Slo-Syn as indexer

[rlee53]

I would like to use a small synchronous motor, such as a slo-syn or oriental motor, in an indexing application. Around 60 indexes per minute, one revolution, triggered by a photocell. It will be triggered to stop when the crank arm passes a prox. The motor will have a crank so there is very little starting inertia as it will be stopping at top dead center of the stroke.

Question: How to control. I am looking at a small PLC/smart relay controller such as the Siemens LOGO. The brochure indicates it can have 4 relay outputs, 10A for resistive load, 3A for inductive load. The motor need .5A continuous.
Besides the RC in the motor connection diagrams, do I need some protective elements between the controller and motor such as fuses, relay, starter, contactor etc., or can I drive it directly from the PLC or smart relay.

 

[itsmoked]

Sure! You always want protection. If you use a PLC (fine idea) to control the motor with some sort of relay (solid-state or mechanical) you want some sort of protection in the power leads coming from the source to the motor. You can use a small panel mount breaker or a fuse. Look at the motor's current draw and then use a slightly larger rated breaker or fuse. That type of motor will not have a large starting current.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[powerjunx]

rlee53,
As itsmoked suggested, a protective device is a must no matter how small it is.

 

[rlee53]

Thanks all.

So I just need to add a fuse or breaker. Will the frequent starting and stoping, 60/minute, be a problem for the Logo's relay output? It has 4 relay outputs, 10A for resistive load, 3A for inductive load.

 

[MikeHalloran]

If the load torque goes negative after TDC, as with a spring loaded cam or a piston compressing something, you may have recurrent problems getting the motor to actually stop at TDC.

Take a look at stepping motors.





Mike Halloran
Pembroke Pines, FL, USA

 

[OperaHouse]

If you want to go both directions, there may be a problem with using solid state relays. I remember years back a friend had this reversing setup with two triacs. He kept blowing out triacs when one would false trigger while the other was on. This would make the motor look like a dead short to the triac. A small value resistor in series would limit the current, he went with a relay. A good solution wouls be a solis state on and use a relay for direction. I would calculate the lifetime number of cycles that you expect It is pretty easy to get a half million cycles and that is close to just the mechanical life of the relay.