Purpouse of parts + functioning of coffee grinder motor - Page 1
Forum section: electronics / beginners

author: todorp
author_rank: Regular Contributor
timestamp: February 20, 2020, 06:27:08 pm
content: Hi, my coffee grinder stopped working and I disassembled the motor just to see how it works. I am a complete newbie regarding electric motors and electricity in general. So I just wanted to ask I few questions regarding the parts found around the motor (shown in the following) photos + in general how this motor is supposed to work (at least can someone tell me what it is called [ Specified attachment is not available ]:What is the purpouse of the big fat yellow cap between inputs' line and neutral?What is the purpouse of the big fat yello cap attached to the stator?Is the blue thing a cap? What does it do? There are two of those on opposite sides of the statorWhat is the black tubular thing? Something to do with temperature (a kind of braker)?Thanks a lot guys,Tod

author: wraper
author_rank: Unknown
timestamp: February 20, 2020, 06:30:18 pm
content: Those are X and Y type safety rated capacitors. They are simply for electromagnetic noise suppression. Motor will work without them just fine.

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2020, 06:46:44 pm
content: It's a universal motor.https://en.wikipedia.org/wiki/Universal_motorAs mentioned above, the capacitors are for noise suppression. They have a low impedance to high frequencies, in the >100kHz rang and high impedance to low, mains frequencies, in the 50Hz to 60Hz range.The yellow capacitors are X-rated, no that's not a porno, but a safety rating, which means they can safely be connected across the mains, without posing a fire risk.The blue capacitors are Y-rated, again another safety classification, this time meaning they can be connected between the mains and chassis, without electrocuting someone.http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdfhttps://www.illinoiscapacitor.com/pdf/Papers/EMI_RFI_interference_suppression.pdf

author: Gyro
author_rank: Super Contributor
timestamp: February 20, 2020, 06:50:36 pm
content: Quote from: wraper on February 20, 2020, 06:30:18 pm... Although it is unlikely that they are responsible for the problem (unless a fuse or RCD tripped), so no need to remove them.The most common reasons for motor failure are worn down brushes and overheating. You should be able to see that the brushes are in decent condition (the motor normally shows other signs like speed variations too).The black tubular item that you pointed out will either an interference suppression inductor or a thermal fuse. Given the way it is tightly tied to the winding, my bet would be thermal fuse.If you have a multimeter, you can do simple continuity tests (unplugged) to trace the wiring. Check the switch contacts and the continuity across the black cylinder (from one of the bush holders to the switch from the look of it). If it is open circuit then it will be a thermal fuse. If so, you will need to carefully detach it, cut open the sleeving and replace it with one of the same temperature rating (hopefully marked on the body). The replacement will need to be crimped (not soldered) to the existing wires, safely insulated with the same thickness of sleeving as the original, and tied back into place.

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2020, 08:16:00 pm
content: Are you sure the motor is faulty? Going from the pictures, it appears to be in good condition. There doesn't seem to be any signs of overheating and the commutator and brushes look good.Test the motor by connecting it to the mains, in series with an old 100W incandescent light bulb. The bulb should briefly glow brightly, then go very dim, when the motor spins up to speed. You can then test the motor on its own, with no light bulb to limit the current.I think the fault lies elsewhere.

author: wraper
author_rank: Unknown
timestamp: February 20, 2020, 09:31:17 pm
content: Quote from: Zero999 on February 20, 2020, 08:16:00 pmI don't see condition of brushes in any of pictures .

author: Brumby
author_rank: Unknown
timestamp: February 20, 2020, 10:27:03 pm
content: Brushes:... which look fair.Commutator looks very good.

author: Jwillis
author_rank: Super Contributor
timestamp: February 20, 2020, 10:41:51 pm
content: Thermal fuse could be blown. Check continuity of the component with black shrink wrap around it.

author: wraper
author_rank: Unknown
timestamp: February 21, 2020, 03:20:16 am
content: Quote from: Brumby on February 20, 2020, 10:27:03 pmLeft brush not visible at all. Length of right brush is not clear, it easily might be worn off and barely touching. You won't ever see even a half millimeter gap because once even a tiny gap appears, motor stops spinning.

