I received a 12 volt portable battery JumpStarter for my birthday last week. Cool.... but....

In past years, I've used a 12v car to start my 1931 engines.... but have always been a bit afraid of what it might have done to my gauges.. but after all these years, they're going strong and 12 v really turns these babies over in a hurry!

So, here's my question -- With a 12 volt supply, what could a guy add in series in order to step it down to 6 volts? Somehow adding a big honking wire-wound resistor seems to be the right thing to do... but then how do you prevent it from getting hot, etc?? Wouldn't this be a good doo-hickey to keep around??

Any ideas for an easy way to use 12 volts to start a 6 volt system?

Hi Bill,

I have used a 12-volt system/battery to start 6-volt cars for years with no damage. The trick is to jump from the positive terminal of the 12-volt battery to the positive terminal on the 6-volt. The negative jumper is connected to the negative terminal on the 12-volt battery. The other end of the jumper is connected to a poor ground on the vehicle being started, such as a bumper bracket or an accessible spot on the frame away from the starter. The objective is to use the poor ground circuit to reduce the available current and therefore provide some protection to the 6-volt system.

Now for the real instructions: This should be a two man job with one person operating the starter and controls on the car to be started, and the second person operates the final connection with the jumper cable. The cable is NOT connected until the operator is ready to attempt the start. The cable is then connected to the chosen spot while the operator attempts to start the vehicle. The instant the vehicle shows evidence of starting the ground jumper is disconnected.

Also do not have any lights "on"---such as the brake lights on a 1934 and 1935 are on when the parking brake is applied and ignition is on.Also later cars with an automatic dome light-be sure doors are closed before hooking up cables.

The 12 volt supply is a great power sorce to use when traveling.Can power a CB radio all week with out recharging - as well as cell phones too.

I've used chevradioman's method many times with good success. I have even on occasion did the whole job by myself although that is not the best option.

I've used 12 a volt battery to start my 34 after a recent engine rebuild, however I did something a little different than Ray. I connected negative to negative on both batteries but positive from 12 volt to starter terminal on 34. I did this on my own and left it connected, as the 12 volt was only used when the starter was engaged. I did this many times whilst sorting out a few problems.
Can't guarantee any of this, but it worked fine for me
Chris

Unless the 1934 is wired different down under than our version, your method placed 12-volts across every electrical device on the car continuously (if the device was on) and only when you engaged the starter did the starter get the 12-volt shot.

The main source of the voltage enters the wiring harness by way of the large red wire that attaches to the starter switch located on top of the starter. If you had disconnected that wire prior to attaching the 12-volt jumper, then only the starter would receive 12-volts. However, unless you used another jumper wire to the coil the engine would not run.

To better understand this discussion take a look at the wiring diagram located in each year repair manual.

"Perhaps now is a good time to mention. NEVER USE A MODERN CAR TO JUMP A 6-VOLT SYSTEM. This could cause serious damage to the modern car electrical system."

I'm still listening...

Am I to believe that no one has ever damaged their gauges by jumping their car with a 12 volt battery? Gee, that seems to run against common lore.

Now, I understand that some are saying that you need to immediately disconnect the battery as soon as the engine starts... but is this really the "trick" that prevents damage?

And I assume that Ray's warning about not using a modern car, is because it'll (the alternator will) try to increase voltage and amperage during the sudden discharge.

So without any further input, the conclusion right now is that these nifty 12 volt JumpStart battery packs will probably work just fine (with little risk to components) for use on most vintage 6 volt cars....

HellO!! I Think i might be in trouble then,,,,A couple years ago,I jumped a 53 chev with a 93 S-10,,,Ya know,,,12 volt to 6 volt,,,The car started,the thing about it is the plastic on the cable handles where getting hot and started melting,,,While the car was running i took the cables off the vehicles(carefully)I tried it a couple more times after that,But now i think i should try something else,,,Like maybe popping the clutch,,i think that's a little safer,,,Dave

Another safety point that I failed to mention in my first post on this thread is:

"WHEN MAKING THE FINAL CONNECTION TO THE GROUND, THE CHOSEN LOCATION SHOULD BE AWAY FROM THE BATTERY AND NOT DIRECTLY TO THE NEGATIVE TERMINAL ON THE BATTERY"

The reason for this is to prevent an explosion caused by the sparks that are generated when you make the final connection, therefore we wish to be as far from the battery as is practical.

Batteries are dangerous:

1. They contain acid that can burn you.

2. They contain gas that can explode or ignite.

3. They contain enough electricity to burn or shock you.

Finally: When making a jump from 12-volt to 6-volt system use a cheap set of jumper cables. The inferior cables will act as a resistance to the circuit and reduce the current draw on the system.

