PLC Digital Output Card is It Only Give 500mA?

Most solenoids (assuming you mean a water control valve type solenoid) need about 9w minimum.
The big Question is ... 500mA, at what voltage? (I know you said 'digital' possibly implies 5v)
500mA at 240V AC is 150W, plenty to operate a solenoid.
500mA at 12v DC is maybe enough if you can find the right solenoid.
500mA at 5v isn't going to do it. (Although there are special latching solenoids which will operate down to 4 volts on short pulses of low current)
I suggest you read the spec' for the solenoid and the output card.
I suspect you need a relay as you have already surmised.
Del

In our area 24VDC solenoid valve,

Fardan

... and what wattage is the solenoid?
... and what voltage is the output from the board?
Read the specs' for pities sake.
If you haven't got the spec's then google the board and solenoid part numbers, c'mon, make some effort.
If I have to come over there....
Del

Thanks pal, you gave good answer,

so it depends on the spc's of card and solenoids,

my last respond is just to tell 24Vdc and not meaning I want you to respond again.

fully appreciated

As Del has instructed - check your specs on the relay.

If you have a seriously big relay, most PLC manufacturers offer a relay output card that will handle several amps. I have used these, with smaller amperage draw relays, as an interface card to try to isolate the "noise" of the relay you are running from the PLC system. For most "ice cube" and "octal base" style relays, the 500ma card will handle them. If your relay has too much draw for the 500ma, put in an interface relay with a lower draw coil and a good rating on the contacts.

You also will have to check what the maximum allowable draw is for the output entire card. Often the 500ma is good for only a few of the outputs at once, if this is not a relay style output card, but one that draws from the PLC backplane source. With a 500ma output per channel, the card maximum will likely be around 4 amps. (this is just an estimate for example - check the card specifications to be sure and stay under the card maximum too)

But as Del said - check the specs to be sure.

And, of course, you will want to protect your driver (Output card or Interposing relay) from the reverse voltage spike produced when the relay is turned off. I've seen many a driver destroyed when this wasn't done.

Adding a diode (1N4005) across the relay coil is a frequent method of doing this that clamps the reverse voltage at 0.7 V.

Alternately, putting a MOV across the relay coil is another method that will de-energize the coil much faster by clamping the reverse voltage at a higher level.

The card may not be the weak point. I saw a pressure transmitter totally fried after an E-Stop button was pushed, and they did this twice before someone decided to look into the problem. The E-stop ran a very large contactor which had as expected, a very large coil. The surge from that coil relaxing found the weakest link in the 24VDC system, which was not the PLC cards, but a pressure transmitter. The transmitter power was not directly wired to the coil supply. They had seperate sub-feeds off the 24VDC power circuit. The surge went through the entire 24VDC system looking for this weak point. The bad part of this was the control panel was designed and built by a panel shop associated with a very very large electrical equipment manufacturer. I could not convince their engineer that the coil needed a diode across it. When he wasn't looking I installed one and cured the problem.

Right on.

As already mentioned it depends on the card and solenoid.

AND

Sometimes it is better to put a relay between the card and solenoid you need to drive, because:

- relays are far cheaper than the PLC card, so if the cable at the solenoid end is shorted (due to miswires or being submerged in muddy water) nothing important is damaged. Same for voltage spikes.

- a dead relay is easier to source than a PLC card, especially in remote areas.

- relays can allow the local repair person manually turn the solenoid on & off, which is handy for fault finding.

- relays can isolate a PLC from line bourne electrical noise, lightning strikes etc.

Thanks all,

fully appreciated

Fardan