24V Battery System

1950 - 1952, M38, questions, discussions, regarding anything related to the M38.

24V Battery System

Postby FrankenJeep » Thu Mar 09, 2017 8:23 am

I've tried to keep my Jeep as original as possible, but I am thinking of going to a 12V system. I would keep the 24V parts for the next owner.

There are some disadvantages to the 24V system that, perhaps, the Army was not considering at the time 24 was considered. The flaw lies in having 2 batteries in unprotected series connected together. If one battery develops a weak cell, it will draw against the other battery. Ultimately it will draw down the system until it won't start. The same holds true with modern 12V systems where an additional battery is installed, for example, to operate high-current radio systems. Modern systems use a battery isolator to counteract this draw-down problem. Currently, batteries actually last about a year before I must replace at least one.

I know Joel is a stickler for originality :lol: , and I am, too. But, I'll tell ya, that positive ground stuff really plays with my dyslexia! :lol: I"d like to install some modern radio (ham) equipment in my Jeep, but, again, when you start "tapping" into one battery to get 12V, you may have the same problem of drawdown. Now I have a battery disconnect, and I disconnect it after every use.
SO! In your opinion, would going to the 12V system detract from the sale value of Willis the Willys? :? Not that he's up for sale, ya know..............

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Re: 24V Battery System

Postby Ben Dover » Thu Mar 09, 2017 9:38 am

Positive ground?
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Re: 24V Battery System

Postby dpcd67 » Thu Mar 09, 2017 4:10 pm

I had a 53 Ford F100 with 6V positive ground, but no jeeps.
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Re: 24V Battery System

Postby Ben Dover » Fri Mar 10, 2017 11:51 am

All WWII thru CJ Jeeps were Neg Ground.
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Re: 24V Battery System

Postby FrankenJeep » Sat Mar 11, 2017 6:36 pm

Ben Dover wrote:All WWII thru CJ Jeeps were Neg Ground.


Dunno what's goin' on there, but this one is positive. And I HATE it!
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Re: 24V Battery System

Postby Radtech » Sat Mar 11, 2017 8:04 pm

Willys never made a pos ground jeep.Where did you find the pos ground generator and voltage regulator?The starter will turn the same way no matter the polarity.I have run 24v and 12v radio gear in my M38 at the same time and have never had problems with the battery.
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Re: 24V Battery System

Postby FrankenJeep » Sat Mar 18, 2017 7:20 am

Radtech wrote:Willys never made a pos ground jeep.Where did you find the pos ground generator and voltage regulator?The starter will turn the same way no matter the polarity.I have run 24v and 12v radio gear in my M38 at the same time and have never had problems with the battery.


The generator and regulator all appear to be original equipment. *I* did not "find" anything; it was already there. I carefully checked the polarity with a VOM. When the positive lead is placed to positive, the negative to ground, it reads backwards. Reverse the leads, it reads 24V. So how could this be IF the Jeep was originally negative ground? It would not make sense to change it, but because it WAS the way it was, I assumed it was positive ground. In the back of my mind I didn't recall them being positive gnd, but it had been 40 years since I had messed with the M38.

When I got this Jeep, it WAS all boogered up. The lights ran on 12V, the engine ran on 12V but cranked on 24V. Distributor, plugs all was 12V with conventional wires, etc, but the huge generator and regulator is 24V. I had all that changed over to strictly 24V. And when it was all back to 24V, it read positive ground. I left it that way. Didn't LIKE it that way, but assumed it was correct. So now, the question is, HOW to correct it? Who the H bunged it up like that? HOW did they GET it that way? I figure, tho I don't know, ignorant, but well-meaning people, assumed they couldn't get parts for a '51 Jeep, so they (shall we say) 'engineered. something to make it work. The exhaust is not correct, so I don't get that true Jeep "singing" sound we are familiar with :cry: . How difficult will it be to get it BACK correct? Obviously, I've got some work to do! :(
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Re: 24V Battery System

Postby dpcd67 » Sat Mar 18, 2017 8:05 am

Just look at the battery, or batteries and find the negative terminal. Trace that negative cable and tell us what it is connected to. The frame, or something else, like the starter.
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Re: 24V Battery System

Postby cjv-35 » Sat Mar 18, 2017 9:10 am

Believe you might have to switch the wires around on your ammeter.
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Re: 24V Battery System

Postby FrankenJeep » Sat Mar 18, 2017 2:17 pm

cjv-35 wrote:Believe you might have to switch the wires around on your ammeter.


If you are speaking of my VOM (Volt-Ohm meter) it is the same as it has always been when I bought it in 1976. It is used for not only auto, but also for electronics.
The black wire is negative, red is positive. I don't have an external ammeter. :)

And before I finished this note, I went back and re-examined the wires OF the Jeep. This is an M38, so one battery is under the right side of the hood. The other, of course, is in the cowl up top. The (front)positive + terminal goes to chassis ground to a nearby bolt. A jumper then travels from the negative - of the battery to the other battery's positive + terminal. The negative - connects to the starter solenoid. Now, by virtue of the positive terminal connecting to chassis ground, this is what I concluded is a postive ground system. If you try to connect it any other way, it will spark. Once again, when you check the system normally (positive to positive, negative to negative) it reads backwards (RED llead to +, black to -, the meter goes backwards. Reverse it (red to ground, black to positive, it reads FORWARDS 24V. :cry: You can't (?) have positive to negative. ?????????????? It will arc.

SO! What gives? How could it be reversed? WHO reversed it and WHY? Is it easy to do this by accident? (I wouldn't think so) :oops:
To me, this IS back'ards! IOW, positive should connect to positive and negative should always be ground. But this one is NOT :( HOW could someone do this? I didn't, and I wouldn't WANT it this way. So how do I fix this? :?: :roll:

The more I talk about this the confused'er I git! :oops: :|

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Re: 24V Battery System

Postby Ben Dover » Sat Mar 18, 2017 3:14 pm

There are two Operator TM's, 9-804, September 1950 and 9-8012 January,1956. Both indicate that the Generator and Voltage Regulator are 24 Volts Negative Ground. TM 9-8012, Page 199 indicates that the negative Post to the front battery is grounded to the Frame And that the Cowl Battery (Page 200) has its Negative Cable from the Negative Post hooked to the Positive Terminal of the Front Battery, it's all explained in Paragraph 156 of the same manual. Page 193 of the same manual has a beautiful easy to read wiring diagram of the Generating System it clearly shows that the two batteries are set up with a Negative Ground.
Trust your TM. :wink:
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Re: 24V Battery System

Postby dpcd67 » Sat Mar 18, 2017 4:55 pm

Yes, and I would say that you can't possibly have what you say you have, but you looked at it, and verified it, so I don't know what to say.
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Re: 24V Battery System

Postby Gaston C Barmore » Sun Mar 19, 2017 2:56 pm

To have a functioning positive ground system in your M-38, your generator and voltage regulator must have been modified. GHA-4802 generators are Group 4 two-brush generators with have the negative brush grounded to the case. The field is also internally grounded. See TM-1825B page 16.
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