BEST way to switch a solenoid with PLC?

I have an AD DL05 with DC IO. I'm wanting to switch a 3 way air solenoid (driving an air cylinder) "up to" twice per second. Constant run time would be an hour or so per day at most. Most jobs will require a run time of less than an hour. As I understand, speed and number of cycles pretty much eliminates using an electro-mechanical relay.

I figure a 24VDC coil SSR driving a 110 VAC coil solenoid is an option. I've got an old 110 VAC solenoid that was pulled from a scrapped machine.

What about 24VDC coil solenoids? Do these switch faster than 110VAC coil solenoids?

What type of surge (spike) suppresion should I use to protect the DC outputs on my PLC?

Thanks in advance.

snaggletto said:

What about 24VDC coil solenoids? Do these switch faster than 110VAC coil solenoids?


Thanks in advance.

Click to expand...

Here is some reading for you
http://www.plctalk.net/qanda/showthread.php?t=41563&highlight=ac+dc+solenoid+speed
The last post on this thread sums it up. Check with the manufacturer.

So, this is kinda like what motor oil is best used in your car? Ok then, I will buy an SSR to drive my old 110VAC solenoid.

Still yet, do I even need to protect the PLC output when switching an SSR? Do I need to protect the SSR contacts from the solenoid coil? Thanks.

snaggletto,

In my opinion there is no need for extra protection of a DC output that is driving a SSR. This because there is no inductance or magnetic field to collapse.

The SSR on the other hand could benefit from some protection. The exact types are likely to spark (pun intended) a long winding thread. So I'll put my two cents worth in right now. A fuse would be mandatory. In addition for AC inductive loads, I prefer MOV's (metal oxide varistors).

snaggletto,

Are you still "pecking"? As in this thread?
http://www.plctalk.net/qanda/showpost.php?p=87337&postcount=1

An SSR, 25 amps or less will have a Triac output with built-in Snubber. An MOV across the output (pins 3&4) is optional. With Triacs, back EMF can cause false triggering of the Triac's Gate, causing the solenoid to 'chatter'. That's why most have Snubbers built-in.
The SSR input is an optoisolator - an LED. No protection is needed.

For 40 amp and up, back-to-back SSR's are used. SSR's don't have the problem of false triggering. Some have built-in snubbers, some don't. I prefer a snubber as good practice. I like to know the back EMF is supressed, rather than letting it dissipate through the wiring and create electrical noise.

Thanks for the input on the MOV and fuse to protect the SSR. I'll give it a shot.

No, the drilling machine problem was solved with a CNC vertical machining center (milling machine) and a vibratory bowl fed track that auto-loads parts into a fixture to be drilled. The "pecking" motion and the RPM and feedrate of the drill is all programmed on the mill. We have basically doubled our drilled part production rate, dramatically improved our quality and eliminated 95% of the human labor required to do the job.

My current project is this one, http://www.plctalk.net/qanda/showthread.php?t=41534&highlight=cut+length a cut to length machine that cuts 7x7 braided stainless steel "aircraft cable." We use these to make tethers for out parts. We cut all different lengths from 8" through 26" thousands at a time. We have mostly completed the mechanical part, and tests show that we can servo feed our 26" part in ~3/4 of a second. We are working on a powered de-reeler to provide slack in the cable so the servo feed motor doesn't have to pull the weight of the roll of wire. The solenoid valve is driving an air cylinder which cuts the wire when the servo amp gives the "in position" signal. Speed of the cutter is crucial, as this will be the slowest part of the system. This machine, again, will be a DRAMATIC improvement over the previous labor intensive monstrosity.

Our shop is small and low budget, but I've got big ideas Thanks for the help.

I usually buy stuff from Automation Direct because of prices and accessibility, so I was considering this http://web1.automationdirect.com/ad...ys_-z-_Timers/Solid-State_Relays/AD-SSR210-DC. They mention an "internal RC (snubber) network." Will this be sufficient to protect the SSR from the 110VAC air solenoid?

As for a fuse, I would never imagine the solenoid pulling anywhere close to 10A (rating of the SSR in question). What size fuse and why? Thanks.

Be aware that an AC switching SSR can take up to 17 milliseconds to turn off after the input to the SSR is switched off.

snaggletto said:

I usually buy stuff from Automation Direct because of prices and accessibility, so I was considering this http://web1.automationdirect.com/ad...ys_-z-_Timers/Solid-State_Relays/AD-SSR210-DC. They mention an "internal RC (snubber) network." Will this be sufficient to protect the SSR from the 110VAC air solenoid?

Click to expand...

Yes.

snaggletto said:

As for a fuse, I would never imagine the solenoid pulling anywhere close to 10A (rating of the SSR in question).

Click to expand...

It will pull infinite current if it burns up or the wiring shorts. SSR's can expand and/or smoke when feeding a short.That's my experiene with hockey-puck types. Not sure what would happen with the heatsink type.

snaggletto said:

What size fuse and why? Thanks.

Click to expand...

Size about 4 times the current rating of the solenoid. This allows for surge current when energizing.