Why Is Thickness Sander Motor Stalling

[Gerry Gruber]

Hi Mario. Yeh, your and Dick's posts have me thinking that changing out the bearings is perhaps top of list.

Thanks also for your experience with the the 2hp motor on the 15 amp breaker. Unfortunately, my shop and the breaker panel are separated by a finished basement family room with gyproc ceiling (i.e., no suspended ceiling through which to fish wires). So, wiring upgrades will be complicated. However, your experience suggests to me the alternative of running a 1.5 or even 2hp motor on my existing 14 guage/15 amp circuits, and if the breaker repeatedly goes off, I then bite the bullet and upgrade the wiring.

O.K. Time to open up this motor. Nurse... scalpel please.... er.... philips screwdriver...

[David Malicky]

DT has an interesting point on the spurt of energy. That would depend on what rpm the spurt occurs at. On slowdown, the mechanism switches over at a pretty low rpm. Do the spurts occur at a similar rpm that you hear the 'click', or higher?

Bad bearings seem unlikely to me for a few reasons... motor is pretty new, runs at only 1725rpm (6203 is the likely bearing, rated to 12k+ rpm), and if the motor were sending a sizable portion of 1 HP into a small bearing, it would get very hot and die quickly. As Mario mentioned, bad bearings are noisy -- is the motor quiet at speed?

[Bill Hicklin]

If the bearings were so far gone as to cause the problems you're having, you'd hear them loud and clear.

[Will Morrison]

Gerry: DO NOT assume that time will discharge a cap. In a LEAKY one, yes, it will. In a good cap, that charge can last literally for YEARS. There are plenty of people who have had large parts of their personality and years taken off their lives because they assumed a cap was discharged. They can put you on the floor or even kill you.

To discharge a cap, especially a high voltage one, NEVER put a screwdriver across the terminals unless you like potentially welding the two things together. Make a jumper cable with a resistor in between the two clips, preferably about a 47K or more, of about 5 watts. That is overkill, but I prefer that to exploding parts. Clip one side of this to the positive terminal and the other to the negative terminal. Let it sit for a few minutes to be sure, and you're talking a safe cap.

Caps are kind of like batteries, they can and will store a charge for a long, long time. They will also release it very fast, potentially giving you a zap like nothing you've ever felt before. It only take 40 MILLIAMPS of current to stop the human heart, and that is NOT much power at all. A cap can deliver MANY times that.

Protect yourself at all costs. Caps are replaceable, you aren't.

[Gerry Gruber]

Hi David M. The spurts were coming pretty late in the winding down. I can't be sure, but it is very possible they were close in time to when the click occurred. I thought a few times that the motor was off entirely before one of these spurts occurred. I've got the motor apart now, and there is no obvious (to me) problem with the switch. Once disassembled, there is about a .025" gap on the one point and a .035" on the other. On both, there is a small (about 1/16" diameter "burn" dot where contact is made. I don't know whether that is normal, or whether the points should be shiny clean. But, they are definitely not welded together. Not a great picture, but you might be able to see the burn dot:

switch.jpg (44 KiB) Viewed 17680 times

The spring mechanism that opens the switch after start looks fine too. I manually slid it inward to the "open" position it has when up to speed, and it moved fine. No apparent mechanical problems.

The bearings are in fact 6203RZ and 6205RZ. The motor is quiet enough at speed. Definitely no ratttling or crunching sounds that are obvious - to Bill's point.

No obvious problems with the capacitor (i.e., no deformity to the capacitor).

No obvious damage to the windings (i.e., from a visual inspection):

windings.jpg (49.81 KiB) Viewed 17680 times

And, there is practically no dust on or in the motor at all. It is quite clean.

Thanks Will for the safety points on capacitor decharging. I did in fact put a screwdriver across the terminals (only read your post afterwards). And, good news... I still have all my hair. There was no charge there at all - at least no spark at all. I guess, as David M. had mentioned, the capacitor probably discharged through the windings. But, for future reference, many thanks.

Should I sand that little burn spot off the contacts? I do have a cheap multimeter. Should I try to the check the capacitor and/or the windings with it?

What about the manual overload protection:

overload.jpg (50.76 KiB) Viewed 17680 times

Could it be faulty and cut in prematurely?

All the connections on the overload protector look OK.

[David Malicky]

Hi Gerry, Good work taking it apart and inspecting things! And the pics are very helpful. Now it's a process of elimination.

So, if the spurts are indeed the start winding kicking in, as DT suggested, then the switch would be working normally. When you say you thought the motor was off entirely before a spurt, could you say more what exactly happened? Was the motor switched off and spinning down, then a spurt?

