Installing a temperature switch to the outside of a brush DC motor, to avoid overheat damage, any input?

[jimtmcdaniels]

Hi,
I'm looking for any input, advice, knowledge, experience on this subject:

This is for my E300 Razor Scooter, which I have modified the controller shunt to allow more current and plan on over volting soon as well.
I'm planning on installing a $2. high temperature cut off resetting switch, like those sold on Aliexpress in various set temperatures and both normal open and normally closed styles, to the outside of my OEM brushed 24v 250w DC motor, to avoid overheat damage.
Kind of like that famous Electric cars suspenseful pursuit scene from the classic1971 Sci Fi movie "THX 1138". Where they have to wait for the motors to cool off or something, to get going again.
So that if and when I'm pushing my motor too hard for too long, up hills etc., the controller will shut off the motor before any damage.
I just wait 15 minutes or more for a proper cool down and start riding my scooter again, no harm done is the plan.
I see I should be able to wire a normally open temperature switch to the controller's brake lever circuit which is also normally open, but closes and cuts off the motor when the rear brake lever is applied.
I suppose super glue might be the best simple thing to use to attach the switch to the motor body. Super glue should be able to take the heat and also conduct the heat to the switch.

WHAT I SEE THUS FAR:

These Razor brushed DC motors, as well as all the various watts sizes and voltages sold online, don't have Any high temp thermal cut-off-protection build into them. In spite of the fact that high priced E-bike and E-Scooters do have cut off protection and many of our home electric appliance motors do as well, such as our vacuum cleaners, clothes washers, etc.
Surprisingly, I haven't see Anyone in a forum installing an after market high temp thermal cut off to these motors. But I have seen on YouTube, people over heating and permanently damaging/killing these DC brushed motors when over current/over volting.
These lower watts motors are much cheaper and much lighter and can take a beating, a real sweet spot. And fitting a much larger watt motor can be impossible in the OEM motor's location.
None of these brushed DC motor companies seem to list the high temperature limit of their motors which depends on the materials they use. I've tried to ask these motor companies but haven't gotten a reply.
From what I've found online concerning DC motors in general, the heat is mostly generated in the electrical energized spinning Armature.
An estimate to be that the stator's maximum temperature which it can reach/be exposed to for short periods of time without the risk of permanent damage, might be around 266 F (130 C), before the Armature's winding's insulation begins to melt off. When this occurs, the outside metal case temperature of the motor, where the heat dissipates from, will be less, say approx. 176 F (80 C).
I suppose a 149 F (65 C) high temperature switch might be about the right temp to stop the motor for a cool down. No might have to go lower in temp...hmm.
Currently I stop my scooter rides occasionally to check the motor's outside temperature with my hand from time to time, especially after steep hills.
I've read online that the typical human can tolerate briefly touching something that’s about 60 to 65 C (140 to 150 F).
If I can't touch the motor without releasing to the count of 4 seconds, then I'll take a 15 minute brake for it to cool down.

WHAT AM I MISSING, ANYTHING?
Has anyone tried installing a high temp cut off switch?
Anyone know what temperature the motor's outside case might reach before motor damage?
Any suggestions, comments, criticism, etc?!

Thank you for your time & help!

 

[E-HP]

Has anyone tried installing a high temp cut off switch?
Anyone know what temperature the motor's outside case might reach before motor damage?
Any suggestions, comments, criticism, etc?!

Thank you for your time & help!

Whether an external sensor works or not will be influenced by how you are heating up the motor. For instance, if it's warms up steadily over a long distance, and external sensor may work. But, if it heats up going up a super steep hill, chances are the motor can fry before heat ever transfers to the external case. The hand method is better than nothing, and an external sensor will be an improvement, but an internal sensor added to the windings can be nearly foolproof. When a motor heats up quickly, the case may remain barely lukewarm, since the heat hasn't transferred to it yet, so just keep that in mind.

 

[jimtmcdaniels]

Thank you yes I'm aware of that and that is a concern of course.
Yet can this same switch be added to the windings? The windings are spinning but perhaps it can be added just inside the motor case or perhaps mounted on the outside motor cap end instead of the body would be a quicker response to a sudden temperature rise.

Perhaps someone has more details on this, if they've play around with this in the past.

Some e-bikes have motor temperature displays. Exactly where on the motor are those sensors mounted I wonder, but I suppose they are brushless hub motors?
I believe it's been stated someone's hub motor failed at 87 C on their display.

