What are recommended max temperatures for motor & control

[swbluto]

Hello, I'm now getting my electronics to complete my scooter that I'm upgrading with an outrunner and I am going to implement temperature control. I bought sensors for the controller and the motor but now I need to know what a recommended maximum temperature should be! I was thinking about placing the sensors on the motor's coil(The magnets are moving, so those won't do it.) and somewhere on the controller where it gets hot(like the mosfets, most likely).

So, any ideas? While motors running at a lower operating temperature are obviously better performing, it obviously can't be too low or the performance of the motor would be limited much more than it would at a higher limiting temperature. But, at the same time, I kind of want to protect the motor and controller from over-heating as a result of adapting it to something it wasn't designed for(and, in effect, abusing it.).

The motor is a standard HXT motor 2-pound 230-kV motor that'll draw approximately 30-70 amps continuously and the controller is a Castle Creations Phoenix HV 85 amp controller.

 

[fechter]

The idea is to find the highest allowable temperature where nothing fails.

For a motor that uses hall sensors, the hall sensors will probably fail first. Most hall sensors are rated for 150C, and will fail somewhere above that.

Next thing to worry about are the magnets. Good quality magnets will also be good for somewhere above 100C, but some can be demagnetized as low as 80C. On an outrunner, the magnets will tend to run much cooler than the windings.

Good PVC wire insulation (lead-in wires) might melt around 105C. Teflon is good for much higher temp. The magnet wire insulation also comes in different grades, and the max allowable temp on them varies. I think class H is 180C rated.

Here is a good reference on motor temperature ratings:
http://www.motorsanddrives.com/cowern/motorterms4.html

Unless a motor is designed for high temperature, I'd probably try to keep it under 100C
Generally, the windings will heat up the quickest, so should be where you put the sensor.
Sensors can be attached with silicone RTV glue, which is a good heat conductor and can withstand very high temperatures.

On controllers, it's a bit different. The power devices (FETs) usually are the main source of heat. According to the datasheets, a typical FET can withstand something like 175C. That's cooking! Capacitors and other parts will fail at lower temperatures. Many controllers I've seen have a thermostatic switch mounted on the same heat sink as the FETs that kills the power if it exceeds 80C. I think even 80C is pretty hot for a controller.

So, if you're thinking like me, instead of just killing the power suddenly when you exceed the max temp, it would be better if the power was gradually ramped down as you approach max temp instead. I'm not sure what a good proportional range is though. If you have a motor with 100C max for example, you would probably want the current to start backing off when you reach 80 or 90, then taper down linearly as you approach 100. Ideal proprotional range will depend on the thermal mass of the motor and controller current among other things.

 

[wrobinson0413]

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