Hot motor

My Taig is powered by a 110V 1Ph 1750 rpm 1/4 HP induction motor or garage sale provenance. My concern is that with use it gets too hot to touch.

I noticed that it was quite warm when I hooked it up first around February. I have used the Taig for brief periods only until now when the heating became quite noticeable.

I run a test today:

1) I run my drill press (3/4HP) for 5 minutes. In an ambient temp of the garage of 27.5C the motor heated up from that to 37.0C. 2) I run the Taig motor without the belt for 5 min. The ambient temp by then was 28.5C and the motor reached 39.1C 3) I repeated the run with the belt and a chuck on the spindle - no other resistance. Unfortunately by then the ambient temp was 32.2C and the motor started at 34.2C. After 5 minutes the temp was 46.1C. 4) I repeated the run with the drill press (ambient 30.9C, went from 31.1 to 40.4C).

The temperatures were measured by an IR thermometer. There was a gradient of temperature in both motors: The front of the Taig motor was considerably warmer than the back, the reverse was true of the drill press motor. The increased temperature was confined to the housing - the shaft and the pulley on it were quite cool (almost 10C cooler). There were no unusual noises or smells, no evidence of sparking. The motor runs smoothly and quietly. The pulley/belt alignment is good as judged by conventional methods.

Questions:

1) Is such degree of heating abnormal? I have never encountered a motor that heats up this much so I assume the answer is yes. 2) What is the likely cause? My first thoughts was "bearings" but why would the housing be hotter than the shaft? Superficially there is nothing to suggest that the bearings are at fault.

Thanks,

Reply to
Michael Koblic
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I vote for it does not matter. Nobody runs a drill press for five minutes anyway. Your motor should have a temperature rise in celsius stamped on the nameplate, or alternatively insulation class. If you post this info, or the whole nameplate, someone here could tell you whether the observed temperature rise is justified. Many modern motors are designed to run relatively hot. You can get a perfectly quantified answer to your question if you post nameplate data.

i
Reply to
Ignoramus29202

I suspect that the motor is fine. Design of a motor affects the temperature of the case. Some get noticeably hotter than others. 40 deg. C isn't that hot. Plenty of motors are rated for operating continuously in a 40 deg. C atmosphere. The windings will be somewhat hotter than the case, but they'd probably need to reach more than 100 deg. C to do them harm. If you want an accurate indication of the winding temperature rise, Jim Cox's book "Electric Motors in the Home Workshop" explains how to measure it using the change in resistance.

Best wishes,

Chris

Reply to
Christopher Tidy

How sensitive are your hands to temperatures?

A ten degree C rise.

An 11 degree C rise.

About a twelve degree rise.

Again a bit less than a ten degree rise.

Note that IR thermometers are sensitive to the emissivity of the area being tested. Shiny metal will have a rather low emissivity. Flat black will probably have a quite high emissivity. Gray paint (which some motors use) will be quite a bit lower than the Black, but higher than bare shiny metal.

The motor for the Taig (if it is like mine) is a self-starting induction motor -- done by "shading" on the poles -- formed by a heavy copper wire welded to form a single shorted turn over only part of the pole. This loses energy as heat -- the smaller the wire, the hotter it will get with the induced current -- but it is necessary to get the motor to start. This is probably a significant part of the heat source in your Taig's motor.

Shiny metal -- so lower emissivity. Compare what the IR thermometer reads with what a contact thermometer reads.

The drill press probably is a capacitor start motor, with a centrifugal switch which switches out the capacitor and start winding once it is up to speed.

There certainly *should* be no sparking in the Taig's motor, since it has no switches or commutators.

The drill press motor is likely to have a centrifugal switch which opens as the motor spins up above a certain speed (maybe about 1/3 to 1/2 of full speed).

Look at the labels on the motors. Good motors should have a "temp rise" spec on the data plate along with the RPM, current, voltage, and horsepower ratings. See what that figure is. It is how much higher than the ambient temperature the motor is expected to get being run for an extended period (say perhaps an hour) at the full horsepower rating.

Yes -- it *is* normal for motors to heat up in operation, and I would expect the shaded pole start type which the Taig likely has to heat up more than a capacitor start motor such as the drill press is likely to have.

Consider the emissivity of the different points you are measuring with the IR thermometer. Your different readings may not mean much when that is taken into account. What is the color of the paint job on each motor?

What kind of bearings do the motors have? I would expect the Taig's motor to have porous bronze sleeve bearings, and you probably could help things a bit by frequently oiling the bearings. There is greater lateral stress on the pulley end (which I presume is what you are calling the "front"), so that bearing would probably heat more from friction, compounding the overall heating from the shaded poles. Also

-- I have seen import electric motors which actually had the case a lot longer than the actual internals required, so the pole pieces could be closer to the pulley end and generate more heat there. Those tended to overheat more quickly, because they did not have enough metal to work efficiently. The motors in the infamous $200.00 H/V bandsaws (4x6") are often likely to be like this.

The drill press -- if it has a *good* drill press motor -- may have ball bearings instead. In that case, most of the heat will come from resistive losses in the run winding, with some more from air resistance. Does the motor blow air out the bottom or the top? That air would carry heat with it. I would expect it to blow out the top, but who knows what you will find.

But mostly -- look at the "temperature rise" spec, and add that to the room temperature when you start to predict worst case rise. (And depending on the source of the motor, that spec may be in degrees C or degrees F.

