Slowing Down A 115V Electric Motor (capacitor start induction type)

[John-O]

How do I slow down this 115V electric concrete mixer? It runs at a constant 25rpm. We need to do prolonged mixes, but at slower rotation speeds. Is there an off the shelf plug-in controller I can use for this purpose, or will it be a bit more complicated than that?

All inputs and suggestions will be highly appreciated.

PS: My apologies for the flipped pictures, they are rotated correctly but somehow flip when uploading.

[John-O]

The motor is apparently a capacitor start, induction type motor (rating 110uf) -  as per the manufacturer.

[Xena E]

Trying to slow down that type of motor with an inverter won't work well.

To be positive, you could try:
Changing the motor to a three phase unit, then if necessary control through an inverter.
Modifying the drive or gearing. Some of those machines use belt drive from the motor to gearbox, it looks like they may be so. You could investigate different pulley ratios.
A big reduction could be done by driving the gearbox from a geared motor. That could have a proportionally lower power than the current motor as the torque would be increased by the gearing.

Xena.


 

[John-O]

We need to change the speed as required, back and forth, so a permanent fix/change will not do unfortunately.

[Xena E]

Then you need a motor that will support speed control: the present one will burn out its start winding and capacitor if you reduce the speed below the pullout of the centrifugal switch.

[John-O]

I just got feedback from Dart Controls www.dartcontrols.com/ and they said capacitor start type motors are made to run at one speed and nobody makes such controllers. 

[John-O]

Then you need a motor that will support speed control: the present one will burn out its start winding and capacitor if you reduce the speed below the pullout of the centrifugal switch.

Yes, it seems that way.

Thank you.

[Xena E]

The only way to speed control those motors is by nature a kludge, and you have to be careful not to stall them, it involves variable frequency inverter drive and disconnecting the start circuit after it is up and running, Its not a job for a newbie, (no offence), and as I said carries a risk of the motor being damaged if it stalls.

No drive manufacturers will back such a system with a guarantee.

Hope you find a solution.

Regards Xena.

[John-O]

Thanks Xena. Yes, I need a simple plug-and-play system, which is not available for this problem. So, I need to find another mixer.