1746-OB16 Module Limitations (SLC500)

Here's what I've got...

SLC504, 1746-OB16 (Transitor) DC sourcing output module. I'm planning on powering small solenoids with this (I understand I will need to use a snubber or diode across the load), but what I really need to know is this...

I've read the specs on the card and they say max. current per channel is .5 Amps and max. current for the card is 8 Amps. The power supply I was planning on using is a Sola 2.5 Amp hooked across terminals VDC and Common. With the limitation of .5 Amps/Channel, I cannot do this right? Any recommendations (besides relay output cards...I have 24 solenoids and that would be 3 relay outs $$$$$)? What are my options?? Thanks in advance! Bobby

You need to know what the solenoids draw (amps).

The loads connected to each output point must draw less than 0.5 amps. The total of all the loads connected to the card must draw less than 8 amps at any given time.

If they draw less than about 2.5 amps in the worst case scenario (all that can be simultaneously powered in the application) then you can use the power supply you have chosen.

DC Solenoids can be anywhere from 3 or 4 watts to hundreds, most around the 6 to 15 watt range.

How many solenoids will you be using and what are the specifications for power requirements?

Okay. This shouldn't be a problem then...the solenoids are going to draw 105mA each, and there will only be one energized at a time with the logic. I guess I am confused about the DC fundamentals of it. I was thinking the power supply would generate 2.5 Amps, all of which would be going through the output, but I think I see where I was wrong! It's not a single path circuit. The circuit runs from VDC terminal to Common and I am making a second path with the output, so current through the channel would depend on the load. Is that where you're coming from and is that correct? I appreciate the quick responses!

phaedrusc6 said:

I guess I am confused about the DC fundamentals of it. I was thinking the power supply would generate 2.5 Amps, all of which would be going through the output, but I think I see where I was wrong! It's not a single path circuit. The circuit runs from VDC terminal to Common and I am making a second path with the output, so current through the channel would depend on the load. Is that where you're coming from and is that correct?

Click to expand...

It's not the available power or the path that makes the difference, it's the load. Current will only flow where allowed and required by the load.

That excess current may be available, but won't be going anywhere unless demanded by the work being performed by the loads.

That power supply will supply voltage and current. It will "generate" zero amps until you connect a load, 105ma with one solenoid, 210 with two turned on and so forth.

The supply doesn't generate current flow, it merely makes it available. The load at the ends of the wires decide how much current is needed. Add up the loads, include some margin for safety and future expansion, and fuse to protect the PLC card and devices.