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

jimtmcdaniels

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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!
 

ElHegpah

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Never seen it done this way. I have seen much lower temps cited as permanently weakening the magnets, closer to 200F.

Many BLDC motors have an internal thermistor, read by the controller, which then shuts down at a specified temp.

I do know the inside of the motor is dramatically hotter than the outside, some have used oil fill, heat sinks, ferro fluid, open cases, some with fans, and even active water cooling.

Not very many board riders or hot rodders here.
 

jimtmcdaniels

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Thanks

Yes hmm perhaps the temps I saw talked about were off/too high.
Although I’ve read some expensive brushless motors use rare earth magnets which are susceptible to permanent demagnetization at a lower temperature then the common cheap motor magnets.
So perhaps those are the lower temps you’ve heard about or not.
Definitely tricky to pin down better.

Well only the brushless can be filled with something to transfer the heat to the exterior.
Perhaps I should consider drilling some small holes in the end caps to let air in and heat out.
Although these motors are sealed and sit close to the ground on the Razor E300.

I can’t see anything else that would be practical enough to try for the E300.
Just looking for the sweet spots of what can reasonably done to make it more suited for adults and able to obtain the sensible 20 mph speed limit our state ans many have adopted in the statutes for e scooters.
 

JettPilot

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to the outside of my OEM brushed 24v 250w DC motor, to avoid overheat damage.

Brushed motor ??? Is that a 99 dollar scooter from 20 years ago ???

Forget about melting the motor, I would throw that thing in the trash and get a brushless motor.

Then we can talk about getting that old tube type black and white TV out of your living room :ROFLMAO:
 

jimtmcdaniels

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Brushed motor ??? Is that a 99 dollar scooter from 20 years ago ???

Forget about melting the motor, I would throw that thing in the trash and get a brushless motor.

Then we can talk about getting that old tube type black and white TV out of your living room :ROFLMAO:
WEL I’ve never! ;)
Oh I do hear you!

BUT on the flip side, we can also talk about how these adult entry E300 13mph top speed e-scooters are new on Amazon for $300, but go for only $50-$70 used on Craigslist.
Also how they have stout steel frames, 9.5” air tires(upgradable to aftermarket 10”) with a 220 lbs rider limit and when over volted to 36v or 48v lithium with a $140 battery pack and $22 new matching volts controller and variable throttle, can have a new top speed of 20mph (which is the legal limit in many states for e-scooters) or 25 mph.
Additionally making these weigh a poultry 40 lbs yet with the change in e-scooter laws makes them very versatile to ride on the streets, bike lanes and sidewalks.
With the price of $25 a minute for the widespread popular e-scooter rentals such as Lime, owning your own e-scooter can save you lots and avoid their limits of times and places to ride.(some cities don’t allow the rentals in parks and the gps shuts them down if a park is entered, or use after certain hours, etc).
Additionally the E300’s OEM 250w 24v brushed motor replacements can be purchased new online with shipping for $32 or better yet a drop in my1016 same mount size replacement upgrade to 350w 24v for $36.
 

jimtmcdaniels

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Depending on the lithium pack parallel size/count you can double or triple these E300’s range while still fitting the pack in the OEM battery compartment without any modification.

Now I would like to learn more about brush vs brushless DC motors.

All I know is that the brushless are like almost 10% more efficient and have the energized with electricity copper wire windings magnets stationary on the outside while the permanent magnets are spinning at the core of the motor.
Where brushed motors are the opposite with the permanent magnets on the outside with the energized with electricity copper wire windings magnets spinning on the inside, thus requiring the brushes to conduct the electricity to the spinning core.

I don’t know things like why the brushless are more efficient and more expensive and what the other pros and cons are between the two designes.

Can you answer any of this please?
 

smutboy

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Im pretty sure you would need a normally closed (NC) temp switch rater then a normally open (NO) switch being that a normally open one would keep the cirute cut till it heated up enough to close the swich. unless I'm misunderstanding how you want to wire it. If your going to wire it in to the break cut off so it would do the same as applying the break and cut power to the motor then a NO would work. BUt if your going to attack it with any sort of glue I would use something more suitable than super glue such as maybe some epoxy or even better use a heat-sinking epoxy like what is just to glue heat sinks on to computer chips. which will not only be able to take the heat. it will also help transfer the heat in to the switch.. epoxy also unlike super glue doesn't break its bond with a little bit of heat. and it also will be able to withstand some bumps or vibrations which super glue does not tend to hold up to shocks of vibrations. and super glue also breaks down and loses it bond if it gets soaked with water. I would also go with a switch that's rated for a much lower temp than 200f being that by the time the outside of your hub reaches that sort of temperature the temp on the inside is going to be a lot hotter than 200F
 

jimtmcdaniels

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Thank you
Yes I thought a 65c(149F) switch might be about right. One motor seller on Aliexpress replied and said to go with a 60c. Another said 100-110c but I'm not sure they understood my Q or perhaps that is the high temp limit of the spinning armature.

