Motor lifetime

Electric Motors and Controllers
Dougt   100 mW

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Motor lifetime

Post by Dougt » Jan 13 2015 1:02pm

In the for sale new section, a guy that is selling QS motors is claiming that they only last 3-5 years before the "steel" "loses its magnetization" and the steel needs to be replaced to bring back efficiency. Since QS builds a large percent of the motors that are re-branded and sold for e-bikes, scooters, and motorcycles, this is worrisome.

I have never heard of this for a motor. And all the steel in the magnetic circuits of these motors is surely choosen to be a magnetically soft magnetic material with low remanence. So having no permanent magnetization over time is desirable.

I understand that some motors may not last due to unpotted/tensioned windings rubbing and shorting, or the magnets maybe partially demagnetizing by running high fields. Or of course, mechanical problems with bearings and such. But the steel? Maybe it is some sort of heat-treatment or such...I know that extremely high permeability materials, such as Mu-metal can lose some of the permeability by mechanical shock- even dropping on floor, but they are extreme specialty materials, not magnetic core materials.

And he talks about how it is cheap and easy to replace the steel...so he must not be talking about the steel the windings are on.

Does anybody have any idea what he is talking about? Maybe the permanent magnets? I didn't want to post there and hijack his for-sale thread with technical questions.
Last edited by Dougt on Jan 13 2015 5:57pm, edited 1 time in total.

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Re: Motor lifetime

Post by amberwolf » Jan 13 2015 5:01pm

Dougt wrote:In the for sale new section, a guy that is selling QS motors is claiming that they only last 3-5 years before the "steel" "loses its magnetization" and the steel needs to be replaced to bring back efficiency.
BS.

None of hte steel *has* any magnetism (at least, it shouldn't).

If anything in their motors beyond bearings needs to be replaced like that, then no one should use their motors, as they'd be pretty crappy products. :roll:

(and even the bearing won't need replacing like that unless they are crappy, too, or else are exposed to pretty seriously bad (atypical) conditions and have no seals/etc).


If the* magnets* get hot enough (past the Curie point) long enough, they can demagnetize partially or completely, but

A) they're not steel
B) you're abusing the motor seriously to get it to that point
C) if you're using the motor within their specs and it gets that hot, their specs are lies

I didn't want to post there and hijack his for-sale thread with technical questions.
You should post it there to call him on the BS. ;)

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Re: Motor lifetime

Post by leffex » Jan 13 2015 5:06pm

Dougt wrote:I understand that some motors may not last due to unpotted/tensioned windings rubbing and shorting, or the magnets maybe partially demagnetizing by running high fields. Or of course, mechanical problems with bearings and such. But the steel? Maybe it is some sort of heat-treatment or such...I know that extremely high permeability materials, such as Mu-metal can lose some of the permeability by mechanical shock- even dropping on floor, but they are extreme specialty materials, not magnetic core materials.
You have the answer in your lines above. Add 3-5 years before repair or any such things needs to be done.
I think all hubs lose magnet power but its not noticiable because the controller will push in "50w extra load" for that loss. My old but not much used 250 grey hub wobbles possible the bearing I dont know. Its DEAD. :cry:

I think the biggest loss of time and anything on a motor running on an ebike is if its axle goes bad or brakes. If its not repairable or the user knows how too its a total loss... Clamped and a bolt added might fix that last issues :D

Have you tried drilling holes in a crystalyte hub then you know what hard steel they use...
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Re: Motor lifetime

Post by Dougt » Jan 13 2015 5:53pm

amberwolf wrote: If the* magnets* get hot enough (past the Curie point) long enough, they can demagnetize partially or completely, but

A) they're not steel
B) you're abusing the motor seriously to get it to that point
C) if you're using the motor within their specs and it gets that hot, their specs are lies

I didn't want to post there and hijack his for-sale thread with technical questions.
You should post it there to call him on the BS. ;)

I would add that a permanent magnet can be partially demagnetized by strong external fields. I don't have any idea if the fields from say putting 200a in the phase wires is enough, but I doubt it (although the demagnetization also gets easier with elevated temps).

