Hub motor internal temperature protection

[Alan B]

The thermistor I have been looking at:

Vishay NTCLG100E2103JB

-40 to 200C
small glass encapsulated axial 2mm by 4mm

10K ohms at 25C
1256 ohms at 80C
339 ohms at 125C
145 ohms at 160C
95 ohms at 180C
64 ohms at 200C

There are other resistance values of this part, perhaps a higher value should be chosen. They to up to 220K at 25C.

These are 35 cents each in 10 quantity at Digikey. If folks agree that this is a good choice perhaps I should get a bunch and make them available in small quantity. It is easy to get these if you order stuff from Digikey, but the minimum order etc makes it less practical for folks who want just a couple of them.

[Hyena]

Alan if you do what I suggested and measure the voltage drop across the hall line you don't need to run any additional wires outside the hub.
I spent nearly 2 hrs yesterday going through different spec sheets trying to find the right thermistor and as yet haven't found one so I suspect I might have to do a bit of trial and error.

The one you posted is a NTC type - or negative temperature coefficient. The resistance starts out high and drops as the temperature rises. If you're using an external circuit to translate this into a temperature reading then that is fine, but if you want to drop the voltage in the manner I'm suggesting you need a PTC type - positive temperature coefficient that increases resistance with temperature. Aside from that the resistance is too high.

Most list the resistance at 25C but what you need to know is the resistance at just over 100C - because IMO that's when you want it to give you the warning.
As I said previously, 100 ohms will drop the hall voltage about 0.5v, enough to easily measure but not enough to stop the sensor working.
I reckon this is the best way to go - you'll get an audible warning at what ever voltage you nominate (determined by the type of thermistor you use) and then if you ignore it and the temperature keeps rising then eventually the resistance will rise enough to cause a voltage drop that will cause a hard cut to the hall line.

So yeah, lets hunt for a PTC thermistor that generates 100 ohms at 100 degrees or there abouts. Or even less - 60 ohms would probably go and we can run 2 in series. Given how they are typically quite non-linear in how the resistance increases we probably need one rated quite low at 25C (which is how they seem to be named) - maybe around 10 ohms ?

[full-throttle]

What he's saying is: the Halls consume 1mA (just for example) normally, when the thermal switch trips it could add a resistor across the power rail adding another 1mA. All you'd need to do then is to make a circuit on the controller's side to measure this current and react to the change.

[icecube57]

How come we cant use a thermal breaker like the ones used in nicad packs to just kill the whole 5v. It would break the connection and kill power to to the motor and to restore power would require the motor to cool down. Having a breaker thats around 120C-150c. This would leave the bike dead in the water but by you pulling the signal down with the resistor it seemed kinda harsh and abrupt .... have u rode with this implementation yet?

or better yet just have 2 small wires going going into the axle and use a thermresistor in or near the windings and wire that inline with the return voltage of the throttle. As it warms up ang gets critical it will increase in resistance to bring the throttle voltage down by a small amount to limit speed and in a round about way limit current giving the motor some im to cool. That way you arent left dead in the water and still have power to get some where to let the motor cool down.

[Alan B]

I selected the above thermistor earlier, it is not for your technique but instead for measurement as you suspected.

I have one question on your approach Hyena. If you connect the thermistor inside the motor in series with the power lead to the hall sensors, where can you measure the voltage at the node? The node you want to measure is inside the motor, no wires from that node leave the motor. The regulated 5V line coming from the controller should not be affected by this thermistor, it is a regulated voltage. In any case it would differ between controllers. You could measure the signal voltage coming back from the hall devices as his is a function of the node voltage, that is an interesting approach but would require the use of a peak reading meter as the hall signals are switching. Is this what you meant?

The next challenge is to find a thermistor that meets your other requirements and is small, cheap and works up to 200 degrees C.

[John in CR]

Hyena,

I'm in a different situation with unknown temp sensors already in the motor with wiring for the sensor coming out with the wiring harness. I need to figure out how to take advantage of it.

I like the idea of containing it in the motor due to lack of space on the route out. My only issue with it is that the motor will cool far quicker in low load use than sitting in the off position. I've always worried about roasting the mags and wiring by stopping, and now I always include a good half mile of easy riding at the end of any aggressive rides.

John

[itchynackers]

This is what I was planning on using... http://dkc3.digikey.com/PDF/US2011/P2225.pdf but I haven't installed it yet for reasons mentioned above. I believe it is better to coast or use low power rather than stop. I have found that after stopping, the internal motor temp rises for about 2 minutes, then slowly decreases.

[Hyena]

What he's saying is: the Halls consume 1mA (just for example) normally, when the thermal switch trips it could add a resistor across the power rail adding another 1mA.

