Electronics > Repair
Zodiac Tri Pool Chlorinator Repeated Zener Diode Failure
Frankster:
Hello
I have a Zodiac Tri Chlorinator that had a zener diode (D25 in schematic) fail in it earlier this year (a common failure I believe.) I traced out and drew the main board circuitry using TinyCAD and is attached. At the time I replaced the shorted 0.5W 24V Zener with a 1W and thought that would be the last of it.... until last week that is. So a beefier Zener and still it failed short..
The way I see that section works is that D25 limits the voltage for deriving VCC for PFC/PWM IC U1 from 2 sources -
1. On initial power up from the parallel winding of L5 through voltage doubler C39, C40, D23, D24 so that U1 has VCC and can perform PFC even whilst charging tank cap C6.
2. Under steady state conditions from +380V bus through R46 and R47.
Steady state conditions put I zener at 380/200,000 = 1.9mA, thus P zener = 24 x 0.0019 = 0.046W. Surely should not trouble a 0.5W zener.
I am thinking that it is transient or initial power up conditions that are causing the zener fails. I bought a 5W zener, but before I soldered that in, I started thinking maybe adding a zener boosting transistor would be better.
I'm not sure so I thought I'd ask those with far more knowledge what they think?!
coromonadalix:
I would check your 2x 100 k R46 R47 resistors, the c41 c39 c40 capacitors and the 2 In4148 diodes
You could try an low power 500 ma 24vdc "3 legs" regulator, they can go up to 40volts ?? that would help, they have internals protections.
Frankster:
Thanks for the reply. I have checked those components and could find no faults.
You suggest replacing zener with a 3 pin reg like a LM317?
coromonadalix:
yep maybe it could resist thoses spikes you talk ?
jmelson:
Ugh, terrible circuit! There's a 100 uF cap charging to some sizeable voltage, then dumps into the Zener through the opto-coupler. It is surprising the opto has not also been blown. I don't think upping the Zener is the answer. I'd think maybe a series resistor somewhere should be added to limit the current when the opto turns on.
Jon
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