Re: Cooling fans - is the AC frequency a factor?


"Steve" <emailstevecooke@xxxxxxxxxxx> wrote in message
news:cfa4be70-1b3c-4c4e-8cdb-739215fa08ed@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I am building a piece of equipment for the aircraft industry that uses
a 115V 400Hz electrical supply. I have found I need to fit a cooling
fan (like a PC one but a bit wider - about 5 inches diameter) and have
got a 120V 50/60Hz one.
Will this work? Impedance wise a higher frequency would mean less
current drawn by what is presumably a mainly inductive load, but my
main query is are fan rotation speeds related to the AC supply
frequency? If so I guess trying to run a fan at about 7 times it's
rated speed would not be a good idea so I haven't yet tried it.

I worked on avionics equipment for a lot of years. I retired in 1997. Back
in 1966 while in the Air Force, fresh out of Avionics school. I was sure a
115 vac 400 cycle transformers would work just fine on 60 cycles. "I was
young and knew every thing." An old Master Sargent wired up a 400~ 115 volt
transformer to 60~s. He said watch and learn. Within 15 minutes the
transformer overheated and started to smoke. I've remembered that lesson
all these years. Transformers and induction motors are frequency sensitive.
Has to do with current flowing in the core of the transformer. Some test
equipment is designed to run on both 60 and 400 cycles.

I would be very careful using 60 cycles in circuit designed for 400 cycles.
I think in most cases it will not work. If you do try to run the equipment
on 60 cycles. Be sure to not leave it unattended even for a short period of
time because when it starts overheating smoke and fire will be close behind.




.

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