Guidelines for Safe Motor Temperature?

Asher

Well-Known Member
So there's a temperature gauge, and extended high temperatures are bad for the motor.

What's a desirable temperature range?

What's a safe duration for high temperatures? Eg how many minutes/seconds?

In general, I'd like to know good tips for avoiding frying the motor, or at least prematurely.



As always :), there's nothing on the Juiced site.
 
Search this page for "temperature" for some useful info. http://www.ebikes.ca/learn/power-ratings.html

It varies from motor to motor, but it sounds like in general you don't run any risk of frying the motor unless you are continuously putting a lot of power through the motor (~1000 Watts for CCS or RCS) for extended periods of time (60+ minutes) in high heat conditions where the heat from the motor can't dissipate well.

That being said, high heat is the enemy of all electronics, so I'm sure that even normal riding has wear-and-tear effects on the life of the motor, as well.
 
Magnet wire of the motor is insulated by a thin coating, a varnish. It will last indefintely if run cool. Substantial heat, especially when any moisture is present, begins a process called hydrolysis, wherein a copper-corroding acid begins to form from decomposition products of the insulating varnish. For this reason, a short period of very high operating temperature that will not cause the motor to fry, will still contribute to evenutal failure of the copper wire, possibly a break in the winding or a connection.

But more likely, if the varnish actually burns instead, all it takes a a single turn-to-turn short to set the destruction chain reaction underway. More overheating results faster and faster. A cascade of turns may short one to another and the motor smokes or if totally enclosed, just stops.

https://www.google.com/search?q=mot...rome..69i57.9940j0j1&sourceid=chrome&ie=UTF-8

Magnet wire varnishes have continuously improved in the past century since the first phenolic resin coatings were applied to magnet wire, with revolutionary performance benefits, around 1912. Before that year, magnet wire was quite bulky, varnished with a linseed oil varnish and overspun with fine cotton or silk fiber affording excellent flames and smoke by a shorted out motor in thermal runaway death throes.
 
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So on the Juiced bikes, the display only provides the controller temp IIRC, not the motor temp.

That said, what actual temp can we expect to begin doing damage??? I am assuming it would be somewhere near 100 C??? But that is just a guess.

FWIW, I saw my highest ever controller temps today on the ride home, temp topped out at 67C. I was riding into a brutal 20mph headwind the whole way home, near the end is a ~ 3 mile gradual climb that slowed me down to ~ 16.5 mph in level 3 assist. I am usually climbing this same area with speeds > 24mph, and temps are usually around 54C. In both situations I am in level 3 and pulling 600-700W for the duration of the climb. As most of us should be aware, the motors are far more efficient at high speeds and much less energy gets wasted as heat. Grin Technologies motor simulator bears this out very nicely.
At any rate, I am curious as to when to start worrying about temps as the ambient temp was around 82F; and I am sure to see this climb into the low 100's by midsummer.
 
One of the most significant statements (to me anyway) was that it takes upwards of 1-2 hours for a hub motor to reach thermal equilibrium. If so, then it would have to be a looooong hill on a blistering day to cause a serious problem. I believe anyone in his/her right mind, under those conditions, would take a break before the motor gave up the ghost.

Another important statement: "In practice, most better quality motors have high temperature enamel on the copper windings and can survive excursions in the 150-180°C temperature range without damage." 150°C = 302°F. Woo.

So let me see if I have this straight: Your motor gets hotter and cooler as your effort, the ambient temp, wind, etc., vary. It can get well above the boiling point of water before being damaged. It takes an hour or two before it gets there. And I passed out from the heat and exertion about 15 minutes ago. Is that about right?
 
Haha well put Bruce.

There was zero information from Juiced so I had no idea what the margins are, sounds like they're pretty healthy.
 
Another important statement: "In practice, most better quality motors have high temperature enamel on the copper windings and can survive excursions in the 150-180°C temperature range without damage." 150°C = 302°F. Woo.
Bruce, I'm curious where you read this quote?
Based on that seeing temps below 150C are unlikely to create any thermal damage on our bikes????
 
Bruce, I'm curious where you read this quote?
Based on that seeing temps below 150C are unlikely to create any thermal damage on our bikes????
It was in the article that Philerooski suggested: http://www.ebikes.ca/learn/power-ratings.html

Long article; that quote was pretty far down.

