Hub motor high frequency noise

[jordanjozsef]

https://www.youtube.com/watch?v=TUgNQ72AzVk

I've purchased a new hub motor, but ever since I have it, it always makes a high frequency noise and it's louder than usual. I also found out it eats much more amps that it should, however it feels powerful and it's not resonating. At 50 km/h the motor draws 1000W from the battery, and at 85 km/h it draws 5000W, which I thought it's fine, but I've been told it's too much. Also I opened up my motor and the phase wires' sealing looks burnt, but only two. Is it possible that I purchased a faulty motor or is my wiring bad? I tried the motor with 3 controllers, same noise, I used the study cable to learn the correct rotation direction. Is it still possible that I have to manually match the phase and hall wires? The motor is rated at 3000W, it should handle 5000W just fine. Weight can't be the problem, me and the bike weights only 120 kgs.

 

[jordanjozsef]

https://www.youtube.com/watch?v=PuCyktZXXQM
I just took another video, showing that it's that loud.
I tried all 36 phase - hall combinations, there were 3 correct, but all of them gave me this performance.

 

[Punx0r]

1000W for 30mph/50kmh is about right for a bicycle with an upright rider. Couple that with the fact you've checked all possible hall signal combinations suggests your problem is not a false-positive hall configuration.

I can't view the video at the moment so can't comment on the possible source of the noise.

85kmh = 53mph so 5000W seems a bit juicy for that speed.

Beware motor ratings though - to paraphrase, there are lies, damn lies and (some) motor ratings. Depending on the vendor. If you post your motor spec someone may be able to relate their experience on true/real world performance capability.

 

[jordanjozsef]

I hope that you can check out the video soon. The stator is 45 mm wide, so it could be a 3 kW rated motor. I have to mention that I'm driving the motor from 120V, so that could make more noise at low RPM, because high voltage is very inefficient at low RPM. It's not that loud at higher RPM, but I also tried out my 300W 36V rated hub motor with the same voltage and it still had no noise or at least not that loud. So I think maybe the cover is thin, so it won't block the noise, maybe the acoustic is bad, I could fill the center of the stator with some acoustic sponge to dampen the noise and glue onto the cover too, but it will just make the heat transfer worse, so I wouldn't try it. At higher RPM it seems to be okay, so I could either use smaller wheel or lower voltage. Or convert my hub motor to mid drive using belt to drive the rear wheel. That way, I could find the most efficient gear for my needs. At the moment I could go 140 km/h with the larger wheel, but even the smaller wheel give me enough top speed 110 km/h.

 

[amberwolf]

The stator is 45 mm wide, so it could be a 3 kW rated motor.

so is the mxus 3k (450x), but unless it's in a small wheel (like 20" tire diameter or less) it may not be able to sustain that. it can do it in bursts in bigger wheels...

then there's motors like the qs205, which has been used at more than the 3kw it's rated at, sustained, without problems (and with bursts of several times that), in larger wheels.

(i have both here now and have inspected the innards of v1 and v3 of the 450x, and the qs205 v3, and the qs is built much much better than the 450x's, in every way i can see).


regarding noise: there's a few things that cause motor noise, including electrically.

the covers, if close enough to the windings, can, if there's a high enough current, be vibrated by the eddy currents induced in them from the windings. if the cover's mechanical properties happen to make it resonant with that frequency or a harmonic of it, it could amplify that enough to be heard.

similarly, if the windings are loose on the teeth, they might be able to vibrate similarly, and induce noise into the stator, axle, thus bike frame and covers, etc.

these types of noise should change with different controllers, as the various frequencies used should be slightly different. the more different the controller technology or firmware design is, the more pronounced teh difference in sound should be.


bearings, if not lubricated, or if damaged (lke from excessive side-loading such as during incorrect installation procedures), can have assorted sounds from friction, which generally change with loading. these types of sounds will usually be different while riding than while wheel is offground spinning at the same speed. the pitch will vary with speed on these, too.

many motors (the qs205 being one exception i've personally seen inside of) have very very little clearance between the covers and the stator. sometimes a tip of a ziptie or other tiedown, or even a winding strand, may just barely touch the inside of the cover, which can make various types of noises, including what may sound like squeals or whines. the pitch will vary with speed on these, too.

