What about a K-type thermometer?

[Eclectic]

So I bought one of these K-type thermometers:

http://www.ebay.com/itm/251531789729?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I pushed the tip of the thermocouple in the hole in the axle next to the phase wires; zip-tied the wire along the phase wires and mounted the meter on the top tube. The probe wire is a little short but I made it work. My question is…Is this a valid way to get real-time temperature readings. I know I’m just getting axle temperature and it would be much better to have a sensor on the stator into a CA v3 but this was a lot less time and money.
I have some other questions about the results but my first question is can I trust what I’m reading?

P.S. Only the tip above the heat shrink (on the probe) is in the axle.

 

[MadRhino]

It haws to be as close as possible to the copper windings, there is the critical temp that you want to monitor.

 

[teklektik]

I use axle temp monitoring with my V3. I positioned the thermistor deep into the axle to avoid the heat loss/temp drop of the dropout and sidecover.

Works quite well for slow heat buildup from simple overvolting - monitored temp increases lag throttle increases by about a minute. Works best with smaller diameter stators.
See topic: Motor Temperature Monitoring via Axle.

 

[John in CR]

People on ES typically put their probes too close to the copper to get an accurate reading of the motor temperature. The factories put them on the stator steel about 1cm from the copper to smooth out the short spikes in temp that the copper can see before the stator steel gets hot and can't quickly sink heat away.

Yes the axle temp can give you temp information, but the heat is pretty slow getting there, so it would only be useful in continuous operation, not the dangerous stuff for motors while is lots of accelerations from low speed and/or riding hard which can ruin a motor in 10's of seconds. It would be useful to learn the conditions that heat the motor up, but I have little doubt that I could take teklektik's rig to a steep enough hill and burn his motor up before his temperature sensor had time to tell the controller to shut down. I probably works great for his use though, but would definitely recommend no weakening the solid side of and axle in such a manner, since axles are one of the weak links of hubmotors. Guys great at the electrical side of things do mechanical stuff that floors me sometimes.

As an item of interest regarding axle temps, I have 20mm wide steel dropouts that clamp to the motor axle, and at the end of a ride my internal temp probe reported 75°C at the stator laminations, and my IR thermometer showed the exposed axle to have a 10°C higher temp on the motor side of the dropout compared to the axle end. I forget the axle temps, but they wouldn't be comparable between rigs, so to avoid misleading I wouldn't post it anyway. That 10°C difference on the axle surface only an inch or so apart really surprised me.

 

[teklektik]

...but I have little doubt that I could take teklektik's rig to a steep enough hill and burn his motor up before his temperature sensor had time to tell the controller to shut down.

Gosh - why didn't I think of that?
I guess I must have put the link to the explanatory thread just for looks...

• CAVEAT:This is NOT an effective technique for general motor temp monitoring for obvious reasons, but it seems to work for moderate powered builds where the primary heat difficulty is slower heat buildup from prolonged higher wattage running. The approach responds too slowly to effectively monitor sharp temp increases from suddenly dumping megawatts of waste heat either from low rpm loading (steep hill climb) or from a high powered motor/controller. Certain riding styles can reasonably push any motor to a sharp temp increase that can cause damage before this approach would detect the temp increase. 'Nuff said.

...but would definitely recommend no weakening the solid side of and axle in such a manner, since axles are one of the weak links of hubmotors. Guys great at the electrical side of things do mechanical stuff that floors me sometimes.

As for weakening the axle - it's a 3mm hole in a 14mm outer shaft - far smaller than the wire bore on the other side that somehow manages to withstand the 1600W this tiny motor consumes. Sometimes the opinions that are given without bothering to examine links and the actual details of the build floor me sometimes...

... my IR thermometer showed the exposed axle to have a 10°C higher temp on the motor side of the dropout compared to the axle end.
... That 10°C difference on the axle surface only an inch or so apart really surprised me.

Unsurprising behavior - heat is conducted from the stator down the axle and into the sidecover and dropout - hence placing the thermistor in the motor side of the axle under the stator instead of at the axle end -- as mentioned above and in the linked thread.

I positioned the thermistor deep into the axle to avoid the heat loss/temp drop of the dropout and sidecover.

 

[John in CR]

...but would definitely recommend no weakening the solid side of and axle in such a manner, since axles are one of the weak links of hubmotors. Guys great at the electrical side of things do mechanical stuff that floors me sometimes.

As for weakening the axle - it's a 3mm hole in a 14mm outer shaft - far smaller than the wire bore on the other side that somehow manages to withstand the 1600W this tiny motor consumes. Sometimes the opinions that are given without bothering to examine links and the actual details of the build floor me sometimes...