 

[amberwolf]

You can put the switch on the windings of a brushed motor, but you must use a switch that can handle the full current of the motor as it is operating, *and* can successfully shut off the current under full load. It will also require the switch to be capable of handling the full worst-case voltage (which can be quite high because of "flyback" voltage caused by collapsing current in the windings). If it can't, the arc across the opening contacts will either weld them shut again, or it will continue arcing and heat the thermal switch and area around it like a welder would, and can start a fire. In either case, the current doesn't stop flowing and heating continues....


FWIW, the thermal cutoffs inside appliance motors are usually a thermal fuse, not a switch or breaker, and must be replaced to allow it to operate again. (same for those inside transformers of various kinds of power supplies). Some lower-current devices like heating blankets and pads often use thermal breakers that self-reset, but they don't need to handle flyback voltages from motors and other inductive loads.

Some larger appliance motors, or those sealed within casings like compressor motors, and stuff like welder transformers, etc., will use thermal breakers/switches, but they are rather larger than the tiny ones you see in the typical stuff above.


Temperature *sensors* in brushless motors are often placed near or within the windings on the stator. (you can't do this on a brushed motor, becuse the windings are spinning, unless you add a second set of brushes just for the sensor signals, and design the detection circuitry around the discontinuous signal).


The simplest way to implement a thermal switch (not sensor) is to use it to cut off not the actual motor power, but instead cut off the throttle signal, or the 5v to the throttle itself, etc. The sensor can be placed anywhere outside the rotor / armature, in any motor, but I recommend shielding it and the wires to and from it against RF / electromagnetic interference (EMI), because especially in a brushed motor there is a crapload of that generated at high currents/loads, and it can cause incorrect operation of a system if it gets into the control lines.

 

[jimtmcdaniels]

Yes ok
Well Aliexpress has "Thermostat 45C 50C 85C 90C 95C 150C Bimetal Disc Temperature Switch N/O Thermal Protector degree centigrade" that are in different versions incased in either metal, ceramic or plastic:

https://www.aliexpress.us/item/2251832801938038.html?spm=a2g0o.productlist.main.53.a7db557b2NrxnI&algo_pvid=d2c58aaa-3fe8-49ee-b59a-edc90398f222&algo_exp_id=d2c58aaa-3fe8-49ee-b59a-edc90398f222-26&pdp_npi=3%40dis%21USD%210.38%210.38%21%21%210.38%21%21%40212250c216886989364937019d076b%2166920752699%21sea%21US%213607765048&curPageLogUid=sFFHE9WySnyv

None say the wires are shielded.
Perhaps the ceramic or plastic are shielded enough because of the case material...
I could wrap the wires with aluminum foil and then electric tape I suppose would qualify for shielding.
I don't know, what do you say?

Yes as I said, I plan to connect the temp switch to the controller where the brake lever also connects. So the controller will handle the motor power cut, not the temp switch.

Also, according to the internet and my experience, the common household vacuum cleaner does have a thermal switch/breaker, instead of a non resettable thermal fuse.
Even our household garbage disposals typically have a red reset button on their bottom which is not just a fuse which has to be replaced when triggered.

Also what would you say about drilling small holes in the motor end caps? These motors sit very low to the ground just in front of the rear tire and are sealed for obvious reasons..

I'm looking for the sweet spots reasonable upgrades for this Razor E300 to make it more suitable for adults and our 20mph state speed limit on e-scooters. These E300's are so affordable used, often because their lead batteries need replacing and with a new Lithium ion battery pack and new variable speed throttle and controller, seems the best way to get the OEM top speed of 13 mph up to the 20 mph and bring up the acceleration and hill climbing abilities into adulthood. All while keeping its extreme portability and simplicity etc.
While keeping open an affordable motor upgrade to say 350w if the OEM dies down the road.

Thank you for your help and expertise

 

[amberwolf]

Yes ok
Well Aliexpress has "Thermostat 45C 50C 85C 90C 95C 150C Bimetal Disc Temperature Switch N/O Thermal Protector degree centigrade" that are in different versions incased in either metal, ceramic or plastic:
None say the wires are shielded.
Perhaps the ceramic or plastic are shielded enough because of the case material...

Unlikely. They don't have any reason to shield them; it's up to the device designer to do it if the application requires it (some will, most won't).

Metal cased switches have the metal of the casing that can be used as a shield, if you connect it to the shield of the cable, as long as there is no electrical connection from the casing to either of the contacts inside the switch.

I could wrap the wires with aluminum foil and then electric tape I suppose would qualify for shielding.
I don't know, what do you say?

