Best Motor Protection, Controller components / sourcing, etc.

Thread Starter

WaterSafetyFirst

Joined Jan 16, 2017
3
Motor protection:

We intend to market a device with a Chinese DC stepper motor driving a linear actuator rated to 1000 Lbs. using a controller with a potentiometer switch (like a trigger switch).

The manufacturer only rates the motor for 20% duty cycle, which ain't really enough for the design.

We are leaning towards a larger motor, and even an external muffin fan on the motor (would be nifty to have it temperature activated, but then it could be playing thermal "catch up", so we think we'll go with 100% always on cooling fan since all this is plug in the wall, not battery).

As backup, for users who fail to follow the recommended duty cycle, we want to throw in an Auto Reset Thermal Cutoff Switch For Motor Overload Protection - - or - - an Auto Reset Polyswitch (amperage limiter).

We don't have any experience with which one of these typically is the more reliable, which has the longest MTBF, so we would hope some of you with more experience incorporating these into motor designs might share with us.

We understand that each type switch probably has to cool off before it allows motor operation to proceed again and that might frustrate some power users who refuse to "follow the duty cycle rules".

Does one type switch cool off and allow operation to resume faster than the other ? Is one more reliable with longer MTBF ? Seems to me the thermal cut off method has a bit of a limitation in that on one hand you get the most reliable readings by having the thermal cut off switch intimately pressed against the motor shell (even wrapped against) - - - but on the other hand this impedes evenly distributed cooling with the fan.

Any other design issues incorporating these type switches we should need to know about ?

Brush DC versus brushless DC - - - is one type preferable over the other in case you have a motor that encounters a fair amount of use/potential overheating ?

Any suggestions on the type of controller we should be sourcing for most reliablity ? (specifically types of components on the circuit board that separates a "cheap" controller from a robust controller).

One designer told us just upsize the controller board.

For example, if the motor is rated 1/5th HP, buy a board rated for 1/2 Hp or similar.

Thanks for sharing,
 

MaxHeadRoom

Joined Jul 18, 2013
20,025
I guess ideally the mechanism should be designed for maximum anticipated use, rather than have a time limit built in.
The advantages of BLDC over Brushed is with the former, the heat generating windings are in the stator and can, and usually do, have heatsink outer construction.
With brushed, all the heat is in the rotor and can take time to radiate to the outer case, in which time damage may have been done.
You indicate a stepper motor which is a heat generator, regardless of RPM.
If you want rpm control then the PWM way is fairly simple for brushed, and gets a little more complicated for BLDC as commutation sensors are necessary, these usually come with the motor but the drive has to be able to use them.
You can get small servo controllers, A-M-C etc for that size motor which gives bi-directional control.
Is the rpm automatic or manual?
Max.
 

Thread Starter

WaterSafetyFirst

Joined Jan 16, 2017
3
MHR:

Thanks for the suggestions.

Sounds like BLDC the way to go for best stripping off any excess heat from motor.

Due to commutation sensors, etc. on BLDC sounds best to require same company provide everything if possible so it all works together properly.

This would be totally manual control.
 

MaxHeadRoom

Joined Jul 18, 2013
20,025
Do you want the control to be manually variable?
i.e. Pot etc?
I have mixed and matched BLDC motors with quite a few drive manufacturers with no problem.
Max.
 
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