SCR and Chlorinator theory

[Bradium]

Hi
I suspect the SCRs on my 240v pool chlorinator (Australian poolrite surchlor 2000) have failed. The number on the two SCRs is S4065J. I have found details here and assume it is the same SCR as it is written clearly on my SCRs. **broken link removed**

When I look up the specks of these, it says that the trigger voltage is 2v. I have filled the cell with salt water from the pool and find the voltage being produced by what I think is electrolysis is .6v to .7v at the cell and the gate. This, I assume, is the voltage source for the gate as it goes directly from the cell to the gate. It would also appear to be protection if the cell runs dry.

I have 9v ac at the two SCRs but no DC output from them. I therefore believe that the transformer is ok.

I would appreciate if someone could shed some light on this basic design to assist me in troubleshooting the problem.

If the voltage applied to the gate is less than 2v, can it work?
Could the part number be misleading?

Regards

Brad

 

[betwixt]

If the trigger voltage is 2V, anything less than that will not cause the SCR to conduct. You must be careful how you measure it though, after being triggered, an SCR stays conducting until the voltage across it's anode and cathode drops below a certain level, probably around 1V or so. The trigger only has to be a very brief pulse and the chances are you wouldn't see it on a normal meter, an oscilloscope would be needed. I am not familiar with the machine but it does sound as though something is wrong with the SCR firing circuit rather than the SCR itself. The normal SCR failure symptom is they go short circuit rather than open circuit.

Brian.

 

[Bradium]

Thanks for the Advice Brian. It is most appreciated.

regards

Brad