[MRCG] Variable Frequency Motor Drive for 400Hz/800Hz Radio Power

[John P. Caldwell]

Hi Mark,

There have been numerous "I wonder if" posts about using a VFD to produce 3
phase 400Hz power and lots of folks that claim I can be done.  It won't work
as the a VFDs output is dependent on the load it sees.  A 3 phase motor
under speed control by a VFD has to spin up to the appropriate speed that
400Hz would be equal to and for the time it takes (even milliseconds) it
takes for the frequency of the output and load to stabilize at 400Hz, the
magnetics (iron) in the radios power supply will instantly reach saturation
and stop acting like transformers.  It might be possible to use a VFD to
spin up a 3 phase motor of sufficient size (and load) that it would act
buffer to allow a power supply to be switched on.  This is only a guess, I
have no idea if it would work.   I think someone else responded and
suggested you find a surplus invertor or rotary generator (Dynamotor). That
would be my advice as well.  When I started playing with 618T's I found a
Leland dyno that ran on 28V and supplied 1200VA of 115V 3 phase 400Hz power.
It worked pretty well until I replaced it with a 3000VA static inverter that
came from a government auction.  I might still have a couple of the Leland
sets, I'll have to look.  BTW, if you're playing with 618T's you may want to
consider joining the Collins 618T groups.io group.  Lots of good info there,
and we've got a pretty good files section including depot overhaul manuals.

 

Best,

John W8SDA