Solid state relay.. will this scheme work?

Cryogen

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Join Date
Oct 2005
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NH
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As some of you know, I am using a solenoid valve that needs different voltages to activate based on the duty cycle. Currently, it does not run at 100% duty cycle so I have the PLC output (24V) directly connected to the valve. But we plan to add a mode that would keep the valve at 100% duty cycle, the valve needs 12V for this. I plan to use a 12V power supply to make this work. A logic in the PLC will determine whether the valve should be at normal duty cycle (24V) or 100% duty cycle (12V).

To make this work, I plan to use a 24V output from the PLC (mode) to activate a relay. The relay will switch between either 12V or 24V. This switching may happen frequently so I plan to use a solid state relay. The relay should have atleast one NO and one NC contacts.

SS1.JPG


Will this wiring scheme work? Any comments? Also, I was probably looking at all wrong places, but I couldn't find a solid state relay for this yet. The valve is 10W. Can someone recommend a good and simple solid state relay??
 
This sounds like what you're describing....

See attachment - page 12

AMMDU module, part no. 50085


Kevin H
 
You miught want to look at that carefully. I don't think the relay will allow you to run the voltage basically in reverse. you need the load on your common terminal and the voltages on your 'outputs'.

You may want to just put a diode in the 24VDC line connect the two outputs in parallel. Actually, many outputs will already block reverse current into the module so you may be able to connect the outputs directly together at the load.

I don't remember from the original post but why do you need to drive the valve with 24VDC at all? Why not just always drive it with 12VDC?

Keith
 
My mistake - Keith is absolutely correct..you can't use the AMMDU unit directly for this application, it wouldn't switch the voltage in that direction.

A workaround would be to use the AMMDU module C/O to switch another pair of N.O opto-couplers supplied with either 12 or 24V but this isn't what you asked for and would be 'cleaner' to do directly by the PLC, programming an output to switch a SSR for each voltage.
 
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looks like you just need one relay. hook the normally closed contact to normal cycle and then have the plc shift the relay and close the normally open contacts when you want to go to 100% cycle.
 
I remember this application

It was originally discussed here: http://www.plctalk.net/qanda/showthread.php?t=28964

Well, one thing I forgot to mention is we use this tubular solenoid valvevalve to cycle several times a minute (upto 300 times a minute). So it is not possible to use a relay with different voltage supply.

Also, different duty cycles require different voltage for the valve to open. At 25 to 50% duty cycle it can run with 24V (thats how we have been using so far). But for the valve to remain open with 100% duty cycle, 24V burns the coil when open for more than 5 mins. It needs no more than 13.8V at 100% duty cycle. Thats the reason we want to use a resistor.

In that same post I offered this link: http://www.crydom.com/userResources/productFamilies/38/crydom_dc60.pdf

I think I see the problem now. SSR's usually have just one contact set and you need 2. You need DC control at 24vdc and DC switching of 12 or 24vdc.

What I would do is contact Crydom directly, they make a din rail mount for there PCB relays; which may offer either a multiple output unit OR the use of 2 relays, one NC, and one NO. in a small package.

You may be able to use 2 of these: http://www.crydom.com/userResources/productFamilies/38/crydom_dc60.pdf

Now that I have written all this I may have confused myself and others in the process. I thought I had a grasp on the application but not sure now. Maybe some of this will help in some way.
 
And that would help how?

Rich1955 said:
omron makes single to 3 PH SSR

Cryogen, if you are now going to have two supplies, and a PLC, uhhh... why not just use two outputs? If relay modules can't handle the switching speed, then use one 'standard' 24vdc transistor output, and another card hooked to the 12vdc supply?

Myself, I'd still go ahead and make a little breadboard with a couple MOSFET's or regular transistors on it, and use two outputs from the PLC to drive the 'High Voltage' or 'Low Voltage' gates (bases). With two outputs, you could also decisivly turn the solenoid off, which you cannot with the '24' or '12'v scheme.

mebbe I'm missing something, I'm not too bright :(
 
Cryogen, if you are now going to have two supplies, and a PLC, uhhh... why not just use two outputs?

Well, using the relay with multiple contacts ensures that the two voltages aren't applied at the same time.

It wouldn't be good to connect 24V to 12V... it'd cause a few problems.

If he wanted to shut it off, he could add another relay after the 24 and 12 choice, to disconnect both options from the solenoid.
 
Can you swap the logic for NO and NC? Replace the contact for the 12 volt supply with a diode. Cathode to the solenoid coil. Use MR852 from Digikey. High speed 3 Amp.
Standard DC output SSR for the 24 volts. SSR off=12V, SSR on=24V. In the other thread, you wanted 13.2 volts. The diode will drop .7 volts. Set the 12v supply for 14V. If it won't go that high, use a 15V supply and adjust down. This setup will work fine with no back circuits, noise, etc.

If you can't invert, then you need 2 SSR's. One NO, the other NC.
Use the DC60 series from Crydom. DC60S3 for the NO, and DC60S3-B for the NC.

You can get DC60S3 from OPTO22 for $11.00, but I don't see the B series on their site. Call them - I assume they are the OEM for Crydom.
 
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Thanks for all your replies..

Tharon, the 24V is from the PLC so if I need to shut the valve. I choose 24V and do not supply that output.

Mickey, I plan to connect both the 24VDC and 12VDC supplies to the same common.

Keithkyll, that is a good idea.. i wonder if I can switch the 12V with the SSR but have the 24V connected through the diode instead. I have a IN4004 diode here.. Can I use that?
 
Lets see if we can understand the application

I made that long post but by time I finished I was slightly confused so backed off to think about it.

I THINK
The valve in question is being "pulsed" up to 300 times a minute. This is using one output of a plc, undoubtedly there is not another output available. If this is a correct evaluation then need to rethink everything.

You will need a second (2nd) output regardless of what you use if you want it done automatically through the programming. If plc outputs can be isolated then you can wire the different voltages thru 2 and use either to the valve. As mentioned if the commons of the 2 supplies are bonded then there will be no conflict in potentital difference.

If the outputs can not be isolated then you still need a 2nd output with a standard relay to switch the load voltages, then run the switched voltage thru any DC switching SSR and pulse it using the original output.

The SSR like the DC60 and possibly several others have the high speed switching capacity, what you have to do is determine the best method to switch the load voltage from 24 to 13.2.

Hopefully you can take the time to fully clarify how the system works i.e. what you have to work with.
 
I cant imagine a valve operating so fast as to need a solid state over just a regular mechanical realy. what is this on?
 
Cryogen said:
Keithkyll, that is a good idea.. i wonder if I can switch the 12V with the SSR but have the 24V connected through the diode instead. I have a IN4004 diode here.. Can I use that?

1N4004 is rated at 1 amp. That's at your limit. It may get quite hot. It's fast, but not as fast as the Motorola (On Semiconductor) device.

The diode won't work on the 24 volt side. With zero volts (24V off), the diode will conduct the 12 volts. If 24 volts is supplied, the diode will stop conducting, and block the 24v from feeding back to the 12. This won't work in reverse.
 

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