I didn't come away thinking that temps below 150C would not cause any damage. Kinda like any mechanism, really: if you use it at all, there will be normal wear and tear.
 
(snip)...I didn't come away thinking that temps below 150C would not cause any damage. Kinda like any mechanism, really: if you use it at all, there will be normal wear and tear.

My opinion is that cool running can perpetuate a motor's lifespan indefinitely. This is a nominal 110VDC motor, the first mains-powered appliance motor ever marketed, whose original purpose for this example was likely to drive a sewing machine in a tailor shop.

Here it is run at very low power, about 10% of its rated voltage. 1887 original and unrestored,

I think the first ebike motor system was patented in the 1890s...and while this is not on-topic, the topic is life extension for our ebike motors of today.
Nothing lasts forever

(not a D cell, anyway, grin)

The lifespan of properly closely-fitted plain bearings, properly lubricated, run without dirt or water in the bearings, is nearly virtually forever.

The lifespan of ball bearings run clean with oil and not heavily loaded is also virtually forever.

The life of a motor winding depends on many variables, right? Yep.

There is thermal expansion stress, repeated countless times during its operating life, and that very thin layer of enamel or varnish that, if it fails at any one small spot where one turn crosses another, ends things.

Also, the higher the operating voltage design of a small motor, the finer is its magnet wire. And if hydrolysis, due to very high sustained operating temperature is acting as a slow, corrosive poison, the more certain it is that the wire will break somewhere and open circuit the motor.

I do not know if the hydrolysis mechanism (if it is even present) counts for much in the brief operating lifespan of an ebike motor. It may require thousands of hours to produce that effect. I have no experience or intuitive feel for hydrolysis failure and no actual case histories to refer to. Personally I have doubt hydrolysis, even if present, would harm your ebike motor in the bike's service lifetime.

Ten years ago, with my first ebike, a Currie with the outboard chain drive motor, I ran it overvolted, 36V instead of 24. Even with a healthy forced air ventilation of the little, brushed motor, it ran great and drove the bike at 25mph nearly, for....about 10 miles of a deliberate torture test. Then it suddenly fried.

The motor was about the same physical size as the little motor inside our Bafang cases, I suppose.

But the Currie failure is not indicative of what our Bafang hub motor can handle. Clearly, the Bafang, made in vast numbers, survives higher power outputs and passes away the resultant internal waste heat a lot better than that old Currie system, which was intended for only 15mph ebikes.

Does our Bafang and controller combination limit current if the motor temperature rises too high?

BTW, sidebar: that 1887 motor had accumulated many operating hours at full rated voltage, as evidenced by the deeply grooved (yet still very thick) commutator. The only "restoration" I did to the motor was to lathe level the commutator bar with a hand held blade, letting the motor run, cutting down the copper bars to get a flat working surface again. The laminated shim brass brushes were squared and trued. Why were the brushes made of such a relatively abrasive material then? Because graphite brushes were not yet invented. It was a few years more before graphite, still the brush standard today, was found to be the solution to the sole wear point of these early electric motors.
 
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My opinion is that cool running can perpetuate a motor's lifespan indefinitely. This is a nominal 110VDC motor, the first mains-powered appliance motor ever marketed, whose original purpose for this example was likely to drive a sewing machine in a tailor shop.

Here it is run at very low power, about 10% of its rated voltage. 1887 original and unrestored,

I think the first ebike motor system was patented in the 1890s...and while this is not on-topic, the topic is life extension for our ebike motors of today.
Nothing lasts forever

(not a D cell, anyway, grin)

The lifespan of properly closely-fitted plain bearings, properly lubricated, run without dirt or water in the bearings, is nearly virtually forever.

The lifespan of ball bearings run clean with oil and not heavily loaded is also virtually forever.

The life of a motor winding depends on many variables, right? Yep.

There is thermal expansion stress, repeated countless times during its operating life, and that very thin layer of enamel or varnish that, if it fails at any one small spot where one turn crosses another, ends things.

Also, the higher the operating voltage design of a small motor, the finer is its magnet wire. And if hydrolysis, due to very high sustained operating temperature is acting as a slow, corrosive poison, the more certain it is that the wire will break somewhere and open circuit the motor.

I do not know if the hydrolysis mechanism (if it is even present) counts for much in the brief operating lifespan of an ebike motor. It may require thousands of hours to produce that effect. I have no experience or intuitive feel for hydrolysis failure and no actual case histories to refer to. Personally I have doubt hydrolysis, even if present, would harm your ebike motor in the bike's service lifetime.

