Electric motor question?


I have a Marathon Electric 1/3 hp 1725 rpm 1 phase 115 volt electric motor that runs the circulating air fan on my wood stove. I've had it in operation for well over 15 years in the winter heating months and runs quite continuously (starts and stops on stove air jacket temp) during high heat demand - which is most of the time between November and March in my part of the country. I am wondering if anyone might have any suggestions on what, if anything, should be done in the way of maintenance to insure that it doesnt crap out at a bad time being that it has alot of miles on it?? Would it be worth taking into a shop to be inspected / rebuilt or do I just break down and just replace it with a new one?? I really have no idea how close to full load amps it draws??? But it does and always has run quite hot around the housing so that it feels quite hot to the touch. It is mounted low and behind the air jacket of the woodstove and is pullied with a belt to the fan. It does not get any appreciable heat build up from the stove itself. It does have oil wells on both end bearings which I have added to several times each winter. Any thoughts or recommendations would be appreciated... Thanks... Steve
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wrote:

Usually you only have to put oil in the cups about every 5 years. It probably says on the label. Use something like 20w non-detergent motor oil. They do make a special oil for the purpose.
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Just do what you've been doing and the motor will probably outlive you. If you are really concerned, take the name plate data and order a replacement from some place like Graingers. It sounds like a pretty common motor, and shouldn't be very expensive.
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Find out where you could get replacement motor in fairly short order and since it sounds like a pretty standard 1/3 HP motor so there may be several sources. But no need to buy one at this stage. Well lubricated that motor may last for ever! Waht mght eventually go is the starrter contacts (if any) and they can sometimes be repaired. Some appliances use 1/3 HP for example. Maybe keep a 'used' standby motor from an old washing machine etc. Not usually necessary but one detail to check might be direction of rotation.
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.
Single phase motors have two windings. One winding is directly connected to the power supply the other is out of phase with it either by means of an external capacitor or a difference in the inductance of the winding. This second winding may only be connected to start the motor or it may be permanently connected. If is is starting only, it is disconnected by means of a centrifugal switch as it runs up to speed. You can often hear the click of this switch as the motor starts and stops. In any event the motor can be reversed by reversing the connection of either winding (but not both). This is done in the terminal box, usually there are metal links and a diagram. If the start winding, centrifugal switch or the capacitor ever goes open circuit the mtor will not run but just remain stationary usually making a humming noise, It needs to be turned off pretty quickly or it will burn out. However if you can give it a twirl, it will run up to speed (in either direction) Keeping your fingers out of the belt of course!
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Besides oil and blowing the dirt out not much else you can do. I suppose you could replace the bearings. See if there are ceramic replacements available, they will last forever, no more oil. I did this on an equipment blower 17 years ago, still going 24/7. Probably the best thing you could do is go ahead and get a spare.
Jimmie
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Some motors blow air through the motor, some blow air around the motor. If air is blown through the motor, check to see that blockages are not causing the high temp.
Some motors are designed to run hot! I forgot what brand it was, but it was a prominent mfr, and it ran so hot I called them up, and they said it was normal for that style of motor. You could fry an egg on it! I can't imagine that was a good design, but there it was. You could call marathon and ask them about the temp.
Cleaning/degreasing the outside of the motor will help with heat disappation.
Make sure that what you have for lubrication is indeed an oil well, and not a grease port. If req'g grease, usually motors have grease fittings for a grease gun, but not always. Oil every month couldn't hurt, but you are already doing what 99.9999% of the population doesn't do!!.
Getting a spare is never a bad idea: Motors go by frame type as well, so note the frame number on the label. Motor rewinding houses often have hundreds of motors on back shelves, and you could get a spare for a fraction of the Grainger's price. Make sure the shaft diameter is the same, or, if smaller, get a bushing or equivalent pulley, and have it all pre-set up. Or makes sure the old pulley can come off, and fit the new motor.
Have a spare belt, as well. And make sure the belt is not too tight.
Imo, the looser the belt, the better, as long as there is no slippage. Purists will disagree, but I think the physics is on my side. Purists will say pressing the belt in the center span should have about 1/2" play, but I say as much play as will still prevent slippage is better: easier on the belt, easier on the bearings, and on the pulley, and likely results in a slightly less power consumption via less friction. A $10 clamp-on ammeter from HF could be used to readily test this notion. However, you don't want the belt so loose you risk it jumping off the pulley, either. Tight belts can wear aluminum pulleys clear away, sometimes with razor sharp sides! And proly also too-loose belts.
I also tend to use 3L belts (thinner) in place of 4L belts, except in automotive applications. They just seem to fit better, seem to offer less friction. But, I'm sure this practice would make a purist's teeth hurt.
And the caution about rotation direction was good.
--
EA



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wrote:

Thanks for all the great info!
I have always had the belt set to run on the loose side. It is just tight enough to where it doesnt slip or jump off so i guess I had that one right... I probably have more than an inch of play in the center of the belt. It actually runs tempwise and soundwise as it did when it was new so maybe I have been doing the right things with it? I have always tried to keep the air openings clean but as I said it has run hot since it was new?? I am quite certain the holes I have been putting oil in are for oil and not grease.. But good point also. Thats a good idea about the clamp on ammeter. I'll look into getting one. Also I will check into getting a spare motor just to have on hand in case.... I was just worried that it could all of a sudden quit on me with no warning signs..... Thanks again! Steve
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Steve wrote:

>

The motor nameplate might have a rating like "40 degrees C Rise". That would mean the motor running at full load might run 40 C degrees (72 F degrees) higher than the air temperature at the motor. That could be up around 150 degrees F.

If the motor was supposed to be greased it should have zerk fittings (which grease guns attach to). For oil there is commonly a spring loaded cover over a tube, or something like a plastic bushing with a hole in the center.
Over oiling can be a problem. Oil can get inside the motor producing problems, such as start switch failure.
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.
I wouldn't say it would quit without warning signs but they could sneak up on you and get you while you are not looking. That's why its just best to be prepared and have a spare on hand for a motor that's that old. It may take you a few days to get a replacement and you are concerned about being without its use for a period of time.
Jimmie
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Of course it can! Some motors give a bit of warning, run hot and squeal. Some just burn a wire, and die in an instant.
--
Christopher A. Young
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