Jumpers

[BobDeSoto]

I've heard of people using a 12 volt battery to speed up the starter.

My 1951 DeSoto is all stock - 6 volt positive ground - fluid drive .....

Can I jump start it leaving everything as it is but use a 12 volt battery

and jumper cables?

[Ivan_B]

I would not do that on my car ? I am also not carrying any jumper cables for that same reason. If you want to be prepared, I would just get a spare battery for the trunk and charge it once a month

 

Correction: if the 12v battery has contacts for each cell, then you can use half of it, or reconnect it parallel for 6V. But I have not seen batteries with individual cell contacts these days...

Edited November 10, 2023 by Ivan_B

[Sniper]

If there is any juice in the battery a push start should do the trick.

[Sam Buchanan]

2 hours ago, BobDeSoto said:

I've heard of people using a 12 volt battery to speed up the starter.

My 1951 DeSoto is all stock - 6 volt positive ground - fluid drive .....

Can I jump start it leaving everything as it is but use a 12 volt battery

and jumper cables?

 

Yes, if the 6v battery has enough juice to fire the coil.

 

Connect the ground of the 12v jump battery to the engine block, turn on the ignition switch, and touch the positive jumper to JUST the terminal of the starter that has the big cable. That will provide 12v to the starter but not the rest of the vehicle. The starter will spin the correct direction regardless of polarity. As soon the the engine catches, remove the positive jumper from the starter.

 

I have jumper cables in my tool bag in the trunk of the P15. 

Edited November 10, 2023 by Sam Buchanan

[Ivan_B]

38 minutes ago, Sam Buchanan said:

I have jumper cables in my tool bag in the trunk of the P15. 

You are radical... I would not dare to try the above trick ?

[Sam Buchanan]

6 minutes ago, Ivan_B said:

You are radical... I would not dare to try the above trick ?

Nothing radical about it, just need basic understanding of how the car is wired. There is no risk to the car if done properly.

[kencombs]

7 minutes ago, Sam Buchanan said:

Nothing radical about it, just need basic understanding of how the car is wired. There is no risk to the car if done properly.

I started working on cars in earnest about 1960

 

 

Still lots of 6v vehicles around then and I have no idea how many we jumped with 12v from the wrecker.  well over 100 I'm sure.   In most cases we  turned on the ignition and made sure the lights, radio etc were off.   The do as Sam stated.

[Bryan G]

I've jumped 6 volt cars a few times with 12v. Just like kencombs said, check the lights...keep the doors closed, roll the window down so you can just reach in. No sense blowing out your interior lights. 

 

The real question: why is your starter turning too slow? It should spin plenty fast on 6 volts, in less something is awry. Got the good, fat battery cables? Clean connections? I just know that my straight eight spins just like a modern vehicle with the stock setup.

[Sam Buchanan]

17 minutes ago, Bryan G said:

I've jumped 6 volt cars a few times with 12v. Just like kencombs said, check the lights...keep the doors closed, roll the window down so you can just reach in. No sense blowing out your interior lights. 

 

Some mis-information is being passed on about this topic. If the positive jumper cable is only touched to the big starter terminal to make the starter spin, it makes no difference if lights, radio, etc are turned on, no jumper voltage will go to them. Only the starter will see 12v.

 

The starter switch in the car IS NOT USED!!!!! Just turn on the ignition so the coil sees its regular 6v. 

 

Think about it.

Edited November 10, 2023 by Sam Buchanan

[kencombs]

4 minutes ago, Sam Buchanan said:

 

Some mis-information is being passed on about this topic. If the positive jumper cable is only touched to the big starter terminal to make the starter spin, it makes no difference if lights, radio, etc are turned on, no voltage will go to them. Only the starter will see 12v.

 

The starter switch in the car IS NOT USED!!!!! Just turn on the ignition so the coil sees its regular 6v. 

 

I usually used a remote starter button like you would use for compression checks.   Because I dislike pitting my jumper cable clamps from the arcing.   Plus in our business it was sometimes required to prime the carb, hold chokes open or closed while cranking   That can feed power back through the solenoid to the ignition switch powering accessories that are live with the key on.  

[Sam Buchanan]

The solenoid can't back feed if the starter button circuit isn't activated. I'm describing what you can do in a pinch if the only jumper battery available is 12v. Our 6v cars can be jump started with 12v if the correct procedure is used and no harm will come to the car's electrics. 

[maok]

When making the final contact, do that on the 12v battery +ve or -ve terminal, not on the starter. The contact will cause an arc which may damage your threads on your starter terminal.

Edited November 10, 2023 by maok

[soth122003]

I've used the 12v jump pack with a switch from Harbor Freight the way Sam said, Pos to ground and Neg to the starter and I've never had any arcing or damage to the electrical system. You have to use the old style jump pack with the lead acid battery in it. The new Lithium Ion jump packs have a sensor and if it doesn't read more than 10.5 volts it won't  work.

