Interposing relay surge suppression

rlmunoz

Member
Join Date
Dec 2002
Posts
12
I have read all posts in the forums, but still can't see the visual of the requirements of surge suppression on interposing relays. My application is a 24VDC output from an AB controller to a 24VDC/120VAC interposing relay to drive a hydraulic solenoid valve. To simplify the question, I have attached a picture. Do I need surge suppression on the DC side only or both the DC and AC sides? Do I need anything else?

interposing relay.gif
 
Both, very cheap insurance. See picture and PDF's below for more info on the subject.

UsingSurgeSuppressors.jpg
 

Attachments

  • RelayCoilSupressionwithDCRelays.pdf
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  • relay contact life.pdf
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Thanks...reason why we went with this setup instead of direct 24VDC solenoides is because we are extremely space limited. The 24VDC solenoids were too big.
 
Most of us would use a "terminal block relay" for the 24VDC side. Look up AB 700-HLT1Z24 for an example, altho everybody else makes something like this too. These normally have the diodes built in, for which your electricians and every maintenance guy for the life of the system will thank you.

If you're using general purpose relays, then yeah you're going to need a lot of space.
 
Do great minds think alike? That is the exact same model number that I am using. However, it looks like this only takes care of the relay suppression. I'm thinking I need another AC suppressor across the hydraulic solenoid terminals to maximize the debouncing protection?
 
Yes HLTZ terminal block relay.

Then when your buy your 110vac solenoids, bet them with DIN Plug connections on the solenoid coil.

You can buy a premolded Mating DIN Plug with MOV or RC (and also an Indicating Light) all molded in together.

Yes I know you can buy your own DIN plug only, wire your self, but why bother, and also at 120vac it is better to seal out oils and contamination.
 
Yep, you should install suppressors on the solenoid coils to preserve the relay contacts. The same reason you install suppressors on the relay coils to protect the PLC outputs.

And to lessen noise in the control system all the way around.
 
Hi Guys - I`m new here so be gentle!

I found your fine forum as the result of a Google search, I have recently dipped my toe in the PLC world and liked it - still have an AWFUL lot to learn though

I stumbled across this thread as I`m having an issue with back EMF destroying relays and while I know I need a Diode or similar I am bewildered by the choice

I have read that I should fit a Diode at least 10 times the working voltage (which is 24V DC) - I assume this means under normal conditions the Diode does not allow current flow in either direction but once the back EMF voltage reaches ~250V then the diode allows the excess current to bypass the contacts, thus saving them

Or am I thinking about this all wrong?

Thanks in advance(y)
 
"premolded Mating DIN Plug with MOV or RC (and also an Indicating Light) all molded in together."

I am not familiar with this. Do you have an example part number and vendor?
 
i am having similar problems with a festo valve which uses din plugs and after speaking with our supplier they tell us that they do not do a surge supression din plug for that valve type, could anyone recommend a good solution, its a 24vdc coil been driven by a 1794-OW8 flex I/O module and we seam to replace these once every 4 months
 
paulcs

we use these on our smaller valves, they are from festo and have 2 led's one for coil energised and then the other comes on as it disipates the back EMF
 
1N4007 Works well for a general purpose flyback diode on 24Vdc loads. Might need something bigger for some of the super huge hyd. cylinders and such, but most of them are pilot operated anyhow.
 
Hi Guys - I`m new here so be gentle!

I found your fine forum as the result of a Google search, I have recently dipped my toe in the PLC world and liked it - still have an AWFUL lot to learn though

I stumbled across this thread as I`m having an issue with back EMF destroying relays and while I know I need a Diode or similar I am bewildered by the choice

I have read that I should fit a Diode at least 10 times the working voltage (which is 24V DC) - I assume this means under normal conditions the Diode does not allow current flow in either direction but once the back EMF voltage reaches ~250V then the diode allows the excess current to bypass the contacts, thus saving them

Or am I thinking about this all wrong?

Thanks in advance(y)

ASSUME that line voltage drops to zero when you open the switch (relay contact) controlling your relay. The coil field will decay and generate a voltage on teh line. I do not know about using a diode rated for 10 X line (250 V) but it sure seems like good idea to me. Ones I bought at a local electronics store were 600 V rated - suited me just fine for just a 18V transformer secondary. Use this setup as a 0 to 18 VDC 0 to 25 amp power supply to drive motors, medium relays whatever - diodes are just fine so far.

Dan Bentler
 
cheers damian, when i got to work i looked through one of our machine manuals and it has a note on the drawings to fit a 1N4004 diode to all DC coils, i looked these up also and the difference is this one has a 400v peak repetitive reverse voltage and the one you mentioned a 1000v PPRV, but what do they mean in laymans terms and whats the advantage/disadvantage of the two?
 

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