surge suppression for AC pneumatic valves

[MikeW]

Read relay specifications closely ...

I always install interposing relays on all solenoid valves. If something goes wrong you destroy a $6 relay not the PLC output and the 781 relays are less expensive to replace than fuses.

If the "781" you are referring to are AutomationDirect offerings, be aware what loads you are switching, see page e27-21 under Service Life http://www.automationdirect.com/static/specs/78relays.pdf . They are rated at 200,000 cycles resistive but only 1,000 cycles inductive when you read the "*" note at the bottom of the page. They added this to the specification in 2006 after I installed 6 dozen of them in 2005 and then started having random "control problems" that went away once the 781s were replaced.

YMMV, just my $0.02.

 

[arkyny]

I have used a surge suppressor for this problem that I bought from Grainger. Before, I had spikes destroying inputs on my PLC cards. Since I installed this suppressor, no problems. Wires across the ac input. Grainger #---6ckp1 @ 79.35. You might try one, they worked for me.

 

[MikeW]

I have used a surge suppressor for this problem that I bought from Grainger. Before, I had spikes destroying inputs on my PLC cards. Since I installed this suppressor, no problems. Wires across the ac input. Grainger #---6ckp1 @ 79.35. You might try one, they worked for me.

The relays in the problem facility were surge suppressed. :nodi:

 

[Calistodwt]

As your SOV are an inductive load you need to determine / estimate the value of the inrush current when switching. You also need to determine what the inductive load rating is for your PLC relay outputs. If the PLC relay contacts rating is less than the SOV inductive switching current then you need to install a sutable interposing relay.

 

[Skiroy]

http://catalog.phoenixcontact.net/p...52611858&parentUID=852611857&reloadFrame=true
this is it

EDIT

no try this one
http://catalog.phoenixcontact.net/p...reloadFrame=true&UID=2905417&parentUID=205032

Those look good. I contacted them for pricing. They are basically what I was looking at from Allen Bradley but the cost was $1600.00 for 40 outputs. If this company is cost effective that will be the solution for sure. But if not I have to look into an alternative. So if I were to have to install snubbers I wanted an opinion on how to wire it. I posted some pictures of what Im working with.

You can see the I/O modules are to small and it would look rediculous to have a bunch of snubbers hanging off of them. The valves show how the cable conduit goes into a manifold that supplies several valves power,so I dont see this as a possibility because of lack of room in the conduit.

If you notice the small white terminal blocks located under the wire duct that is under the PLC. This is the only place I see as a possibility.

 

[iant]

move the duct up about 100 mm as well s the PLC
Plenty of room
ther eis no way I would even attempt to drive those valves directly of any PLC Output

 

[Skiroy]

move the duct up about 100 mm as well s the PLC
Plenty of room
ther eis no way I would even attempt to drive those valves directly of any PLC Output

So interpolasing relays with surge supressors are a must here?

 

[Skiroy]

As your SOV are an inductive load you need to determine / estimate the value of the inrush current when switching. You also need to determine what the inductive load rating is for your PLC relay outputs. If the PLC relay contacts rating is less than the SOV inductive switching current then you need to install a sutable interposing relay.

How do I calculate these values?

Here is the PLC specs starting on page 166. I have the
1766-L32AWA/A.

http://dl.dropbox.com/u/96052065/1400 user manual.pdf

 

[iant]

So interpolasing relays with surge supressors are a must here?

the surge supressors ar usually for the interpositn relay coils.
but someting for the valve coil is an excelent Idea

 

[Skiroy]

Does anyone know of any other interpositn relays that are reasonably priced. AB are $40.00 each and I still have not gotten a quote back from the company someone suggested. Any one here know of any interpositn relay from automation direct or grainger?

 

[OkiePC]

So interpolasing relays with surge supressors are a must here?

You have gotten outstanding advice here already, but in a nutshell, for reliability, yes.

I use Quencharc RC network type packaged snubbers for AC inductive loads. They make them with fork terminals to match the width of most NEMA contactor coils. They re bright blue. They may leak enough to light LED indicators, I don't recall the exact unit, but the few (maybe 3 of literally thousands of these things) failures I saw resulted in an obvious physical damage to the little bright blue package. I think we used some with flexible flying leads too.

I recall my previous employer having a fairly high out-of-the-box failure rate with those AD relays, but they bought extra and quickly exchanged the bad ones.

Relay life "is what it is", so go back to a solid state PLC outputs (triac or transistor) to drive any interposing relays if possible...you don't want to compound your odds against the MTBF of relays by using relays to drive more relays.

BTW, my favorite relay is a big pile of them in the dumpster.

 

[iant]

Does anyone know of any other interpositn relays that are reasonably priced. AB are $40.00 each and I still have not gotten a quote back from the company someone suggested. Any one here know of any interpositn relay from automation direct or grainger?

I can guarantee you, I don't and won't pay that much.
I do have a question - how many valves are there?

 

[Skiroy]

http://catalog.phoenixcontact.net/p...52611858&parentUID=852611857&reloadFrame=true
this is it

EDIT

no try this one
http://catalog.phoenixcontact.net/p...reloadFrame=true&UID=2905417&parentUID=205032

Hey guys went on vacation and back with the same issue. I am intrested in these in the link but I never got a espons from the company as far as price. Does anyone happen to know the pricing of these in the 120AC input vesions?

2. Also,
The master contol elay was doing something weird yesturday. It has a MOV but its likely from 1983. How would I test it and how does one figure the specs needed for a particular contactor relay?

 

[Lancie1]

It has a MOV but its likely from 1983. How would I test it and how does one figure the specs needed for a particular contactor relay?

Remove one conductor from the MOV, put an ohmmeter across it. If it is not shorted (burned together from high current) or completely open (burned out all the way) then it is probably good. A Metal Oxide Varistor has a very high resistance. With a DMM you will read a very small capacitance or a VERY high resistance. The only real way to test one for certain is to apply high voltage and see it if the MOV shunts the over-voltage to ground. Of course that can also burn out the MOV! The size is not too critical. Use a voltage rating slightly above (10 to 15%) your operating voltage. Use an amp rating (determines the physical size) as high as you can afford, but at least two or three times your circuit amps.

I am intrested in these in the link but I never got a response from the company as far as price.

Use the link below to find the name of your local Phoenix Contact distributor, and ask the dealer for a price. You will be more likely to receive an answer soonest.

http://www.phoenixcontact.com/onlin...n_pages/Distributor_Search/Distributor+Search