I agree though, a well designed motor with properly selected materials shouldn't have these issues. BTW, I think that company does make the parts for the majority of e-bike hub motor companies, such as cromotor and crysalyte, but those companies may spec superior parts.

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Re: Motor lifetime

Post by Dougt » Jan 13 2015 5:57pm

leffex wrote: Have you tried drilling holes in a crystalyte hub then you know what hard steel they use...
I agree with most of what you posted.

As for hard/soft, sorry I should have made it clear that by "soft" steel, I mean't magnetically soft - which means it doesn't retain much magnetization (low remanence) and the magnetic orientation is easily changed (low coercivity). An example of a magnetically hard material would be a permanent magnet. I will edit my original post to make that clear. My bad on the misunderstanding.
Last edited by Dougt on Jan 13 2015 6:05pm, edited 1 time in total.

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Re: Motor lifetime

Post by riba2233 » Jan 13 2015 5:58pm

They make cromotor so :lol: But I highly doubt that magnet will demagnetize so fast, and nobody should be concerned about that for a very long time.
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Dougt   100 mW

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Re: Motor lifetime

Post by Dougt » Jan 13 2015 6:02pm

riba2233 wrote:They make cromotor so :lol: But I highly doubt that magnet will demagnetize so fast, and nobody should be concerned about that for a very long time.
I agree, so why would a vendor even bring it up? Usually people don't want to say their products will wear out in 3 years, especially if that isn't true. I am just wondering if we are missing something, or if the design or materials of the particular motors listed are problematic. It would be like going to a car dealership and them telling you that the steering wheel needs to be replaced every 3 years - even though you know that steering wheels usually never wear out, why on earth would someone trying to sell you the car say that unless there was an issue?

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Re: Motor lifetime

Post by amberwolf » Jan 13 2015 6:19pm

Dougt wrote:I agree, so why would a vendor even bring it up?
I'd guess they wanna make you buy a new one every 3-5 years, knowing that hardly anyone will ever want to open up their motors and replace anything. You'd be surprised how gullible people are. :(

I can imagine that at least some people would believe their motor needed fixing or replacing even if there was nothing different about it's operation, once the time period ran out, if they'd been told something like this.


I am just wondering if we are missing something, or if the design or materials of the particular motors listed are problematic.
I don't know, but I think it's more likely that someone (the salesman, or wherever he got his info) doesn't understand these things, or didn't understand what they were actually told, or there's a serious language barrier/translation problem (possibly more than one layer).

Cuz there's no steel in a motor that should be magnetic to lose it's magnetism in the first place, regardless of quality of materials or design. ;)

Dougt   100 mW

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Re: Motor lifetime

Post by Dougt » Jan 13 2015 6:27pm

Folks, after doing some reading, I think I have found the answer.

The phenomena is called "magnetic aging".

from wikipedia article on electrical steels:
"...The presence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging when it slowly leaves the solid solution and precipitates as carbides, thus resulting in an increase in power loss over time. For these reasons, the carbon level is kept to 0.005% or lower. The carbon level can be reduced by annealing the steel in a decarburizing atmosphere, such as hydrogen"

from freedictionary.com

"Aging, Magnetic
a change in the magnetic properties of a ferromagnetic material over time. Magnetic aging can result from changes in the domain structure of the ferromagnetic’s crystal structure (irreversible magnetic aging).
Reversible magnetic aging is caused by a rearrangement of the domain structure (seeDOMAINS) under the action of external factors, such as magnetic fields, temperature fluctuations, or mechanical vibrations. This type of aging is exhibited most clearly in ferromagnetics with residual magnetism. Remagnetization removes the effects of reversible magnetic aging and restores the original magnetization of the ferromagnetic specimen.
Irreversible magnetic aging occurs when the crystal structure of a ferromagnetic material undergoes a transition from a metasta-ble state to a state that is closer to equilibrium. This type of aging occurs whether or not the specimen is demagnetized or has residual magnetism. An increase in temperature accelerates irreversible magnetic aging.
The magnetic stability of ferromagnetic products can be improved by subjecting the products to artificial aging. The crystal structure can be stabilized by holding the article at an elevated temperature. Partial demagnetization by an alternating magnetic field is the simplest method of stabilizing the magnetic domain structure of products used in a state of residual magnetism. The best stability of magnetization is achieved when the demagnetizing action used in artificial aging is the same as the demagnetizing action to which the product is subjected during its use."

