Richard <2@mail.vcnet.com> says --
I said >>Once you stall the blower, there's no airflow to cool the motor,
and it
>>will overheat relatively quickly.
>>
>* Maximum load on a blower is with free flow delivery. During a
>cavitation condition, the airflow stalls and, since the motor is not
>working as hard, it speeds up slightly. Also, the typical motor has a
>radial-wheel impeller on the armature to cool itself.
Yes. With no place for the "cooled" air to go, it stays at the motor.
With a no-load motor running at top speed, cavitation occurs. Neither is
an operative condition in a real-world application. I've quit playing
carelessly with squirrelcage blowers after once sticking my hand in one.
>* If energy efficiency is a concern, Dayton motors run so hot you can't
>hold your hand on one that has been on for an hour. However, in KL7-land
>Dayton motors are useful for warming hands in winter.
A good point. In 5-land, it could be useful to monitor air temps in the
grid compartment as well as above the anode. Above 5,000 feet, the ratings
start to change ...
>>
>>But with the junk most of us use, "big enough" is all you need.
>>
>* ... measuring pressure with a manometer is better than guessing. I
>know a K5 who claimed he tell how good a vacuum capacitor was just by
>"eyeballing" it -- until the day we measured the leakage on a vacuum cap
>with my high-pot tester.
So how many kV were his eyeballs calibrated for, and did he have a NIST
certificate for them?
Like I said, "with the junk most of us use" -- a manometer with a
reasonable amount of accuracy is simple to fabricate with a dollar's worth
of clear aquarium air tubing, a ruler, and a piece of stiff cardboard. A
drop of food coloring in the water makes it easier to read.
Jim N6OTQ
|