The kind of shielding you might need (if there is interference, which is common) is to provide a metal enclosure (foil, braided shield like old RF and video / etc cables use, etc, that encloses all of the sensor and the wiring run, at minimum for the whole run inside the motor and near it. The shield should be grounded only at the controller end, to the battery negative there (not connected to any wire / etc that it is there to shield).

If you have any old A/V (audio/video) cables that use an external shield around two or more conductors inside the shield (some headphone cables do this, so do some speaker amp audio input cables), you could use this for the wire from your brake input to the sensor itself. Foil could then be used around the sensor and connected to the braided shield of the cable itself.

You can test to see if this will be needed before doing so, but it's fairly simple to do before installation and then you don't have to worry about it.

Yes as I said, I plan to connect the temp switch to the controller where the brake lever also connects. So the controller will handle the motor power cut, not the temp switch.

That should work fine; the NO switch will remain open until i reaches overtemperature, then close and engage the brake, and the controller will do whatever it is designed to do in that case.

As long as the controller doesn't do (or is setup not to) regenerative braking (regen) and just ceases powering the motor, it'll do what you want it to.

Also, according to the internet and my experience, the common household vacuum cleaner does have a thermal switch/breaker, instead of a non resettable thermal fuse.

That depends; my guess is based on attempted cost savings by the manufacturer...but I don't know for sure why it varies.

Some VCs have actual circuit breakers in them (that you manually reset when they trip. An old Kenmore non-upright I had was like that; The main unit had one, and there was a separate breaker in the separate sweeper unit for the belt motor (this one had to be reset a number of times over the years when objects jammed the belt (usually clumps of dog hair I'd neglected to pick up first).

I never needed to disassemble either of it's motors to see if it had a thermal breaker or fuse in it, so I don't know which one it had.

A B&D shop vac I had did have a thermal fuse (not breaker) inside it's windings, which blew after one of the two stacked fanblade assemblies disintegrated and jammed the motor. The only way to fix it would have been to unwind the motor to get to it, and the other option was to bypass it and leave it unprotected, so I decided to scrap it instead. :/

An upright I can't recall the brand name of (but was expensive, given to me when the owner upgraded because it only worked intermittently), I think german made? used a thermal switch mounted inside the motor casing at the brush mount (where it often gets hotter than anywhere else outside the windings on the armature). But it also used an SCR/TRIAC based speed controller for the motor, rather than just running it full speed all the time, based on the various settings it had. I've never seen any other VC built that way (not even with a two-speed via diode like my Ryobi grass trimmer has). It also had a regular glass fuse on the speed control's AC input side (no resettable CB).

Most others I've had I have not had to deal with problems on, so I don't know what they have inside.

All of the box fans and other such cooling fans I've had to try to fix had thermal fuses, sometimes embedded in their windings, sometimes just pressed against them by their casings, sometimes tied to them with the cord used to secure the windings down.

Other protected things vary, some with switches, some with fuses...but fuses are cheaper so they get used in cheaper things more often..

Even our household garbage disposals typically have a red reset button on their bottom which is not just a fuse which has to be replaced when triggered.

In the ones I've had apart to repair, that's just a regular circuit breaker, not a thermal one, designed to trip if the motor overcurrents because of a jam on something in the disposal grinder.

Also what would you say about drilling small holes in the motor end caps? These motors sit very low to the ground just in front of the rear tire and are sealed for obvious reasons..

What do you need the holes to do for you?


If it helps, there are quite a few scooter (especially razor) mod threads and posts around the forum that might have useful info for your project. It is probably easier to use the search on the archived version of the forum from before this year to find them (this will only find ones posted before then, but that's most of them).

ES 1.0 Graveyard - Search

 

[jimtmcdaniels]

Unlikely. They don't have any reason to shield them; it's up to the device designer to do it if the application requires it (some will, most won't).

Metal cased switches have the metal of the casing that can be used as a shield, if you connect it to the shield of the cable, as long as there is no electrical connection from the casing to either of the contacts inside the switch.



The kind of shielding you might need (if there is interference, which is common) is to provide a metal enclosure (foil, braided shield like old RF and video / etc cables use, etc, that encloses all of the sensor and the wiring run, at minimum for the whole run inside the motor and near it. The shield should be grounded only at the controller end, to the battery negative there (not connected to any wire / etc that it is there to shield).

If you have any old A/V (audio/video) cables that use an external shield around two or more conductors inside the shield (some headphone cables do this, so do some speaker amp audio input cables), you could use this for the wire from your brake input to the sensor itself. Foil could then be used around the sensor and connected to the braided shield of the cable itself.

