Bad single phase motor? Diagnostic?


I have seen a few single phase motors that acted badly, but not like
this.
I am fixing a few things that I did not have time to fix. One is a
cable winch, powered by a single phase 1 HP motor. The motor runs a
huge worm drive that spins a big shaft on which there are two cable
spools, one on each side.
It also has a brake, which developed rust, and needed freeing. (which
I did)
It has a 115v, 1 HP GE motor 1725 RPM.
Now it runs, but with problems. The problem is that it starts
strongly, then slows down, then the start circuit kicks on, it spins
up again, slows down, etc. I have an ammeter in line (this is my
custom made 110v tester box). The amps go from "over 25" to 10 to back
to "over 25", etc.
If I spin the drive shaft by hand, I do not feel any excessive drag,
it seems pretty easy (I can easily turn the shaft with just two
fingers).
So, what could explain the motor slowing down? My answer is that it is
probably a cap start/cap run motor and the run cap is bad. The motor
has only one hump, which sort of disagrees with my explanation. Does
this explanation makes sense? Could it be something else?
I will start looking, pretty much, right now, but thought that someone
may know some clever trick.
thanks
i
Reply to
Ignoramus4694
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Is it a 120/240 motor wired for 240?
Dan
Reply to
dcaster
forget it there was nothing werong the brake dr4agged too much at high speed it runs great now
** Sent from my Google phone ** I apologize for any typos **
Reply to
Ignoramus4694
Please remit $45.70 for diagnostic.
Reply to
Stormin Mormon
Dan, I think that this is "it". It is likely a 110/220v motor, wired for 220v, that I tried to run from 110v. It runs, but does not have the power it ought to have. From HP, drum diameter, and RPM of the winch drum, I calculated the pulling force as 650 lbs, if friction losses in the worm are estimated at 10% of power. (ideal force would be 740 lbs).
I am kind of surprised that this worm drive winch has a brake near the motor. I thought that worms cannot transmit power backwards. I can post pictures of it if anyone is interested. It does no look like a typical winch.
i
Reply to
Ignoramus4694
The efficiency of worm reducers is related to the ratio. Best case, a 10:1 reducer will approach 90%; a 60:1 box will be closer to 65%.
Rule of thumb is that anything above 40:1 is self locking. But you can't count on it, especially if you're trying to stop an overhauling load, or if there's vibration present.
Reply to
Ned Simmons
It reduces 1800 RPM to 22 RPM (as measured by me with a stopwatch in my cell phone). In other words, the ratio is 1:81. See
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I see. Now I know why they disabled the brake with a steel wire.
i
Reply to
Ignoramus4694
Worms can work backwards if not "self-locking". See refs to self-locking in (where the first one pictured probably isn't self-locking) and in
which says "Theoretically, a worm gear will not back drive if the friction angle is greater than the worm lead angle. However, the actual surface finish and lubrication may reduce this significantly. More important, vibration may cause motion at the point of mesh with further reduction in the friction angle. Generally speaking, if the worm lead angle is less than 5°, there is reasonable expectation of self-locking. [...] If safety is involved, a positive brake should be used."
Ignoramus4694 wrote later:
Reply to
James Waldby

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