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2020, 08:51:10 am
content: Quote from: wraper on February 21, 2020, 03:20:16 amYou're right. It isn't 100% conclusive, but I've seen motors with badly worn brushes before and they're generally in poorer condition than this one, which looks fairly new. Fortunately it's easy to check with a continuity tester, to rule out any doubt.

author: todorp
author_rank: Regular Contributor
timestamp: February 21, 2020, 09:09:32 am
content: Thanks a lot for the tips folks.Zero999, since you say it is universal motor can it be run using low dc voltage: I am not too confortable playing around with 220V yet :-), but I have a DC regulated power supply that can get me 2A @ 50/60 Volts DC...Regarding the brushes I will post some nicer photos of these. I hope to have more photos and info this we (play time :-)).

author: Gyro
author_rank: Super Contributor
timestamp: February 21, 2020, 09:18:37 am
content: Don't you have a basic DMM or even an analogue multimeter? Continuity tests will be far more helpful in locating the actual problem, and safer too.Just to repeat, with the motor unplugged from the supply.

author: Zero999
author_rank: Super Contributor
timestamp: February 22, 2020, 02:12:14 pm
content: Quote from: todorp on February 21, 2020, 09:09:32 amYes, the motor should run slowly at that voltage.

author: Jwillis
author_rank: Super Contributor
timestamp: February 23, 2020, 12:47:57 am
content: You can make a basic continuity tester with a battery and a small light bulb or LED . If the bulb or LED lights theirs continuity.

author: beanflying
author_rank: Super Contributor
timestamp: February 23, 2020, 12:59:20 am
content: Quote from: todorp on February 20, 2020, 06:27:08 pmFar more likely in my experience with coffee grinders is the motor is likely not the cause so look for these too.Micro switches on or near the bean hopper or even magnetic reed switches and a missing magnet on or in the hopper. The Micro switches in particular are susceptible to getting coffee dust between contacts and failing and magnets fall out and go through the burrsIn the case of a Doser type (Cafe style) there is also a microswitch and paddle as a crude level control. The hopper ones are fitted to reduce the risk of dumb dumbs putting fingers into the burrs. Not all grinders have this sort of thing fitted but a lot do.Depending on the grinder some also have a start stop relay in the base rather than run the motor power through any switches but generally that is for the larger ones than your pictures indicate.

author: Gyro
author_rank: Super Contributor
timestamp: February 23, 2020, 08:28:39 pm
content: The OP's first two pictures appear to show the whole setup, it looks like just one switch (of some kind - it's upside down). Maybe it performs the interlock function mechanically before actuating that switch.I'd still like to see some continuity testing, from the mains plug, through the switch, thermal fuse etc. It's the only way to narrow down the problem. Seeing the motor fail to spin on a bench psu will be as useful as seeing it fail to spin on mains, just safer.

author: james_s
author_rank: Super Contributor
timestamp: February 23, 2020, 08:34:55 pm
content: Quote from: Zero999 on February 22, 2020, 02:12:14 pmI would expect it to run quite quickly at 50VDC, probably a significant fraction of full rated speed although the torque will be considerably less.Most 240V universal motors will quite happily start to run on 12V or less.

author: todorp
author_rank: Regular Contributor
timestamp: February 24, 2020, 09:36:19 am
content: Hi, the switch is ok: it is a mechanical thing which makes contact when you push a button on the grinder cover (non very solid but seems to work).I have check the brushes and these seem ok too : 3rd photo.The tubular structure seems another noise suppressor of some kind (what is it?) : 3rd photo.I found a first culprit, a blown fuse hidden inside the connection wire : 2nd photoHow should a DC power supply be connected to test the motor? +12V to the LINE wire and 0V (GND) to NEUTRAL wire?Thanks,Tod

author: Gyro
author_rank: Super Contributor
timestamp: February 24, 2020, 12:33:04 pm
content: Quote from: todorp on February 24, 2020, 09:36:19 amYes, that's a ferrite bead noise suppressor, basically a lossy series inductor. You can happily put the sleeve back over it and secure it again.QuoteIs that the one that was sealed inside the black heatshrink sleeving and tie-wrapped to the winding? If so, it is probably a thermal fuse and indicates that the motor got a bit hot. As the motor windings don't look discoloured then maybe you were just a bit too enthusiastic with the coffee grinding.The markings aren't clear on the photo, they should give a temperature rating (or at least a current rating if it is just a fuse). The metal crimps make me think it is a thermal fuse though (soldering would overheat it).QuoteIt doesn't matter about polarity. As it is a universal motor, it can be connected either way round and it will spin in the correct direction, just like it does on AC.

