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benjybolox

Cpm1a Switching 24vdc, 1.5amp Solenoids

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Will a CPM1A with relay outputs switch 24dc, 1.5amp solenoids on and off without dying very quickly?

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From Manual #W317-E1-1, Relay output rated at 24vdc 2a maximum. This rating provides for 100,000 operations of the relay. Additionally, is 1.5a the inrush or steady state rating of the solenoid?

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As far as I know it is the steady state. I didn't think you got inrush with DC, not sure why I thought this. Should I put a diode parallel to the solenoid or is this not needed?

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It is recommended to put a diode on an inductive load.

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Just from an old phart's perspective: Why risk a $300 PLC for an extra $10 relay? I'd put in an interposing relay.

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You don't need to be an old phart... You can also be a relatively young upstart who has been around a bit.... If using a transistor output card use a interposing relay. Put a free wheeling diode in parallel with the coil to disipate the emf. If using a relay output i would still use an interposing relay and i would also use a diode in parallel with the coil of the relay.

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A diode of type 1N4007 will do the trick come to think of it mabey a 1N5404 / 1N5408 (both rated at 3 AMP) might be more suitable.

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Don't you think is better to use a DC SSR? I used in many applications and it works very well. Regards, GreyWolf

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Thanks everyone for your help. Got myself some little omron relays G2R-1-SNDI , with 24v coil and built in diode. These will do the trick Im sure

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... G2R-1-SND relay has a diode accross the coil (shown in circle), protecting the switching device (PLC). This is great, it will help ensure longevity for the PLC output relays / transistors. However, a diode accross the accross the switched load is what we recommend as this will enhance the life of the relay contacts. See diagram below showing solenoid load connected to output of relay with suppression diode connected in reverse bias to suppress back emfs (visable arcs on relay contacts) when load is switched off, and help ensure longevity of the relay contacts. Alternately, a G3R SSR relay will fit into the same base, but your relay solution with a diode accross the load will likely be much cheaper. Nibroc Edited by Nibroc

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Thanks for your help, however I have a question about the positioning of your diode. As far as I can remember, current will try an continue to flow in an inductor if interupted suddenly (hence the arcing at the contact). Fly wheel diodes provide a path for this current to continue to flow once the contacts are open, preventing the arcing. from your diagram it looks like arcing would continue to occur as there is still no path for the current to flow into the solenoid, apart from acrodd the open contacts. Before reading your post i would have put a diode between negative and terminal 3 of the relay, providing a loop for the current to flow after the contact has opened. However I do see that the positioning of your diode will prevent spikes going to the power supply. Am I missing something?

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Oops .... diagram was incorrect!! I have updated the diagram, and is now correct. Nibroc

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