Best way to switch D.C Coils...

I am starting an upgrade of a Desma Rotary Injection Press which uses 200vdc coils for its hydraulic valves. What is the best way to switch this load?

I have upgraded other Injection presses, but they use 24vdc coils and I used Opto22 solid-state switches. It hasn't been easy to find a solid-state device for this voltage. What about relays and suppression? Anyone with any experience in this situation?...

Eric,
200 DC seems an odd voltage, are the coils quite large?

The Opto22 relay outputs use reed relays and won't handle much power without welding shut.
Perhaps you could use a solid state AC output module with a separate rectifier for each coil, that must be cheaper than replacing all the solenoids. You would need a transformer wound to give the correct DC voltage.

There are other ways of controlling DC coils that I wouldn't try to convey without a sketch.
If you are interested send me a simple wiring drawing and I will respond. [email protected]

Roy

HexFETs come to mind as they could be easily
driven by PLC transistor outputs and are
fairly hardy in inductive switching. It's a rather odd voltage for automation stuff. I would use appropriate suppression in any case as 200 VDC coils could have fairly high inductance. Products packaged for automation might be hard to find.

Regards
cww

Whatever you use to drive it, relay or Transistor, make sure that you use a flyback diode, or Zener Diode across the coil (See internet or textbook if you are unclear as to configuration). This will keep your coil from generating infinite voltages (or better said, approaching infinity until it cooks some component). You probably want to use a flyback diode unless your off switching time is very critical.

Make sure if you have an unregulated DC power supply to switch the coil that your drive circuit can handle the *peak* voltage of the ripple of your Transformer/Rectifier/Capacitor type power supply. 120VRMS for instance has a peak of 170V (multiply by square root of 2).

~KEJR

There are some industrial products available that might fill this need such as these DC switching solid state relays:

http://www.power-io.com/products/hdd.htm

http://www.crydom.com/products/productFamily.aspx?id=39

http://www.teledynerelays.com/industrial/s60dc40.asp

You will need a diode for suppression across the solenoid.

Thanks for all the input. Because of price I will probably go the way of relays and snubbing. The original system uses limit switches and general purpose contactors to switch the 200vdc coils(and has done so for 30+ years!) I was given some excellent sources for future use and and very appreciative of them.

Thanks everyone.