Ten years ago, with my first ebike, a Currie with the outboard chain drive motor, I ran it overvolted, 36V instead of 24. Even with a healthy forced air ventilation of the little, brushed motor, it ran great and drove the bike at 25mph nearly, for....about 10 miles of a deliberate torture test. Then it suddenly fried.

The motor was about the same physical size as the little motor inside our Bafang cases, I suppose.

But the Currie failure is not indicative of what our Bafang hub motor can handle. Clearly, the Bafang, made in vast numbers, survives higher power outputs and passes away the resultant internal waste heat a lot better than that old Currie system, which was intended for only 15mph ebikes.

Does our Bafang and controller combination limit current if the motor temperature rises too high?

BTW, sidebar: that 1887 motor had accumulated many operating hours at full rated voltage, as evidenced by the deeply grooved (yet still very thick) commutator. The only "restoration" I did to the motor was to lathe level the commutator bar with a hand held blade, letting the motor run, cutting down the copper bars to get a flat working surface again. The laminated shim brass brushes were squared and trued. Why were the brushes made of such a relatively abrasive material then? Because graphite brushes were not yet invented. It was a few years more before graphite, still the brush standard today, was found to be the solution to the sole wear point of these early electric motors.
Reid, that motor is built like a Russian dump truck! Do you think our motors are equally over-engineered? (Which is not a bad thing BTW.)
 
Reid, that motor is built like a Russian dump truck! Do you think our motors are equally over-engineered? (Which is not a bad thing BTW.)

Opinion piece:


Our motors today are better than ever. I have a worn-out roof ventilator fan, got it from Grainger in 1984. It ventilated the garage for over 25 years, on virtually 24/7. A G.E. sleeve bearing motor with ports to squirt the occasional oiling. Over twenty-five years on a vertical shaft mounted, capacitor start, about 1/3HP motor. So simple and it would have lasted longer if I had not neglected the oiling for its last several years of operation. Sleeve bearings lasted almost 25 years! There is no wear-out to well-fitted, well-oiled plain bearings run in clean conditions within their proper load rating. And lightly loaded ball bearings may be said to be even more long lasting. They simply won't wear out, ever

Electric motors run unstressed really do last about forever. And it's not just electric motors, but any machinery we look after and do not run at or near its limits, can last and last. Ask any trucker how far his engine goes? Or any (for example) Toyota product user!

We really have a "right" to expect our ebike components to last as long as the bike frame. These are still the early years of the industry. The Bafang motors we have in our CCS bikes are pretty good and getting better by shear numbers. The maker sees no end to his growing market; the maker has no interest in making a short-lived motor. The motors we have, built to a very thin profit margin, no doubt, are still pretty good, overall! And some are more lucky individuals than others. Some will outlast their owners, 10,000 miles or more. It is the nature of highly complex assemblies, that the weakest point of lack of perfect tolerance control (for example, a ball bearing inadvertantly a too-loose OD fit in its carrier) or planetary gear centers not quite equally alike between the three, and so forth...) may make my bike's Bafang quieter-running than yours (mine is silent in most of its engagements and if it is not, I shut off the power for a moment by coasting, then hit it again to get the sweet, silent running engagement). Or your relatively noisy Bafang may long outlast mine.

More perfect quality control will come from Bafang in years to come. A thousandth of an inch may make a huge difference in the noise of a motor. But in time, I predict that our bike motors, even if they were not to advance in design one little bit, will become longer lasting or more reliable, because Bafang needs to distinguish itself by ever-better QC, while keeping prices level to prevent competitors from usurping their primacy.

And as for microscopically-small working clearances making the make-or-break difference? That 1887 motor I sold years ago still had virtually zero-shake in its bearings, less than .001" clearance, despite the many hours it had run. In plain bearings, a very small oil clearance, only, of about .001" per inch of shaft diameter, is vital. Or the bearing will wear out rapidly.

In pianos (am a piano technician/tuner) the pivoting parts, called flanges, are of woolen felt bushings carrying brass pivot pins called center pins. They are very precisely fitted, all by hand and within an ideal working clearance range of plus or minus one ten thousanth of an inch. Their fitting is done by hand, by feel, and it is a very simple and sure thing to fit the finest, smallest machine parts by hand. Watchmakers traditionally do (another childhood hobby I never fully mastered) work to amazingly small tolerances by feel and by sight and sound.

