ELECTRIC MOTOR PROBLEMS
My old belt drive, split phase, sleeve bearing furnace/ac blower motor
started giving me problems several weeks back; would not restart (humming)
without tapping on it with the handle of a screw driver or small
hammer.After nine years of use l figured the motor just wore out and l
bought another motor identical in every way to the old one except for a .2
higher amp rating as the old motor was no longer available from A.O. Smith
and the one l got was the advertised replacement.Old motor was V2054, new motor is VB2054. Well, the new motor is doing the same thing, if only on an intermittent basis!I've been at this for weeks with no positive results.Eliminated possible circuit board and relay problems at furnace and thermostat by wiring and running motor from several other different outlets with the same problem.The motor, once running will run just fine, seemingly forever without any signs of overheating; it is the restart that is causing the problem.90% of the time it will need a light tap and it will kick in, albeit with a good spark; also l discovered that when l need to do that l did not hear the click when it shut off and when it wants to restart but can not without the tapping the plug at the power cord feels quite hot at the plug and the motor without a load i.e. belt will restart just fine. When l put my identical old motor in 9 years ago, it did just fine, worked immediately, I am using a replaced but identical belt and the squirrel cage is clean and moves easily.l can not really read any amps or voltage fast enough as I am busy tapping the motor and once started amps and voltage are reasonably within limits.l even had the electric company lay an upgraded line today and move me to a feeder closer to the house! l live in the boonies and reasonable service is hard to come by here.Could l by coincidence have purchased a bad motor?Again, it has the same problem even when plugged into another outlet; at restart it is a hum, then a click and then nothing without a tap and when plugged in through the furnace the motor seems to pick up heat until restarted; l guess that is because it keeps getting a signal from the thermostat to start but can not on its own.Sorry to be so long winded but l wanted to get as much detail in here as possible. one running through furnace to run the motor through a different outlet it gets hot after repeated attempts by the motor to start. even backed up an already acceptable belt tension, the alignment is proper as l can see it, squirrel cage pulley moves smoothly and has been lubricated, the motor is split phase without a capacitor mounted on top. Regarding comments by ''Rouse when l do hear the click ever so faint at shutdown it will restart, without it no; but why does the problem not occur when the belt is removed?Also one thing l failed to mention is that at times, although very rarely l do hear a quite (healthy?) audible rasping, sliding ratcheting sound when the motor does shut off; l think this occurred when l had the motor running from another outlet.
(More added..July 8, 2009)
From what you stated, you've exchanged the split-phase motor with a
similarly sized unit, tried different outlets, the belt torque is
reasonable & the squirrel cage is free. Still ongoing intermittent
starts.
It is quite possible that ur cord just has just developed a bad connection over nine years of motor starts. You said the plug is getting hot which indicates that there is a substantial voltage drop within it under starting load current. Molded plugs can go bad over time. I would consider replacing the cord & its attached motor connection lugs. A new cord & some fresh lugs are relatively inexpensive. You may also find that ur old motor may be perfectly fine. ----------------------------------------------------- ----------------------------------------------------- You never stated if you checked for proper voltage at the motor terminal block. Please check & make sure you have proper voltage at the load when the motor is called (into service). If you greased the bearings on the new motor, too much grease can force the grease down into the centrifugal switch preventing it from closing properly at standstill. If this is the case, clear power, remove the motor, open up the end bell & inspect the centrifugal switch & remove any excess grease. The centrifugal switch is normally closed to about 75% of motor speed when it will open up dropping power away from the motor start winding. You might want to inspect the centrifugal switch anyway to make sure it is closed at standstill. If you have to tap the motor to get the centrifugal switch to make it, the switch or its contacts may have a problem. Burnish the switch contacts if they need it (and you don't want to return a relatively new motor). If this all checks out, maybe you did get a bum motor with a bad centrifugal switch or faulty start winding. I'd return & try out another motor.
Your both the motors are ok. The problem is starting torque.
When the load is high the motor is not able to deliver the starting
torque. Since it is not able start the current increases as if locked
rotor, 5 to 7 times & but natural the motor will get heated because of
higher current & may burn the winding. Now the load increase is from
where, is to be understood. In ur case may be the belt tension is too
great. So try little loosening it & it will start. You have already noticed that without belt it starts fine which confirms that load becomes too great to give the initial starting torque. Aso see the driven pulley bearing condition may be it needs the bearing lubrication at the driven end. Also check the alighnment of the belt- alighnment of driving & driven pulley. If they become skew the load increases due to higher friction values. Lastly you check the belt size. If the belt thickness is changed it may give more of friction so the problem remains only with the load on motor & nothing else. Follow all explained above one by one & the problem would be over. Still if the problem persists then Capacitor capacity, mounted on motor, is to be increased to increase the starting torque.
It sounds like the motor is not switching in the start
capacitor. I believe the click you sometimes hear when the motor idles
down, is a centrifugal switch that reconnects the start capacitor to
initiate the next motor start. If I understand ur description correctly
you do not hear the click before the next failed start. When you tap on
it, the vibration probably causes the centrifugal switch to close on the
capacitor. It sounds like mechanical problem that would be fairly easy to cure, maybe with a little spray lubricant formulated for electrical equipment, that is available at most hardware stores. You can probably get some help from an appliance store. I suspect if you read the current when the motor was trying to start you measure equivalent to locked rotor amps which is about 5 times the running load amps. This will overheat a motor quite rapidly. It sounds to me like you have a defective new motor, but like I said, you may be able fix this one & ur old one if you took it apart & worked on the start switch.
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