M38a1 is over charging its batteries

RichJohnson · Post by **RichJohnson** » Tue Jun 17, 2008 9:19 pm

Ive got 2hns and noticed they are drying up. I checked voltage and Im getting 32 on idle and it just goes up from there. When I throttle up, water oozes out of the battery caps.

What do I do and what is likely wrong.

bubagun · Post by **bubagun** » Wed Jun 18, 2008 12:56 pm

I had a similar problem...My M38 OVERCHARGED all the time. I never checked my generator output except by the guage in the dashpanel or for voltage out-put and I diddled with the analog voltage regulator endlessly. I finlay "threw in the towel" and installed one of the later, M-series electronic units....problem solved. It worked for me at least.

Post by **wesk** » Wed Jun 18, 2008 9:03 pm

Try cleaning the contacts on your mechanical regulator. I prefer using the mechanical regulator since it is easily repaired and adjusted. There is no technical data available to support repairs and adjustements on the transistorized units. There are also no parts available for them. They were designed from the get go as throw away units.

Had the second poster installed a freshly overhauled mechanical regulator he would have experienced the same good result.

We have the necessary applicable exerpts from the TM 9-1825B that apply to the Auto-Lite regulator on our download section. I have the applicable Delco mechanical regulator repair, overhaul and testing data on our old Yahoo Group files page.

Important Note: Dicsonnect battery whenever you want to remove the regulators cover. Use only a metal type point file and a quality electronics contact cleaner. [/u]

RichJohnson · Post by **RichJohnson** » Wed Jun 18, 2008 10:13 pm

Thanks Wes, Do you think that one of the points is just stuck down, allowing full generator volatge to apply to the batteries?
A task I will attempt by saturday. I think I have a points file around here somewhere. A few years ago my m37 generator turned into an electric motor and I followed your advise and did the same maintenance.

Post by **Ryan_Miller** » Thu Jun 19, 2008 7:58 pm

Wes,

I was looking through the info I have on the generator and regulator.

The generator out put at idle should be 24 - 25V and at 3000 rpm around 28 V

The regulator should be a constant 24 V ?

I am going to use that test set up I bought from Kevin at Star Electric Ordinance to test my generator and a couple of voltage regulators.

The test unit came with a manual on how to test these units, but says to refer to the service manual for expected voltages.

Ryan

Post by **wesk** » Fri Jun 20, 2008 1:43 am

The generator out put at idle should be 24 - 25V and at 3000 rpm around 28 V

The regulator should be a constant 24 V ?

Not sure where you read the "constant 24V". The control and reference voltage is fairly constant but the regulator is not tasked to put out any voltage, it is tasked to supply a regulated voltage and current signal to the generator and disconnect the generator from the battery when you shut down.

Post by **Ryan_Miller** » Fri Jun 20, 2008 4:48 pm

What should the value be coming from the regulator when the test unit is hooked up?

If I read it correctly:

24 to 25.5 volts if the batteries are fully charged. Engine not running.

At idle it should read close to the same.

At about 1200 RPM it should read 25 to 27 volts.

At 3000 RPM it should read 27 to 28.5 volts.

Generator test:
voltage reading above 26 volts then the generator is ok and the regulator needs work. If it shows nothing over system battery voltage (22 to 24) then the generator needs work.

Post by **wesk** » Sat Jun 21, 2008 11:15 am

The test adapters allow you to intercept current and voltage figures at 7 locations and these seven locations are used for a dozen or more tests which are done while the engine is off, on at idle, on at cruise on with a load applied, by using different connections and all with a temperature range chart to correct your readings. So you'll have to be more specific on which test, with which leads connected where and under what operating conditions. Since these test are or can be quite complicated and should be followed in a very organized manner it's best to not try and address them piecemeal on a web board. The bottom line for quick notes here is at idle the meter reading across the battery 24 volt positive terminal and ground should be at least slightly above battery voltage you had before starting the engine or 24 to 25 volts and at cruise (about 3000 RPM) it should be about 28 volts. If these numbers are not in the proper range then the simple test is to disconnect the generator from the regulator and full field the generator. If the generator puts out 28 or more volts then the regulator is most likely the cause of the problem. Then one should proceed to the detailed step by step test sequences and record all results at each step. If the generator did not produce at least 28 volts then pull the generator and have it repaired and start with the basic voltage check again.