I would expect a ball bearing three phase motor to have the lowest temperature rise for a given horsepower.

I don't see the rise on the drill press to be a problem, as you don't need to come in contact with it under normal conditions. For the Taig -- make a shield to keep your hand from touching the motor's case, and ideally add a fan to push air through the motor at all times that the motor is running.

Good Luck, DoN.

Reply to
DoN. Nichols

Hmm ... when I drilled, and then power tapped 40 1/4-20 holes in some 1/4" thick steel plate, I think that either the drilling or the tapping phases took over five minutes each. The motor was switched off while I popped the drill chuck out of the spindle arbor and popped in the TapMatic tapping head, but that was only a couple of minutes.

Agreed.

If it has complete nameplate data. Sometimes the motor will not have it -- for whatever reason.

Enjoy, DoN.

Reply to
DoN. Nichols

I expect that the heating is about normal, overheating due to a fault would be more noticeable, such as odors and/or noises.

Many domestic North America and western Europe manufactured appliance or general purpose utility-duty motors have an insulation rating of 105C. Nearly all quality industrial rated motors' insulation is rated 105C. Chinese consumer market motors very likely aren't.

If the motor side of your pulley is solid flat, it can interfere with air flow, depending on it's size.

As a rule, I nearly always disassemble used motors for inspection, cleaning and oiling. Depending on the previous use of the motor, it could have a build-up of wood dust, lint (buffing wheel) or various other byproducts which could be restricting air flow.

If there is a data plate or label on the motor, check to see if the insulation class is shown, and if there is any rating for duty time.. cont for continuous, for example.

Reply to
Wild_Bill

"Michael Koblic" fired this volley in news:DDqdm.111318$ snipped-for-privacy@newsfe14.iad:

It doesn't sound terribly out of line. Decently-made motors typically are rated for an _internal_ temperature rise of up to 40C.

If it's one of those light-housing open-frame motors, there can be some eddy losses in the frame as well as the stator. Plus, the stator is usually in intimate contact with the frame, and conducts copper loss heat as well as stator excitation losses into the frame.

LLoyd

Reply to
Lloyd E. Sponenburgh

If it's a shaded pole motor, getting very hot is normal. They're designed to run that way. Shaded pole motors are inefficient compared to other types of motor (for the reason Don gives above). Some get too hot to touch even when running unloaded.

Best wishes,

Chris

Reply to
Christopher Tidy

etc.etc.

Thank you all for helpful responses.

The insulation class is B so the temperatures seem well within acceptable limits. I could find no evidence of a capacitor so shaded pole is the most likely explanation.

To fill in the details some of you commented on:

1) The IR thermometer read within 1.5C of a thermocouple on all surfaces except the shiny ones where the diff was 2C. 2) To confirm that the pulley/shaft were indeed cooler than the housing I used the scientific method of touching both.

All in all a satisfactory result.

Reply to
Michael Koblic

Sadly no.

It's the motor design. Cheap to make, not so good to run. People have had much better results with a 24 VDC electric scooter motor, about

150 W. You can machine steel for 30 minutes and the motor barely warms up, plus you get excellent speed control. They are being surplused right now.
Reply to
N Morrison

My little DP came with a 1/6 HP motor that would get too hot to touch almost before you turned it on. Now it has a 1/3 HP I bought three for a dollar and I can work all day and still grab it. Gerry :-)} London, Canada

Reply to
Gerald Miller

1/4 Hp is VERY large for shaded pole - I'd expect split phase with a centrifugal starting switch. That's pretty well standard for an unloaded start application.
Reply to
N Morrison

Motors up to 3/4 hp were used back in the '30s and '40s. They didn't need a starting condenser, slip rings or centrifugal switch. They did run hot, but were often not continuously rated.

I had one on a 1942 drill press.

Mark Rand RTFM

Reply to
Mark Rand

Thinking about this a little more, I doubt it's a shaded pole motor. I've never seen a shaded pole motor as big as 1/4 hp (if anyone has, do let me know). Usually the biggest is about 1/16 hp. Above that the power losses get significant.

It's probably a split-phase motor. These have two windings: the main winding, which has a high inductance and a low resistance, and the start winding, which has a low inductance and a high resistance. As a result, the two magnetic fields produced are out of phase, which is the condition required for starting. There will be a switch somewhere to control the start winding. Either a centrifugal switch, a relay or a special momentary switch (the second two are fairly rare). Split-phase motors do not require a capacitor, but their starting performance is poorer than that of capacitor-start motors.

Best wishes,

Chris

Reply to
Christopher Tidy

Was it definitely a shaded pole motor? If so, I'd be interested to see one of these. An unusually large shaded pole motor is a type I haven't seen, and I'm fond of early motors.

There was another kind which didn't need a capacitor, slip rings or a centrifugal switch. It has a special start-run switch with momentary and latching contacts for the two windings. Bob Minchin kindly gave me one.

Best wishes,

Chris

Reply to
Christopher Tidy

I powered my taig, before I gave it away, with the enclosed motor from a floor mounted fan. this ran very hot over time. sooooo I mounted a computer fan to blow air over it. it still got warm but not so much that it caused any concern.

you do have a cooling air supply blowing over it??? all the bigger motors have a centrifugal blower built in so dont need the assistance. a mains voltage computer fan and a lash up shroud should fix it. Stealth pilot

Reply to
Stealth Pilot

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