125 VAC motor won't start

Start capacitor most likely, they fail fairly often, if its a pool pump a good pool supplies shop may have them. JC

if you have a capacitor on the motor or near by in the circuit? try replacing it.. If you don't have a starting cap, then you may have a stuck centrifugal switch in side the motor, that is normally located at the rotor end where the wires go in..

They do make some set ups with external time delay relays that connects the start winding, this done at times if the motor needs to be reversed. Most cheaper ones use a bi-metal relay..

Probably this is a motor with a centrifugal start switch; there's an 'extra' winding that only kicks in at slow revs (or on a cold start) to get it started in the right direction.

If you're comfortable disassembling the motor, look for springloaded arms on the rotor, and a push-plate that rubs a rod. That rod is the switch actuator, look for dirt on the contacts. There's sometimes a start capacitor in series with the switch, it's the second suspect if cleaning the switch doesn't solve the problem.

Hi thanks to you all for the replies.

I opened the motor.... there is a very rusty capacitor inside it.... the markings are unreadable.

I disconnected the capacitor and tried to test if the capacitor still works by using a tester with different ohm settings... I always got no readings.... I guest that means that the capacitor is broken?

If so, now the problem i getting a new capacitor with the right size...

The motor data is:

dual voltage 125/250 V

Amps 21.0/10.5

2.0 HP (SF 1.10 SF)

This is a single phase Magnetek Centurion SE motor powered at normal 125 Volt housedold power.

My understandi is that i should look for an unpolarized motor star capacitor rated at 270-324 microFarad at 250 Volt

Is this correct? Thanks so much for your help!!

Hi, I guess this a pool/spa pump? Magnatek centurion is probably an A.O. Smith motor.

Are there any other identifiers on the motor plate that are readable? If so go to the AO Smith website

Literature library

Manuals

Replacement Parts

Download the parts catalog PDF, it gives all the cap values for motors but you need some identifier to select the correct part. If you have the SPA/Pump filter manufacturer it easier to find a good pool supplies shop and ask, my local pool outfit is pretty good. JC

This may help

JC

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

TRy a higher voltage capacitor.

A motor starting capacitor is designed to carry AC (alternating current) when an alternating voltage is applied. Did you perchance substitute a capacitor rated for 220v DC? That would almost certainly pop.

--
Jack Myers / Westminster, California, USA
 
Our policy is, when in doubt, do the right thing.
                -- Roy L. Ash, ex-president, Litton Industries

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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This is a typical centrifugal start switch assembly.

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

TEEHEEHEE SIMPLE I HOPE YOU CHANGED THE STARTING CAP BY NOW

SIMPLE SIMON TO THE PIE MAN NOTHING LESS NOTHING MORE

I AM PROTEUS

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.

G=B2

The motor probably has a starting winding, capacitor, and centrifugal switch in series across the AC line. As noted, the most likely problem is the capacitor, but the switch could also be open, possibly by a bit of dirt between the contacts.

Without the starting winding, yes, the motor will run equally well in either direction.

It may be, given your symptoms. But a DC continuity check isn't a good indication of whether a cap is good or not.

Contact the manufacturer of the appliance that contains the motor. They should know what size you'll need.

--
Paul Hovnanian  paul@hovnanian.com
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Have gnu, will travel.