View Full Version : 28 V 60 amp alternators

04-26-2006, 15:36
First; let me introduce myself. I don't have a military vehicle and probably won't ever unless the right diesel van comes along at GL but I do have an interest in military equipment when it serves a practical purpose for me.

I've recently aquired a bunch of 60 AMP 28VDC alternators for an RV project. I'd be grateful for some assistance in figuring out which ones work.

I'm in the process of building a test stand but when that's donw I'll still be clueless.

No one in my area is able to test them so I'm on my own. Using the limited resources of "what's lying around" I am attempting to test them and get some idea which ones might be good.

using a 1.5 HP motor I've gotten two results on two of the alternators;

One spins freely with 24V applied to the field voltage. There is no voltage at the power side. When I attach a drained (but not dead) 24V battery to the power post the brakes come on hard and the motor stops spinning.

The second one begins to brake when the field voltage is applied even when there is no load.

If I get it spinning good without the field voltage applied, put my meter on the power post I get about 1.5 VDC. I leave the meter in place, apply a field voltage of ony 12VDC and I get a spike at the power post of 28-29 V for a second before the motor chokes and can't spin any more.

Am I making sense?

I am puzzled that the field voltage creates such resistance even when there is no load.

I've read everything I can on alternators but I can't quite interpret my results.

Ulitamately I need a more substantial poweplant to keep the alt spinning under load.

I'd be grateful for any insight offered.


04-27-2006, 00:02
This is what I do. Place gen in a vise, ground the vise, apply 24 volts to the main battery terminal on the gen, jump the field wire to the main battery terminal on the gen. DO this first and try to spin the gen by hand. It should be tough. Next step, attach a high speed drill to the bolt on the front of the gen where the pulley goes, spin the heck out of it and use a volt meter to check for correct voltage when the field is jumped. There is also a voltage adjustment screw inside the gen.

04-27-2006, 05:19
OK, that's what I've got on several of them. With 24 V on both the field and the battery terminal It's very hard to turn.

I can turn the voltage adjust down i\until it spins freely

So this is normal?

So there is always that much drag on the alternator when the truck is running? I thought if the battery was topped off the alt should freewheel?

THanks this is very helpful.