Get bucked by shorting old hub motor?

maybe a short within the coil wouldn’t be too bad but between phases could lock up the motor

How to avoid that?

Well, first you got to locate the problem......So what is the problem exactly?

I’m fine just wondering if anyone has had experience w a shorting hub. It seems a hell of a risk especially on the front wheel. If a loose wire shorts to the stator or motor case and another later or w every tooth wound there’s the risk across coils. I’ve had it happen on a skate hub motor long ago and fell off. Then again maybe it’s not so bad on a bike. Even the magnet wire insulation has a rated life assuming best case scenario

I’ve tried it from full drag race to full short. Was a bit of a shock and a hard jolt but no crash

Hummina Shadeeba said:

How to avoid that?

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never use direct drive motors, only use motors that freewheel the wheel itself once the motor stops

that's the only way to "guarantee" this can't happen.


the problem you are describing is called plug braking, if you wnat to read up on circumstances and ways to employ it.


you could put fuses in the phase wires in each coil, on each tooth, so that any overcurrent from such a short would blow the fuse, limiting the length of time the short will affect the motor rotation to the length of time it takes the fuse to blow. the fuse would have to be sized, probably experimentally, so it would never blow from normal phase currents.

realistically, however, in a well-constructed motor that is not being abused beyond it's design limits of heat dissipation, or being corroded by exposure to weather/etc., the internals of the motor will never fail this way.

the problem could still happen in the controller fets, which will cause the same effective result, but again, in a well-designed and built controller that's not being abused beyond it's design limits, it's not going to fail like this.

the problem could still happen in the phase wires, anywhere between the motor windings and the controller fets, if they are parallel to each other within the same cable, and they get hot enough to melt the insulation. but sizing them so they don't get hot, or running them in completley separate cables that can't contact each other, will prevent this.

physical damage to the cables that allows them to short would stillc ause it, but again, running them as separate cables that couldn't contact each other in this situation would prevent this.

@larsb what kind of short was it and why didn’t your motor lock up? A short in the coil I don’t think would be a wheel-locking disaster but across from adjacent coils or in any way the phases touching while loose, and adding enough time, it seems an eventuality of a launch no? Surely the big car companies aren’t allowing magnet wire of different phases to touch or have any risk of shorting to the case or stator.

Controller fets blew completely, so the phases were shorted. Didn’t lock up the rear wheel as we were two on the bike :wink:

amberwolf said:

Hummina Shadeeba said:

How to avoid that?

Click to expand...

realistically, however, in a well-constructed motor that is not being abused beyond it's design limits of heat dissipation, or being corroded by exposure to weather/etc., the internals of the motor will never fail this way.

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the enamel is for sure going to fail eventually. The magnet wire rated temp is for 20,000 hours at the rated temp and only that. If u go above that temp or with rapid temp changes as often happens the enamel will deteriorate faster. It’s assured to fail eventually even in best case scenario. Motors wound with a coil on every tooth as typical..the voltage across the touching coils, which is often across phases, would be the highest voltage I think and most likely to break down first.
The lrk winding at least would eliminate the chance of shorting across teeth.

You make a great point on the front motor aspect and loose wire.
I have a front 9C generic, and I got a loop of wire straying 8" out and zip tied. I notice that when I lock up at a bike rack, I have to be ultra careful so the wires dont snag. Already came close with the wire bundle catching and almost ripping out some of the pins in the harness. But if I were to not be lazy, zip tie them to the fork better, I would still have to be careful at bike racks to lock up.

I shorted phase wires trying to figure out the sensored combo, blew the controller. I was using alligator clips that were like 14-16awg wires and they melted instantly and blew something inside the controller, probably a fet, high side or low side. I did find which one, but it was a Lyen. At the time just replaced with a Greentime, or ebay generic.

Always better to have a rear hub motor, always better to have nice neat wire routing.