What I see is online in discussions on electricscooterparts archived forum, I found it is stated the brake lever switch on the Razor E300 is normally open to the controller,
However it may have changed in late versions so I will verify before ordering the temp switch. If it is normally open, then I will have to be sure to wire it in parallel. If it is a normally closed, then I must wire it in series.

Yes an epoxy might be perfect. That seems like a great idea.
Allowing me to fully surround/encase the switch to assure it pickups the temperature signal well from the motor heat soak.
I see typical epoxy has a temp rating of 300 f or higher.
I could use a 2 part runny liquid epoxy I got from the dollar tree or the plumber's putty epoxy I have as well.
Actually I might use the super glue for the initial bond and to hold it in place against the motor outside and then cover it with the epoxy.
I will clean the surface first with rubbing alcohol to remove any oil film etc.
 

smutboy

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Thank you
Yes I thought a 65c(149F) switch might be about right. One motor seller on Aliexpress replied and said to go with a 60c. Another said 100-110c but I'm not sure they understood my Q or perhaps that is the high temp limit of the spinning armature.

What I see is online in discussions on electricscooterparts archived forum, I found it is stated the brake lever switch on the Razor E300 is normally open to the controller,
However it may have changed in late versions so I will verify before ordering the temp switch. If it is normally open, then I will have to be sure to wire it in parallel. If it is a normally closed, then I must wire it in series.

Yes an epoxy might be perfect. That seems like a great idea.
Allowing me to fully surround/encase the switch to assure it pickups the temperature signal well from the motor heat soak.
I see typical epoxy has a temp rating of 300 f or higher.
I could use a 2 part runny liquid epoxy I got from the dollar tree or the plumber's putty epoxy I have as well.
Actually I might use the super glue for the initial bond and to hold it in place against the motor outside and then cover it with the epoxy.
I will clean the surface first with rubbing alcohol to remove any oil film etc.
or maybe just use the super glue for testing in case you have to remove the temp switch if you need to use a different temperature switch. all you will have to do is use a tool such as the handle of a screwdriver while holding the screwdriver end in your hand to just tap the switch or the body of the hub near where it's attached and the super glue will just pop right off. Then you can use some nail polish remover or acetone to clean of any residue

tho one other thing that just occurred to me is how are you going to route the wires to the switch in a way that the wheel can still turn, which had me wondering if it might even be better to instead of using one of them reed style thermostat button temperature switches, maybe something like a tiny thermister might even be better being they are really tiny about the size of a small resister or diode. and you very well might be able to insert it right inside the motor and feed the tiny thin wires threw the hole that the motor's wires come out from the axel. you can get thermister switches in different temperatures and sizes and shapes too. https://www.newark.com/c/sensors-tr...stat-switches?contact-operation=normally-open

some of the more advanced motors and controllers and displays use a different type of thermister of some kind inside the motors that can read the temperature and send it to the display to be able to cut out the motor if it's overheating. and I think they even allow someone to program in what temperature to shut off the motor at.
 

jimtmcdaniels

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Well the motor isn't a hub motor so it doesn't rotate.
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.
 

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smutboy

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Well the motor isn't a hub motor so it doesn't rotate.
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.

ohhhhhhh well then in that case that should be really easy to do..
 

ElHegpah

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Wow, the my1016. That was what the original Currie ebikes used, funky, but they worked. Reliable and cheap.

There was a guy, DrkAngel I think, did a lot of mods on those. Mostly overvolting and changing gearing, to avoid overheating. Don't remember if any cooling mods. They DO overheat fairly easily, getting the gearing right with the voltage was important. 24 to 36 upgrade you need to change gears.
 

jimtmcdaniels

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Well they are 24v from OEM but over volting is the simplest way to increase the 14 mph OEM speed, acceleration, hill climbing, reduce wire resistance to allow more watts in OEM size wires, take advantage of the OEM battery compartment having elongated room for more cells in series in a pack which fits the compartment.
 
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