shaded-pole AC induction motor trouble-shooting - Page 1
Forum section: electronics / general

author: edy
author_rank: Super Contributor
timestamp: July 26, 2012, 07:46:05 pm
content: Hi folks,I'm new to the forum but have been watching EEVBlog for a while. I have an electronics question but it is more "electrical" than it is "micro-electronic" which seems to be the focus of EEVBlog. I hope someone can answer it. It has to do with a motor that runs my Range Hood... It is a Broan model # 10941071 (used to be K7448000).After only 3 years, it has stopped working. At first I thought it may be the variable-control knob "pot" switch which turns on the motor and then lets me adjust the speed (I assume it is just a voltage regulator). However, when I tried another AC motor from another Range Hood it worked.... Successfully turned on the fan and adjusted the speed. I would have liked to just use the test motor from the other range hood, but it was a different bracket/screw/fan-hole sizing so I couldn't just use it.So I am wondering, I physically inspected the motor and hooked it up to the mains and get nothing. My test motor when hooked up to the mains will turn. Once again, confirming the motor is the problem not the variable-speed "pot" switch. Physically removed some of the paper around the primary coil winding ("stator winding") to see if my fuse burned out, but it looks fine to me.Next step, I guess is to check the resistance across my motor with a meter. Should be finite and low I assume, if infinity then something is broken in my winding, and I guess unless I plan on manually winding up my motor again it's done for.I was hoping for some help with someone who has played around with these types of motors, the cheap ones found in most house-hold fans/range hoods and knows common issues with them. Also wondering why after only 3 years it is already toast? I should mention that the motor was extra noisy for some time (like 4-6 months) prior to this. I didn't know why, I couldn't see any problem with the fan blade, I thought maybe it was hitting something but when I checked it out it seems to rotate smoothly. So this may give some insight into what could have been the start of failure and possible cause!Thanks in advance!

author: edy
author_rank: Super Contributor
timestamp: July 26, 2012, 07:51:57 pm
content: ... One more thing...To make matters worse, the entire stainless steel range hood costs about $250 new. Since I only need the motor, when I sourced the part from Sears or a local Broan distributor to the public, they want around $100 for just the motor! Meanwhile I know commercial contractors or industry can get them for probably $30-40, and surplus stores carry bins full of these for cheap.As Dave "That Crazy Australian Bloke" would say....... "Aaaarghhhh!"

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2012, 07:58:55 pm
content: There is a 2uF capacitor associated with that motor. it most likely is either open circuit or very low capacitance. Replace it with another one, 2uF 400VAC motor run capacitor, and it will most likely work again.

author: Kremmen
author_rank: Super Contributor
timestamp: July 26, 2012, 08:37:16 pm
content: +1 for the cap.Only if the motor has been gruesomely abused physically, or heavily overloaded (as in stalled under power for long periods of time) is there likely to be anything wrong with the actual motor itself. Induction motors effectively do not wear out in normal use. The cap might though, especially if it is a One Hung Low quality component, as Dave likes to put it.So, as SeanB suggested, replace the cap with a same value motor rated (quality) component and your problem probably goes away.

author: G7PSK
author_rank: Super Contributor
timestamp: July 26, 2012, 08:49:14 pm
content: You said that the motor was noisy before it stopped working suggesting that there could be a bearing problem, Can you turn the fan by hand easily it should spin if you blow on it, if it is stiff or seized when powered up you should hear a hum from the winding's if so try some oil on the bearings.

author: edy
author_rank: Super Contributor
timestamp: July 26, 2012, 11:13:14 pm
content: Thanks for the help everyone...The motor spins effortlessly... no problem at all, it is not jammed or locked up at all. The only component I can find on the motor winding is a fuse. There is no capacitor anywhere I can see on the motor.The only capacitor I have seen is on the "variable control speed" knob, but as I mentioned before when I was using it with my other "test" AC motor from another range hood, it worked no problem. So I don't think my "variable controller" knob circuit board is to blame, since it does the job on another similar type of motor.Also, when I try to plug the bad motor directly into the mains power supply 120V AC outlet, my "test" motor works but my bad motor doesn't turn at all. The shaded-pole type of motor shouldn't need any extra circuitry to get it to start turning, from what I understand.Nevertheless, I will try a resistance test and see if I can get any reading through the winding coil, as there may be a break in the motor circuit. I will look at the caps but usually there is physical damage (like a pop-out on my Samsung TV power supply) but I didn't see anything here. I'll look again and report back!

author: Psi
author_rank: Super Contributor
timestamp: July 26, 2012, 11:24:50 pm
content: Yep, if its a simple shaded-pole motor then it doesn't need the capacitor. (some more advanced shaded-pole motors use caps but i doubt you have one of those)I suspect you will find the winding is open circuit.Small shaded-pole motors often have tiny windings (thin wire) that can break easy.

