6v to 12v question

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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David V
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6v to 12v question

Post by David V » Thu Apr 19, 2018 12:27 am

I want to change my 6v Jeep to a 12 v Jeep. I've looked at the threads for this conversion but still have a few questions.

I want to say first of all that when I found my jeep in 2004 - in a terrible state - she was running a 12 v battery but with a 6v starer and 6v dynamo.
This has always puzzled me.

I understand that my 6v starter would be compatible with a 12 v battery. What's the difference ? The size of the brushes or more than that because maybe I can just change the brushes ? Or it's the whole core wiring.

For the dynamo, I've been looking online at 3 shops in France - and see 6v dynamos at 40 amps and 12v dynamos at 25 amps. So is this same dynamo that just puts out half the amps ? In which case I can just keep mine.

I've also seen a bigger 12v dynamo putting out 55 amps. But they seem to be unavailable.

Sorry but I'm just not good on electrical things.
44 MB 356111 "Charlotte" since 21/02/06 - Capstan winch
42WLA 70443 "Lily" since 16/1/10


Mark Jesic
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Re: 6v to 12v question

Post by Mark Jesic » Thu Apr 19, 2018 12:41 am

David, i know a fair few have changed to 12v, but the majority keep them at 6v, there were never any issues about it during the war, but its your jeep, to do as you wish. I see your point though, as a cold start can be a bit sluggish.

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David
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Re: 6v to 12v question

Post by David » Thu Apr 19, 2018 12:47 am

If for daily use maybe using a standard 12V alternator instead of a dynamo & regulator (keep the regulator in place for looks, not wired up) is an option, but personally I think 6V works just fine as long as your mass connections are good?

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Re: 6v to 12v question

Post by Wolfman » Thu Apr 19, 2018 6:18 am

As you suspected, David, the difference between 6 and 12 volt starters is in the windings. You can change a 6 volt starter over to 12 volt. Would require replacing the armature and Field windings. Really not necessary. There are a lot of 6 volt starters that are in converted 12 volt systems and they work fine. Have one or two myself. They have been that way for years without any problems.
The difference is in the resistance and number of turns in the windings. Not just changing the brushes. You said you are not into electrical stuff so I won't go into a long explanation. Only thing to watch is, when cranking a 6 on 12 volts, the starter will heat up a lot faster. Don't crank too long and burn the starter up.
As for the generator, same thing. 6 volt is set up to put out 6 volts. Some have said they get 14 volts out of a 6 volt generator. ???? I have never tried it. Best to change the generator and regulator over to 12 volt. Or install an alternator.
Other things to change, the lights, obviously. And something needs to be done with the ignition coil. A 6 volt coil on 12 volts will work, for a little while, but it will heat up quickly and the points will burn up faster. You need to either replace the 6 volt coil with a 12 volt coil, that does not use an external resistor or put an in-line ignition resistor in the wire going from the ignition switch to the coil + terminal.
One more possibility. Would be easier and cheaper in the long run. Batteries come with different cranking amp ratings. Human nature to buy cheap but that is also the lower cranking amp. battery. Spend a little more. Buy a higher cranking rated battery. It will make a difference in how your jeep cranks over. A good electrical system service may help as well. Clean the battery post & clamps and all the electrical connections. Including the ground cable and strap connections. Even the surface between the starter and engine block. That is a connection.
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Re: 6v to 12v question

Post by Wolfman » Thu Apr 19, 2018 6:59 am

For you and I.
Getting those stupid screws out, that hold the pole shoes in, is a challenge.
There is a special tool to do that. A cradle, the field housing lays in, with a lever that has a big screw driver bit attached, with a lever attached to the screw driver.
Don't have one of those, but I made something similar, that fits into my drill press.
You just have to be creative sometimes.
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Re: 6v to 12v question

Post by OldPappy » Thu Apr 19, 2018 9:12 am

Most of the old Jeeps I have owned were converted to 12 volt systems by prior owners. The M38 from 24 volts to 12, the CJs from 6 volt to 12.

With all three of those it was done with an alternator, new coil, and such as that.

The CJ2A I have now was converted to 12 volt, but instead of an alternator it has what appears to be a 12 volt generator probably from an old Chevy.

As said already, the 6 volt starter will work as it is. It will turn over a little faster, and like was also said will heat up if cranked too long.

The generator on this CJ2A does not fit the bracket very well and has some "creative" Bubba adapters made of junk. So, that will have to be attended to on my build. Haven't decided whether to go back to 6 volt, or do the 12 volt conversion the right way to get better light output.
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Re: 6v to 12v question

Post by David V » Thu Apr 19, 2018 9:33 am

Wolfman wrote:
Thu Apr 19, 2018 6:59 am
For you and I.
Getting those stupid screws out, that hold the pole shoes in, is a challenge.
There is a special tool to do that. A cradle, the field housing lays in, with a lever that has a big screw driver bit attached, with a lever attached to the screw driver.
Don't have one of those, but I made something similar, that fits into my drill press.
You just have to be creative sometimes.
I know ! I took my second starter apart years ago to replace the bendix and cannot get the bushes back in. It's been sitting in a box in pieces ever since.
How do you do that ?
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Re: 6v to 12v question

