alt.engineering.electrical

Don Kelly wrote:
> "Palindrome" wrote in message
> news:3ZU_i.152062$Nb1.132967@fe01.news.easynews.com...
>> TE Chea wrote:
>>> I notice electrical & electronic devices ( if hot ) all
>>> work better if cooled.
>>> Thanks for any advice.
>>>
>>>
>> All equipment is designed to work within a certain range of environmental
>> conditions. Operating outside that range will generally result in
>> immediate failure or a dramatic decrease in reliability. Even within the
>> range there can be wide variations in expected life and efficiency.
>>
>> As for your motor, if cooling is required to keep its internal
>> temperatures to within design limits, then indeed it is highly likely that
>> it could spin faster and/or use fewer amps if cooled.
> ------------------
> Not so---

Of course so. If a motor overheats due to lack of cooling to the point
where insulation fails - then it is highly likely to run slower (indeed
actually stop turning) and take a great deal of current - Cooling
would indeed have made it spin faster and use fewer amps..

Read my previous paragraph, "Operating outside that range will generally
result in immediate failure or a dramatic decrease in reliability".

"If cooling is *required*..... it uses fewer amps is cooled. --- It
will typically take enough amps to trip the breakers if not cooled, if
cooling is a requirement.

> all that cooling will do is allow the motor to be run at above its
> rated load torque-either continuously or for a longer time without
> overheating.

No. Not if cooling is required to run at its rated output. *Additional*
cooling is required to allow it to run over its rated output..

> The current is dependent on load torque which may or may not depend on speed
> (voltage related).
> All cooling will do is extract heat more effectively - it will not affect
> the production of heat.

No. The production of heat will change dramatically once the motor fails
due to overheating. Cooling can prevent overheating and thus can affect
the production of heat.

>
> Cooling will not allow faster "spinning" nor will it reduce the current.

Yes it will - compared to the motor in its failed condition, resulting
from overheating as a result of lack of cooling.
> It
> will allow higher load torques resulting in higher currents without
> excessive temperatures (and lower speeds depending on the motor
> characteristics).
> These are opposite to what you have said. In general at lower currents and
> higher speeds, the need for cooling is reduced.

No. This doesn't apply once overheating has caused damage. See above.
>
> Motor considerations regarding performance and cooling are quite different
> from those of solid state electronics. Tom Grayson has it right.
>

I didn't say that he had not. I was simply making the point that speed
can reduce and current can increase as a result of a reduction in
cooling. Thus, cooling can result in lower current and higher speed.

--
Sue