and coil. Other than adding a solenoid to the starter, I can't figure any way to use a 12v jump battery pack.
 
My understanding is that there's no danger jump-starting a 6V pos-ground system with a 12V neg-ground battery so long as you only leave the 12V connected for the few seconds required to start the car. The danger to the ammeter and coil are in heat buildup, and they're just not going to accumulate enough heat to do anything in a few seconds.
 
I have done this many many times over the last 40 or so years . Never any damage to any component electrical or mechanical . This is how I do it . It is a two man operation or man and woman . The lady sits in the car and pushes the starter while you do the technical bit . I use long heavy duty jumper cables . Connect the jump cables to the 12 volt battery and connect the positive clip to a head nut . With your able assistant sitting in the car while he/she pushes the starter you push the negative clip hard on the starter terminal . As soon as the motor fires remove the clip from the starter (you are just pushing it on the starter terminal do not clip it on)Remove the positive clip from the cylinder head nut ,job done . If it is just a flat battery the motor will fire up right away hot spark and good spinning starter motor . If you are chasing other problems limit duration to 5 to 10 seconds no more . Feel the coil and starter if you are having prolonged attempts you could cook the six volt battery if you overdo it but I never have . The jumper cables provide a voltage drop as does the starter motor so the coil does not get the full 12 volts anyway .

John in Suffolk County England .
 
I have done it single handed when an able assistant was not available . It is a two handed job as you have to push down on the starter switch while making the connection . Both ways there are sparks but that does no harm but keep open flammable items out of the area of course .

John in the same place .
 
john charlton said:
Feel the coil and starter if you are having prolonged attempts you could cook the six volt battery if you overdo it but I never have . The jumper cables provide a voltage drop as does the starter motor so the coil does not get the full 12 volts anyway .
Click to expand...

Yes, the jumper cables provide a voltage drop. So does the car's 6V battery, which will absorb current to recharge itself. For a few seconds I don't think there is a concern, and yes, I've done it too. If someone wants to take the time and do an experiment, hook up a voltmeter to the wire coming off the starter or fuse block, and jump the car with 12V. Report back on what you see.
I'll bet a Heady Topper that it is considerably less than 12V. (It should vary with the state of charge of the 6V battery though)

I seem to remember checking cranking voltage once on a 12V modern system, and it was 9-10V. When you draw 200 amps for a big load like a starter, the voltage drops.

When I've jumped with 12V the starter did turn more smartly than with the 6V alone though.

I do agree to turn off all the light before doing this, no point tempting fate. If you need a jump, why are the lights on in the first place?
 
Remove the 6 volt cable and wire from the starter, bolt them together and tape them up. Connect your 12 volt cable to the starter post and the other 12 volt cable to chassis ground and you're in business. 12 volt for starting and 6 volt for running, lights and charging.
 
katy said:
Remove the 6 volt cable and wire from the starter, bolt them together and tape them up. Connect your 12 volt cable to the starter post and the other 12 volt cable to chassis ground and you're in business. 12 volt for starting and 6 volt for running, lights and charging.
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Seems like this would only work in the narrow range where the 6V is too discharged to turn the starter but not too discharged to run the coil.
 
Oldgearz said:
Has anyone set up their 6 volt A so they can use a 12 volt jump battery? I can do this on all my 8N tractors because there is a solenoid which separates the ignition system from the 6V starter. In other words the ignition system stands on its own. On an A this is not so. The starter voltage is connected to the ignition circuit, and while the 6V starter will work fine on 12Vs, I don't want to put the 12 volts through my ammeter and coil. Other than adding a solenoid to the starter, I can't figure any way to use a 12v jump battery pack.
Click to expand...

Just connect + to + and - to - leave the jump box 12 volt on the 6volt battery, let the electrons flow completely out of the jumper box, remove the cables from the box, start your A. The trick is don't crank your A with the box connected or with jumping 12 volts to 12 volts as you will harm the jumper box.
 
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