[PRCo] Re: More Thoughts on 1600s versus 1700s

[robert netzlof]

--- John Swindler <j_swindler at hotmail.com> wrote:
> >Fred Schneider mentioned:
> >The cars with blown motors probably could be made
> >peppier than those with internally vented motors,
> >because the external fan on the MG set
> >could keep the motors cooler at lower speeds.

> >But I have never seen any proof that 
> >specs for the limit relays were changed on
> >cars with blown motors.

> However, why would the operating characteristics of an electric
> motor differ 
> with temperature?????  Isn't the ventilation needed to keep the
> motor from 
> overheating to point where insulation fails and motor
> self-destructs??  
> However, a gas motor does seem to run better after it has 'warmed
> up'.
> 
> Any electrical engineers available???

Will a physicist do? As I recall, the original point was that the
motors cooled by fans built into the motors had the lowest air flow
just when the current through the motor was highest. That is, the
least cooling was supplied when the greatest heating was in progress.

It's not that, by improving cooling, one makes the motor put out more
power; rather, by improving cooling one can dare to make the
motor put out more power.

I think the gist of the remark "...never seen proof that...limit
relays were changed..." is "while improved cooling made zippier
performance possible, no one took advantage of that potential by
allowing higher starting current".

You're right, heat does it's evil by "frying" insulation. There may
be some minor changes in motor performance by slightly altering the
resistance of conductors and/or altering the magnetic properties of
the iron. I suspect, though, that these are minor compared to the
irreversible and cumulative damage to insulation.

Bob Netzlof

=====
Bob Netzlof a/k/a Sweet Old Bob


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