Post by dpcd67 » Thu Apr 19, 2018 9:38 am

I have owned three jeeps and one 53 F100 with 6 volt starters running on 12 volts. No issues so far and one has been running for 40 years.
If dynamo means generator, (TM standard nomenclature is important), then I would just put an alternator in it for general use. I assume you aren't showing it.
I have 6 volt vehicles too; there is a reason we don't use that any more.
I know nothing about electricity, disclaimer.
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David V
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Re: 6v to 12v question

Post by David V » Thu Apr 19, 2018 9:46 am

dpcd67 wrote:
Thu Apr 19, 2018 9:38 am
I have owned three jeeps and one 53 F100 with 6 volt starters running on 12 volts. No issues so far and one has been running for 40 years.
If dynamo means generator, (TM standard nomenclature is important), then I would just put an alternator in it for general use. I assume you aren't showing it.
I have 6 volt vehicles too; there is a reason we don't use that any more.
I know nothing about electricity, disclaimer.
I just don't like the look of an alternator. It's not jeep for me. So a 12v generator seems the way to go.
As for 6v, I totally get you. When all is fine, OK. But my jeep lives in a lockup at the moment and cold starting is just unreliable even if she's in good shape. When she was in the house garage it was a different story.
Good news on the starter ! Thanks.
44 MB 356111 "Charlotte" since 21/02/06 - Capstan winch
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Re: 6v to 12v question

Post by rjbeamer » Thu Apr 19, 2018 10:27 am

This might be the answer for some of you folks that want a 12 volt alternator but want it to look like a 6 volt generator.
This is a quality product if that is what you are looking for.



https://iaf.azureedge.net/images/bctd/i ... wergen.pdf


https://www.streetsideauto.com/p/powerm ... YASABEgKcN


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Re: 6v to 12v question

Post by Wolfman » Fri Apr 20, 2018 4:40 am

Back a way, David V ask about getting the brushes back in.
Don't know if you mean holding the two brush carrier arms in place, against the V shaped spring while putting the pivot pin in, which can be a little challenging
or
Holding the brushes out while sliding the field housing in place, over the armature.
I have a tool for that one. It is a cone shaped, aluminum piece that fits on the armature shaft, up against the commutator. The large end of the cone is slightly larger that the diameter of the commutator. When installing the field housing, the brushes are slipped on to the small tip on the cone shaped tool and as the housing is slid into place, the cone spreads the brushes, so they slide easily into place on the commutator. A lot easier than trying to hold all four brushes out while putting the housing on.
I have had this tool for a long time. Found it on a tool truck I was looking through. I suppose they are still available or it would be easily made, if you have a lathe.
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Re: 6v to 12v question

Post by twinflyer17 » Fri Apr 20, 2018 4:55 am

David V wrote:
Thu Apr 19, 2018 9:46 am
So a 12v generator seems the way to go.
I have a 12v system in my GPW and use a 12v generator. I also hid the 12v regulator in an original 6v case. To the average person, they have no clue it's 12v. To the jeep 'expert', all they will notice is the 12v battery. I'm hoping to do the opposite of you and switch it back to 6v one of these days, but I'm in no rush since the look is still close to original.
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Re: 6v to 12v question

Post by David V » Wed May 16, 2018 1:41 am

I was told this morning (by a guy who's been around jeeps all his life) that I can keep my 6v 40amp Autolite generator in my jeep but put in a 12v battery and 12v regulator (and lights, fuel gauge etc) without any problem. I'd like to understand the electrical logic behind this. I'm not good on electrics. By my reckoning the power from the 12v battery is going to the 12v coil and 12v points but it's being charged by the 6v generator through the 12v regulator. So the 6v gen is not going to suffer from a power surge. And the regulator (I have a an electronic one) should level out the power being fed to it by the 6v gen.

When I found this jeep years ago it was running the same 6v gen but with a 12v battery.

So 6v 40 amp = 12v 25 amp ?

I have found a 12v 25 amp gen (looks exactly the same as my 6v) and a source for a 12v alternator but still hesitate.

Pros and cons ?

Thanks

David
44 MB 356111 "Charlotte" since 21/02/06 - Capstan winch
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Re: 6v to 12v question

Post by Wolfman » Wed May 16, 2018 3:54 am

I have heard stories that people have excited a 6 volt generator enough to charge a 12 volt battery. ??? That would be asking a lot of a 6 volt generator.
As far as putting a 12 volt battery in a 6 volt system. I see it a lot. On farm tractors. Most old farm tractors that have magnetos, don't need a battery to work. Jeeps do. So all the tractor needs is an occasional charge on the 12 volt battery to stay up and start the tractor. The jeep battery is going to have a constant drain. Needs to be charged while running.
As for harm ?
The output from a 6 volt generator is most likely not going to get high enough to close the contacts on the cut out relay or activate the electronics in the 12 volt regulator so the generator is never actually connected to the 12 volt battery. It just keeps the fan belt tight.
In your jeep, you need something that keeps the battery charged. 6 or 12 volt. If you convert, I would recommend a 12 volt gen. or alternator.
Mike Wolford
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Re: 6v to 12v question

Post by OldPappy » Wed May 16, 2018 4:50 am

Wolfman is correct.

The simple solution is an internally regulated alternator, but if original look is important to you a 12 volt generator is what you would want.

The Jeep I have was converted by a previous owner using a 12 volt generator, probably from an old Chevy. It works fine, but does not fit the original brackets, and has a cobbled up mess of junk holding it in place. If I end up using that generator I will fabricate a better bracket.
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