My guess is that the selection and processing of the steel used in the motor is very important in whether this becomes an issue or not. Using cheap or unsuitable steel, or maybe pushing the steel beyond it's intended performance envelope, could lead to magnetic aging and consequential losses in power and efficiency.

another interesting webpage on magnetic material selection for various applications and resistance to magnetic aging: http://www.cartech.com/techarticles.aspx?id=1624
So the question is...how high-tech is the material selection in a $200 motor?
Last edited by Dougt on Jan 13 2015 6:37pm, edited 1 time in total.

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Re: Motor lifetime

Post by amberwolf » Jan 13 2015 6:32pm

Dougt wrote: BTW, I think that company does make the parts for the majority of e-bike hub motor companies, such as cromotor and crysalyte, but those companies may spec superior parts.
Cromotor might, but I don't think Crystalyte even knows (or really cares) what they get / sell, based on the highly inconsistent results we see on their motors.


Regarding magnetic aging, since none of the steel in there should be magnetized in the first place, there's no reason to worry about it losing any of that magnetism. ;)

So, it doesn't apply.

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Re: Motor lifetime

Post by Dougt » Jan 13 2015 6:45pm

amberwolf wrote: Regarding magnetic aging, since none of the steel in there should be magnetized in the first place, there's no reason to worry about it losing any of that magnetism. ;)
So, it doesn't apply.
I disagree - I think it could possibly lead to problems. Not saying this is happening, but the shape of the hysteresis loop of steel undergoing flip-flops in magnetization polarity, such as the stator steel does in a operating motor, is very important in regard to energy losses. Any changes to the loop from magnetic aging could affect both the strength of the magnetization (permeability and saturation) ie motor power, and the energy losses, ie motor efficiency.

Now, honestly, I have no idea how pronounced magnetic aging affects these properties, but it seems to be in-line with what the vendor is talking about.

I also think that magnetic aging should be non-issue for a properly designed motor. That is just my hunch based on what I've read and my experience in electromagnetics in the past. But my experiences in electromagnetics hasn't involved much with steel cores.

If QS motors is using just regular mild steel for the laminations, then there likely will be problems.
Is there anyone out there who is expert in this sort of thing?

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Re: Motor lifetime

Post by QSMOTOR » Jan 14 2015 1:43am

Hello Dougt, Thank you for your interest in QS Motor.
Here is my comment below about life time for reference only.
The life time of motor depends on usage.
For general usage, it's about 3-5 years, and it will be 5-7 years if it work in good condition.
For testing and abusing usage, the lifetime will decrease accordingly.
Btw., Our motor could work 5000 hrs without damage in Lab.

Here is the main points below.
1.Moisture ingress slowly corrodes the stator & magnet, the parts will get rust and lead to other issues (E.g. electric leakage)
Vito: We will place waterproof glue sealant on edge of the rim of the motor, and around the wires coming out of the motor by the stator.
Then the motor will be IP54, which means the motor can work in raining day (even heavy rain), and can drive through the puddles/mud,
but can't work under the water completely.
Moreover, for V2 & V3 type motor, we choose waterproof connectors.

For QS Motor, we paint transformer oil on cooper and magnetic steel to keep from moisture and rust.
And now, we are testing to put some mineral oil for better performance.

2. High Configuration abusing motors (high input power), which lead to heat issue.
And demagnetize partially or completely.
Vito: We choose NdFeB with different grades. It might be demagnetize in high temperature (e.g. 120°).
For QS Motor, we install temperature termo resistor/Thermic Probe inside of stator.
When it reach 120°, controller will turn off.