Those clearances sound small to me (for a centrifugal switch, 1/16"+ is more typical), but they should be enough to prevent 120VAC from jumping across; maybe others know more? You could try bending the steel Z bracket on the 0.025" one to match the other. Are the 2 switches wired in parallel or series? The burn dots are common, but it's good to clean them. The main thing we can't tell yet is if the mechanical and electrical parts are sync'd correctly -- tough to visually check on a TEFC.

Yes, at this point I would check the windings, looking for a fault but realizing we may not find it (multimeters apply just 3-9V). An appliance repair or HVAC shop should have a Megger, but might as well check it with a multimeter first. Some links:
http://www.deanbennett.com/testing-subm ... motors.htm
http://www.snipsmag.com/Articles/Featur ... 00f932a8c0____
http://igor.chudov.com/manuals/ElectricMotors.pdf
http://glencampbell.wikispaces.com/Tren ... hase+motor
The wiring can be confusing to figure out, as often little is labeled and some junctions may not be accessible. With some typical wiring diagrams for capacitor-start motors, inspection, and Ohm checks, it can be deduced. Resistance checks below about 10 Ohms are tricky as the resistance of the multimeter pins to metal can be 1-2 Ohms (dig the pins into bare metal). The ground isolation checks in the first link above are easiest to do.

[julian tobey]

A bit of juvenile levity-- I have been a motorhead (technically an enginehead) for over 50 years. A favorite prank in an auto shop was to remove a Delco points-style ignition capacitor(then, called a condenser) laying around on a workbench gleefully waiting for some fool to pick it up. As you might expect, maximum glee was felt by those of us who had suffered the jest ourselves. On a modern racing grade magneto, a careless contact with a sparkplug wire will put you on the ground, and that one is not funny.
Hope this helps?

[Clay Schaeffer]

Hi Gerry,
You would not necessarily need to change the wiring to run a bigger motor - IF- you rewire the circuit as a 15 amp 220V circuit. You would need to change the breaker and all the receptacles, and obviously no longer be able to use them for 110V machines. A 2hp motor will draw between 9 to 11 amps @ 220 V.
Running a motor that draws more amps than the wire should handle is not a good idea even if the breaker doesn't blow. Breakers fail two ways when they get old. Either they trip prematurely or they fail to trip. If I had a 15 amp breaker that wasn't tripped by a constant 18 amp load I would replace it.
It is always best to have a qualified electrician check your particular situation before rewiring anything.

[Gerry Gruber]

Hi David. I said I (had) thought the motor was completely spun down when the spurts occurred, because with the dust collector running (and with ear protection on), I couldn't tell when the motor was completely at rest - I simply didn't hear it anymore when the spurt came. But, I suspect in hind sight that it might still have been spinning and most probably very close in time to when the switch would kick in. Unfortunately, at this point, I would have to reassemble the motor to confirm this. (If need be, I can do that.) But, no I had not yet cut off the electricity to the motor when the spurt occurred. I was about to... thinking OK it sounds like it has completely stalled, and then... whoops... it's still trying to spin. When I was using the old table saw switch/breaker, the motor would spurt maybe once as the motor spun down and then it would die (i.e., the breaker would trip). When I removed the old table saw switch/breaker, and just plugged the motor directly into one of my circuits, this spurting happened multiple times, and if I recall correctly, after a couple of spurts continued to run albeit sounding pretty wierd (i.e., at a slower speed), at which I unplugged the motor, fearing that if I left it go on too long I would irreparably damage the motor.

The following picture says to me that the two switches are in series:

So, I'm going to go to school on this multimeter I have, and see if I can find out anything further about the windings. Thanks for the links to the "How to" pages.

Hi Julian. That practical joke was shocking! I'm all for practical jokes, as long as they are not played on me.

Hi Clay. So if I understand you correctly, I could use my 14 guage wiring to run 220 service to my workshop?

[Clay Schaeffer]

Hi Gerry,
You can use the same wire for 220 as 110. At 220 V the wire will handle the same amperage but twice the wattage. This means a motor will draw half as many amps when wired for 220V as when it is wired for 110V. Effectively a 1.5 hp motor is maxing out a 15 amp circuit at 110V, while a 2 hp motor is comfortably running at 9 to 11 amps on a 15 amp 220V circuit. Both legs (black and white wire) of the 220V circuit are electrified so the same size wire can carry twice the wattage.

[Gerry Gruber]

Hi Clay. Thanks so much for that. It opens up another option - converting one of my existing 110v/15 amp 14 guage circuits to 220, which would make a 1.5 or 2hp motor more feasible.

[David Malicky]

Hi Gerry,

Good info. It does sound like the rpms were pretty low, and thus likely the switch was engaging then and not the cause of the problem. Yes, the contacts are in series and that makes it even less likely the switch is the problem -- if either became stuck closed, the other would break the circuit.

