Maximum length of cable from digital output to solenoid valve

[bmsg]

I have an application where digital outputs from a PLC will be required to operate a solenoid valve in the field - 800m away(i.e., a cable length of 1600m between the PLC DO terminals).
The solenoid valve is rated 24V DC, 12W and will work upto 22V DC.I want to use a 1.5mm2 copper cable (say), which has a resistance of 13.14 ohm/km. The digital output card is rated for 24V DC (say). Will the valve operate at all?

Or, do I have to use a higher interrogation voltage and solenoid valve of a higher voltage rating?

I know this is all a simple problem involving Ohm's Law - but, somehow, I am not sure.

Will someone comment?

 

[torontogill]

bmsg

The simple answer to your question is no, the solenoid will not operate if it requires a minimum of 22v.

The length of cable run is 800m (not 1600), you qoute the resistivity of 1.5mm cable as 13.14ohms, that means the 800m run will have a total resistance of 10.51ohms. The rating of the solenoid is 12w @24v, that gives us a current of 500mA (0.5A). So applying ohms law, we get a volt drop of 5.255V, so the voltage at the solenoid end of the cable will be 18.745v. You could adjust the power supply output to say 29-30v, then there will be enough voltage for the solenoid to operate. check that your DO card in the PLC will accept this higher voltage at it's terminals first.

Paul

There are 10 types of people in this world....
Those that understand binary and those that don't!