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Converting motor to sync (or at least trying to)
Hi Everybody,
(pardon the long post, if you're not interested in the how, only
the results, skip down to the last paragraph ;)
While scrounging for EI cores for my home-brew paralleling choke,
I happened to find 5 AC motors. Seeing my 10 gage wire hasn't
shown up yet, and seeing I have access to a milling machine and
time to kill....
The motors I have are a 1/40th HP, 1650RPM, a 25MHP (1/4 HP I assume),
1725RPM, and three 1/3 HP, 3450RPM. The first thing that struck me
was that the 1/4 HP was just a little bigger than the 1/40th HP, but
the 1/3 HP are twice the size of the 1/4.
I thought I'd practice on the 1/40th HP first, so I downloaded the
"SYNCMOT.ZIP" file from Terry's site and started following the
instructions.
On disassembly, I found it rather difficult to identify the dead poles
in the stator windings. (the motor is small and things are a little
cramped in there :) It looked like there was only a single dead pole,
so I measured the center to center dimension of the last active poles
with a dial caliper at .570". (the rotor had a diameter of about 1.85")
I took the rotor over to the milling machine. I mounted a vice on the
milling table, and clamped the rotor in it. I used a 3/4 inch 4 flute
cutter to machine my first flat. I thought I'd take off just a couple
of thousandths first, good thing too. after running down the length of
the rotor, I found that the sides of my flat were not parallel. I
unclamped the rotor and found that a tiny piece of grit was holding up
one of the rotor, so my cut wasn't parallel to the rotors axis. After
cleaning everything and re-clamping, my second cut came out with the
sides perfectly parallel. I made a couple of passes, lowering the
cutter each pass until I had a flat, .570" wide.
I cut the other 3 flats the same way. Cutting the opposite flat first
by resting the first flat on the bottom of the vice. Cuts 3 and 4 were
cut with the first two flats contacting the jaws of the vice. When
done I had the 4 flats machined to the same width.
I actually thought that getting the flats 90 degrees from each other
was going to be the hardest part. In reality, that was no problem at
all. Making sure everything was clean so that my cutter would be
perpendicular to the motor axis was the hard part.
OK, I put it all together and mounted it on a 2x4 so it wouldn't run
away from me. I didn't have a strobe light, so I took it into my
office so I could put it under a florescent light. There were 3 wires
connected to the motors windings. A red wire, a white wire, and a
green wire. (The green wire was kind of a blue green) There was also
a case ground bolted to the outside. I deduced that white was common,
red was start, and the blue green was run. Not having a start cap
handy, I tried connecting the white and blue green to ac power
leaving the red wire unconnected.
Hmmmm....
Somewhat less than stellar performance.
I found 4 positions, 90 degrees apart that the motor wouldn't start
from. I could also get the motor to spin in either direction if I
"helped" it spin up. When running, it didn't run very smoothly and
got a little warmer that it should. Under the florescent light it
gave no indication of synchronization. At this point, I don't know
if I cut too much, or not enough. If I didn't cut enough I can cut
some more and try it again. If I cut too much, the motor is trash.
Seeing that this motor was a test case anyway, I'll be milling off
a bit more on Monday just to see what happens.
Anybody have any thoughts on what went wrong here???
Paul
btw, I've downloaded "STROBE.ZIP" from Terry's site and I'll build
that next week as well. That should work better than the
florescence.