Driving a 180V PMDC motor from 230V AC mains

[schmitt trigger]

It is shaft (mechanical) power.
A small, low-cost motor like the ones likely to be used on a commercial treadmill, are about 75% efficient, ball park value.
So just add a 33% factor to all your results above.

 

[MaxHeadRoom78]

Incidentally I did an empirical test of one of those motors, no flywheel or load fitted, I found that starting from zero and raising the DC gradually through the rpm/voltage range, the current was constant at around 2 amps.
Max.

 

[Futterama]

It is shaft (mechanical) power.
A small, low-cost motor like the ones likely to be used on a commercial treadmill, are about 75% efficient, ball park value.
So just add a 33% factor to all your results above.

Thanks, I'll do that.

Incidentally I did an empirical test of one of those motors, no flywheel or load fitted, I found that starting from zero and raising the DC gradually through the rpm/voltage range, the current was constant at around 2 amps.
Max.

Would this mean that those 2A are the efficiency losses? That equals roughly 25% of the max current of 8.3A - just what schmitt trigger anticipated regarding motor efficiency.

 

[schmitt trigger]

That is correct. Those are mechanical (friction, windage) losses plus magnetic losses. And a few copper losses.

When the load increases, and thus the armature current, the copper losses increase very rapidly (I^2 * R) and the end result is closer to 30% loss.

 

[Futterama]

I have been talking to a friend, and he thinks the motor flywheel will help even out any voltage variation from the input voltage, to a point where it might not be a concern.

I will start out by adding 1000µF, this should keep the rectified DC voltage above 200V even at full load. I do know that the capacitors ripple current capability is the limit, so I'll make sure to not exceed that during testing.
I'll run the motor and look for any signs of torque/speed ripple in the prop balancer software. If so, I'll try to manipulate the PWM to compensate for the varying voltage.

I have been searching for information regarding a LC filter, maybe this could help me smooth out the DC without adding a ton of DC link capacitors.

 

[MaxHeadRoom78]

I have been talking to a friend, and he thinks the motor flywheel will help even out any voltage variation from the input voltage, to a point where it might not be a concern.
.

Don't expect or demand a rapid RPM response change rate.
Max.

 

[Futterama]

My mind keeps on working and I stumbled upon something new to me, universal motors.

These motors are everywhere, also in 2kW power tools like 230mm angle grinders. I took a look at my 230mm angle grinder, rated 2000W and 6000 RPM. The gear ratio is 3.67:1 so when the grinding wheel spins at 6000 RPM, the motor spins at 22000 RPM.

Since a characteristic of the universal motor is high starting/stall torque, I was thinking, what would happen if a "designed for 22000 RPM"-motor was loaded enough to only spin at 3000 RPM? Would the motor overheat or would it easily handle this because the torque goes up as speed goes down? I my use-case, the motor spins up the propeller to be balanced, then runs for a few seconds at measuring speed e.g. 3000 RPM. So the motor is running for max 20 seconds at a time.

The DC treadmill motor has a price tag of $164 as a new spare part for a discontinued treadmill.
A brand new Makita 230mm angle grinder rated 2000W has a price tag of $98.

So the universal motor from an angle grinder is cheaper to get a hold on.

What I'm considering here is that for the propeller balancer sensor to pick up any imbalance in the propeller, the imbalance would need to have enough force to vibrate the whole motor. It will of course require a larger imbalance to vibrate a heavier motor, so I'm thinking with a lower weight motor, I will be able to pick up on smaller imbalances, hence improving my final propeller balance. I think the treadmill motor is heavier than the angle grinder motor, but I will need to verify this. Maybe it's just the flywheel on the treadmill motor that adds the weight, but this is also something to consider, do I really need the flywheel? It might provide for a smoother rotation, but it adds weight which counteracts vibration.

 

[schmitt trigger]

Don't do it. It will burn out.

EDIT: see my updated comment below.

 

[Futterama]

Don't do it. It will burn out.

You mean the universal motor will burn out with such a high load? Of course, the load would be a propeller, and the PWM to the motor would be adjusted for 3000 RPM, meaning maybe the PWM duty cycle is only 30% for a small propeller and maybe 70% for a bigger propeller. But the biggest propeller would require full power to reach 3000 RPM but perhaps the current would then be higher than specs because the motor is rated 2000W at a certain RPM, in the angle grinders case, 22000 RPM? And at lower RPM, the current goes up?

 

[MaxHeadRoom78]

With a Universal motor a Triac controller is typically used to control rpm, current is dependant on load.
Without some kind of feedback to the controller they are hard to control precisely as they essentially operate in a run-away condition being a series wound motor.
The flywheel application will give you smoother control at a cost of response time to rpm change.
Max.

 

[Futterama]

Without some kind of feedback to the controller they are hard to control precisely as they essentially operate in a run-away condition being a series wound motor.

Ah, yes, that could pose a problem as I need a pretty constant RPM while doing the vibration measurements, otherwise the vibrations would be hard to identify on the FFT graph if they keep changing frequency due to RPM changes.

The flywheel application will give you smoother control at a cost of response time to rpm change.

I don't have much need for a good response time, but the smooth rotation and steady speed are more important. I haven't considered RPM feedback to the controller yet, but since I already need a feedback to the balancing software, I could easily read out the RPM pulses to the motor controller as well, so it can keep a more steady RPM if needed.

I'll stick to the PMDC motor and try not to let my mind wander off into alternatives

 

[schmitt trigger]

Sorry, sorry, sorry...
I thought that you were planning to mechanically load the universal motor to lower the RPM!!
You are planning to lower the voltage. I take my comments back.

But again, it is best if you stick to the PMDC motor. The speed of the universal motor varies widely with both the voltage and mechanical load.