You can test to see if this will be needed before doing so, but it's fairly simple to do before installation and then you don't have to worry about it.




That should work fine; the NO switch will remain open until i reaches overtemperature, then close and engage the brake, and the controller will do whatever it is designed to do in that case.

As long as the controller doesn't do (or is setup not to) regenerative braking (regen) and just ceases powering the motor, it'll do what you want it to.



That depends; my guess is based on attempted cost savings by the manufacturer...but I don't know for sure why it varies.

Some VCs have actual circuit breakers in them (that you manually reset when they trip. An old Kenmore non-upright I had was like that; The main unit had one, and there was a separate breaker in the separate sweeper unit for the belt motor (this one had to be reset a number of times over the years when objects jammed the belt (usually clumps of dog hair I'd neglected to pick up first).

I never needed to disassemble either of it's motors to see if it had a thermal breaker or fuse in it, so I don't know which one it had.

A B&D shop vac I had did have a thermal fuse (not breaker) inside it's windings, which blew after one of the two stacked fanblade assemblies disintegrated and jammed the motor. The only way to fix it would have been to unwind the motor to get to it, and the other option was to bypass it and leave it unprotected, so I decided to scrap it instead. :/

An upright I can't recall the brand name of (but was expensive, given to me when the owner upgraded because it only worked intermittently), I think german made? used a thermal switch mounted inside the motor casing at the brush mount (where it often gets hotter than anywhere else outside the windings on the armature). But it also used an SCR/TRIAC based speed controller for the motor, rather than just running it full speed all the time, based on the various settings it had. I've never seen any other VC built that way (not even with a two-speed via diode like my Ryobi grass trimmer has). It also had a regular glass fuse on the speed control's AC input side (no resettable CB).

Most others I've had I have not had to deal with problems on, so I don't know what they have inside.

All of the box fans and other such cooling fans I've had to try to fix had thermal fuses, sometimes embedded in their windings, sometimes just pressed against them by their casings, sometimes tied to them with the cord used to secure the windings down.

Other protected things vary, some with switches, some with fuses...but fuses are cheaper so they get used in cheaper things more often..



In the ones I've had apart to repair, that's just a regular circuit breaker, not a thermal one, designed to trip if the motor overcurrents because of a jam on something in the disposal grinder.



What do you need the holes to do for you?


If it helps, there are quite a few scooter (especially razor) mod threads and posts around the forum that might have useful info for your project. It is probably easier to use the search on the archived version of the forum from before this year to find them (this will only find ones posted before then, but that's most of them).

ES 1.0 Graveyard - Search

Ok I'll try searching more although I may have already found what I can in previous searches.

The holes would be to help cool the motor.

 

[amberwolf]

Ok I'll try searching more although I may have already found what I can in previous searches.

If you've already looked thru them, then don't worry about it (I didn't know you'd already done so).

The holes would be to help cool the motor.

To really help cooling something, holes generally should be as large as possible, so that they have less interference with the air passing thru them. Small holes can still help, if there's enough of them and/or they're in the right area. It's something you have to experiment with to find the best solution with the least modification.

If you have the time to look around for them, there are a few threads about hubmotor cooling via various methods, which may help you in this even though it's a different kind of motor. Not everything in them will be useful because of the different mechanisms, but some will be. John in CR experimented with air hole sizes, shapes, etc., in hubmotor covers (which are spinning, while yours are stationary), for instance.

If you add a type of fan to the motor output shaft, like that on an alternator (or vacuum cleaner) that just centrifugally throws air away from the shaft, it'll suck air thru the motor from the other end via whatever holes there are on both ends, making it more efficient even with small holes...but it also gets noisier, and this kind of fan only helps at higher speeds, and not at the low-speed/high-load times where the motor is likely to build up heat pretty quickly and doesn't have much other airflow thru or around it either.

 

[jimtmcdaniels]

Cool
Thank you

I'll have to see how well and how often the temp switch kicks off the motor.
If it's a lot then I'll consider compromising the water proof motor case ends with holes and/or adding forms of heat sinks to the outside.
Fingers crossed here ha

 

[jimtmcdaniels]

PS:
Here is a pic with the same model Scooter's foot standing on cover removed.
As you can see, the brushed motor is mounted just in front of the rear wheel and is chain driven.
This pic shows the oem 2 lead 7ah batteries in the tray and the controller and wires to the side exterior circuit breaker, power switch, and charge plug are in front.