Squareback alternator testing armature

[wittenbn]

I have a revised square back 78 amp alternator which I think has a shorted armature. Twice it has over heated and melted one of the brush holders also damaged the voltage regulator. Is there a way to check it out. A normal resistance meter is too weak to show any short.

 

[Dana67Dart]

You could check the amps being pulled by on the field cir.

A Megger is what you need



Have you checked each of the field terminals to ground. They should both be open cir assuming your setup is set for isolated field voltage regulator (ie electronic, v shaped connector)

 

[67Dart273]

Sorry, a megger is designed to find high resistance shorts---at high voltages. .

Go to MyMopar and download a service manual, latest one is 73. There's a procedure in there to measure amp draw of a rotor. There should be specification in section 8 somewhere listing rotor current draw


Pay attention to the battery voltage you apply. Do you understand anything about ohms law? At low resistances and voltages, "a little bit" of change, either voltage or resistance, can have a large effect on amperage.

I don't recall anymore, seems to me I'd expect around 4A with maybe 6A maximum

 

[Dana67Dart]

I don't recall anymore, seems to me I'd expect around 4A with maybe 6A maximum

Your memory is pretty good. 6.2A Square back. NOT revised square back. (Google BBB 7007)

 

[AJ/FormS]

We used to test their continuity while in a magnetic field, using a tool we called a "Growler"

 

[Dana67Dart]

Like this?

 

[67Dart273]

I was under the impression a growler is only good for commuated armatures, AKA starters, generators, and "universal" motors

 

[67Dart273]

Also OP make sure both brushes and the field are all open to the case, "infinity"

 

[Dana67Dart]

Sorry, a megger is designed to find high resistance shorts---at high voltages

When I have used a Megger we were looking for broken down insulation between windings and other voltage leaks.

If the insulation is broken down, as an example (10 windings could be shorted making fewer total windings), increasing current draw and reduced output

But that's just my experiance

 

[67Dart273]

When I have used a Megger we were looking for broken down insulation between windings and other voltage leaks.

If the insulation is broken down, as an example (10 windings could be shorted making fewer total windings), increasing current draw and reduced output

But that's just my experiance

Well you can megger from the brushes to the case, yes. That will not check for a short between turns. I've got two old hand crank Biddle meggers. I think one is 500V, and if I remember, the other is selectable, up to 1KV