Linix Motor getting hot

[ICEUK]

My salsa R2 has 8mph motors, I scraficed torque for speed and it's been an ok trade off but in the last couple of weeks they have been getting really hot without really working hard, I have had the chair for 3 years and done 3k miles in it and never had this problem in previous summers.
I have ordered some new brushes but do you think over time electric resistance inside the motor has increased that now causes the motors to get really hot. I can put my hand on the motor but for no more than 5 seconds, the chair refuses to move if they get hot and I go to turn

[ICEUK]

As a thought could it possible be the power module itself? I have a vicrtron smart shunt and when the chair is not moving when I try to turn from a stop the shunt only read 30-35 amps

[Burgerman]

Ignore the shunt. It lies to you. Well not so much lies but it cannot and does not tell you anything about MOTOR amps. You may find that hard to comprehend but its normal to have anything up to 120A per motor (240A total) and still only draw a small battery current. Maybe 1/4 of the total motor amps.

And below is how you SHOULD be checking motor Amps.

Not that when I turn in place, at very slow speeds, the M1 and M2 current is over 100 amps each! Thats 200 plus total. But the BATTERY current is a fraction of this. That is not always the case, it depends on the motor pulsewidth % at the time. At stall with low impedance motors, you may pull 120A (MAXIMUM POSSIBLE) and put crap loads of temperature in both motors while battery amps is say 35A...

Thats because battery Amps = 24V x 35A or 840 battery watts...
And the motors low impedance meand that 2 motors x 100A each (200A) x the MOTOR VOLTS of a pulsewidth limited aveage 4.2V. It cannot provide more than 4.2V (ACTUALLY 2 of 2.1V per motor) as this is the exact same 840watts. Power must balance on both sides of the equasion.

Heres how you actually visualise all this in REAL TIME while using your R-Net powerchair.
This is displayed as you drive about.

Note MOTOR CURRENT (M1 and M2 total) and BATTERY current re very very different at low speed high torque situations.

[Burgerman]

The power module has the ability to sense heat caused by high MOTOR currents, and then to protect itself the power module reduces torque (Amps) allowed while it cools. So it rolls back torque directly.

What causes heat?
Resistance in the power stage mosfets. And high average currents.
What causes rollback and low or no power? Software trying to stop the mosfets from going up in smoke...
The power module has no idea of the actual temperature of a motor.

You can help prevent this thermal rollback by:
Fitting new motors. Old tired ones suck up more Amps and power for any given load/speed as efficiency falls over lifespan. Weaker magnets, dirty or burned commutator, wear in gearbox etc.

Losing some weight. Seriously. Weight and load (and so heat) are in direct proportion to each other.

Dont choose 8mph motors. They suck more amps, by around 25% at EVERY speed, and every load. Thats is all ending up as heat in the power module and motors. It also causes faster battery fade and higher peukert, and so quite severely increases heat and decreases range and battery lifespan.

Dont use in warm weather. You are halway there to the heat problem before you start.

Dont use fat low pressure tyres. Also "flat free" foam filled tyres cause high loading.

Hills. Hills murder motors, overheat controller power modules, wiring and batteries.

And a tiny fraction of 2 or 3 of these things above all conspire against the stock chairs and helt help this heat problem.