OK that's a good option, that way I can simply switch in a known resistance when things get hot rather than trying to find an exact thermistor with the resistance I need. Although being able to watch the voltage drop by using the thermistors increasing resistance would be a good warning that things are creeping up.

How come we cant use a thermal breaker like the ones used in nicad packs to just kill the whole 5v. It would break the connection and kill power to to the motor and to restore power would require the motor to cool down.

This is what I suggested initially but it does cause a harsh cut off - if I you just pull down the hall voltage a little without cutting it out all together you can run a warning buzzer from this.

Having a breaker thats around 120C-150c. This would leave the bike dead in the water but by you pulling the signal down with the resistor it seemed kinda harsh and abrupt .... have u rode with this implementation yet?

Having a breaker yank the 5v line should result in exactly the same result as dropping the voltage down (or not having the hall plug connected at all for that matter)
I haven't ridden with it, only bench tested. But it should work fine.

If you connect the thermistor inside the motor in series with the power lead to the hall sensors, where can you measure the voltage at the node? The node you want to measure is inside the motor, no wires from that node leave the motor. The regulated 5V line coming from the controller should not be affected by this thermistor, it is a regulated voltage.

During my tests (video in first post) I was measuring the voltage drop at the 5v connector on the controller. I put it on cruise controlle so the motor was happily spinning on its own, then slowly increased the inline resistance in the +5v wire and the voltage dropped accordingly. So it can't be too regulated...
Adding the resistance 6" from the controller or 2 feet away inside the motor shouldn't make any difference.

Agreed, this will vary from controller to controller though.

I'm in a different situation with unknown temp sensors already in the motor with wiring for the sensor coming out with the wiring harness. I need to figure out how to take advantage of it.

Aren't those scooter motors the gift that keeps on giving
How many wires come off the temp sensor ? If they're a simple 2 wire thermistor you can connect a multimeter across the wires and see how the resistance varies and then use that to run a temp gauge circuit (or at the simplest learn what the resistance is when it's really hot and simply watch for that on the multimeter)

You're right though, riding slowly is better for cooling (especially with a drilled motor). On one one my bikes that does have an internal temp probe I notied the temp jumps a good 5 degrees when I get home and stop (on a hot day I threw a wet towel on it to cool it down and it sizzled and steamed!)

[amberwolf]

I came to the thread to suggest using the CA to limit power rather than cutting it off, but Hugues already has:

ideally:
i'd rather add an extra tiny wire, going to the CA, with a neat little display of the temp, with programmable treshold and alarm ? or why not, pulling down the amps automatically

i don't remember seeing much CA programming on the forum, is it possible at all ? there would be other things to add to that little box...

The code is not publicly available, AFAIK. At least one person has essentially made their own, though (heathyoung, with the "anal cyclist"). But Justin has stated that an in-progress version might have more inputs for things like thermal sensors and torque sensors, and whatnot (assuming it's not already done, or possibly partly available via the RC type CAs).

But yes, this is what I would want. Still, you can do a "thermally-scaled current-limit" even now if you like, by building an op-amp circuit that takes the thermal sensor analog output and scales it so you can then add it to the shunt voltage, and pass that on to the CA. This will result in incorrect A, Ah, and Wh readings, though, so an alternate method is proposed below it.

The positive shunt wire to the CA would be cut.
The first op-amp would read the thermal sensor, and possibly scale it (or use a second one to scale it). (variable scaling is needed because it is how you set how fast the thermal input begins to interfere with the normal operation of the system without compromising the actual current limiting you may already be using.)
Another op-amp would read the shunt voltage, simply buffering it.
Another would add the shunt voltage and the scaled thermal sensor voltage together.
The output of that would go to the CA on the positive shunt input wire.

The result of this is that as the temperature rises, the CA will read a higher current than is really there. The CA would be setup so that it can limit throttle input based on the current draw, so once the motor heats up to the point where even "normal" usage pushes it's reading over the limit, it'll throttle back to keep the current down so you don't keep pushing the motor too hard and destroy it.


Because the above method screws with the main purpose of the CA (keeping track of A/Ah/Wh), you could instead use the speedo input for this. It's just a bit more complicated to do the electronics for. Naturally, this sacrifices a different function--speed monitoring/distance.

Disconnect the CA speedo input from either the hall or the wheel sensor
Thermal sensor analog output goes to a variable scaling circuit (op-amp?) so you can alter the amount of effect the temperature has on the system, and how soon, without going into the CA settings all the time.
Scaling circuit goes into a voltage-to-frequency converter, which can probably made from the 555 timer. Basically you are emulating the "speed" of the wheel with the pulses from this.
The output of that is connected to the CA's speedo input.
Then set the CA for a maximum speed limit of whatever works for your scaling factors.