So, the run winding is probably the best place to look next. 3 possibilities for insulation breakdown: to ground, to the start winding, or to itself (short-circuit between some windings). Those resistances should be ~infinite, ~infinite, and something between 1 and 3 ohms (not an easy measurement). Since the problem only occurs after 5 minutes of running, the motor probably has to be hot to detect the fault, but cold resistance numbers would help for comparison.

[Gerry Gruber]

Hi David. I've done some readings with my multimeter, but it is a cheapy multimeter... an analog version, which I bought on sale for $10 a few years back. So, keep that in mind.

Grounded winding: The "How to" videos and articles tell me to set the multimeter to Ohm, which I did. I set it at the RX10 setting (which I understand to mean, multiply the result by 10. I also have an RX1K setting available.) I touched the two multimeter leads together and adjusted the meter to read "0". I then touched one lead to the green ground wire (attached to the casing), and the other to the yellow/black, white, yellow and red wires (4 different wires). In every case, the needle did not move from the infinity position on the far left (which I take as a good sign).

Just to confirm the appropriate wires to be using for these tests, the following is the label on the side of the motor:

I am running the motor in reverse on "Low Volt", and so when running, the red, white, and yellow wires are joined to the white (line 2 from my house circuit) wire. The Yellow/Black wire is attached to the black (line 1 from my house circuit). So, I am not sure which of the red, white, and yellow wires are start and run. But, I am guessing it is yellow and white wires. So, the tests I did were:

Yellow/black to green = infinity
Yellow to green = infinity
White to green = infinity
Red to green = infinity

I also ran these tests at RX1K and again no movement of the needle.

Shorted Winding:

Here I set the multimeter to Ohm RX10 setting again, and zeroed out the needle. Then I did the following tests:

Yellow/black to white = 1 Ohm
Yellow/black to yellow = 1 Ohm
White to yellow = 2 Ohm
Yellowblack to red = infinity

These measurements may be off by .25 Ohm either way, as it was somewhat difficult to read, and the needle moved around a bit depending on how and where I touched the lead.

I also checked the capacitor. I first ensured there was no residual electricity in the capacitor. I then set the meter on ohm RX10, and then touched the leads to the two capacitor terminals. I think the first time the needle jumped about half way to the right and then slowly moved back to the left. Subsequent measures, the needle barely moved at all. I repeated this again a day later, and again the first time the needle moved across (this time maybe a quarter way across) and then slowly returned to infinity. Subsequent tests immediately after showed no movement. I am assuming this is simply because the meter needs a bit of time to recharge between tests.

Question: When doing the ground and short tests, should the centrifugal switch be closed? The tests that I did were with the motor completedly unassembled, and the two leads from the winding that went to and from the centrifugal switch were unattached. However, I could easily join these two leads - effectively closing the switch and redo the tests if that is the correct way to do it.

I do not have any specs on what the resistances should be for this motor - no manual, and no online doc showing these specs either.

And, as you indicated David, if there is a wiring problem, it would probably only be observed after the motor ran for 5 minutes. Does it make sense to reassemble the motor, run it until the problem occurs, and then take an immediate measurement to see what the resistance is at that point?

[Gerry Gruber]

I just connected the two leads - that would normally connect to the centrifugal switch when the motor is assembled - with a paper clip. I then redid the multimeter tests, and the results were the same, both for ground tests and short tests. Although I don't quite understand why... if these leads are not connected to the centrifugal switch, is not the start winding circuit "broken" at that point, in which case one would expect to read infinite resistance?

[David Malicky]

Good work figuring out the multimeter. Unfortunately if the meter has a max ohm range of x1k, it probably won't be able to detect insulation faults (insulation should be in the Mega-ohms... bad insulation might be 0.2 Mohm, 200,000 ohms). Most digital meters will do Mohms, though multimeters don't apply enough voltage to detect most insulation faults. HF has a $5 meter that may be worth a try, but the <10 ohm accuracy is poor. Before spending money, you could call a few HVAC or appliance repair shops to see how much they charge for doing a megger test on a motor -- that's the only meter that can test the insulation with certainty. Or if you want a better multimeter anyway, figure $40+. Or there are meggers on ebay for ~$50, but that's all they do and the high voltages have some safety issues.

Disconnect the capacitor from the circuit for resistance tests -- it will absorb current and throw off any readings. As you noticed, using an ohmmeter on a capacitor reads higher and higher resistance with time -- this is because the ohmmeter works by sending out a small DC voltage and monitoring the current. (Ohmmeters get resistance as voltage/current.) So the capacitor slowly charges up and the current slowly drops as the cap becomes 'full' (at that voltage).

Remember low ohms are hard to measure accurately because the contact resistance can be in the same range, and low-$ multimeters usually do it poorly. You can practice technique by ohming a screw head, wire tip, etc.