author: Jimmy
author_rank: Regular Contributor
timestamp: July 26, 2012, 11:32:31 pm
content: Yeah small break in wire would be the common cause as psi suggested. The noise would have been the windings vibrating which is the cause of the problem, You can fix that buy adding some resin to the winding and baking it but you would need to find and fix the break first which would be a pain.I suggest looking on ebayhttp://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=broan+hood+motor&_sacat=0one of them might be it and much cheaper cutting out all the middle men

author: edy
author_rank: Super Contributor
timestamp: July 27, 2012, 05:25:58 am
content: Hi everyone,I've managed to attach some photos of the variable speed pot connected to the motor. You can see all the components on there and also the back of the PCB which should allow somebody to draw up a schematic to explain the circuit (any volunteers?) :-).I manage to see 4 resistors, a diode, a variable pot knob, 3 brownish/orange caps? And a large black cap?, and some chip (Q2004F51)) attached to a heat-sink bracket looking thing? I'm not really sure about all of the components and how exactly it works.

author: amyk
author_rank: Super Contributor
timestamp: July 27, 2012, 07:18:44 am
content: It's a triac dimmer, similar to the type used for lighting. Google "triac dimmer" for more info; their schematics are all going to be nearly identical. The "diode" is actually a diac.Q2004F51 I can't find a datasheet on but here is one that contains Q2004F41 and Q2004F31.http://www.littelfuse.com/data/en/Data_Sheets/E2Triac.pdfAnyway, there shouldn't be anything wrong with it.

author: 6502nop
author_rank: Regular Contributor
timestamp: July 27, 2012, 04:02:15 pm
content: From the datasheet, we can extrapolate (< love that word!) the device:Q = Transistor/Triac200 = Volts4 = AmpsF = Package (TO-202 in this case)3/4/5 = Qiv (3=25V, 4=50V, 5=75V)1 = Revision? Series? (It only appears on the "F" package.)So, that'd probably be a 200V, 4A, 75Qiv Triac in a TO-202 (which it looks as if it is). Nice thing about Triacs is that you can always bump up the spec when replacing. If you can't find the Q2004F51, then use the Q4004F51, Q4006F51, or Q6006F51 devices.I'm also with G7PSK on the bearings. It may be spinning fine by hand, but what happens when it gets to operating speed? Double-check things in that department. I have a Brother HL series laser that has the scanner prism motor problem - the lube dries out and it can't spin at rated speed, causing an error and one helluva noise (it sounds like the damn thing is about to leave orbit). A drop or two of Automatic Transmission Fluid (ATF - I prefer DexronII) applied from a sponge-tip (use an eye liner applicator stolen from the GF/wife) fixes the problem. And don't let her know you're stealing her stuff!nop

author: edy
author_rank: Super Contributor
timestamp: July 27, 2012, 04:16:22 pm
content: Hi folks,I goodled "triac dimmer" as suggested and found the following schematic, seems to be close as it has the right number of components. A triac and a diac, 4 resistors, 3 caps and a fuse? I will have to check all the wiring on the PCB but I am assuming this is the basic layout for all such dimmers.The board checks out fine, it works normally on another "test" motor I have.Regarding the bad motor, it does not even begin to turn, or make noise. So likely a coil break maybe caused during the time it had made some noise and vibrated... Could have been enough to wear out a wire bend or solder connection? Will check once I have the meter handy.

author: edy
author_rank: Super Contributor
timestamp: July 30, 2012, 04:34:26 am
content: SOLUTION !?Ok so I got a hold of my meter and tested the resistance across the motor and found the FUSE was to blame! Aaargh! It is hidden underneath the paper-like wrapping around the coil "stator" wire. I have attached a picture of it.It says on the part:123 UMI2A 130 deg C250 V ~ M3<PS>E JETI thought the darn thing would look different like burned up or melted if it was killed. No, it looks normal? I have never seen a normal one before, so maybe this is how they look burned? Kind of frosty white, while a new one would be clear? Anyone know?Any case, testing the coil itself (after bypassing the fuse) showed continuity in the circuit. So it was the "bloody fuse" (as Dave would say it). So any idea on this part? Costs? Availability? Alternatives that would work?

author: David_AVD
author_rank: Super Contributor
timestamp: July 30, 2012, 04:41:34 am
content: It's a common thing in transformers and motors to protect them when the temperature rises too much.Make sure you replace it with another of similar specs, clean the bearing so that it runs smoothly and you should be good to go.

author: lowimpedance
author_rank: Super Contributor
timestamp: July 30, 2012, 05:52:08 am
content: Yes a thermal fuse, if you have to use solder (most likely) to fit the new one be careful not to overheat the leads during the process. Use some damp tissue etc to keep the body cool and use a decent iron to solder the connections. Make sure you electrically insulate the same way as the original.Also make sure you clean and degrease your range hood filters!.

author: SeanB
author_rank: Super Contributor
timestamp: July 30, 2012, 03:23:06 pm
content: Normally I crimp those in, using small crimp connectors ( or recover those it had and reuse them) and glass fibre sleeving over it all.