On 2008-02-17, Jerry wrote:
"DoN. Nichols" wrote in message
...
On 2008-02-16, Jerry wrote:
[ ... ]
Hi Don
I have fallen short on my study in this 3 phase stuff. When I was
doing
the testing with my litle dyno on 3 phase motors, I recognized that the
bigger the capacitor I used to spin up even the fractional HP 3 phase
motors, the quicker the motors spun up. I suspect I never approached
the
"too much" capacity.
You may not have even reached the level of "right value". :-)
You were perhaps using oil-filled AC capacitors, instead of the
electrolytic motor starting capacitors which are more common in motor
applications -- because they are smaller and they cost a lot less.
Oil-filled AC capacitors are a lot more tolerant of long start
times.
[ ... ]
You have alot of information on Converters. I began a study a few years
ago by building a dyno and using Excel to make charts of HP while running 3
phase motors from a single phase line. Don Foreman taught me lots and lots
about all the stuff I built and tested. he is world class instructor. I
have disassembled the dyno but keep the set of four 200 mic electrolytics in
parallel that I can apply to the unfed motor lead thru a solid state switch.
Hmm ... that is enough to handle rather large horsepower motors.
I use the capacitors to spin up 3 phase motors here at home. I wont be
surprised if i sometime fail to spin up a small 3 phase motor due to the
excess capacity.
I have several VFDs in systems I work on. So, I do like them and have
used alot for stuff I've built. I even repaired a 120 KW solid state
converter last week. It is fixed frequency at 60 Hz in and 400 Hz out.
The problem is 'I dont know what I did to make it work'. Thats not too
satisfying, but the unit did get shipped after I disassembled part of it and
then put it back together.
An interesting device -- and something which I would like to
have -- except much smaller -- to run an old gyrocompass and an
artificial horizon which want 115 VAC 400 Hz. Probably on the order of
20 W each.
But, the more I learn about "Static Converters", the more I respect their
value to home use where space and budget is a factor.
I'm not too sure about the budget matter. The price from
vendors seems to be not too different from that for a VFD from eBay or
one of the good dealers -- at least until you get into seriously high
horsepower ratings.
Enjoy,
DoN.
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