Bad single phase motor? Diagnostic?
Ignoramus4694
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
dca...@krl.org
wrote:
Is it a 120/240 motor wired for 240?
Dan
Ignoramus4694
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 **
Stormin Mormon
--
Christopher A. Young
Learn more about Jesus
www.lds.org
.
"Ignoramus4694" <ignora...@NOSPAM.4694.invalid> wrote in
message
news:Kcudnb627bJHlF_W...@giganews.com...
Gunner Asch
Sounds like something is dragging in the winch itself.
Unless the motor is being run NOT attached to the winch..at which point
Id say the run cap is bad or leaking badly.
Gunner
"First Law of Leftist Debate
The more you present a leftist with factual evidence
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more difficult it becomes for him to refute it without
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This is despite the thread you are in having not mentioned
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Ignoramus4694
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
Ned Simmons
<ignora...@NOSPAM.4694.invalid> wrote:
>On 2010-04-11, dca...@krl.org <dca...@krl.org> wrote:
>>
>> Is it a 120/240 motor wired for 240?
>>
>
>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).
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%.
>
>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.
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.
--
Ned Simmons
Ignoramus4694
> On Sun, 11 Apr 2010 20:41:17 -0500, Ignoramus4694
><ignora...@NOSPAM.4694.invalid> wrote:
>
>>On 2010-04-11, dca...@krl.org <dca...@krl.org> wrote:
>>>
>>> Is it a 120/240 motor wired for 240?
>>>
>>
>>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).
>
> 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%.
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
http://igor.chudov.com/tmp/Winch/
>>
>>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.
>
> 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.
>
I see. Now I know why they disabled the brake with a steel wire.
i
James Waldby
> 220v, that I tried to run from 110v. [...]
> 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.
Worms can work backwards if not "self-locking". See refs to
self-locking in <http://en.wikipedia.org/wiki/Worm_drive>
(where the first one pictured probably isn't self-locking) and in
<http://www.daltonbearing.com/martin-sprocket-and-gear/martin-gears.aspx>
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:
> <http://igor.chudov.com/tmp/Winch/>
--
jiw