By that logic you could drill out the solid side axle with the same size hole as the wire side, a very bad idea. You weakened the axle, period. FWIW where it matters, no it's not a 14mm shaft. It's more like a 10x14mm flat bar often made of questionable steel. It may work great for you, it's just not the kind of thing to recommend to others.

Plus it's unnecessary anyway, because you're still looking at a temperature change. Installing it deep only results in a higher temperature. The temperature near the axle end can be just as useful, and if that wasn't true, then your deep inside the axle measurement wouldn't be useful either.

 

[teklektik]

By that logic you could drill out the solid side axle with the same size hole as the wire side, a very bad idea.

You weakened the axle, period. FWIW where it matters, no it's not a 14mm shaft. It's more like a 10x14mm flat bar often made of questionable steel. It may work great for you, it's just not the kind of thing to recommend to others.

I think we all have a clear idea of the shape of an axle (!) - no one said it wasn't weakened - you seem to be trying to force an argument where there is none. Whatever logic you wish to apply, remarks about boring the axle to the same as the wire side is your idea not mine. Twisting statements to be able to argue from the extreme is a cheap trick and you are just barking at the wind.

This is a matter of degree and effect. This same size shaft is used successfully for multi-kW motors. In this case it's a sub-2kW motor and the supposition is that a small effective reduction in end-shaft cross-section is harmless due the strength headroom that allows the same shaft to be used in motors with substantially greater power and weight. Here the dimensions of the axle are bound by the de facto standard of dropout size and shaft diameter - not by a motor-specific design criteria. Overvolt a massive motor and you will twist an unmodified axle as it come from the factory. It's foolish to let (inapplicable) extreme situations preclude modifications to the component in cases where the motor cannot hope to generate such failure conditions.

As for recommending it - it would be useful if you had actually read the thread which simply relates the build experience and results. The closest thing in the thread to a recommendation limits the utility to "small diameter" "low to moderate" powered motors.

Plus it's unnecessary anyway, because you're still looking at a temperature change. Installing it deep only results in a higher temperature. The temperature near the axle end can be just as useful, and if that wasn't true, then your deep inside the axle measurement wouldn't be useful either.

Quite the contrary - the criteria for effective use of the CA is not merely that there is some temperature change, but that the temperature changes and reaches something close to equilibrium quickly. Further, it needs to be reasonably immune to environmental factors such as air speed and ambient temperature.

Your end-axle monitoring approach generally fails to meet both these requirements.

• There is the matter of propagation time of the heat through the axle and past the sidecover/dropout which even you have noted have a heatsink effect. The more thermal mass and heatsink effect, the longer the temperature will take to reach equilibrium and the longer it will take for a meaningful temperature measurement to become available. The difference in responsiveness of end vs mid axle monitoring is clear.
  
  In addition, the sidecover/dropout are exposed to moving air and the resulting differences in heat dissipation due to speed and ambient temperatures are clearly different that those in the interior of the motor. In a situation where the V3 must be configured a priori for specific operating limits, introducing variable environmental factors would make the entire monitoring approach unworkable without constant adjustments and tuning.

You sure have gotten your knickers in a twist about a thread relating experiences with what is clearly stated as an experiment - and a successful one at that. If you don't want to do this - don't. Easy peasy...

 

[Eclectic]

OK I'm back. Let me ask this. Is this method good enough for what I'm am trying to find out. I am wondering if on my commute if I run WOT most of the time, am I causing any problems? When I get to the top of one of my very long hills, does everything seem to be ok? I only have a 9 FET Lyen controller and an 800W motor on 12S LiPo. I am not too concerned with the lag time and losing all the small detail, just a good idea if I am doing something bad.

 

[teklektik]

I am not too concerned with the lag time and losing all the small detail, just a good idea if I am doing something bad.

Ya - sorry about the digression.... I posted the link to the axle monitoring thread above so you could see some of the discussion there and follow a link or two to other threads where axle monitoring has been used with varying success. This is a situation-dependent question with no clear answer, so reading some of the anecdotal evidence may be helpful.

Your temp probe is a good device, fast response and broad range, but the measurement point and environment are working against you. I have a similar unit - very handy to answer lots of temp questions....

Anyhow, in spite of the variables, you do have the advantage of primarily being concerned about a commute so you have repeating trip characteristics. You might use your probe to measure the highest temp during your commute and then stop at that point on a subsequent trip and do the hand-on-the-motor test to get a workable seat-of-the-pants indication of whether you are flogging your build too hard. Here you are not asking your probe to tell you an exact temperature, just to tell you with good certainty where things are the worst - then you resort to a subjective or measured case temperature assessment (gear motor cases aren't too great an indication, DD cases are much better). That may be enough to give you peace of mind for your commute, regardless of whether you continue to use the sensor to try to get meaningful temp readings.