 

[jordanjozsef]

The covers of the hub motor are flat, so I think there isn't much clearance, that could be a problem, but if I could make a thick aluminium plate and screw it on the cover, it would decrease the resosnance, right? The loose winding would cause the noise, however I can't do anything against that. Only if I rewind the whole motor, but I don't know how hard is that. I have time for it, but I don't want to mess it up, the motor was $250. There are no other noises, it's a new motor, so the bearings shouldn't be a problem. I think it's the cover and/or the loose windings then.

 

[Punx0r]

It's worth trying sticking something to the outside of the covers to see if you can damp it. Maybe any old thing as a test and if it works go for the thick ally you suggest that won't inhibit heat dissipation.

Harmonics can be a fickle thing. A certain motor on a certain controller at certain settings can just "ring" like a bell. If you're running 120V then at low throttle the input to the motor would be quite high current even at very low throttle/slow speed but very short pulses.

 

[dogman dan]

FWIW, every time I ran a motor with enough power to melt it quickly, it howled like a jet engine. These were the smaller 500w rated " 9 continent" type DD hubmotors. Feed em 4000w, and they scream. ZZZZZZTTT.

 

[jordanjozsef]

I injected Statorade when I bought the motor, maybe that's the problem? BTW I just tried an e scooter motor with the same controller and voltage, and has no loud noise, so that motor is faulty.

 

[amberwolf]

i can't imagine how statorade would cause a noise...but it doens't mean it's impossible.

but...how did you get it in there? remove the cover? drill a hole? etc?

if I could make a thick aluminium plate and screw it on the cover, it would decrease the resosnance, right?

if that's what's causing it, then you could first just try sticking some rubber pads to teh outside in random spots on the cover flat areas. if it doesn't change, it's probably not the covers, so no need to do more on those.

The loose winding would cause the noise, however I can't do anything against that.

there's stuff called coronadope, and other similar lacquers meant for insulating transformer and motor windings, that can be dripped down into the windings and along the stator laminations. it's pretty thin, so it will "soak" into the windings and laminations and act like a glue to hold them in place and not vibrate (at least as much).

it's a new motor, so the bearings shouldn't be a problem.

they're probably not bad, but even a new motor can have bad bearings, becuase if they install them with the wrong method, they can damage them. if they heat them up enough they can damage or evaporate the lubricant in them. there's a few things that can be done to destroy "new" bearings during motor manufacture. :/

 

[E-HP]

At 50 km/h the motor draws 1000W from the battery, and at 85 km/h it draws 5000W, which I thought it's fine, but I've been told it's too much.

https://www.ebikes.ca/tools/simulator.html?motor=MX4503_SA&batt=cust_96.2_0.2_30&cont=cust_100_200_0.03_V&hp=0&axis=mph&wheel=24i

Looks like it's extremely efficient, since 5000W is the load at that speed, and with all of the losses, the battery power should be more like 6kW. You need hubsinks if you're riding that fast for more than 17 minutes.

 

[jordanjozsef]

Now I see why it's so noisy, I opened up a quiet motor, it's 14 years old, but still works well, and now I see the difference. The windings are well tightened down with some rope and I think it's also coated with some lacquer, so it has no chance to vibrate. Also the stator looks "twisted" which is new for me.

 

[Punx0r]

Tight, well laquered windings will vibrate less. Have a look at this article for a bit on magnetically induced noise: https://eomys.com/e-nvh/notes-on-electromagnetically-excited-noise-and-vibrations/article/magnetic-noise-and-vibrations-in-electrical-machines?lang=en/

Transformers hum or buzz due to magnetostriction, but it seems electric motors are a bit different.

The skewed stator slots reduce torque ripple (cogging) by smoothing the transition of each tooth between magnets. This should also reduce noise.

 

[jordanjozsef]

if that's what's causing it, then you could first just try sticking some rubber pads to teh outside in random spots on the cover flat areas. if it doesn't change, it's probably not the covers, so no need to do more on those.

I tried it, because today I was cleaning the covers and heard that frequency so I thought I should try the rubber. It made more quiet, it could be further improved by using epoxy for the coils to stick them together, but it was much easier.

Anyway this motor has flat covers on both sides, but on Aliexpress it has a bulged one on both sides, even the Feedback's pictures has a bulged one, so only mine is flat which is the reason why it's noisy, because the flat cover resonates better and it's closer to the coil.