A good lesson....

[Pinkie]

I have been trying to track down and charging problem for 2 days. The first problem was the batteries were junk, got new batteries. The truck fired up quick! I tested the voltage at the batts with the truck running, 24 volts. I tested the exciter wire (small one) going to the alternator and had 24 volts with the switch on. I cleaned the grounds on the alternator and battery cable. Nothing. I was starting to lose my hopes. I went to the parts duece and looked at the alternator and it was the same. Cool. I went back to the currently running deuce, climbed up in the engine bay and was about to start taking cables off when I leaned my hand against the belts.
To my surprise the belts where so loose, they were not turning the alternator fast enough. I tightened the belts up and low and behold I have about 27 volts to the batts! I am very happy. Now I can concentrate on installing the new mirrors before Aberdeen in stead of messing with the charging system!

J.R. "Pinkie"

 

[alphadeltaromeo]

Good find JR!

 

[amanco]

Got a question, (me learning here again!) How do you check the charging capabilities of a sealed system, such as the generator on my M37? Put a meter on the guage on the dash? That would be post regulator, how about pre regulator? Say if you wanted to check to make sure the generator is up to snuff?

 

[cranetruck]

Not sure what you mean with "sealed system", the DC generator is regulated by the externally housed regulator in the M37 (also my M35 25 amp system). You can still monitor the performance on the dash gauge, which shows the same voltage as you would measure at the batteries, which in turn is the generator output.

 

[amanco]

By sealed I mean no exposed places to put a meter. AKA water tight. I just want to check the output of the generator. Reading at the guage should be regulated, just wonder what the actual output of the generator is and how to do it.

 

[cranetruck]

The regulator regulates the generator, so the voltage at the batteries is the actual generator output.

 

[amanco]

See, I just learned some thing else! Thanks! I know this is elementry, but electrical is not my slice of pie. I am more a wrench guy.

 

[cranetruck]

Here is a schematic, just follow the connection on top from GEN on the top right to BAT in the lower left in the picture. Same wire from generator to battery, with a low resistance to monitor current and an SCR switch to turn the circuit on/off as needed by the regulator.

 

[amanco]

Ok, well I think I have a problem. Truck off, nothing on, I have 24.4 volts at the batteries. Brand new batteries. Truck running, (fan belt tight) I now have 24 volts at the batteries. Should I be expecting around 27 volts also? This is with a new regulator. Any thoughts? Bad generator?

 

[cranetruck]

You may have to polarize the generator. Let me check up on the procedure and get back with you. Also, of course make sure the cables are good, ring 'em out with your VOM.

 

[Pinkie]

Boy I created a stir! I checked the "exciter" wire which is the small wire that feeds the alternator. You should have 24 volts with the master switch on. After that you should have 27-28 volts at the batts. If not then I would guess you either have a ground problem, which is common, or the alternator bit the dust.

 

[cranetruck]

I think Keith is discussing his M37 system, a generator with a separate regulator. No "exciter" wire.

 

[amanco]

Yes, I guess that is why I was wondering if I could check the generator seaperate from the electrical system to see if I was getting any thing out of it. I have heard of polarizing a generator though, antique generators made in the early 1900's require polarization.

 

[amanco]

Now here is how you polarize a generator: http://web.utk.edu/~tprather/FoothillsTractorClub/TechTips/PolarizeGenerator.html My question is how do you do this to a generator that has no access to any electrical connection, one that is sealed against water getting to it for fording purposes and also sealed against me checking it out?

 

[cranetruck]

From an article in MVM issue 101 Feb 2004.

 

[Crazyguyla]

Here is a schematic, just follow the connection on top from GEN on the top right to BAT in the lower left in the picture. Same wire from generator to battery, with a low resistance to monitor current and an SCR switch to turn the circuit on/off as needed by the regulator.

Bjorn,

Is that schmatic simular to the non trasistorized 25 Amp regulator?

 

[cranetruck]

...Bjorn,
Is that schmatic simular to the non trasistorized 25 Amp regulator?

The functions are there, but the old way was with relays that switched on and off very rapidly.
See TM 9-8000 for description of operation. Images below from 1956 issue.

 

[jimk]

Just some conjecture - the gen/alt does require HP. The load rises -substantially- as the output V exceeds the bat V. I could see it (output) loitering at 24 where load is very low, then -causing- the belts slip when put to task. JimK

 

[Uglyranger]

Keith:
For $75 you can get a Military Vehicle Electrical Adapter Set at Saturn Surplus. Go here and look at the first item (with picture):
http://www.saturnsurplus.com/electrical/electrical.htm

 

[amanco]

Well, I picked up an NOS generator from eBay and walah....I installed it, polarized it and now the generator gauge shows the system is charging. I kind of figured that was the problem. Complete rebuild kits are also available so I will rebuild the old one for a spare. I definitly want one of thoes Military Vehicle Electrical Adapter Sets.