Large electric shop pedistal fan motor ran briefly, stops. Will restart but runs at reduced speed.

Discussion in 'General Electronics Chat' started by electronis whiz, Jul 3, 2016.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    I'm trying to figure out why this fan is not working properly. We had a somewhat similar issue before, I thought maybe something simple like connection issue, bad cap, etc. Found the original cap had a bulge, but I think it still acted properly when I ohm tested it and applied a DC voltage to it. Found a replacement Dayton brand capacitor from Granger worked no issue, now acting up again.

    This Dayton cap has no sign of bulging, my meter shows that the value is within spec, I applied 60V DC in both directions (as this is an AC cap) and it seemed to hold a charge, but it dropped surprisingly fast for only being connected to a digital meter. Not sure that is normal with these oil caps, or if they should keep the charge like an electrolytic.

    I did some searching online and this issue seems to be either related to a run capacitor or a governor type issue. I can't imagine this fairly small motor on a fan having a governor. It seems like a fairly basic dual speed induction motor that needs a run capacitor. Fan runs on normal 15amp 120V AC 60HZ.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Maybe obvious but does it revolve freely, it does not take much to load these fans, and the bearing may be dry?
    Oil filled motor run/start caps are pretty reliable.
    Max.
     
  3. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    I unplugged it, took the front blade cover off, gave it about a 1/2 turn by hand and let it spin down it kept spinning at least 5-10 turns. I tried same thing again and tried to slowly stop it by hand and it didn't really want to come to a stop easily.

    Checked all the leads they all seem to read with something I'd expect. Nothing with infinite resistance, nothing with 0 resistance, infinite resistance to the chassis. I think at most one winding or connection setup read like 1K ohm, another at the least was probably close to 200 ohms.

    I want to say the last time this happened the cap seemed perfectly fine when tested, but was bulged and replacintg it fiexed the issue. The last cap we got was also rated like 170V so possible that was just too low to work well, and it's plugged in on cirruits with saws, etc that cause voltage sags and maybe surges.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Another rarer cause is a defective rotor, where the rotor bars are no longer shorted for some reason.
    Max.
     
  5. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    Still kind of investigating what issue is with this. I want to say the cap failed because seems sis similar thing before. They say online though govornor could be bad. A motor this size and application though I can't imagine would need one. Somewhere they mentioned brushes too, but I can't imagine that as there are not ports to change the brushes. I've also never seen a brushed motor with a start or run capacitor. Usually fans and things like this that aren't real high torqe just use shaded pole type motor concept with a metal drum for the rotor. Generally only need brushes if it's a universal motor, high torqe like a saw, etc or it is a DC motor.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    These are very basic (simple) squirrel cage induction motors, if you replace the cap, ensure it is AC motor run type, usually listed as such.
    Max.
     
  7. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    I always called those motors shaded pole, but yes I think this is what it is.

    We decided to try and replace the cap and see what happens. Ordered a new Cornell Dublier 4UF 370V film capacitor for use as run caps on AC motors.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You either have shaded pole or start/run cap but not usually both.
    The shaded pole performs the same function (phase shift) as the cap.
    Both are squirrel cage induction motors.
    Max.
     
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  9. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    Okay that helps have to keep in mind for future. I didn't think shaded pole was the proper term as usually those are the small ones used in small fans, timers, etc. Somewhat similar setup though in they have no brushes and the rotor is basically mostly a chunk of metal with no real windings like a brushed motor.

    I'll post back when new cap comes and get that installed. Hoping that fixes it, if not probably plan B either replace the motor somehow, take it somewhere to have fixed. I could do, but I've not had good luck with motors and getting things perfectly lined up so they work properly, and brushes are usually hard to fix on some motors if they are present.

    I did put some 3in one oil in the oil ports today. From what I've seen in the past these things usually go to some oil absorber pad or into the bearing. I put about 20-25 drops of oil in each, it came up the tube a bit then it disappeared like something absorbed it. Didn't see it leak out anywhere so makes me think the pads may have been low.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    An induction motor rotor may look like a metal 'drum' or a chunk of metal but in reality it has windings embedded in it in the form of shorted aluminum bars.
    Without these the current would be Very small and no rotation.
    http://www.globalspec.com/reference...ac-and-dc-motors-ac-motors-ac-induction-motor
    Max.
     
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