I would open the centrifugal switch so its contact resistance isn't a variable. The run winding resistance is easy to measure: if the switch is open and/or the capacitor unplugged, just check the resistance across the main inputs. Finding the start winding is harder. But for this motor's problem, we don't need to know the start winding resistance, just that there's not an insulation fault between it and the run winding. I.e., there should be Mohm+ resistance between either end of the start winding and either end of the run winding. Look at the wires going to/from the switch and capacitor--one of those is a start winding lead (and 1 will probably just connect the 2). Check resistance between each of those and either main input: resistance should either be in the 0-10 ohm range, or Megaohms+. If you find something like 10k ohms, that's would be start-run insulation fault.

Yes, reassembling the motor sounds like a good next step, to compare hot and cold.

[Gerry Gruber]

I decided to purchase a "better" meter, and picked up an Innova Autoranging digital meter (about $50 from Canadian Tire), and redid the above readings which were about the same:

green to black/yellow: infinity
green to yellow: infinity
green to white: infinity

black/yellow to white: .8 ohm
black/yellow to yellow: .8 ohm
white to yellow: 1.6 ohm

I then removed the capacitor and left the centrifugal switch open (i.e., removed from the motor entirely). I then redid the same tests with the same results.

I then re-assembled the motor and conducted the tests again (i.e., capacitor was connected as was the centrifugal switch). Same results on the resistance tests.

I then ran the motor for 30 minutes. It did not stall during this time. However, that's probably because I wasn't using it in the sander during this time, but rather simply had it spinning on my workbench. The pulley was still removed as was the hood that goes over the fan. I also had the capacitor connected but just hanging off the motor during this time, and the junction box was left open. I did this so that I could readily access the wiring after the motor had run for some time.

After 30 minutes, I unplugged the motor to turn it off. The centrifugal switch clicked during the spin down. I then discharged the capacitor, but left it connected to the motor. I then redid the resistance tests. No change from before when the motor was cold.

I then disconnected the capacitor and redid the tests again, and again same results.

So, either I didn't do the testing right, or an insulation fault is not the cause of the problem, or there is an insulation fault and I simply didn't work the motor enough to get the fault to manifest itself.

I did notice as I ran the motor for the 30 minutes that the motor casing got warm - particularly at the pulley (non-fan) end of the motor. In fact after about 25 minutes, the casing at the pulley end was so warm/hot that I couldn't keep my finger on it for more than a second or two. So, I am starting to come back to the bearings... I am wondering whether the bearing at the pulley end is faulty. I am thinking that I will replace this bearing and rerun the motor. The motor did not sound bad - no crunching or rattling sounds. And, it felt OK to spin by hand. But, the heat was quite evident. Now, I didn't have the hood over the fan, and perhaps that contributed to the heat build-up, as the fan hood seems designed to direct the air over the motor casing. I suppose I could put the fan hood back on and run the motor again for 30 minutes to see whether the motor runs cooler.

[Clay Schaeffer]

Hi Gerry,
It wouldn't surprise me if it was a bad bearing. Bearings seem to be a weak spot in Chinese motors. When the motor is spinning free very little stress is put on the bearing, but when it is attached to the machine the tension from the belt tends to pull things out of line. I would replace both the front and back bearings with good quality replacements if you can find them. Sometimes they use bearings of an odd size.

[Gerry Gruber]

Hi Clay. I picked up some new top end bearings, and as soon as I find a bearing puller, I'll install them.

I also spoke with my local Busybee manager yesterday, who says he's been fixing electric motors for ever, and he was sure it was the bearings, but most likely the capacitor. So.....

And then, talking with my dad on the phone last night (he had been using various electric motors all his life running a grain farm), the issue of the length and guage of the circuit that I was using came up. As I mentioned in previous posts, my workshop is at the other end of the basement from the service panel. So, the circuit is probably about 30 feet of 14 guage wire to the outlet. Add to that another 25 feet of 16 guage extension cord, and maybe that was contributing to the problems as much as anything. I was reading on a different online board that suggested long circuits with undersized wires could result in lower voltage, and as a result higher amps to compensate. The moter might run fine, but heat build-up would occur. Is this something that I could simply determine by sticking a multimeter in the end of my extension cord - to see what kind of voltage I am getting? Or would I have to take this measurement while the motor is running - which obviously would be a bit more tricky? I guess one could also try to measure amps being drawn while the motor is running, but I believe to do that would be even trickier - i.e., I think I would have to have the multimeter connected in series (i.e., between the power source and the motor). I think my head is starting to hurt.....

[Bill Raymond]

You may want to try shortening the extension cord--or, better yet, using a heavier duty extension cord--as well.

[Gerry Gruber]

Hi Bill. Yeh, I think I'm going to replace my two 16 guage ones with 12 guage. The in-wall circuits are 14 guage and I can't do much about that, other than a rather messy rewiring (i.e., poking holes in gyproc). But, to use a higher guage extension cord is a pretty painless upgrade. I can't shorten them, but I can upgrade the guage.