 

Joe Lee

[Sam Buchanan]

9 hours ago, maok said:

When making the final contact, do that on the 12v battery +ve or -ve terminal, not on the starter. The contact will cause an arc which may damage your threads on your starter terminal.

 

Good point. Or you could clip the positive lead to the starter terminal then make contact with the ground lead on the engine block to spin the starter. The polarity of the jump battery doesn't actually matter since no jump voltage is being fed into the car, just the starter and it doesn't care about polarity.

 

Once again.....DO NOT USE THE STARTER BUTTON in the car! Doing so will back feed jump voltage into the car through the starter solenoid. If this concept is confusing, spend some time with the wiring diagram to see how this is a safe procedure when applied properly.

Edited November 10, 2023 by Sam Buchanan

[kencombs]

9 hours ago, Sam Buchanan said:

The solenoid can't back feed if the starter button circuit isn't activated. I'm describing what you can do in a pinch if the only jumper battery available is 12v. Our 6v cars can be jump started with 12v if the correct procedure is used and no harm will come to the car's electrics. 

Or the remote start button that I described earlier is used.   Same results, two big terminals on the solenoid are bridged while cranking.

[Sam Buchanan]

7 hours ago, kencombs said:

Or the remote start button that I described earlier is used.   Same results, two big terminals on the solenoid are bridged while cranking.

 

I don't want to belabor this topic but maybe it is educational to some. What you are describing with bridging the battery and starter terminals on the solenoid is not the same technique I've described. Unless I'm missing something you are connecting the 6v battery to 12v when the jumper cables are connected to the battery. I don't know if this is harmful to the 6v battery but what I've described doesn't have this risk since the 6v battery never sees 12v.

 

Or maybe you are disconnecting the solenoid from the 6v battery? If I have misunderstood what you are describing please feel free to elaborate further.

Edited November 10, 2023 by Sam Buchanan

[BobDeSoto]

I was wondering ------

If I take jumper cables and connect them to a 12V battery

while the 6V is in the car (keeping it simple) while it make

the starter spin faster and will it harm anything on either end.

[maok]

3 minutes ago, BobDeSoto said:

I was wondering ------

If I take jumper cables and connect them to a 12V battery

while the 6V is in the car (keeping it simple) while it make

the starter spin faster and will it harm anything on either end.

 

Yes, the 12v battery will make the starter spin faster, general rule with electric motors, higher the voltage, faster the spin, more mechanical resistance, higher the current(amp) draw from the battery.

 

And yes, the 12v battery will blow things like light bulbs, etc if designed for 6 volts. Do what Sam has suggested and make sure not to have those devices switched on.

[Sam Buchanan]

9 minutes ago, maok said:

 

Yes, the 12v battery will make the starter spin faster, general rule with electric motors, higher the voltage, faster the spin, more mechanical resistance, higher the current(amp) draw from the battery.

 

And yes, the 12v battery will blow things like light bulbs, etc if designed for 6 volts. Do what Sam has suggested and make sure not to have those devices switched on.

 

Connect the 12v battery directly to the starter and DON'T use the car's starter button and it won't matter if lights, etc are on or off because they won't see 12v.

[Los_Control]

My 2 cents on it .... It can be done in a emergency situation.

If I'm at home in my garage ..... I do not consider it a emergency situation.

To me if you are at home, if you need to assist it with 12 volts to turn over fast enough to start. .... You have a problem .... fix the problem.

 

You need to know your wiring well and know exactly what is getting power to avoid possible damage.

Not really a question a forum can answer ..... Nobody here knows what has been done to your wiring system over the years.

 

In my case I feel like a total dummy when it comes to automotive wiring.

I am in the process of converting to 12 volts and building a new wiring harness for my truck.

Just saying I have a 12 volt GM alternator mounted, not wired yet. I have a 12 volt battery. All my original wiring has been removed .... only wiring I have left is power to the ignition switch turning power on off to the coil. ..... I know I can start my truck with a 12 volt battery ..... I still wont do it.

 

I know I need to add a ballast resister into the system to drop the voltage to protect the points ... I have not wired it in yet. So I start it with 6 volts.

I did start it on 12 volts for a short time .... I just knew it was not the correct way to do things.

 

Just too many if', and's butt's & why thrown into it.  ....... On the roadside getting a jump from a 12 volt battery to get it where you can fix it ... sure.

Just doing it at home for no good reason ..... not for me.

 

[Young Ed]

About 2 weeks ago I was trying to get Dad's 55 Chrysler with 331 hemi running for storage. Found out I'd forgotten to disconnect the battery in the spring. Charged it a little and got it running only for it to die in the street while I was trying to turn it around. 12 jumped right from my minivan to the Chrysler and got it started back up. I don't believe it hurt anything! The dash lights were sure brighter for a min though. 

I got it turned around and left the charger on it overnight. Started on its own the next day so nothing too wounded.