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Snubber design with SSD relais

sukandar

Hi,

I'm currently working with a pneumatic valve that I want to operate with an SSD relais.

I had some cheap "hockey puck" SSD relais available, but somehow they don't work reliably, as the valve often doesn't switch off.

So now I'd like to do it the proper way.

 

The valve is rated at 230VAC / 10W, thus 43mA.

The "hockey puck" is completely overrated at 25A.

I don't have a datasheet for it, but looking at similar devices I understand there could be problems with the minimum load current as well as off-state leakage current.

I also opened one of them and figured out the schematic (image attached)

The opto-triac is an EL3063 (I have omitted the input side), the power triac is a BTA24-800.

I am not entirely sure about the 100nF cap which could also be a VDR or something, but I assume the 22nF+47Ω pair is called a snubber and should protect the triac. From my understanding it is also responsible for the leakage current which I guess is what causes the valve from switching off.

Or is it caused by something else?

In any case I was wondering if it might be sufficient to change the values of the snubber components, and how would I calculate them?

 

I guess I could also start from scratch with a simple opto-triac (e.g. just the EL3063), but for the project the screw terminals of the hockey puck come in handy, so modding it is my preference.

 

Thanks much for any ideas!

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  • Hi,

     

    the Triac needs some current to stay on. When a very large Triac is used, it is still full of charge carriers that will support the load current for some time, and if that is very low like in your case it will just stay on. My recommendation would be to use a smaller Triac. Unfortunately we (Fairchild) don'T make them, so you will have to look elsewhere... Anyway, putting a smaller Triac in the big package should present no issues.

     

    good luck and let us know!