Problem with nonresponsive relay

[sedso10]

Hey everyone...I'm new here and was hoping yall could help me out with a proble...

I've got a temperature controller which controls an SSR via an 8v output. The SSR is then connected (through a switch) to a valve. My problem is that the SSr will open the valve, but it doesn't seem able to stop when the temperature control lets off...I think it could be an interaction of the valve/SSR b/c if I simply flip the switch off-on quickly after the temperture control quits then the valve does stop...I hope tht makes sense and ANY help would be greatly appreciated...Thanks


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[Skogsgurra]

Are there snubbers parallel to the SSR? They are known to let enough current through to keep coils activated.

If you cannot remove the snubber, try and connect a lamp (correct voltage, power a few tens of W) parallel to the coil. If it drops out then, it is snubbers or some other capacitance (cables, perhaps).

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[OperaHouse]

As said before, the problem is that many electronic controllers expect a heavier load than the input of a solod state relay. The leakage current of the controller is enough to keep some of them on. A lamp would provide a good load, but could be a failure point if the lamp fails leaving the heater on. This could be improved by operation of lamp at lower voltage with two lamps in series. Having the controller operate an additional mechanical relay would also be a solution. Another effective way would be to place a capacitor and resistor in series. This combo would be placed on the input terminals of the SSR. This would provide a load without generating heat. A typical value would be .47uF and 220 ohm resistor. They sell these in a convenient package called a RC snubber for relays. Though usually used on mechanical relays to absorb kickback spikes, one or two (some have a value of .1uF)would work in this application. They are in a convenient small package and are available with UL & CE.

 

[sedso10]

Thanks for the help guys! I am stil having trouble however - I connected a 220ohm resistor and 1uF (I couldn't find a .47 here) tantalum capacitor in series between the negative SSR output of the electrical controller and the SSR. Now the valve doesn't turn on at all...Is the 1uF capacitor too big? Did I put in wrong? Thnaks guys

 

[Skogsgurra]

Huh?

WHERE did you put it?

The lamp (or snubber) shall be parallel to the load (coil).

And, please, please, do not use a tantalum capacitor! They are polarized. Can't take AC. Also, what voltage is that capacitor for?

I think it is time that you get professional help with that.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[OperaHouse]

The capacitor and resistor are in series. This combination is placed in parallel with the input of the SSR. The capacitor voltage should be appropriate for the application. I assume the output of the controller switches 120V, so the capacitor should be rated 400V DC or higher. This works, but prefer to use a capacitor that is "X2" across the line rated for AC. A tantalum capacitor is only rared for low voltage. If connected as described, this capacitor should have shorted and the system still worked. I was encouraging the use of an off the shelf RC snubber.

 

[Mike2468]

The SSR's output has a tiny leakage current. It is not enough to turn the coil ON, but once the coil is ON, the leakage is enough to hold the coil ON, regardless of what your controller is doing. That is why, once you flip the switch in the circuit, the coil drops out as expected.

Just add an additional load to the output of the SSR. A small light bulb is fine such as a 25 watt or greater.

 

[Skogsgurra]

Do people at all read threads?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...