Current limits?

Hello all,

This is not precisely a plc question but...

I have a pair of small (~0.5 hp) split phase motors on a machine. I want to stop them slightly before the rotors are locked. (Currently we are just using run time as the limit.)

I would like to control based on torque or current. Does anyone know of a device that provides a (reliable) device with a discrete output and a precisely adjustable current trip setting?

Thanks,

Thomas

I do - I used 6 of them on some 90W motors to detect if they were jammed.
Will get the MFG and model for you as soon as I search through some old documentation...

We've had good luck with N-K http://www.nktechnologies.com

Check out products made by Symcom, Inc. in Rapid City SD. This is exactly their mainstream line of business.

They make a variety of motor monitoring products but the most well-known is "MotorSaver" and "PumpSaver".

Tom and Dick: Thanks for the info these look like they might work.

RoTaTech: If you find anything, I'll keep an eye on this thread.

Again, thanks all.

Thomas

Thomas said:

Hello all,

I have a pair of small (~0.5 hp) split phase motors on a machine. I want to stop them slightly before the rotors are locked. (Currently we are just using run time as the limit.)

I would like to control based on torque or current. Does anyone know of a device that provides a (reliable) device with a discrete output and a precisely adjustable current trip setting?

Click to expand...

I'd suggest putting variable frequency drives on the motors. With modern IGBT-based drives, it is quite possible to have speed ranges from -150% to +150%, with 100%(+) torque throughout the range. You can even run them at zero speed with 100%(+) torque.

You can do internet searches, but there are probably 25 decent manufacturers that can supply these. Vacon, Siemens, ABB, and AB are four that come immediately to mind. At least three of these can be run in torque-control mode. All of them have the capability to be precisely current-limited.

Good luck.

Did I mention this is a small (read "cheap") improvement I'm playing with?

Don, these are single phase motors. Forget frequency drives. Except for extremely narrow obscure circumstances, variable frequency is for three phase motors only.