RE: (ET) More lift motor thoughts

["Elie, Larry \(L.D.\)" <lelie ford com>]

Chris, if you really want to know, measure the ROOM TEMPERATURE resistance 
of the motor.  To do that 
accurately you need a 'bridge'.  Failing that, measure the actual voltage 
and current accurately within 
the first 3 seconds of operation (before the windings start heating up).  
Then you can calculate exactly 
when the windings will loose their insulation.  

I had a stuck lift motor switch on the tiller.  It was wired right.  You 
could smell the varnish melting 
in about 3 minutes.  It can't take 3 batteries indefinitely.

Larry Elie



-----Original Message-----
From: Christopher Zach [mailto:czach computer org]
Sent: Tuesday, April 19, 2005 9:40 AM
To: Elie, Larry (L.D.)
Cc: Elec-trak list
Subject: Re: (ET) More lift motor thoughts


> I think your rear is on the wrong taps.  They should BOTH be run off 
> "18V".  
> Getting the taps wrong is REAL common.  Even though I can count 
> batteries, checking 
> with a volt meter saves some work and money later.  The motor will run 
> on 24V... for 
> about 3 up and down cycles...then the insulation melts.

Nope. I checked the voltage: 19 volts or so right after the motor died. 
I have a 24 volt tap on the back of the tractor, but that's an Anderson 
plug and used for the Homelite stuff (which has not blown up despite it 
being 18 volt equipment)

Now I am running it at 12 volts and it seems a lot happier.

> In addition; GE did NOT re-wind the motor; it's a standard "12V" 
> automotive motor.  
> They knew the duty cycle, which is part of what governs the winding 
> temperature, 
> would be short.  This is not unique.  The starter motor in your car 
> would melt if 
> you ran it at the nominal 12-14V for say 1/2 hour.  The torque on a 
> motor is proportional 
> to the current in the windings times the number of winds.  The torque 
> does not 
> know anything about voltage, BUT; the to get the current up requires 
> voltage.  To get 
> the current REAL high requires MORE voltage.  That's when ohmic losses 
> come and carry 
> you away; voltage=current times resistance.  To get more windings you 
> use small gauge 
> wire, which is higher resistance.  In addition, the wire resistance 
> increases with 
> temperature.  This is something every motor designer deals with.  So if 
> a motor is not 
> expected to see continuous duty; the lift motor or a starter motor, you 
> just design for 
> that case and hope no one tries to run it too long.

Hm. Then it's possible that Delco made different types of motors. I'll 
post some pictures of the armature, but I will say it went from creamy 
perfect to cremated. I ran it on 12 volts for about 10 minutes with nary 
a problem, so I don't think it was a short. And just about all of the 
windings on the armature were turned into burned caramel, so I don't 
think it was a single short.

The other thing was the amount of commutator crud. I literally sanded 
down the commutator with fine-grit paper just to make it shine. And the 
condition of the field windings; they were burned and shorted.

Chris