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6 Volt Jump with 12 Volt portable Jumper

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Can a 6 volt battery be jumped by a 12 volt portable jumper or 12 volt in another vehicle? Having a starting issue when motor is shutdown and restarted while hot. Battery acts like it is dead until car cools off. Initial cold start is very quick.

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I can't believe that would be a good idea. Since the 6 volt battery is not dead, you are adding anther 12 volts thus 18 volts are surging thru the system designed for 6 . Try to find out why the engine has the starting problem. Perhaps adding a no gain 12 volt starting system would solve the symptom--not the problem. Glenn Lorei b6vt

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When jumping your car the batteries are in parallel. So voltage doesn't double. Capacity does. That being said, you will be applying 12v to a system that is made for 6v.

Edited by oldbuickone (see edit history)

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The ford factory service lit advises to only send the 12 v to the starter side of solenoid. I have jumped with 12 in a emergency..spins like a dream..starter can handle it easily..but...very dangerous potential, gases escaping from battery can blow up..just keep sparking connections away from batt..be quick and positive. And brief..don't turn anything else on. Or. just bump /push it......pop in gear..always park on slight hill,

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Can a 6 volt battery be jumped by a 12 volt portable jumper or 12 volt in another vehicle? Having a starting issue when motor is shutdown and restarted while hot. Battery acts like it is dead until car cools off. Initial cold start is very quick.
My '41 Continental did the same thing when hot. After I cleaned up all the connections to make sure of a good ground everywhere and got big 0 ga wires from batt to relay to starter, it got better when cold, but still dragged when hot. Turned out the starter and the flywheel were not aligned. Binding caused the dragging. I gave the starter and flywheel a little more room to move relative to each other and now, the problem is only present when it's 100F outside, I've been driving stop and go around town and the temp gauge is bumping against the 'hot' reading. Otherwise, it spins pretty nice even after running. Good luck. This seems like a typical problem with these cars. Some even have gone to 8v batteries.

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8 volt batteries will burn out your 6 volt bulbs. I jump my starter with 12 volts if necessary, never the battery. If you have hot start problems, send your coil to Skip Haney in Fla and have him rebuild it. You will never have any more hot start problems. Make sure you have proper size battery cables and clean ground connections from starter to pan.

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Absolutely on the battery cables. Must be size "0". I've had them made out of welding cable by a local battery shop.

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Probably better if you unhook all accessories at solenoid on firewall, run a separate wire to the ignition resistor under the dash up high, and use a 25 or 50 amp, 1.2 ohm resistor in the ignition circuit. You really don't want to fry the coil. I did this when I first bought car and wanted to make it run but not buy a 6 volt battery that would run down and die while I slowly rebuild everything. Of course with the starter switch out of the circuit, you have to jumper the solenoid terminal to ground to pick up. Easier to get a 6 volt battery charger, or do a 12 volt conversion.

Abe

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I picked up a stack of 60 Way of the Zephyr from the 1970's through the '80's. There sure are a lot of hot start articles. The knowledge is out there and not many would have left the showroom floor if things had always been that bad.

I have seen cars that didn't start hot because the gummy distributor plate didn't have all night to creep back to start position. A six voly won't tolerate too much advance, especially if a little extra fuel peculates into the manifold. A hot condenser coil can cause an erratic spark.

Just methodically go through the systems testing and verifying.

Some life, huh, sitting in a living room chair reading 40 years old magazines about 70 year old cars. If I take a break I usually choose between reruns of "F Troop" or the neurology textbook next to the magazines.

Bernie

Bernie

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8 volt batteries will burn out your 6 volt bulbs. I jump my starter with 12 volts if necessary, never the battery. If you have hot start problems, send your coil to Skip Haney in Fla and have him rebuild it. You will never have any more hot start problems. Make sure you have proper size battery cables and clean ground connections from starter to pan.

Will a bad coil cause a slow starter speed when the engine is warm like rockitdoc describes? I was thinking a weak coil would have a weak spark, but not affect the cranking speed...

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The Ford factory service lit advises to only send the 12v to the starter side of solenoid. I have jumped with 12 in a emergency..spins like a dream..starter can handle it easily..but...very dangerous potential, gases escaping from battery can blow up..just keep sparking connections away from batt..be quick and positive. And brief..don't turn anything else on. Or. just bump /push it......pop in gear..always park on slight hill,

That first sentence is the essence of safely boosting with 12v. If the car has a remote starter relay/solenoid that switches the starter current to the starter from the battery, there will be NO voltage on the starter side terminal until the starter button is engaged. 12v can be applied to that post with your booster cable and then use the neg clamp as the start button. When the neg 12v clamp is clamped on the engine it will crank without backfeeding the 6v system thru the relay. Turn the ignition on to power up, use booster cable neg to crank the engine, remove when it starts. You will not be using the 6v battery to aid in cranking so you are dependent upon a good connection at the booster cable clamp which is sometimes difficult to maintain.

An alternative method would be to subject the system to a momentary 12v by connecting the pos 12v booster clamp to the battery and then covering the battery with a heavy towel or rags in case it blows and connect the 12v neg booster cable to the block as soon as someone else hits the starter button, then remove neg clamp as soon as it starts up. This will keep sparks away from the battery and also protect you just in case....The system will be subjected to appx 10v while cranking if the donor battery is not being charged or donor engine running. Just be sure all lights and accessories are turned off when you key on to start it.

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Will a bad coil cause a slow starter speed when the engine is warm like rockitdoc describes? I was thinking a weak coil would have a weak spark, but not affect the cranking speed...

A bad coil wont affect the starter or cranking speed. Check or replace the starter solenoid on the firewall. They get burned and corroded inside causing a high resistance in the starting circuit.

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There is a previous thread which describes a no gain 12 volt system. As long as there is NO feed back to the 6 volt system you wont have a problem.

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Instead of a 12 v booster you could use a spare Optima 6v battery to boost with. They can be carried in any position and don't leak.

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Instead of a 12 v booster you could use a spare Optima 6v battery to boost with. They can be carried in any position and don't leak.

I just purchased a 6 volt Optima battery since a portable 6 volt battery booster costs about $800.00 My 37 Buick has had trouble with the hot start as well, but seems to have been solved when the generator belt was tightened. (I will know for sure once spring arrives and I get the car on the road again.)

I will be building a carrying case for the Optima battery and will fabricate a pair of short (3 feet) jumper cables to go in the box with it.

What size (gauge) should the cables be for a 6 volt system? I've heard 0 gauge.

Greg

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If your starter will not turn over the engine when hot, here are some items to check.

Check battery condition. Most battery stores like NTB can check the capacity of the battery as well as its condition. Even a fairly new battery can fail.

Check for bad or undersized cables. Connect a volt meter between the NEG battery terminal and the terminal on the starter, crank the engine with the ignition off. Read the voltmeter. The reading should be 0.3 or less. A higher reading means excess resistance in the starting circuit..

Check the ground circuit by connecting your voltmeter between the POS terminal of the battery and the case of the starter. The meter should read 0.1 or lower when cranking the engine.

Check the rotor for rotational play. A worn rotor can change the timing enough to prevent the starter from turning the engine smoothly.

Check for hydraulic lock caused by gasoline leaking from the carburetor into the cylinders or coolant leaking into the cylinders. Remove the spark plugs and look for wet plugs.

Remove the starter and have it checked for worn bushings, wrong field coils, worn brushes or dead spots.

Your starter turned over the engine when new, if it is not doing it now, something needs to be fixed. You should never have to jump the car, unless the battery is run down.

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