Relay - What to look for

If I have a 24V digital output card and I want to switch a 240V 1 amp pump what type of relay do I use?

Is it a 24v power relay? Is there a naming regime for relays, like 24V (coil) 240V 1 amp (load)?

Can anyone suggest a good din rail mounted option?

Thanks,
James.

hmm

Many brands of relays you can use.
Indeed, coil and load is allways specified.

1A are small relays.

Google for: 24V relay omron din

Regards,
Gerry

jimmycooker said:

If I have a 24V digital output card and I want to switch a 240V 1 amp pump what type of relay do I use?

Is it a 24v power relay? Is there a naming regime for relays, like 24V (coil) 240V 1 amp (load)?

Can anyone suggest a good din rail mounted option?

Thanks,
James.

Click to expand...

Thanks for your reply, am i right to say that the load side is often rated in amps only, and the kW / volatage load can vary around this using formula K(Watts) = V(Volts) x A(Amps)?

Just a thought.

"Pump" to me implies a motor load.
An induction motor will typically draw 400 - 600% FLA at start up.

You should check the specifications on the relay for the inductive amp rating.

Hope this helps.

Jimmy
I think it good to think in terms of load ie
What are the voltage and current requirements of motor AND as said allow for starting current.

The coil voltage and current must match the capabilities of PLC output too.

Generally it is best to put in a MOV to protect PLC output from voltage spike from relay coil collapsing field when turned off. Need and importance rise with rising coil size.

Dan Bentler

leitmotif said:

The coil voltage and current must match the capabilities of PLC output too.

Generally it is best to put in a MOV to protect PLC output from voltage spike from relay coil collapsing field when turned off. Need and importance rise with rising coil size.

Click to expand...

Did you mean diode? If the output is 24VAC, then MOV could be used, but if it's a 24VDC transistor output, a reverse biased diode is normally what's used, but only if the specs of the relay coil are at the high end of what the output point is rated.

He should easily be able to find a 24vdc relay with 5 or 10amp contacts that draws very little current (<25% of his output point mA rating), and shouldn't need any additional protection.

http://www.automationdirect.com/adc...-z-_Timers/10A_Electro-Mechanical_Cube_Relays
http://www.automationdirect.com/static/specs/qlrelays.pdf

Well he did not say AC or DC so made generic. Have seen so much AC control just automatically thought MOV. OOPS.


Dan Bentler

Don't most smaller relays like he'll be using already have a resistor in parallel with the coil for the inductive kick? Do most of you still add an additional protective measure?

Shawn

Questions that need answered are is this 240VAC or DC? Single phase or 3 phase?

If you are controlling a pump motor then you probably need a motor starter a 24V coil, overloads and an external set of fuses or a CB protecting the 240V feed. I say probably because the pump motor may have some kind of internal overcurrent protection.

With all due respect, it sounds like the orginal poster is not qualified to design motor control circuits. There is a difference between being a programmer and a actually drawing up a circuit and spec'ing components.

Please call in a professional.