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From: bud-- on 4 Aug 2010 11:23
a453 wrote:
>
>
> I searched but found no reference to my motor.. it's a bit old.... the
> old capacitor is all rusty and unreadable so with some approximation on
> "similar " motors I trend to install a new 220v 108-130 MFD
> capacitor.... the motor ran fine for a bit and then the capacitor
> "popped"... I guess I burned it....
>
> SHould I try use a capacitor with a higher or lower MFD number (the
> motor runs on ordinary houseol 115-120volt power) thanks

It is common for motors to use a capacitor to start the motor - it is
disconnected by a switch in the motor when the motor approaches running
speed.

Some motors have a capacitor that is permanently connected - a run
capacitor.

Some motors have both a start and run capacitor.

Since the cap died after the motor was running my guess is that the
motor uses a run capacitor. Or the start switch is not opening?

A capacitor that is designed for temporary starting can't be used as a
run capacitor. Your replacement cap was maybe a start cap where a run
cap should have been used? Does the motor have a start switch? Is it
opening? I have never seen a motor with a cap inside.

I think Grainger sells motor caps and you might get an idea of what is
out there. Run caps have a lower mfd rating than start caps.
From: tm on 4 Aug 2010 11:40

"bud--" <remove.budnews(a)isp.com> wrote in message
news:1f8fb$4c598618$cde8d539$3707(a)DIALUPUSA.NET...
> a453 wrote:
>>
>>
>> I searched but found no reference to my motor.. it's a bit old.... the
>> old capacitor is all rusty and unreadable so with some approximation on
>> "similar " motors I trend to install a new 220v 108-130 MFD capacitor....
>> the motor ran fine for a bit and then the capacitor "popped"... I guess I
>> burned it....
>>
>> SHould I try use a capacitor with a higher or lower MFD number (the
>> motor runs on ordinary houseol 115-120volt power) thanks
>
> It is common for motors to use a capacitor to start the motor - it is
> disconnected by a switch in the motor when the motor approaches running
> speed.
>
> Some motors have a capacitor that is permanently connected - a run
> capacitor.
>
> Some motors have both a start and run capacitor.
>
> Since the cap died after the motor was running my guess is that the motor
> uses a run capacitor. Or the start switch is not opening?
>
> A capacitor that is designed for temporary starting can't be used as a run
> capacitor. Your replacement cap was maybe a start cap where a run cap
> should have been used? Does the motor have a start switch? Is it opening?
> I have never seen a motor with a cap inside.
>
> I think Grainger sells motor caps and you might get an idea of what is out
> there. Run caps have a lower mfd rating than start caps.


I think you are exactly right about the start switch. The contacts are
likely
welded shut so when the motor starts, the start cap is left in the circuit
until
it overheats and blows. Then the motor will not restart. Also, many of those
start caps have an internal fuse.


Can the OP determine if there is a start switch?


tm



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From: GrendelsLair on 4 Aug 2010 14:09
This is a typical centrifugal start switch assembly.
http://www.powertransmission.com/issues/0608/butler1.jpg
As the motor comes up to speed the washer on the left side pushes the
starting switch contacts open.

Start capacitors are for intermittent duty only, i.e. starting the
motor.
Values run from 100-300 MFD and voltages need to be in RMS, not DC
volts.

Jeff

From: Proteus IIV on 9 Aug 2010 14:44
On Jul 31, 6:18 pm, a453 <a...(a)a453.nospam.nospam.com> wrote:
> Hi all I have a pump with a 2HP 125 V AC motor. All of a sudden the
> motor wont start anymore. If I switch it on it just does a humming sound
> and then thermal protection kicks in.
>
> If I initiate the rotation of the motor by hand when the power is on the
> motor does start working. The curious thing is that I can make it run
> clockwise or counterclockwise by simply initiating the rotation by hand.
>
> My guess is then that some electronic component that "tells" the motor
> the direction in which to rotate is now broken and the motor "does not
> know" any more wheter it must rotate clockwise or counterclockwise....
>
> What should look in the electronics to try fix the motor? Condensers?
> Diodes?....

TEEHEEHEE
SIMPLE
I HOPE YOU CHANGED THE STARTING CAP BY NOW

SIMPLE SIMON TO THE PIE MAN
NOTHING LESS NOTHING MORE

I AM PROTEUS
From: stratus46 on 9 Aug 2010 21:35
On Jul 31, 3:18 pm, a453 <a...(a)a453.nospam.nospam.com> wrote:
> Hi all I have a pump with a 2HP 125 V AC motor. All of a sudden the
> motor wont start anymore. If I switch it on it just does a humming sound
> and then thermal protection kicks in.
>
> If I initiate the rotation of the motor by hand when the power is on the
> motor does start working. The curious thing is that I can make it run
> clockwise or counterclockwise by simply initiating the rotation by hand.
>
> My guess is then that some electronic component that "tells" the motor
> the direction in which to rotate is now broken and the motor "does not
> know" any more wheter it must rotate clockwise or counterclockwise....
>
> What should look in the electronics to try fix the motor? Condensers?
> Diodes?....

Didja try just giving it a good 'thwack'? There are some small GE
induction motors used in machines at work that sometimes get cranky
because the start relay is flaky. One smack solves it for a year or
more. No capacitor in this motor, just a relay.

G²
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