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  • #16
    Paul, that reminds me- I have yet to procure an old hvac pm motor to play around with, though I was told 'No problem, I'll get you a couple'. I wonder if anyone else has mucked with one of those, and what kind of results came out of it?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #17
      Originally posted by darryl View Post
      Paul, that reminds me- I have yet to procure an old hvac pm motor to play around with, though I was told 'No problem, I'll get you a couple'. I wonder if anyone else has mucked with one of those, and what kind of results came out of it?
      I have a dozen of them ranging from 60 watts to 1hp.

      i found a 100watt ish pm motor and its 18inch dia fan, with 2 volts per hz, which was convienient as i was able to drive the fan and a 120v psc compressor (using 2 transformers to turn 120v 3 phase into 120/130v 2phase) from a single, 67$ chinese vfd

      Many of the larger 56frame inverter motors are 12 coils, 10 poles. You can rewire them for double delta and get 800rpm out of them from a 36volt ebike controller. 18 watts waste power consumption at no load.
      most of the time the inverter fails. But i have found shorted coils (where the wires cross over eachother, easilly repairable) and debonded magnets.. Which you can epoxy back on.

      I lasered a 4:1 ratio planetary gear set out of 3/8 acrylic and used one of those motors to drive a 21 inch diameter 15 pitch propeller at 190 rpm.. Which was enough to push my brothers 26 foot sailboat (4500 pounds, 22foot at thr waterline, 7feet wide at the waterline) at1.4 miles per hour at 36v 7 amps consumption. Thr ebike controller i have maxes out at 9 amps so, we were running out of volts.. Will try again with 48 volts.

      My prior attempt pushing the boat with a 10inch prop5 inch pitch , the motor produced 19 pounds of thrust at 36v 7 amps which was enough to push the boat about 1.1 mile an hour.
      Last edited by johansen; 09-15-2020, 09:42 PM.

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      • #18
        Originally posted by darryl View Post
        Nothing has been mentioned about whether there is a centrifugal switch in the motor. That would complicate things a bit That would mean a start cap, and if that is 15 uf, then it's a pretty small motor. How large or small is this thing? I suspect that it doesn't have a switch, and the cap is meant to be in circuit all the time. Then I think it's correct that it goes to the highest resistance winding- working to cause a phase shift so the main current can start and maintain rotation. In this case, the correct value of cap would make just the right amount of 'shift' for optimal power production, plus lowest wasted current and lowest motor hum. It might not like a 10 uf, and it might not like a 20 uf.
        Those gearmotors are "typically" PSC motors, and anything listing the capacitor in the low tens of uF is virtually certain to be a PSC.

        One can find the best value capacitor, the ideal value is the one that shows the LEAST current under full load. PSC motors can have very high power factors, and it is perfectly possible for some to have a PF of 1.0 at the optimal load, which is usually max load.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #19
          Happy ending. Got a 15 mfd run cap this morning, hooked it up, runs great - 85 rpm at the gearbox output. Bound to be useful for something, even if I don't know what yet.

          Yes, not really a "start" winding, but I had to call it something..."Auxiliary winding"? "Capacitor winding"?
          Yes, cap to higher resistance winding - what I meant, just not what got typed.
          No, no centrifugal switch, strictly a PSC motor.
          "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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