Bascially this will send pulses more often for higher temperatures, emulating a faster-spinning wheel. Once the pulses reach the specified rate, the CA will trim your throttle back to prevent further overheating. I don't know if this will work as well as doing it via the current-limiting, but it is at least an option.

You could probably OR the two signals together, so it can count wheel speed still, and can still limit actual system speed if you like, but it will not be accurate because it will be counting thermal sensor pulses, too.

[parabellum]

What if thermal breaker activates circuit that acts like blinker shutting off hall signal for short instant and restoring it for longer while, repeatedly doing that until temp breaker recovers on lower temp? Short 1 sec cutoff following by 10 sec normal operation or so.

[John in CR]

I'm in a different situation with unknown temp sensors already in the motor with wiring for the sensor coming out with the wiring harness. I need to figure out how to take advantage of it.

Aren't those scooter motors the gift that keeps on giving
How many wires come off the temp sensor ? If they're a simple 2 wire thermistor you can connect a multimeter across the wires and see how the resistance varies and then use that to run a temp gauge circuit (or at the simplest learn what the resistance is when it's really hot and simply watch for that on the multimeter)

The Fedex man dropped off a couple of more in the afternoon, so now I'm comfortable in hacking one up to see how light and compact it can be as a mid-drive. They're the quietest hubbies I've had, I guess due to almost no extra air space in there and small diameter. High efficiency, effective mountain climbing switch, compact, silent, only a 3:2 gear reduction needed for 50mph with a 26" wheel makes mid-drive regen a reality with no need for an $80 freewheel.

You're right though, riding slowly is better for cooling (especially with a drilled motor). On one one my bikes that does have an internal temp probe I notied the temp jumps a good 5 degrees when I get home and stop (on a hot day I threw a wet towel on it to cool it down and it sizzled and steamed!)

.

I don't have enough controller to get the ventilated motor hot, 10ga phase wires have become our choke point. Here's the hill profile of my son's favorite ride. He weighs 80lbs less and his bike 30lbs less, so our old reliable emoto hubbies work for him. My cargo bike wasn't happy at all hauling me up, but the new motor doesn't even blink switching to low speed for the steepest stuff. There's a pretty good curve at the 2km point, so it's hard to carry much speed attacking that steepest stretch at the 2.1km point that approaches 30% grade which eases up to only 14% for over 500m. It a real hubmotor test that few would pass and almost none that can both make the climb and do over 50mph in wheel.

Waterfall ride hill profile.JPG (20.3 KiB) Viewed 432 times

[John in CR]

I'm in a different situation with unknown temp sensors already in the motor with wiring for the sensor coming out with the wiring harness. I need to figure out how to take advantage of it.

Aren't those scooter motors the gift that keeps on giving
How many wires come off the temp sensor ? If they're a simple 2 wire thermistor you can connect a multimeter across the wires and see how the resistance varies and then use that to run a temp gauge circuit (or at the simplest learn what the resistance is when it's really hot and simply watch for that on the multimeter)

The Fedex man dropped off a couple of more in the afternoon, so now I'm comfortable in hacking one up to see how light and compact it can be as a mid-drive. They're the quietest hubbies I've had, I guess due to almost no extra air space in there and small diameter. High efficiency, effective mountain climbing switch, compact, silent, only a 3:2 gear reduction needed for 50mph with a 26" wheel makes mid-drive regen a reality with no need for an $80 freewheel.

You're right though, riding slowly is better for cooling (especially with a drilled motor). On one one my bikes that does have an internal temp probe I notied the temp jumps a good 5 degrees when I get home and stop (on a hot day I threw a wet towel on it to cool it down and it sizzled and steamed!)

.

I don't have enough controller to get the ventilated motor hot, 10ga phase wires have become our choke point. Here's the hill profile of my son's favorite ride. He weighs 80lbs less and his bike 30lbs less, so our old reliable emoto hubbies work for him. My cargo bike wasn't happy at all hauling me up, but the new motor doesn't even blink switching to low speed for the steepest stuff. There's a pretty good curve at the 2km point, so it's hard to carry much speed attacking that steepest stretch at the 2.1km point that approaches 30% grade which eases up to only 14% for over 500m. It a real hubmotor test that few would pass and almost none that can both make the climb and do over 50mph in wheel.

That last few hundred meters to the top is on foot btw.

Waterfall ride hill profile.JPG

[NickW]

Look at the manual for the CA. you can use the Vi pin on the CA pcb to do on the fly current limiting.

it talks about using a pot, but it shouldn't be too tough to rig something up to work with some resistors and your thermistor.

That won't screw with your speedometer or watt meters.

-Nick