Relay Question

Currently we are using AC Solenoids for Hydraulic Valves. The powers that be wanted the new solenoids changed to DC. The specs I pulled from Vickers is that it needs to be 24VDC and the solenoid is rated at 30Watts. That is bigger than the normal output card that we use for DC outputs. (AB 1746-OB16). I talked to the engineer here about it and he said to put relays in between the card and the solenoids. That didn't work we are going through the relays fairly quickly. Is this an application for a Solid State relay. I am just a maintenance guy that is tired of changing the relays. Any thoughts would be nice.

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My Allen Bradley rep said to use a bigger relay. The current relay is rated for 10A at 24VDC. I forgot to include that.

How often do the relay's cycle? Standard electro-mechanical relays are only rated for about 100,000 cycles, moving parts wear out.

Solid state devices have zero moving parts and last for millions of cycles.

What's going bad on the relays? The coil? Is the coil rated for 24V DC or AC? 30 watts at 24V in the steady state should only be 1.25A so your 10A contacts should be more than sufficient. Does the solenoid have any surge current or wattage on its nameplate? How often do these valves cycle on and off?

Yep, Solid State Relays would fix your problem, just make sure you either get one with a 'free wheel diode" built in or you add one in parallel with each coil. The realys I use for the same application are by Crydom and DIN rail mount, I add an ultrafast diode. Relay part no. CMX60D10-MS11. You might have to watch the part numbers, Crydom seem to use different numbers in ths US and Europe.

Bryan

The contacts are welding together. You can take the relay apart and clean the contacts and they are good to go again. Currently they are cycling about 15,000 times per week 50 weeks a yeat. That was a concern of mine was that they are just getting to the end of there life cycle. What is the life cycle of the Solid State Relay?

Your high cycling frequency calls for solid state relay instead of elctromechanical. Check with your Vickers supplier to see if they have a recommended surge suppressor for each valve model. They may even have a part number. You will probably be able to find a substitute for less money, but purchasing the manufacturer's recommended unit may elicit more cooperation from Vickers if you continue to have problems.

Also, check the ladder logic controlling the valves. If these are dual-solenoid types, make sure that both coils are not energized at the same time, not even for a single scan of the PLC. Energizing both coils of a dual solenoid valve at the same time dramatically increases the current.

mikeyboy,
Reread BryanG's post "Free Wheel Diode" ( short for surge protection)
See PDF's below for some info on this. Whether its electromechanical or solid state you need to protect the contacts.

Definately fit solid state, but as Mickey says you still need to protect the device from the surge as the coil is released.

Most manufacturers will supply premade leads with Hirschman/DIN plugs that have surge protection. We normally use MURR leads, pt no 7000-18021-226-0500, but you can also buy the plugs on their own.

It would also be a good idea to fit a fuse on the switched supply to the Vickers coil to add extra protection on the SSR.

Jon.

There are currently Turck DIN connectors with built in surge suppressors on the solenoids. Thanks for the tip about both sides of the solenoid being ON at the same time. I think they might be for 1 scan but I can change that. I have a call into my Vickers rep to see what they recommend. Again thanks to everyone that responded it at least gets me in the right direction.

Jon R said:

Definately fit solid state, but as Mickey says you still need to protect the device from the surge as the coil is released.

Most manufacturers will supply premade leads with Hirschman/DIN plugs that have surge protection. We normally use MURR leads, pt no 7000-18021-226-0500, but you can also buy the plugs on their own.

It would also be a good idea to fit a fuse on the switched supply to the Vickers coil to add extra protection on the SSR.

Jon.

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Vickers sells a plug for their coils that has surge supression with an indicator led. I second the need of a fuse. It makes trouble shooting easier. IE when you short out the power supply thru the solenoid or cable.

Make sure there is no chance of both sides being on at the ame time if your trouble is with the coils burning up.

I suspect the inrush of the solenoid is eating away at your contacts.

I had a similar issue once with 2 amps DC destroying 5 amp relays.

A bigger relay will just last longer. You could also parallel several contacts if you have unused contacts on the same relay.

I installed a varister in series with the positive side of the output. Clamped the output at 4 Amps in my case. Select the varister that fits the amp load.

While it saves the relay contacts, this might not allow a solenoid to work properly as it needs the inrush to overcome the initial movement of the valve.

I am using on this project a new type of solenoid that is very low wattage and has a small circuit built in that eliminates inrush.

Not sure what is available for hydraulics.

You need a different solenoid or use multiple contacts on the same relay or a big relay to prolong the life from months to a couple years.

Of course SSR is the real solution, but they may cost too much for some budgets.

I don't see any advantage to switching to DC solenoids.

Bigger wire , you still need conduit, more current for the same load compared to 120AC.

But that's why they are in charge.

Yeah I didn't see the need for the DC solenoids either. They make a 12 watt Hydraulic Solenoid but the salesman said he would not guarentee it working with the high hydraulic prussure we run here. Our pumps are set at 3000psi and after the valve we sometimes use intensifiers to make it 10000psi. Solid States are more expensive but so is the time to get the maintenance man over to the machine replace the relay and get the operator running again.

Also I was wondering if there is an issue with having too many valves on at one time. We use this same setup where we are only turning 1 valve on at a time and it works great. On the setups it fails on we were turning 11 on a one time now we are only turning 4 on at a time but going to 4 didn't help. Eventually in the cycle we have 16 valves all energized at the same time. They do not all turn on at the same time but the are all on at the same time. This is the only difference between the setups.

I don't think having multiple coils energized at the same time has any bearing on your problem. You say that the mode of failure is that you are welding relay contacts together. That suggests the problem is arcing across the contacts, probably when the coil is deenergized. That will be eliminated by switching to a solid state relay.

Ken Moore said:

Standard electro-mechanical relays are only rated for about 100,000 cycles, moving parts wear out.

Solid state devices have zero moving parts and last for millions of cycles.

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Aren't the general purpose relays rated for millions of cycles?