Temperature inside hub motors - choosing a thermal fuse

miuan

10 kW
Joined
Nov 26, 2009
Messages
992
Location
Slovakia
So I cracked my motors open the other day to replace broken halls. I saw the rear BPM was a bit roasty so decided to install a 105C temp cutoff switch inline with hall supply. I did the same on the front GM mini and epoxied the switch to the windings to have a direct contact for quicker operation. Went for a run yesterday but soon it turned out the 105C switch blew too easily.. it took a short (1km) ascent on the GM mini only (rear not connected yet) at 20mph. long story short I got home no problem, but it took the switch too long to close again so I had to pedal for quite a while on my own.
For me it's surprising I can reach 105 degrees on a regular flattish commute so fast. The motor case was barely hand warm at that point. Now I understand why the BPM windings were so toasty.. I must have got it to 150deg regularly since the case got quite hot at times riding at 30-40mph.
So I'm back shopping for some higher temp swithes. Which temp should they take without damage? 130 or 150 degrees?
 
Why not use a bbq thermometer as described quite a bit in the forum. That was you can monitor temps and back off a bit rather than just getting all power cut off. Yes it's a bit of stuffing around and you have to get two very thin wires through the axle but I reckon it's worth it. Make the wires long enough and mount the display part of the thermometer on your handlebars.

I toasted my MAC doing the same sort of thing- too many volts and amps and it got burnt. Now I have the BBQ thermometer and oil cooling and it's great. Runs on 2kw no problems.

If you do stick to the thermal switch, I personally wouldn't want to go any higher than 105 C anyway. Magnets start to weaken permanently even at those sort of temperatures apparently.
 
Thanks, I have considered that but in all honesty, both oil/air cooling and temp sensor wiring have been beyond my modest ability so far. This switch is a very simple last resort measure to protect the motors from permanent damage. Since I run two motors, they should not get too hot unless I only run the mini front motor like I did yesterday. The question is, how hot may the windings get without risk of damage to them or the gears. The magnet ring was only hand warm to touch, so I guess it must have been much cooler than the windings.
 
If you can change the halls on your own you can definitely install a temp sensor. Just hit up ikea for a bbq temp sensor (3.99), rip of the metal probe end and that's all you need. Get some thermal paste, slap the sensor on the windings, and you're done. It shouldn't take you longer than 10 minutes. :)
 
I like rc onboard temp sensors best because of how small and light-weight the display is. You want it light so you can just sticky it to your handlebars rather than having to devise some kind of wacky mounting apparatus.
TG3: $16 at amazon.com
http://www.amazon.com/Moores-Ideal-Products-On-Board-Gauge/dp/B0006NAMUE
314Un5qFfFL._SL500_AA300_.jpg
 
i have some 115o temp switches for the charger hacks. you could mount it on the stator where the halls sensor power lead is tied down with the zip tie. put it in the red power lead, see if that works. lemme know if you want one.
 
Move the thermistor switch to the stator steel near the windings instead of attached directly to the windings. That's where the motor factory installs the thermistor on the high efficiency hubbies I use. They use a 95°C trigger temp, but these motors have a lot more steel and the thermistor is at least 1cm from the windings. That way the short spikes in winding temps don't trigger the switch and it's better tied to the stator temp as a whole.
 
John in CR said:
That way the short spikes in winding temps don't trigger the switch and it's better tied to the stator temp as a whole.

Thanks John, this is exactly what I've been after.
 
miuan said:
John in CR said:
That way the short spikes in winding temps don't trigger the switch and it's better tied to the stator temp as a whole.

Thanks John, this is exactly what I've been after.

Plus just moving it a little is the easiest change. Take some pics, and if possible measure the motor itself while you have it open. Stator diameter and width...thickness of wire bundle for the phases. If you pull it all the way open, the sun gear and ring gear tooth counts, and pics of those planetary gears. I have some ideas for BPMs.

Also, I have some cooling ideas for geared hubbies. Temp cutoff is protection, but getting rid of heat faster is a motor improvement. As long as you don't ride on the beach or on salty snowy roads it's easy.

John
 
John in CR said:
Also, I have some cooling ideas for geared hubbies. Temp cutoff is protection, but getting rid of heat faster is a motor improvement. As long as you don't ride on the beach or on salty snowy roads it's easy.

John

Yeeeeessssss??????? Spill it John..... :wink:
 
John in CR said:
Take some pics, and if possible measure the motor itself while you have it open. Stator diameter and width...thickness of wire bundle for the phases. If you pull it all the way open, the sun gear and ring gear tooth counts, and pics of those planetary gears. I have some ideas for BPMs.

First off, the BPM2's side cover was a bitch to undo, as was the DNP freewheel. The change from bolts to threaded covers plain sucks. It may work fine for the 250W motors, but the BPM has much more thread to undo, and the thread is farther from centre, requiring at least twice the torque to manage.

There was a guy at pedelecs forum who had the SWXK5/BPM2 tool for 20 quid, but the forum mods failed to allow my membership within a week or so. Being unable to contact him, I ordered this one for 50 euro.

http://www.ebike-solutions.de/de/Shop/Motoren/Motorenwerkzeuge/Werkzeug-zum-Oeffnen-von-Bafang-SWXK-Motoren

As turned out later, it still needed some angle grinder love to work with BPM2. Nothing serious but I live in an appartment, the grinder is scary noisy - and it was already 8pm :)

The four grooves in cover are providing some grip, but unless I secured the tool with two carpenter clamps, it kept slipping off, rounding the grooves and making the grip even worse. So my advice is DO YOUR BEST to keep the sucker inserted as deep as possible in the grooves.

The cover required about 20 hammer strokes at the tool crank end to break loose. After about 15 strokes it began to give a tiny bit, so out of desperation I feared all the crap cast aluminium thing was fainting .... it wasn't fortunately.

Inside, the gears were well greased, but the grease went deep black as expected. I did no measurements, but immediately noticed the stator had substantial width. I'd say the lams had at least 18mm, similar as the new eZee claims to have.

All bearings were smooth to touch, no damage at first sight. However the hub had some play when built in the wheel. As with my MAC, the clutch likes to seize occasionally at high torque, then break free again after 1-2km.

So far no more impressions. Gonna open it again soon as there is something rubbing inside.. probably my fault. I'll make some pics if memory allows.


John in CR said:
Also, I have some cooling ideas for geared hubbies. Temp cutoff is protection, but getting rid of heat faster is a motor improvement. As long as you don't ride on the beach or on salty snowy roads it's easy.

The gears need dust free environment as they roll on a blobful of grease. Even in my sealed motor, the grease had become black pretty soon. Are you able to seal the geared part of motor while leaving the motor vented?
 
parajared said:
I like rc onboard temp sensors best because of how small and light-weight the display is. You want it light so you can just sticky it to your handlebars rather than having to devise some kind of wacky mounting apparatus.
TG3: $16 at amazon.com
http://www.amazon.com/Moores-Ideal-Products-On-Board-Gauge/dp/B0006NAMUE
314Un5qFfFL._SL500_AA300_.jpg
Does anyone know how high these go in the temp range?
I want to mount a temp gauge on the cylinder head of my air cooled motorcycle.
 
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