6-volt batteries

[revgawright]

Was wondering if anyone could help me with a battery question. Is it recommended to jump start a 6-volt positively grounded car (my 39 LaSalle) with a 12-volt negatively grounded car? What precautions should one take? What are the risks to either vehicle? Thanks in advance for all responses.

Even though Sally has been stored away for the winter, today was such a beautiful warm sunny day that I couldn't resist the urge to take her for a spin. She had other ideas, however. She just wants to hibernate until spring.

[Dave Shepherd]

Not a good idea, as far as the starter and ign system , momentary 12v is ok, but what about the dash gages as you turn the key on?  In your case I would slow chg the battery with the correct charger

[Alan Harris CLC#1513]

You have two issues here-voltage and polarity. I have seen people jump a 6 volt car from a 12 volt without apparent damage. I would be afraid to do it except in the most dire circumstances. I think that there is just too big a chance of burning something up.

Polarity is less of a problem. You can jump a + grounded car from a - grounded car if you disconnect the battery on the donor car. After that, you can connect positive to positive and negative to negative and you should be fine.

[Wayne Womble 12210]

You should have a helper and only do it while actually trying to start the car, but it will not hurt anything.  Just attach the negative cable to the negative and the positive to the positive ( frame ground in this case).  Have your helper touch the cable to the donor battery just as you hit the starter and release as soon as you let up.  Done it many, many times.

[R Sotardi #11719]

What year car will be the donor?  You should not take a chance of jumping anything directly from a modern  (computerized)donor car with the engine running .Reason: any power surge flowing back into the donor  car can blow a chip, circuit or internally regulated alternator. Advice: jump start  your La Salle with a portable battery pack. Turn off All accessories!  .  Connect the pos cable to the LaSalle positive battery terminal. Quickly touch the negative cable to the starter terminal, and have a helper press the starter button as you touch that terminal. When the car starts pull off the neg cable ASAP. Don't leave it connected.

[TJ Hopland]

The polarity does not come into play as long as the cars are not touching when they are connected. 
You just connect + + - - it does not matter which is 'grounded' again as long as the two cars are not touching.   
Now if they both had metal bumpers and were touching that would create a - to + connection.  That in itself is not going to cause a problem because there is not a complete circuit between the two cars.  As soon as you connect one cable you will be making a complete circuit which in this case would be like connecting the cable direct across the battery assuming the physical connection between the 2 cars was 'good' or low resistance.   

You dont want the 12V car running because you then have more like 14V, no sense making it worse.

I have done it many times with no apparent issues.   You dont want to leave things connected any longer than needed or crank the 6v car for an extended period. If it does not start quickly give up.  Most of my experience is with tractors that have minimal (if any) electrical accessories.

You know 'back in the day' this had to happen all the time.   I was not around then to know how often it was a problem but the 'old timers' that told me (and it looks like a few others) to go ahead and do it did not seem to have any stories about bad things happening. 

The jump box is not a bad idea.   Those usually have pretty limited capacity so the voltage is going to be dragged down pretty quickly. 

[Philippe M. Ruel]

If the question is "is it possible to start a 6-volt car by jumping a 12-V battery ?", my answer is YES, I have done it many times, too. Which car is grounded where has no importance, as you can read above, as long as grounds are not connected together.

If the question is "do you recommend it ?", my answer is NO, because I once burnt the generator armature by trying it too many times on a stubborn engine (remember why you jump-start ? usually because engine won't start at first crank). Knowing the price to pay, I would do it again on MY OWN car, but I'd never tell anyone "do it on your car, it doesn't hurt".

By the way, it will not hurt a good 6-Volt starter, but may finish burning a "lazy" one, too (remember, etc.).

[Tito Sobrinho]

The best thing for a hibernating car like yours is to install a 6 Volt Battery Tender Plus before the hibernation. It charges and maintains it.  Mine is a 1.25 Amps, which I bought at Battery Plus.
My automotive electrical friend told me that with a generator (Dynamo) one could run the engine for 1 week and not completely  charge the battery.
After a long period of hibernation, I would check the specific gravity in each cell in order to see if the battery is worth it.