Battery explode??? It sure can. Had that happen to me about 35 yrs. ago. Jumped a car to the tractor. Sure glad I wasn't looking over it but it sure scared the h--- out of me. Never tried it again but might try one of your methods. Can't even remember which one blew. :rolleyes:

Don't leave the key on an extended time or you may blow the 6 volt coil up if the points are closed. If it pops the coil it will make you say a few choice words.

Everything has been pretty much covered here but I will add that my 48 jeep cj2a was sometimes a little slow or plumb balky about starting at -30 or so and I often jump started it from a 12v and never hurt a thing. The secret of course is to limit the time the 12v is hooked to the 6v system. And for sure batteries will explode and had this happen in a service station when a customer checked his battery on a 50 **** after a 70 mile run, had to hose him and his face off in the rest toom.

I am confused now...

What is a safe car to jump start my 6 volt? When out on the road, if I need a jump, what type of car would I look for?

Also,

I have always wanted to make a set of jumper cables that would eliminate this problem, anyone know what it would take, or if it would work?

"Perhaps now is a good time to mention. NEVER USE A MODERN CAR TO JUMP A 6-VOLT SYSTEM. This could cause serious damage to the modern car electrical system."

Hi packrat,

If you are on a tour and there are other cars that use 6-volt systems you can use any of them for a "JUMP".

An uninstalled 12-volt battery may be used following the instructions posted earlier.

You may use one of the portable "Battery Supplies" that have been mentioned earlier. Again follow the caution instructions when using a 12-volt supply.

In an emergency you may use a modern car provided you disconnect the negative (-) cable from the battery before the "JUMP" and follow the instructions posted earlier.

ray,

to clarify, you mean to remove the negative cable of the modern car from its battery, so as not to involve any of that modern car's electrical system...

essentially, once disconnected, you are simply "borrowing" the new car's 12-volt battery for the jump...


epi

epi, you are right on!

Hey Raymondo! If you take the "K" from the "OK" graemlin next to "epi" and you add the "K" to "epi" you have "Kepi", which is "Chevrolet's" name. Kind of tricky how he did that huh?

dog,

now you did it...my secret's out and the tax man will now know how to find me... epi

Ok Chevrolet, I now have the goods on you ....name and VCCA #......now if I could just find what the zip code is for Bowtie California, I could send you some junk snail mail..Ha!

Go look in your garage Kepi Doodle, because the tax man is laying under your '40 pickup!

hey mr. mackie,

zip code?..whazzat?..I'm the guy that routinely gets the g&d about the fifteenth of the month, remember?..our zip code must be s-n-a-i-l...


epi

I was reviewing this old posting while searching the site. I want to carry one of those portable jump starters with me since I drive a lot of less-travelled" roads with my 6V 39 Mstr Dlx. Before I buy a 12V jump starter, is anyone aware of a dual voltage 6V/12V model? I've searched the web for a couple of hours and found plenty dual 12V/24V models and quite a few 6V/12V gragae battery chargers, but no 6V/12V jump starters. Thanks!

P.S. Gene: Franklin will be at Grand Junction and looks forward to seeing you and your wife. Unfortuantely, I'll be traveling back here to Germany.

I always carry my 12 V booster pak on trips...Its already in the trunk of the '50.I have never used it for my cars but comes in handy when others are having problems.The advantage of the 12 V is that it really spins over the slugish 6 V cars when they have a problem.Also good for cell phones, CB's etc.

Thanks Gene. I did some mores searches on the site after my question and saw a posting from a couple years ago where you said you carried a 12V model. Seems like that's the way to go. Take care and have a safe run to Grand Junction!

When I had my '53 in New England, I wired a switch that would connect a motorcycle battery to the distributor and give me a hot spark. I could then start at much lower temperatures than normally. Often the engine will turn over, but the current drain can be so high the battery voltage goes low enough to reduce the spark. The '53 would start at remarkably slow cranking speed with this hookup.

I should have said that the small 6V battery was switched in parallel with the main battery once the engine started. If you are prone to leaving the lights or radio on, you can isolate the extra battery when the engine stops. Then it's hot for a roll off or to give a good spark if there is a little life left in the main battery.

So if I read you right, the small battery was charged in parallel with the starting battery but when you switched to start it was out of the circuit with the cranking battery? How did you wire the switching device?

Ray said:

Could you also use a short pig-tail for the negative end that is weaker? Like a smaller wire with alligator clips on both ends that you could then clip to the end of the - cable and then to the ground?

Mack, this was 1960!
I'll see if I can scan in a diagram for you.

Louis C.,

Use smaller wires only if you want to melt the wires. You could use resistor wire I suppose, but it's not really necessary.

It doesn't get much clearer than the quote. Just follow those instructions.