author: todorp
author_rank: Regular Contributor
timestamp: February 24, 2020, 01:13:11 pm
content: Hi Gyro,QuoteThe black heatshrink sleeving contained the ferrite bead noise suppressor: I have already put it back in place.QuoteI managed to read the markings on the thermal fuse: Aupo 102°C P1-3A-F 250V - F4JET. I will try to get a replacement from amazon or ebay. By the way do you think a 120°C or 130°C 3A fuse could work? I saw these are more common on amazon. The 102°C 3A seems available from aliexpress only and takes like 1 month for shipping...I will try to connect the motor to the DC power supply and see if the motor runs (even without the fuse).

author: Gyro
author_rank: Super Contributor
timestamp: February 24, 2020, 04:31:35 pm
content: You would probably do better with a local electronics distributor than either Amazon or aliexpress, Somebody like RS, Farnell or Digikey. 120-130' is quite a step up from 102'C. I would stay with at least close to the existing one as the manufacturers tend to set them quite closely to maximise protection. I am curious about where this one was mounted as I couldn't see it in any of your earlier photos - presumably somewhere with good thermal coupling to the the motor [Edit: Ah, under the yellow capacitor, with a second surpressor?].It's fine to test the motor without it, but you will obviously want to reinstate the fuse for safety protection when you start using it again.EDIT: I see that the Motor is rated Class-E for thermal rating. That means maximum hot-spot rating of 120'C. The hot-spot would occur deep in the winding, rather than the surface, so by the time you have the additional thermal insulation/temperature drop of the fuse being on the outside and in insulating sleeving, 120'C rating would definitely be too high for protection. 102'C is about right.

author: todorp
author_rank: Regular Contributor
timestamp: February 24, 2020, 06:16:49 pm
content: Hi Gyro, you are right, the thermal fuse was mounted close to the winding under the yellow cap. Before substituting the thermal fuse I wanted to perform some more tests.I powered the motor using a bench power supply. I used 12V and can see that the motor is drawing 100 mA of current but not spinning at all. I tried 20V@170 mA, still not turning.However I noticed that I can turn the shaft by hand only in one direction when the motor is powered: I suppose this means that everything is ok but to run this motor using DC I need a much higher DC voltage. Am I correct?

author: Gyro
author_rank: Super Contributor
timestamp: February 24, 2020, 07:41:22 pm
content: Hi todorp. Yes of course, I can understand you wanting to be as sure as possible. It sounds as if it is trying to turn but is struggling at <10% of normal voltage. At 50V it would probably run quite happily. It is trying to do the right thing though.That is probably as good amount of confidence as you can get. One issue (I think) is that powering on DC won't reveal shorted turns, as AC operation would. Given that the windings look generally good though, I don't think that is a big risk.I had a quick look on ebay with location set to EU and found several 102'C thermal fuse matches with local stock. An electronics distributor would still be the best bet, but one on ebay from a legitimate looking local supplier would be as good or better than aliexpress. As I mentioned in a previous reply, you can't reliably solder thermal fuses - even if you clamp the leads in pliers or wet tissue, you are likely to melt a ~100'C fuse. I noticed some hits for 'thermal fuse crimps' on ebay too, but if you are lucky, you may be able to free the leads of the existing one and re-crimp. Just make sure the result is secure and safely insulated.

author: Zero999
author_rank: Super Contributor
timestamp: February 24, 2020, 08:15:34 pm
content: Quote from: todorp on February 24, 2020, 06:16:49 pmIt's possible you might need a higher voltage, although it does sound like there could be a shorted turn. This would cause the motor to run more slowly than normal and draw more current, causing excess power dissipation and the thermal fuse to blow. Will the shaft continue to spin, if you power it up and turn it by hand?I would bite the bullet and power it from the mains. There's no need to be scared of mains electricity, just treat it with respect and take the usual precautions and you won't get shocked. Secure the motor in a vice, making sure the frame is connected to earth. If there's no convenient earth terminal on the motor, trap the bare earth conductor between the vice jaws and the motor's stator. Try the old incandescent light bulb in series, as I previously suggested first. If the motor doesn't start at all, then it's highly likely it has a shorted turn. You can try without the lightbulb, but use a 3A fuse and keep your hand near the mains switch, so you can turn it off, at the first sign of smoke.

