OT. Small motor

[Keith Nuttle]

I realize this is not probably the best place to ask this question, but collectively the people on this form have experience with every thing.

My question concerns our gas fire place. it is the kind that is vented through the side of the house.

We used it all last winter. This fall when we started it up the fan ran for a while made some noises, and the squirrel cage fan stopped. At that time I cleaned the area under the firebox, there were were some lava stones.

I put it back together and it ran for a while then stopped. Messed with it and tried again and it ran for a few minutes and slowed down and the fan started to hum

I took it out and put a little oil on the shaft and worked it down into the bearings. It has been running for about an hour and a half.

Is it normal for a small motor like is on the fan to run hot? This one is running about 200F. (taken with thermoprobe on a volt/ohm meeter with the probe on the out side of bearing housing over the bearing.)

Thanks

[Larry Jaques]

That's a bit hot, IMHO. Squirrel cages usually scavenge air around the motor, so it should stay a bit cooler in the breeze.

The methods of your testing indicate that you already know that the motor bearings are suspect. (Probably dry) Replace the bushings or bearings if the motor can be rebuilt, or just replace the motor, Keith.

-- The problem with borrowing money from China is that thirty minutes later, you feel broke again. --Steve Bridges as Obama

[Leon]

Is the fan sucking HOT air? What is the temp of the air immediately coming out of the fan? Probably pretty high, the temp from the fan will radiate to the motor.

The fan motor probably should be fitted with better bearings.

[Keith Nuttle]

It is setting on my work bench in my garage ambient air is about 60 with the exhaust blowing into the air above the workbench. No restrictions. Even in the fireplace it will be pulling room air about 70F and blowing it up behind the firebox, and out from above the fireplace. It has been running for about 3 hours now. I wonder how long it will run when put back in place?

I believe this an assembly that come as is from the manufacture. I have not looked for the motor only yet.

[Leon]

OK not recirculating hot air, recirculating room temp air at most. I think you have an inexpensively built motor with marginal bearings. Obviously the bearings either and dry or will now only function with the addition of lubrication. If the later, it will probably run till the lubrication seeps out again.

How long???? Probably for years on end on your work bench. An hour after reinstalling back in the fireplace especially if it is difficult to R&R. ;~)

Seriously I would test it for normal run times for a week on your bench. Any failure at all would dictate replacement with a better motor.

[Ed Pawlowski]

Sounds hotter than usual. I'd be looking at the McMaster or Grainger web site for a new one. Small motors are not worth rebuilding.

[woodchucker]

I have no experience, but I can tell you that it is too hot. Does it have a start capacitor, or run capacitor, or is it a small motor?

Sounds like maybe the winding might be shorting if the bearings are free now. If it is not free spinning, than that is still the cause of the heat.

Figure the motor should be no hotter than 120 at the most.

[Father Haskell]

What type oil? WD40 is a solvent, makes a good cleaner, but dries out. 20 weight motor oil is a better general-purpose lube.

[Artemus]

A bearing temp of 200F indicates a dragging bearing. If the motor has bushings and not bearings there will usually be a felt pad surrounding the bushing. Take the motor apart and clean the inside of the bushing with a q-tip soaked in 3-in-1 oil (the 20W kind is too heavy) then liberally apply the oil to the felt pad and soak it. Let it sit for several minutes then wipe up any excess oil. Clean the gunk off the armature shaft and reassemble. Add a drop of oil to the shaft/bearing interface. I do this to my fans once a year and they are all still running after 10+ years.

Never use WD40 to clean or lube as it will gum up in a few days/weeks and is difficult to get it all out of the felt.

If the motor has actual bearings they may need replacement.

Measure the temps at other places in the motor. If the field windings or iron are excessivly hot you may have a shorted winding. You may also just have insufficient airflow over them on your bench. Compare it to the airflow when installed in the fireplace. Art

[clare]

Forget 3 in 1 - get sewing machine oil, turbine oil, or something like "duratrode", "tuff-oil Lub-it" or "Chevron Handy-Oil ISO 15". I have a tube of each of those 3 - and the shop where I spend 2 afternoons a week has sewing machine oil by the gallon (a leather shop with all kinds of leatherworking and sewing machinery)

[Unquestionably Confused]

[snip]

Several have mentioned the possibility of shorted windings.. Depending upon how long that motor was "stalled out" when Keith noticed the problem, might that not be the problem now? If the bearing/bushing seized up and let the motor cook long enough, simply freeing up the bearing isn't going to do much if the windings have now become a "hot plate"

Any idea how long that puppy was powered up and just sitting there groaning, Keith?

[clare]

MOST of those motors are "impedence protected" and will not dangerously overheat even when stalled.

[Artemus]

Many years ago I needed to lube my turntable and grabbed what I thought was sewing machine oil from the wifes sewing area. It gummed things up quite nicely. ??? Turns out I grabbed her fray check by mistake as it was in a similar bottle. Art

[Keith Nuttle]

OP: The first time it stopped; no. It was the first cool evening of the fall. I turned it on and went about watching TV, and checking the newsgroups on the computer etc. Some time later I noticed the fan was not running. Other times I was monitoring it so it was stopped for a minute or to until it was turned off.

The comments about the windings shorting could be true as the wrapper around the coil has darkened, but on the bench they did not seem excessively hot. The coil resistance is about 9.5 ohms with my cheap ohm meter. There is no continuity to the ground on either tab.

From the first my working theory was the a piece of lava stone got sucked into the fan, and blocked it from turning. The lava stones have been removed. Now I am wondering if that is what happened and the symptoms I am now experiencing are related to the initial stoppage.

This after noon the fan ran at about 200 for about 7 hours and was running well when I turned it off.

With your comments I believe I will do further testing with it in the fireplace. A new one will cost about a hundred dollars, and a service call would be more than that.

It is a cheap motor not worth spending any money to rebuild it,though I may check with the local fire place shop an see if I can get the motor only.

Thanks for all of your help.

[knuttle]

OP: I use SAE 5W40 that I use in the car. I know that works with high temperatures

[woodchucker]

Sewing machine oil and mineral oil are about the same. I have a quart of mineral oil and use it to oil a lot these days as I notice it does not gum up like 3-1.

[Unquestionably Confused]

Not sure if 9.5 ohms is indicative of a short in the windings or not, but with everything you've told us, I suspect it is. I'd go out and check against a small motor here but the shop is in the garage and temperature is falling like a rock right now. I'd rather stay inside by MY wood stove.

Short in the winding is different from a short to ground. The latter is going to blow the fuse or trip the breaker, the former should heat it up as instead of having 2000' of wire in the windings, the "short" will, in effect, shorten the total length of the windings.

At least that's my understanding of it. We have enough electricians hanging around here that if I'm all wet, they'll hose me down and let me hold a plugged in toaster as they do so

[basilisk]

One thing to consider, If the fan is running with a less restricted air flow on your bench it will be loaded heavier than if the flow is somewhat restricted, more flow, more load, more amps, more heat...

Sounds counterintuitive but a blocked fan will draw the least amount of current.

basilisk

[Bruce]

On Sun, 20 Jan 2013 08:09:28 -0700, basilisk wrote (in article ):

Almost guaranteed to be a shaded pole motor. Basically bullet proof but prone to the bushings on the rotor getting scummy.

-Bruce

[Lew Hodgett]

-------------------------------------- Most likely an "air over", fan duty motor.

IOW, depends on the driven fan to provide the cooling air for the motor.

Engineered for application specific duty cycle as a throw away device.

Lew