How to wire surge protected solenoid cable that has a diode to PLC

[JJ1234]

I have a SC9-LS24-3 surge protection solenoid cable from automation direct.

https://www.automationdirect.com/ad...quare_din_style)/9.4mm_(din_style)/sc9-ls24-3

I believe since it has a flyback diode, if I wire it incorrectly it will cause a short.

Its 24v DC, has a ground and 2 wires one labeled (1) and the other (2). The PLC provides the power to the solenoid.

According to the electrical diagram of the part, the current flows through the diode from cable (1) to (2). So this means that the (2) cable should be positive?

 

[Picklemon]

According to wiring diagram 2, the cable doesn't look like it cares about polarity, since it has 2 opposite LEDs ands 2 opposite Zener diodes. Unless there is a defect, the chance if a short looks minimal.

The polarity is going to depend on how the valve needs to be wired and whether your PLC output is sinking or sourcing.

Based on wiring diagram 1, I think (1) should be +24VDC and (2) should be 0VDC.

Let us know what PLC output module and valve you are using and I can confirm the wiring.

 

[JJ1234]

Thanks for the help. I can figure out the wiring. Just wasn't sure if there would be a chance of short.

Doesn't it not make sense to have two diodes opposed to one another? Wouldnt that just not let any current flow and defeat the purpose of a flyback diode?

 

[PLCDontUQuitOnMe]

Thanks for the help. I can figure out the wiring. Just wasn't sure if there would be a chance of short.

Doesn't it not make sense to have two diodes opposed to one another? Wouldnt that just not let any current flow and defeat the purpose of a flyback diode?

Zeners aren't regular diodes. Regular diodes only conduct in forward bias and not in reverse. Zeners conduct in reverse bias if the voltage is higher than the zener voltage (in this case 47v for the 24v version and 200v for the 120v version).



This means the two zeners in reverse bias will not normally conduct, until you exceed the zener voltage, which would happen when turning the valve off and the opening of the contacts will cause the solenoid which is an inductor to release a high voltage in opposite polarity to what is used to turn it on.



So to put it simply, the connectors they show here can be used in either polarity and will provide surge suppression with either polarity. The polarity required will depend on the valve itself and which pole is positive and which is negative (for a DC coil). The surge suppression in the connector will work in either orientation due to the back to back zeners both oriented in reverse bias.

 

[JJ1234]

I see.

Thanks for the help!

 

[James Mcquade]

PLCDontUQuitOnMe,

you can buy 5, 10, 12, 24, 48 volt dc zener diodes.
they will conduct past that point and will give you a voltage less the zener diode rating if i remember my electronics correctly.
james

 

[JesperMP]

If you follow the tech specs for SC9-LS24-3 you will find a diagram no. 1 that is different from the ones you posted. The connector does not have a flyback diode. The correct diagram shows bipolar zener barriers and bipolar LED indicator.

 

[LegacyLee]

A 1N diode wired polarity-correct has never let me down. Why zeners? Zeners for wieners? Why would anyone care to "rise above" the fly back? Zeners are great but not for absorbing that kind of spike. Just a normal diode does that trick.

 

[Bit_Bucket_07]

A 1N diode wired polarity-correct has never let me down. Why zeners? Zeners for wieners? Why would anyone care to "rise above" the fly back? Zeners are great but not for absorbing that kind of spike. Just a normal diode does that trick.

Zeners can be useful for voltage regulation.

 

[LegacyLee]

Sure, but for spike absorption? Overkill. Keep that simple, IMO.