Hummina Shadeeba said:

I’m fine just wondering if anyone has had experience w a shorting hub. It seems a hell of a risk especially on the front wheel. If a loose wire shorts to the stator or motor case and another later or w every tooth wound there’s the risk across coils. I’ve had it happen on a skate hub motor long ago and fell off. Then again maybe it’s not so bad on a bike. Even the magnet wire insulation has a rated life assuming best case scenario

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I was more so thinking of shorting inside the motor after thousands of hours of hard use from deteriorating magnet wire insulation or maybe internal abrasion from vibration between adjacent coils. the LRK winding with every other tooth being wound seems a much safer winding for a hub, and then as long as the stator is fully insulated and the phases are well insulated from the case, then at worst the magnet wire finally breaking down would amount to a short within a coil at worst and i think much less dangerous


depends on your motor but in my experience i can get way more wire on doing lrk and its also much easier to wind as you don't have to worry about leaving room for the adjacent coils, and lrk also has a higher winding factor
(these are just pics off the web and don't have any of my own on hand)

The LRK has so much higher endturn copper that all benefits get lost due to increased resistance losses. I have some links in my revolt winding thread showing this.

It will be good for really long stators though.

O yea these are all thin hub motors in bikes. It is a lot of endturn sticking out. I’ve been flattening it with a press to fit the motor case.

Hummina Shadeeba said:

O yea these are all thin hub motors in bikes. It is a lot of endturn sticking out. I’ve been flattening it with a press to fit the motor case.

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that's a great way to cause exactly what you're talking about--damage to the insulation of the windings, eventually potentially causing exactly the problem you are expecting.

so if it does happen to you with one of these, it's probably because of the press.

I only press the lrk winding so no between phase shorting possible as the pressed endturns are a single coil but it could be more likely to short between coils from being deformed and I wonder. Looking at the wire I use it is tested to 30% elongation with no cracks in the insulation at least, but that’s a stretch not crush test and not the same. I vacuum in an insulating epoxy resin after being wound and what that does for insulation I don’t know either and strangely neither does the manufacturer

I’ll press a bunch, cut it, and look at it with a microscope to see how much the insulation is deformed and thinned

Talked to msw wire and happy to discover they add the enamel before shaping a lot of the wire. I explained in detail how I’d like to compress many end turns on the stator that stuck out maybe 4.5mm down to maybe 3mm and he called it “child’s play” compared to the shaping they do. If u had the ability u could shape off-the-shelf wire to match the stator for great copper fill. Maybe press it into the slot

They sell 240c rated stuff at reasonable quantities.

The enamel layers (single, double..) don’t have an effect on the rating

You would prefer a squared wire for motor winding wire to stuff more copper into the motor?
Interesting.

Thats been talked about here on ES.
edit - well it was easy for me to find, and I suck at using search terms.
https://endless-sphere.com/forums/viewtopic.php?f=30&t=102934&p=1505953&hilit=square+round+wire+winding#p1505953

compared to the shaping they do. If u had the ability u could shape off-the-shelf wire to match the stator for great copper fill. Maybe press it into the slot

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Square wire is very expensive in any size smaller than 15 awg. I’ve used it and in a size 17 or 16 awg it would twist when winding amounting to worse fill, at least for me.

I was thinking maybe you could press round the wire into the slot while winding.

In my experience winding LRK, winding every other tooth, gets more copper in. The end turns are a bit fatter and that’s a slight loss but with a long motor especially it’s not much and LRK has a higher winding factor.

Is a wet throttle more common failure?

The fuses in the phase wires sound like a simple fix. What amp would a person need? Say if you had a 20 amp controller.

How much resistance do fuses add? Phase wire amps can be much more than the battery

Any more insight here. I run rear hubs so less risk. But other people/friends ride my bikes.
One question, will my cutout switches on the brakes still cut power to the motor if this happens?

they can't.

if the motor is shorted, it's shorted.

nothing other than removing the short would unshort it.

if the short is internal to the motor, yo'ud ahve to open the motor to remove the short.

if the short is external to the motor, you'd have to disconnect whatever is shorted from the motor to remove the short.

Ooh Thanks Amberwolf. That makes sense. What size/type fuse would i start with on 20 amp controller? Or circuit breaker?

I don’t know but for sure it’ll need higher than 20 amps as the esc will transform the battery output to higher amps. What esc and settings on it?

A single phase short will work as a serious regenerative brake as the voltage generated in that phase will be shorted with only the wire resistance as current limiting factor. A motor with internal gearing that allows freewheeling is indeed the safest way to prevent injuries. I have seen a hub motor that got damaged with water penetration. When I pulled it apart, 2 of the magnets where loose and stick to the rotor. If they would become loose during riding, it will block the wheel as well.