Machines at basis are so very simple.

A complex or simple machine's interfacing materials: steel, plastic bearings or metal or composite material, the polish and hardness of pivots and precision fit of gear interfaces, and so forth, correctly engineered and assembled and of good chemical stability and not degraded by time or environment, and the assemblage not abused, overstressed in service, generally will outlast ourselves!

Failures are always due to human error in assembly, in maintenance, or in engineering, in misapplication, and not because of any undefinable, intrinsic fault of the devices, ever.

None of our motors or machinery are overengineered in this era of great engineering. Overengineering was seen in the early years of this century, for instance in some of the luxury brand automobiles. Overengineering may be harmless, as in gilding a lilly, or it may be harmful, for instance as was the early quality automobile makers' unwise penchant for cast aluminum four-point motor mount crankcases bolted fast to (twisty) ladder frame rails.

Anything Bafang (for instance) does to cheapen, simplify, the present hub motor, will probably also make it better. They have no reason to degrade the product to try to make it fail early. It has to outlive the warranty period. And to do that, it has to be made at basis to last indefinitely.

Water ingress through the hollow axle bearing the electrical cable is something we as users need to pay mind to, in my opinion.
How would one prevent water wicking into the motor, besides by avoiding axle-deep immersion? The plastic shield cap...is your motor's axle cover cap well fitted and will it prevent water from finding its way into the open end of the axle? Water gets into motors a great deal easier than it can ever get out of a totally enclosed motor, folks...
 
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Well, this week I have given the CCS a pretty decent heat stress test. 2 days ago my commute home was with ambient temp at 100F, and a slight ~5 mph headwind, near the end of my ride and my usual climb over 3-4 miles had my controller temps at ~70C.
Today was much worse, ambient temp was at 96F, but headwind was 15-20 mph, which slowed me down a good bit needless to say. Slower speeds are less efficient for the motor causing more energy to be wasted as heat. Knowing this, I did my best to maintain speed during the climb, stayed in level 3 assist with speeds ranging from 16-24 mph during the climb. Controller temp topped out at 72C, which surprised me, I was figuring on it get higher based on Tuesday.
Seems the ability to shed heat is good enough to meet the needs of most situations. I am sure steeper hills would make this test more dramatic, but I'm not really interested in doing so.
I will say once again, I never would have considered riding home in those conditions on my road bike, the CCS makes it possible to commute even when I perhaps shouldn't.
 
All great and wonderful information BUT for a MAC geared hub motor for instance, what is the highest core temperature I can have for 24 hours straight without any degradation to any of the motor components? Being a scientist/engineer, I want a specific number instead of a range :). If a specific number isn't feasible, what is the component within the MAC motor that will be damaged by the lowest long term/steady state temperature and I'll buy the component, find an oven and experimentally find the answer myself. Don't mean to be a smart ass...I just want to find the answer. Thank You for any help/suggestions.
 
All great and wonderful information BUT for a MAC geared hub motor for instance, what is the highest core temperature I can have for 24 hours straight without any degradation to any of the motor components? Being a scientist/engineer, I want a specific number instead of a range :). If a specific number isn't feasible, what is the component within the MAC motor that will be damaged by the lowest long term/steady state temperature and I'll buy the component, find an oven and experimentally find the answer myself. Don't mean to be a smart ass...I just want to find the answer. Thank You for any help/suggestions.
24 hours straight? Sounds like a non-bicycling application to me. Who is going to ride an ebike for 24 hours, much less in that kind of heat? I guess there is some probability, so close to zero that I'm willing to overlook it. :eek:

Seriously, I doubt that anyone has tested it, because why would they? But if you do, please come back with your results.
 
Just hypothetical on the 24 hours...wanted to fully express that I meant long term and not transient temperatures :) .
 
I found some data courtesy of Justin at Grin Technologies and he ran a MAC motor on his dyno at 150C without any signs of degradation. The problem I see is that as the motor temperature increases, there is the potential for thermal runaway...so if you can monitor your motor temps, I'd probably stick to something around 140C or less. I have my Cycle Analyst set to roll back the power if my motor gets to 140C and I have it set to shut down the motor if I reach 150C. Hope this info helps someone :).
 
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