[ARC5] An Interesting Failure Mode

[Clare Owens]

Vacuum cleaner motors have almost always been universal wound, with the
field coils in series with the armature and they run just as well on AC or
DC.

Clare

On Wed, Dec 14, 2016 at 8:20 AM, Robert Eleazer <releazer at earthlink.net>
wrote:

> Well, even though typically it is -12F outside at 20,000 ft that does not
> mean that inside the Oboe box it was not too warm and toasty.
>
> I have not seen cooling fans used on very many avionics.  The ARC-27 has a
> fan that circulates air between the inner and outer cases, and that was a
> radio used mainly in air conditioned aircraft.  Of course, it is sealed,
> and the wind can't get in and out so the fan needs to cool the case.
>
> My AVQ-55 radar has a fan to blow air into the electronics, and I think it
> was mainly used in unpressurized non-air conditioned fairly light aircraft.
>
> Interesting item on a radar range calibrator I have.  It uses a lot of
> sub-miniature tubes and has a cooling fan.  The equipment works on 115VAC
> 60 cycles but the fan runs on 90 VDC; a selenium rectifier turns the AC
> line voltage into DC.  I assume they did that so that the rotating field
> from an AC motor did not cause interference to the calibrator.
>
> Also, I wonder about that "Hoover vacuum cleaner motor" used in the Oboe
> fan.  I assume that was an AC motor?  Where did they get the AC?  From the
> same power supply that supplied the radar equipment?  And why did they not
> use a DC motor?
>
> By the way, the Oboe system was called that because of the sound it made
> if you tuned the signal.
>
> Wayne
> WB5WSV
>
>
>
>
>
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