[SEL] Westinghouse DC generator

[Rob Skinner]

> checks use your analog meter and check for wet windings by using the 
> highest megohm scale. Just choose one side of each of the 4 pole 
> windings to the frame. Only touch one of the meter leads or 
> you will be reading you bodies resistance. There should be infinite resistance
if 
> all is dry. If not a baking in the wife's oven at about 200°F 
> for a few days should dry it all out.  :-)

Hi Curt,
I'd like to put another spin on the issue...

First, a little analog meter is probably running off nine volts.  You might be
reading a winding as good, but when the winding is powered up with full voltage,
it might be faulty.  A megohm meter is a better tool to use.  It will pump a few
hundred volts through the winding and could detect a faulty winding when a low
voltage meter will not.  

Secondly, a bad winding is not necessarily bad.  A few years back I got my boss
to buy me a really nice digital megger.  You know how fun it is to have new
toys... I had to play with it.  I measured every motor and generator in town.
Shockingly, most showed low resistance, in the neighborhood of a 200k.  Rarely
did I find a generator or motor that was over one megohm.  Yet, all these motors
and generators were in service.  

So the conclusion is that if you use a megger and read a winding as good, you
can be pretty sure it's good.  If you use a small multimeter or megger and get
readings of a few 10's of k or higher, you can't be sure of anything.  Only if
you get a crazy-low resistance of a few k or lower can you say with reasonble
certainty that a winding is bad.  

You can get nice old meggers (megohm meters) off of ebay for under fifty bucks.
They're very useful in working on magnetos, especially for checking capacitor
leakage.

=-=-=-=-=-=
Rob Skinner
La Habra, California
mailto:rskinner at rustyiron.com
http://www.rustyiron.com