[TheForge] Motor Problems

[Blacksmith]

    If the start capacitors are bad, The motor should hum and
start if spun. No hum - no heat - no start if spun sounds like
an open circuit in the run winding or power to the motor
itself.

Bob Willman
The Eagle's Anvil
Bowling Green, Ohio
WB8NQW

----- Original Message ----- 
From: "David E. Smucker" <davesmucker at hotmail.com>
To: "AAA TheForge AAA" <theforge at mailman.qth.net>
Sent: Sunday, June 26, 2005 19:54
Subject: [TheForge] Motor Problems


> While not a direct blacksmithing question this is shop related.
>
> Today my 7 1/2 hp compressor motor quit.  It is a single phase, 1.15
service
> factor, 3450 rpm, 230 volt motor.  Capacitor start, capacitor run.  The
unit
> is not very old, as if that makes any difference now days.  At most the
> compressor has several hundred hours on it.
>
> I have been using it on a regular bases recently and was doing some spray
> paint work at the time.  It kicked in for a few seconds and quit.
>
> I have check the reset on the motor starter and this is not a issue.  The
> pressure switch is closed and when power is supplied to the motor starter
> the coil closes and power is present at the output of the motor starter,
> full 240 volts and no sign of a problem with the overload heater.
>
> At this point I an thinking it is a failed capacitor or a problem with
> starting switch / winding.  I get no smell by the way at the motor
> indicating a burned something and the motor was cool, showing no sign of
> having been working hard.  The compressor might have run two cycles today
as
> I was just starting and the spraying I am doing is not very demanding of
> air.
>
> Also I get no heavy hum, typical of what I have seen in the past with
failed
> starting switches on much smaller motors.  I have removed the belt and
could
> not start the motor by spinning up the motor pulley, but I many not have
> gotten it moving fast enough.
>
> OK after all of that, is there an easy way to test the capacitors, or
should
> I just order new ones and do the swap out testing.  I know there is a way
to
> test capacitors with an VOM meter, but I only have a digital volt ohm
meter.
> It has been a long time but I think with a "meter" type VOM you would
> measure the resistance across the capacitor and it would first be high and
> then drop down as the capacitor charged.  Is there a way to do this with a
> digital meter or some other method.  Second, as I type this I am thinking
> that for any test I want to do I need to disconnect the capacitor from the
> motor, is this correct?
>
> Also what I assume to be the start capacitors (there are two) each have a
> small resistor across the inputs, what is this for?  to bleed off the
charge
> as the motor starts?
>
> Also any way to test the starting winding / switch?
>
> Thanks in advance for any help that is out there.
>
> Dave Smucker
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