7i77 and Pneumatic solenoids

Not sure I am reading this correctly and want to ask before I let the magic smoke out.

Can the 7i77 control typical 24V pneumatic solenoids directly or do I need to place relays between them?

I am looking at using a 5V PS to power the 7i77 and a 24V PS to power the Field Inputs. I think that's correct...

Thanks.

The 7I77 can drive small solenoids and relays directly, but if they draw more than 60 mA
they _must_ have flyback diodes added across their coils if not already present.

Maximum per output current is 350 mA and maximum per driver chip current is 1.4A
This limits you to four 350 mA loads per eight outputs (or 175 mA per output max if all
outputs can be on at once)

Peter,

These are Bosch pneumatic solenoids and proving difficult to track down info on them, but best I can tell they are 24VDC and range from .8 - 1 Amp. I'm still trying to get some definitive answers on this. There are only three air solenoids. They are the power chuck, the tail stock quill, and the parts catcher door. The parts catcher and the tail stock are pretty light duty fare. The other stuff I am considering is relays for safety - like for the servo drive voltage and other stuff like relays for the oil pump. What is a "flyback" diode? I better go google... Thank you Peter.

Thanks, John. I may well end up with those or something similar...

I have dug around a bit more and everything I can find shows that the coils on these can range ( depending on model ) from 2.1 - 5.1 Watts. My Goofle-Fu tells me that this .0875A - .2125A. So... 90mA - 213mA? Does that sound right?

Also, how would one calculate the value of a Flyback diode? And in what orientation are they applied? ( +/- )

I have never seen a solenoid direct driven from the PLC, as well as each output can drive 2Amps.
They have always a relay between. One big advantage is, the relay and the solenoid can have different voltages, DC/AC or instead a solenoid, you can switch a big motor, like chip conveyor, coolant Pump.

I am driving a couple of small 2/2 air solenoids directly from the 7i77. Coil draws 5 Watts, well within range of the 7i77 capabilities.

I don't know what benefits an extra relay would add. Plenty of drawbacks though; extra wiring that clutters and complicates things, another extra component that can break.

Regarding the flyback diode: just about anything will do. Good old 1N4002 for example. These will also fit easily in the plug on the solenoid if you prefer that location.
Wiring of that diode is exactly opposite to output, so the cathode (terminal marked with a ring) goes to the 7i77 output/plus wire in your cable, anode (unmarked terminal) goes to GND/minus wire in your cable.

DaBit wrote:

I am driving a couple of small 2/2 air solenoids directly from the 7i77. Coil draws 5 Watts, well within range of the 7i77 capabilities.

I had started to write a post asking for clarification on this when the light bulb went off. So thanks to all for participating in it.

Even if my solenoids are the highest rated of the type I have found within their models ( 5.1 Watts ), then at most they would draw 213mA. Which is less than Peter's example of using all at once and having 350mA per EACH.

So... ... ... these WILL work. BUT! Because they are more than 60mA, they will need to have the flyback diodes in place.

Have I got this right so far?

Wes, thanks very much for the simple, easy to read explanation as well as the idea/example of where I can install them. Much appreciated.

I'm off to order some diodes in a little bit...

Thank you, boys.

Zahnrad wrote:

Wes, thanks very much for the simple, easy to read explanation as well as the idea/example of where I can install them. Much appreciated.

DaBit - I have to apologize. I confused you and member DaOne when replying and responded to you as "Wes". My apologies.