3.Mechanical reason (e.g. Axle, bearing)
Vito: We choose 40Cr-HRC28 for axle, which is strong enough for general usage.
For bearing, here is list of single-shaft motor below.
No. Name Item Parameter Note
1 6204 Bearing Bearing capacity Cr=13.50KN COr=6.55KN
2 6009 Bearing Bearing capacity Cr=21.00KN COr=15.10KN Disc Brake Side
Btw., laminations is made of silicon steel.

Thank you for your time, there might be something wrong due to my limited knowledge.
You could test one QS Motor for better understanding if possible.

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Re: Motor lifetime

Post by John in CR » Jan 16 2015 8:04pm

I researched the subject a bit, and as long as you don't exceed the thermal limits (let's push the vendor for the actual grade of neo magnets used) and overheat the motor to either break down to varnish on the copper windings or demagnetize the magnets, then the only thing that prevents our brushless motors from lifetime service once you consider the bearings a replaceable wear item is corrosion. Of course that includes corrosion of the exposed ends of the laminations and their inner ring as well (especially if in direct contact with with an aluminum center that causes a galvanic reaction. The new thing I learned in this process is corrosion of the neo magnets.

Every hubmotor I've opened after significant use showed issues with the magnets. I've seen what I assume is nickle plating commonly flaking off, especially in the areas where the stator scraped the coating of the magnets, and with the raw magnet exposed to the air the white powdery residue that results I assume is a reaction of the magnets with the air. None of my motors have shown any change in Kv, and some of them are 6 years old, so it hasn't affected their functionality, but in stock form I believe lifetime service is a pipe dream.

We need to come up with a better coating. The thick spray on 3m paint for motors simply isn't hard enough to withstand the scraping of reassembly. I've tried using a thick wax paper to protect the magnets and edges of the laminations, but that didn't work as I couldn't get the paper all out and had to take it apart again. The best candidate I can think of is a high temp epoxy spray paint, with the most commonly available being that for appliances like stoves. It may not work for some of the silly high temps some allow their motors to get, but they probably start reducing magnetism with them even knowing. If anyone else has ideas for a very hard coating that might work I'm all ears.

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Re: Motor lifetime

Post by amberwolf » Jan 16 2015 11:45pm

If you could build a fixture to very securely hold the stator and rotor during reassembly (and disassembly if you have to service it later), to prevent the magnets from being touched by the stator, you wouldn't have to worry about how hard the coating is.

I'm not sure how difficult it would be to make such a fixture, especially given how powerful magnets are in today's bigger motors, but it must be possible to do.

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Re: Motor lifetime

Post by johnrobholmes » Jan 17 2015 2:42am

Other than bearings wearing/ failing over time, a brushless motor doesn't have a defined life when run within a reasonable thermal envelope. Buy what you want, run it, keep it dry and/or lube the bearings every now and then to make sure water isn't sitting in them. Decades of reliable service unless your controller takes it out or there is a physical defect or impact to damage it.

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Re: Motor lifetime

Post by Miles » Jan 17 2015 6:46am

amberwolf wrote:I'm not sure how difficult it would be to make such a fixture, especially given how powerful magnets are in today's bigger motors, but it must be possible to do.
I just use my lathe.......

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Re: Motor lifetime

Post by Punx0r » Jan 17 2015 10:31am

2-pack epoxy chassis paint should work well. It's safe to brush on, sticks like anything, corrosion resistant and is easily the hardest DIY paint I've used.

You can get some very thin plastic sheet (maybe even mylar) that ought to work better than wax paper for a protective shield.

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Re: Motor lifetime

Post by John in CR » Jan 18 2015 10:10am

Punx0r wrote:2-pack epoxy chassis paint should work well. It's safe to brush on, sticks like anything, corrosion resistant and is easily the hardest DIY paint I've used.
I love to use epoxies when I can, but selecting the right one can be a challenge. Inside our motors requires one specifically formulated for higher than typical heat, and those often require a high temp forced cure and contain aluminum as an additive. With temp limits below 100°C of common epoxy coatings, I wouldn't risk a chassis paint, though otherwise it seems perfect (hard and durable). Some of the harsh environment floor coatings rate for high temps seem like they could work, but I worry about them being overly thick and/or containing additives that could create heat with moving magnets so near. I think these are the reasons enamels and ceramic-silicone-glass are used a paint for inside electric motors. I'm sure some of the ceramic type may be hard enough, but those coatings are difficult to source, especially in small quantities, and they're uber expensive.