RichJohnson · Post by **RichJohnson** » Sat Jun 21, 2008 3:35 pm

I opened up the regualtor and filed all the points. There are three contactors, one with two points on the right, and two with single points on the left.
The jeep still put out 33 ish volts to the batteries.
What do I do now?

Post by **wesk** » Sat Jun 21, 2008 7:35 pm

Follow the data set forth here:
http://www.willysmjeeps.com/v2/modules. ... tit&lid=24

RichJohnson · Post by **RichJohnson** » Sun Jun 22, 2008 8:24 am

I read all of that and really havent got a clue where to start. I figgured out I have a group 4 reguator, and wich contactor is the voltage regualtor, but still dont know what to do. Which test do I perform on it, to look for high voltage to batteries. Then what can I do about it.
There must be just one problem that causes over voltage. Is that repairable or do you just toss the unit and search for another one?

Post by **wesk** » Sun Jun 22, 2008 9:16 am

Try to get in the habit of calling the entire regulator assembly a "Generator Regulator" or just "Regulator". This will eliminate any confusion when discussing it's three parts which are a circuit breaker, current regulator and voltage regulator.

I assume the circuit breaker section of your regulator works ok. That is to say when the engine is not running there is no current flowing from the battery to the generator.The test connections shown in fig. 131 at the bottom half of the figure is where you are now at. The procedures starting on page 185 par. (2) is where you need to start. You will need the necessary meters and loading unit as well as an accurate tachometer and thermometer. The regulator specs in table VIII page 191 for the VBC4002UT and the regulator specs in table IX page 198 for the VBC4002UT are the tables you need to reference.

Remember DO NOT MAKE ANY ADJUSTMENTS TO REGULATOR WITH BATTERY CONNECTED TO IT!

RichJohnson · Post by **RichJohnson** » Sun Jun 22, 2008 5:47 pm

The manual stops at pg 184, and figure 130. Those tables arent there, and I didnt see the description of a test process that you were describing.
I dont have a tachometer and dont know how to load the regulator. Im starting to think I might be getting in over my head.
Isnt there just a simple adjustment I can make to lower the voltage to the batteries, and check them with my meter, without having to go through the whole test procedure with equipment I dont have?

Post by **wesk** » Sun Jun 22, 2008 6:34 pm

Hello Rich,
Take a look at KPsanborn's post below:
http://www.willysmjeeps.com/v2/modules. ... pic&t=2245

I didn't realize the whole section of TM 9-1825B pertaining to the VBC4002UT regulator wasn't on the download.

Go to our Yahoo Group and you can get the whole thing there.

http://autos.groups.yahoo.com/group/M38 ... Electrics/

RichJohnson · Post by **RichJohnson** » Sun Jun 22, 2008 10:17 pm

I am really confused.
Are both the voltage and ammeter armature screws adjusted back and forth untill satisfactory readings are obtained?
If the voltage screw is adjusted, then does the ammeter armature have to retested and readjusted in turn?

What is a carbon pile load reostat or lamp bank? (I thought a reostat was used to adjust voltage supply to equipemnt, IE motor)

How is the current adjusted to half by changing the load reostat or lamp bank?

How are the current readings taken with a standard fluke multimeter, instead of the military mulit connection meter set?

Is this process supposed to be done with the engine running the whole time, and no batteries connected?
Is the test cable supposed to be plugged in between the regulator and the jeep harness?

Can needle nose pliers be used to adjust the nut? It seems that this nut just loosens or tightens the contact spring. How can this adjust the voltage?