A temperature switch to outside of brushed DC motor, avoid overheat damage?

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!

PaulN

jimtmcdaniels
I like your enthusiasm and you certainly have taken a lot of time and effort to detail this “mod” of a 9 mile range $279.00 fun scooter with a targeted demographic of mostly teenagers.
Are you an an engineer and just challenging yourself or someone young that i see a bright future in a technical field?

Personally i would consider going a level up on a little more robust scooter with more range/speed/features. (new or used)
Something like the : TurboAnt M10 that doubles your range and is faster without heat issues with a list price of $449.00

jimtmcdaniels

PaulN
Thanks and those are very good points and it is a close call.

I’m detailing this mod so that it will hopefully be successful. Additionally I find it a bit surprising these motors and none of the mod talking considers adding a high temp cut off switch. I want to make sure I’m not missing anything or reason here.

If the mod goes well, I may buy up to 10 of these over time, to mod and give to friends and relatives as gifts.
Because I see some appearing on craigslist and marketplace for $50-$70 used and our state of Colorado, like many, now allow 100 lbs max w/batteries, 20mph max, e-scooters legally on the streets, bike lanes and sidewalks.
A real game changer and cool experience instead of driving a car.

These are entry level scooters for adults. They do have steel frames, 220lbs rider limit, 9″ air tires(upgradable to drop in 10″ when they wear out) and are small, very portable and light weight and there is a detachable sit down seat option which was sold with the “s” models.

Although they are chain drive and the motors are only 250w and not so good on hills and the oem lead batteries are a sham.
Parts are very affordable and available on eBay and aliexpress.
The oem replacement motor is $32 with shipping and a larger 350w(similar to the TurboAnt you mentioned) for $36 which is a direct fit as well.

Yet with overvolting with a new matching controller an variable throttle all for $20 and a good size lithium ion pack, they can come to life with good speed and range and acceleration. Also the higher voltage seems to help the motor run cooler to a degree as well as the oem wiring.

As far as TurboAnt, they do seem to be one of the better E-scooter companies and I see they are on sale for $360.
Yet there are some red flags with them. Like how they are not sold on Amazon, all the reviews on their site are controlled/filtered by them, they don’t offer for sale much replacement parts, their battery packs are weak and pricey.
Their frames are light weight aluminum which always seems to break easily with any company who offers it.
This site gives independent reviews and 20% of the reviews for TurboAnt’s e-scooters have only 1 star:
https://www.trustpilot.com/review/turboant.com?stars=1&stars=2&stars=3

The range is poor when you look more closely:
The TurboAnt M10 has a Max range of 18 miles (in comfort mode which is 9 mph top speed), so more like 10 miles which limits to a short round trip somewhere.
It has a 36v 7.5 ah battery pack. The battery maker appears to be cheap/sketchy because of all the complaints and premature pack failures in the reviews.

You can’t upgrade their battery packs to something larger/more range, because it won’t fit.

I can get a quality(not a cheap quality pack) from CAOmn on Aliexpress(also sold on Amazon w/very good reviews), a 36v 8 ah battery pack with Panasonic 18650 cells on Aliexpress for $115.
Better yet I can get their 14 am battery pack for $145, that’s double the range.

Prices have dropped on new E scooters. Perhaps in a few years, that will be the better way to go if prices continue to drop and quality improves.
It is a bit of a tough call and I might go that way eventually.

What do you think about my assessment?

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Brushed DC motors can overheat due to excessive current, Mapquest Directions poor ventilation, or prolonged operation under heavy loads. Overheating can lead to damage such as insulation breakdown, reduced efficiency, or even motor failure.

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