author: Gyro
author_rank: Super Contributor
timestamp: February 24, 2020, 09:21:56 pm
content: Hmm, I'm wondering about the shorted turn...- If on the rotor, then it might to be possible to feel it when rotating the motor by hand under low voltage DC, it should cause a 'notch' feeling. It would certainly cause the motor to slow down on mains though.- If it's on a field winding, it would have the effect of weakening the field and cause the motor to over-speed, a bit like an unloaded series would motor runaway.@todorp,did the motor behave strangely just before it failed?It would certainly draw excess current either way though, which might blow the thermal fuse before visible overheating of the winding.I agree, a mains test, preferably dim bulb style, is the only way to know for sure.

author: Gregg
author_rank: Super Contributor
timestamp: February 24, 2020, 09:51:11 pm
content: If you power the motor with mains power (and the incandescent light in series, I hope) be sure to tie it down to something as it may want to twist out of your hand when starting. If it has a shorted or open turn, it may run after you give the shaft a twist but you'll soon be able to tell by the vibration that something is wrong.

author: todorp
author_rank: Regular Contributor
timestamp: February 25, 2020, 01:50:57 pm
content: Quote from: Gyro on February 24, 2020, 09:21:56 pmThe motor was given to me by another person just saying "it doesn't work anymore"...So, using the bench power supply i cranked up the DC voltage using current limiting: the motor started spinning at around 30V@170 mA. I suppose this is a good sign. Next I will take the plunge as many have suggested and try to connect mains power using all precautions mentioned in this thread: light bulb, well fixed motor...Do you people think a variable transformer (something likehttps://www.amazon.it/Bronson-1000-Trasformatore-Variabile-Variac/dp/B07JKZGQT8/ref=asc_df_B07JKZGQT8/?tag=googshopit-21&linkCode=df0&hvadid=346278921589&hvpos=&hvnetw=g&hvrand=6340046301626428526&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1008141&hvtargid=pla-636920724950&psc=1) might be useful to perform tests on motors like this one using lower AC voltages? Or is it just a waste of money?Thanks a lot,Tod

author: Gyro
author_rank: Super Contributor
timestamp: February 25, 2020, 07:46:49 pm
content: Ah, ok.The motor running sounds hopeful, increase the current limit and it should stabilize - as the motor spins faster, it generates more back EMF, which lowers the current it takes (relative to not spinning). Yes, I think you're good to go to the mains + lightbulb test (repeating the warnings about securing it so that you don't have a mains powered motor jumping around your bench).It's hard to know whether it is worth you getting a variac. It depends whether you are going to get decent use out of it for other stuff. The price ismuchhigher than ta replacement motor or grinder. They're useful to have for testing, but a bulb test will usually get you most of the way when testing power supplies on small appliances etc. 1000W is a big one too (although those are probably optimistic watts). You can often find a, good brand used one on ebay cheaper.

author: Zero999
author_rank: Super Contributor
timestamp: February 25, 2020, 09:29:17 pm
content: Quote from: todorp on February 25, 2020, 01:50:57 pmYes, the fact the motor is turning is an encouraging sign it's good.A variable transformer can be a handy piece of test equipment to have, but it's not worth it if you only want it for this test. One important thing to be aware of is the secondary will not be isolated from the mains. The output will share the same neutral as the primary and will need to be treated with the same respect as mains, even if the voltage is set to a non-hazardous level. This is even more important if you live in a location without polarised mains plugs, meaning the neutral can be either conductor.

author: todorp
author_rank: Regular Contributor
timestamp: February 29, 2020, 10:16:06 am
content: Hi guys, I just tested the motor attached to the mains 220V using your suggestions: the motor works!So the fault was with the thermal fuse. I will be ordering a replacement for the fuse and hope to have everything re-assembaled soon.I will try to improvo the ventilation of the motor and not use it for long continuous runs to avoid another thermal problem.I just wanted to say a big thanks to everyone who gave me suggestions and helped explain a bit the workings of these kind of motors (and various parts found around the motor).Cheers,Tod