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M-38 24 Volt charging system
Posted: Wed May 10, 2023 6:10 pm
by 1948willyman
Just lost charging amps on my jeep today. Has two new batteries purchased last few weeks. Looked down at amp gauge and showed 0 Turned lights on and went to discharge. Always kicked up right after engine started and backed off to close to zero shortly. Always stayed on charge side even with lights on. Checked with engine running AND SHOWED 24.5 volts which I assume was battery voltage. Used to always show 28 volts running. Do not know if that was too much or not. Checked all wiring I think was connected with charging system and did not find any issues. What else should I check before removing I guess voltage regulator and or generator. Always done fine until today? Anyone have any ideas what to go to next? Did not know if system goes through circuit breaker or not ?
Many Thanks for input on this.
Posted: Wed May 10, 2023 8:28 pm
by OKCM38CDN
Sounds like you lost the voltage regulator...
Posted: Wed May 10, 2023 8:45 pm
by wesk
Have you followed the steps in your M38's operating handbook TM 9-8012 Troubleshooting Generating System pages 84 & 85? If yes then to isolate the Generator and regulator to determine which is the culprit you simply perform a full field test on the generator.
m-38 24 Volt charging system
Posted: Fri May 12, 2023 10:01 am
by 1948willyman
Done the steps on page 84-85 of TM9-8012 and did not find any issues. Completed the full field test as Wesk stated from Generator Testing Subject Posted on Friday May 14 2021 for full fielding test. When completed as stated the generator quickly went up to 34 Volts just a little off idle speed, So I shut down and assume the problem does not lay with generator. I guess my next step is checking regulator ? Maybe checking wiring and grounds again first although previously did not see anything. To remove lid on regulator, Should I just remove from vehicle and then try to inspect inside for any issues? I guess I could try cleaning the contacts if do not see anything burned or melted. Have a regulator that came off M-170 but do not know if correct one for this jeep or if it is even good? Looked at some of the testing pages on these but looks to be very complicated. Any ideas for an easier check to see if it is the problem or have to bite the bullet and purchase another one.
Posted: Fri May 12, 2023 3:07 pm
by Kendall
If you decide to remove the cover of your regulator in place remember to disconnect the battery cable FIRST!
Posted: Fri May 12, 2023 7:09 pm
by wesk
The full field test takes quick care of which of the two is the problem. The quick and easy "Is it really the regulator???" is a simple substitution of the regulator. What is the part number/model # of the your 170 regulator?
m-38 24 Volt charging system
Posted: Fri May 12, 2023 9:09 pm
by 1948willyman
ID TAG shows to be a Prestolite
PART # VBC or C could be O ? 4004 UT
SERIAL # 72 or 2 could be Z 1426
25 AMP
SPEC. No MIL-R 10265
Posted: Sun May 14, 2023 12:55 am
by wesk
m-38 24 Volt charging system
Posted: Sun May 14, 2023 7:32 am
by 1948willyman
Thanks Wesk for the great info on this as always.
Will look into these sheets of info and try to see what to do. Did remove the regulator yesterday and removed the cover. Did not see any thing that looked burned, melted, or had been hot? Will keep you informed.
Thanks Again
Posted: Sun May 14, 2023 10:24 am
by wesk
If you now have the cover off that regulator you should have several pubs on you work bench:
They are all found here in bold:
Category: Main/24 VOLT ELECTRICAL SYSTEMS
· CJV-35 (0)
· Electrical test set manuals (11) IE Dwell Tach, Coil & capacitor, Mil Std electrical test sets.
Sort Downloads by: Title (A\D) Date (A\D) Popularity (A\D)
Resources currently sorted by: Title (A to Z)
Edit 24 Volt Fuel Tank Sending Unit
Description: Specifications for the 24 Volt fuel tank sending unit found on many 1950's era Military Vehicles. M38, M38A1, M34, M170, etc.
Added on: 17-Apr-2009 Downloads: 1056
Edit 24 VOLT SYSTEM BASICS
Description: Military 24 Volt systems 1950's
Explains how the generator, batteries, regulator and distributor work.
Added on: 11-Apr-2009 Downloads: 1972
Edit Generator Polarization Basics 1956
Description: This applies to the original standard Generator for the M38 and M38A1 that are internally grounded. Describes the basics of what polarization is and how to do it.
Added on: 14-Jun-2009 Downloads: 735
Edit Light Bulb Interchange
Description: 6, 12 & 24V lamps
Added on: 22-Nov-2022 Downloads: 19
Edit Military Wiring Numbering System
Description: Standard Electrical Wiring Numbering System for all Military Vehicles
Added on: 11-Apr-2009 Downloads: 1317
Edit Roscommon addition of 12V system to 24V MV
Description: Adding 12 volt components and circuits to a 24V MV
Added on: 01-Oct-2014 Downloads: 166
Edit Testing 24 Volt Electrical Systems 1956
Description: Testing the Regulator, Generator and the whole electrical system for 24 Volt military trucks circa 1956 U.S. Army Ordnance publication
Added on: 14-Jun-2009 Downloads: 1398
Edit TM 9-1825E Chap 4 Light Switch repair
Description:
Military manual on the light switch - dissassembly, repair/clean and reassemble
Added on: 10-Jul-2011 Downloads: 607
Edit TM 9-2920-215-35 MCZ-4001-UT Serv. Man.