[Wayne Womble 12210]

I would like to hear that explanation.

[Tito Sobrinho]

About what? 

[Wayne Womble 12210]

About why an alternator or generator will not charge a battery fully. It make no sense.   As a matter of fact, it will do it much quicker than a low rate charger. As to whether it is best to do that from a discharged state might be a matter for discussion, but to say it wont charge a battery fully is nonsense.

[Tito Sobrinho]

Seems to me that you didn't read my above post!  I didn't mention an alternator but the relic that you have in your car...generator or dynamo for the Britons. I have the same relic also with a commutator, brushes, etc
Crank your car and leave it on idle for a week and tell me the results and the "nonsense".

My '49 starts to replenish the battery at 35 miles/h and never at 345rpm, its idle speed.

[Wayne Womble 12210]

Maybe you should go back and read yours and mine too.  I did mention a gererator , and nowhere did you say it was to idle for a week.  Who would do that?  Certainly it would have to be at some rpm necessary to charge.  A generator is perfectly capable of charging a battery fully, and assuming you dont have a gigantic BOOM BOX , or some other major draw, it will do it in short order. 

[Jim Stamper]

     This all reminds me of jump starting my 1942 Ford 9N tractor probably 35 years ago. It seldom held a charge so I would jump it with a 12 volt battery just lugged over to the tractor. One very hot summer morning I hooked up the old 12 Volt with cables and climbed aboard. I didn't take the water filler cover off which is a good precaution I don't think anyone has mentioned. The battery is right in front of the steering wheel. Well I may have taken a while to saddle up and it apparently built up some gas. When I hit the starter button there was a huge explosion, one of those close proximity stunners. I was looking at the 6 Volt battery and was just coming to my senses enough to realize the water covers were now gone. It was the three attached plugs type that just push in. About the time I realized it was gone it came back down out of the clouds and landed right back where it belonged. It didn't go in tight but there it was. The battery was undamaged and I went ahead and started the tractor. It was probably my most memorable jump start.

                                                                                     Jim Stamper CLC#13470

[R Sotardi #11719]

Jim, that is why I recommended touching the solenoid relay or directly to the starter terminal. When going to the battery neg terminal directly it puts your mug too close to the vent filler caps. Gas can build up and a spark can ignite the mixture. Nice idea re, removing the caps to let the gases escape. Wear glasses. Ron

[william_b_noble]

years ago, I was jumping my 38 plymouth from a 64 mustang - I connected the wires backwards and not only got a bigger than expected spark, but the mustang battery exploded, showering my lovely assistant with battery acid.  She was unhurt (quick action with a hose followed by a shower), but her clothes disintegrated in the wash.  The advise to remove caps is good.

[TJ Hopland]

I presume the 38 was pos ground?     Were you connecting direct to batteries or were you making the 'ground' connection to the chassis?   I wonder if you made the + to + correctly but then went - to chassis on the mustang and then - to the chassis of the plymouth which was not -.   That would have made a dead short to the mustang, was that the one that exploded?

Remember the reason we taught to make the final connection to the chassis was to get that spark as far away from the battery as possible.  This obviously does not help much if you are making a bigger mistake causing a short. 

[william_b_noble]

I dont' remember for sure now, it was decades ago, and my lovely helper is still with me despite the experience (and others) - but I am reasonably sure, since the plymouth battery is under the seat, that I was jumping from the frame to the pos and from a terminal, probably on the starter.  I dont' remember exactly who did what, but it was (because I went back and checked) a reversal of polarity, and the battery exploded from the rapid generation of gas, it was not a combustion event.

My point is, remove the caps on the 12V battery if you are going to do this - that's all.

[revgawright]

Thanks for all the great responses. Guess I'll just try to charge the battery out of the system and see what that does. If all else fails....there's always a can of ether! :-)