Pool chlorinator - what does the triac do?

Nov 18, 2012 2 Replies
S

I've got a dud Monarch salt water pool chlorinator - no output.



It looks like the triac on the output has failed.


The circuit layout is:


AC ==> Dimmer ctrl ==> Xformer ==> Bridge rectifier ==> Triac ==> Cell


The output triac appears to have failed open. Its an ST branded BTA40.



The triac switches the -ve lead to the cell, the gate is connected directly to a "stud" electrode in the cell.


What's the purpose of the triac?



Seems to me if the cell has water in it the triac is "on", otherwise its "off". I dont have the full cell assembly - is the stud at the top so it cannot run unless the cell is completely full??


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T

**That is certainly easy enough to check. TRIACs usually fail catastrophically.
**I've seen this system before. It's slightly odd, but it works.
**Yup.

**To switch off the juice, if there is insufficient water/salt solution running through the cell.
**Correct. To test, you need to supply a load to the unit, such that at least 10 Amps flows (I used a roll of speaker cable, shorted at one end. Connect the gate to the positive supply through a (say) 330 Ohm resistor.
Trevor Wilson www.rageaudio.com.au
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S

Thanks Trevor - great, you've confirmed my thinking. Looks like its failed o/c.

These triacs are cheap too, ~$10 in 1 offs depending where you get them.

Cheers

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