Hi Gang,
In the past, when converting equipment from 400 Hz power to 60 Hz power,
I've replace the transformer(s), and increased the size of the filter caps.
That was many moons ago.

These days, it seems like it'd be fairly easy to build something like a
switching power
supply but using a fixed frequency at 400 Hz instead. Has anyone done this
yet, and if so, I'd sure be intersted in the details.

Steve

Steve wrote:
Hi Gang,
In the past, when converting equipment from 400 Hz power to 60 Hz power,
I've replace the transformer(s), and increased the size of the filter caps.
That was many moons ago.

This is the smart thing to do IF you don't care about keeping the equipment
original.

These days, it seems like it'd be fairly easy to build something like a
switching power
supply but using a fixed frequency at 400 Hz instead. Has anyone done this
yet, and if so, I'd sure be intersted in the details.

There are switching converters out there. The problem is that if you use
a square wave at 400 Hz, you get all kinds of harmonic trash, so you either
need to use a class B or better stage and suffer extreme inefficiency, or
use a "modified sine" inverter configuration. I don't think it would be
too hard to hack up some of the cheap truckstop 12V-120V inverters to
produce 400 Hz, though.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:

Steve wrote:


Hi Gang,
In the past, when converting equipment from 400 Hz power to 60 Hz power,
I've replace the transformer(s), and increased the size of the filter caps.
That was many moons ago.



This is the smart thing to do IF you don't care about keeping the equipment
original.



These days, it seems like it'd be fairly easy to build something like a
switching power
supply but using a fixed frequency at 400 Hz instead. Has anyone done this
yet, and if so, I'd sure be intersted in the details.



There are switching converters out there. The problem is that if you use
a square wave at 400 Hz, you get all kinds of harmonic trash, so you either
need to use a class B or better stage and suffer extreme inefficiency, or
use a "modified sine" inverter configuration. I don't think it would be
too hard to hack up some of the cheap truckstop 12V-120V inverters to
produce 400 Hz, though.
--scott



I modified a 140 watt unit using information I got from some where.
Only two capacitors had to be changed.
It worked well until I tried to run a motor from it :-(.

No I don't remember the details of the modification, but the new units
would probably be different anyway.

Bill K7NOM

Bill Janssen wrote:

I modified a 140 watt unit using information I got from some where.
Only two capacitors had to be changed.

Was there much RF trash coming out of it?

It worked well until I tried to run a motor from it :-(.

The modified sine wave units need to be derated by about a factor of four
to run electric motors, and the motors do tend to buzz a little. What
400Hz motors do you need to run? Antenna tuner?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott,
One of the advantages of running it at a fixed frequency is that you
could use the primary of the 400 Hz transformer as a tuned circuit by
putting an appropriate cap across it. That would cut down on the harmonics
even if its driven with a power MOSFET.

Since no one seems to have built something like this from scratch, I'll
start doing some bread boarding this week. If I'm able to get a good solid
design, I'll post it.

Steve W6SSP
p.s.-keeping the equipment original is certainly one of my goals

Scott Dorsey wrote in message
...
Steve wrote:
Hi Gang,
In the past, when converting equipment from 400 Hz power to 60 Hz power,
I've replace the transformer(s), and increased the size of the filter
caps.
That was many moons ago.

This is the smart thing to do IF you don't care about keeping the
equipment
original.

These days, it seems like it'd be fairly easy to build something like a
switching power
supply but using a fixed frequency at 400 Hz instead. Has anyone done
this
yet, and if so, I'd sure be intersted in the details.

There are switching converters out there. The problem is that if you use
a square wave at 400 Hz, you get all kinds of harmonic trash, so you
either
need to use a class B or better stage and suffer extreme inefficiency, or
use a "modified sine" inverter configuration. I don't think it would be
too hard to hack up some of the cheap truckstop 12V-120V inverters to
produce 400 Hz, though.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:

Bill Janssen wrote:


I modified a 140 watt unit using information I got from some where.
Only two capacitors had to be changed.



Was there much RF trash coming out of it?

Never checked as it didn't bother anything I was using. (10 GHz amp
power supply)




It worked well until I tried to run a motor from it :-(.



The modified sine wave units need to be derated by about a factor of four
to run electric motors, and the motors do tend to buzz a little. What
400Hz motors do you need to run? Antenna tuner?

I tried to run a military surplus fan.

Bill K7NOM

--scott