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Re: Motor lifetime

Post by Punx0r » Jan 18 2015 10:31am

I think you're right in suspecting floor paints would be too viscous.

You might be surprised how heat resistant automotive epoxy paint is. Lot of hot parts in cars :) I know people who have used it to paint brake callipers with success.

I must admit, I used transformer varnish in my motor and wouldn't choose it again - too soft, too goopy and I doubt it's more heat resistant than other coatings.

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Re: Motor lifetime

Post by hydro-one » Jan 18 2015 11:21am

i know there was talk of the green 3-m winding coating, you need to vaccum infuse it into the windings. bigmoose?
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Re: Motor lifetime

Post by amberwolf » Jan 18 2015 11:27pm

Punx0r wrote:You might be surprised how heat resistant automotive epoxy paint is. Lot of hot parts in cars :) I know people who have used it to paint brake callipers with success.
Depends on the area to be painted in the car. Engine block paint is probably pretty heat resistant. ;)

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Re: Motor lifetime

Post by Noq » Dec 30 2016 3:46pm

Just wanted to chip in and mention that QS motors are pretty legit. I've been running this guy (the 8KW variant) for 8 months, ~1500KM/month and it's been great to me. On startup, I push around 50KW through it (six times its rating, >600A @ 72-84V), and have been getting away with it. One time after start-stopping repeatedly on a hot day, hitting four red lights in a row and riding WOT between them, I had a short because the wires melted a bit. They were vinyl wrappings, not as good (see attachments). Since then I've replaced them with high-heat silicone wires that can withstand up to 200°C and I've been able to continue abusing the poop out of it without issue. The windings are good and the magnets are strong. I can't speak to heat generation since I don't monitor temp, but rarely does the shell get too hot to touch. Customer service is superb as well. If there is ever any shipping damage, you will be able to work something out with the good folks at QS and get a replacement rim or whatever. Watch for rust at the axle/wire entry point to keep it safe for longer. I'm considering adding Statorade to the motor if heat ever becomes an issue, but might wait for my next build because it'll warrant it more (higher voltage). I had to order a Michelin tire for it since local stores didn't carry the right size, but YMMV.

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Re: Motor lifetime

Post by Hummina Shadeeba » Dec 30 2016 11:54pm

Omega brand makes the highest heat epoxy I could find and I use that. If u heat both parts before mixing it gets almost as thin as water. Expensive yet convenient envelopes of small quantity are available

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Re: Motor lifetime

Post by dogman dan » Jan 20 2017 6:17am

YES,, you can cook the magnet till it's dead. I've done it. I have some magnets pulled from a cooked off Heinzmann motor that can now barely stick to the fridge. Uncooked motor magnets stick hard enough to pinch a blood blister on your finger if you are not careful.

And I also agree with the vendor, if water gets in the motor and stays long enough, you can corrode a motor enough to lock it up in a few years.

So don't cook your motor, and maybe let the water out periodically if you ride in a seriously wet climate, replace bearings as needed, and a direct drive motor would theoretically have a near infinite lifespan.

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Re: Motor lifetime

Post by Hummina Shadeeba » Jan 20 2017 12:51pm

Magnets decrease their power slowly over years and if the protective shell isn't cracked theyre good for a very long time

Winding enamel gets cooked and has a shorter life the hotter it gets. My windings have changed color and wish I'd used better more durable stuff and it's out there

Bearings don't like over 200 and will cook the lube. Ceramic are great for heat but I find them loud

The most common death I've seen is due to the phase wires' shrink wrap being damaged and shorting or just breaking off where soldered to the magnet wires

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