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Slo-Syn as indexer

Slo-Syn as indexer

Slo-Syn as indexer

(OP)
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.

RE: Slo-Syn as indexer

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

RE: Slo-Syn as indexer

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

RE: Slo-Syn as indexer

(OP)
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.

RE: Slo-Syn as indexer

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

RE: Slo-Syn as indexer

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.

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