Description: Field & Depot Maintenance Manual for Starter (2920-025-9988) Auto-Lite Model MCZ-4001-UT
Added on: 19-Oct-2021 Downloads: 55
Edit TM 9-2920-225-34 60 / 100 Amp Alt Sys Maint.
Description: Maintenance info for the various 60 thru 100 amp Alternators
Added on: 24-Dec-2017 Downloads: 92
Select Page: 1 2 [ Next Page >> ]
Category: Main/24 VOLT ELECTRICAL SYSTEMS
· CJV-35 (0)
· Electrical test set manuals (11) IE Dwell Tach, Coil & capacitor, Mil Std electrical test sets.
Sort Downloads by: Title (A\D) Date (A\D) Popularity (A\D)
Resources currently sorted by: Title (A to Z)
Edit TM 9-2920-225-34P 60 / 100 Amp Alt's Parts List
Description: Parts list for the 60 / 100 Amp Alternators
Added on: 24-Dec-2017 Downloads: 54
Select Page: [ << Previous Page ] 1 2
and this:
Category: Main/M38 M38A1 M170 M606/Electrical
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Edit 12V equipment added to 24V system
Description: How to add 12 volt equipment to a 24 volt system.
Added on: 08-Jan-2006 Downloads: 894
Edit 24V ignition coil
Description: Maintinance and troubleshooting the M38 24V distributor coil system.
Added on: 08-Jan-2006 Downloads: 937
Edit Auto Lite Voltage Regulator Maintinance
Description: New complete file for Auto Lite regulator maintenance with expected generator and regulator out put values.
Added on: 24-Aug-2008 Downloads: 710
Edit Coil Polarity
Description: What the heck is polarity? Distributor coil polarization and how it affects your electrical system (including spark plug performance).
Added on: 09-Jan-2006 Downloads: 506
Edit Colored Master Wiring Diagram Late M38
Description: Master diagram for the wiring of the M38 with colored wiring lines to make it easier to follow where all those wires go.
Added on: 08-Jan-2006 Downloads: 1995
Edit Delco-Remmy Voltage Regulator Maintinance
Description: Delco-remmy voltage regulator maintinance manual with lots of diagrams.
Added on: 09-Jan-2006 Downloads: 673
Edit Early Circuit Breaker Installation
Description: Modifiy the circuit breaker setup on the M38. Wiring diagram.
Added on: 08-Jan-2006 Downloads: 932
Edit Electrical Test Kits Manuals
Description: Test kits for 24 volt systems.
Added on: 06-Sep-2008 Downloads: 719
Edit Generator Polarization
Description: How to polarize your generator.
Added on: 08-Jan-2006 Downloads: 548
Edit M series wiring number chart
Description: Where does the number 12 wire go to? Find out here and many more.
Added on: 07-Nov-2008 Downloads: 1074
Select Page: 1 2 [ Next Page >> ]
PHP-Nuke Copyright © 2005 by Francisco Burzi. This is free software, and you may redistribute it under the GPL. PHP-Nuke comes with absolutely no warranty, for details, see the license.
And finally the full TM 9-1825E dated 1952. at my cloud link:
https://1drv.ms/f/s!AqEz4MqcTZDBgoxA0o7 ... A?e=E8n4an
voltage regulator
Posted: Wed May 17, 2023 6:28 am
by 1948willyman
I can see why you must remove battery cable before messing with voltage regulator according to Kendall That info was not put on the lid for nothing ,
That is for sure close as everything is.
m-38 24 Volt charging system
Posted: Wed May 17, 2023 6:57 am
by 1948willyman
Did place the m-170 voltage regulator on my jeep and it is charging as normal now . Just as the old regulator did,when working. I figured out, that the original one would charge if you manually held contacts together on the cut out relay. Looking at the service manuals that Wesk placed on site to try and figure out what is going on, that the contacts will not pull together when generator puts out 26 Volts . It appears the winding on the cut out relay must be shorted or burned in two somewhere ? Trying to do some ohm tests to confirm. Would like to repair if possible, but most likely be hard to ever find any parts for it, Always like to keep a spare when possible as I have a good extra generator also. Thanks again for Wesk placing these manuals on here to look at, as this is a dying art in these days. Maybe I could learn how to re-wind a defective cut out to work, as I did in my younger days at school in electrical class, though could not get mine to work like it should have. Went to old school alt/ gen/ starter repair shop locally, but said no experience on this type unit and also was first he had ever seen being almost eighty years old and repairing over 50 years
Posted: Wed May 17, 2023 10:00 am
by wesk
Look for shops with old X-GI's on their staff and/or public service vehicle experience since many were and are 24V as well as heavy trucks and equipment.
