Is anyone familiar with the innards of modern irrigation controllers? Mine is a Hunter m/n PHC-2400I, 24 zones, 24 Vac wall wart. It switches 24 Vac to the valves. The problem is random overcurrent fault events that cause the controller to stop in the middle of a cycle. There is no pattern to which zones (valves) cause the faults. It is within warranty, so a tech came out and swapped it out for a new one. The new one does the same thing.

While the guy was installing the new one, I opened up the old one. Because the daughter card (with zones 13-24) is ***hard soldered*** to the main board, I couldn't see part numbers. What was clear is one TO-220 3-pin device per zone.

My theory is that because I have *two* master valves, both connected to the one MV terminal, the total current for three valves is very close to the overcurrent trip point. I have whatever it takes to build a small driver circuit that is controlled by the MV output (24 Vac) with a beefy output stage. But I would like some insight into the original circuit. Are they using MOSFETs to switch the valves? There is an optocoupler per zone, so that could work.

Appreciate any insight / advice.

ak

 

I have *two* master valves, both connected to the one MV terminal

Could you connect a relay to this terminal and power the two master valves using the contacts?
Found this circuit on the web that might be similar.

 

Yes, either a mechanical or a solid state relay. But I'd really like to know how, if the AC switching system is isolated from the controller, they are communicating the output current. I didn't see anything that looked like a current sense transformer or a Hall effect sensor.

ak

 

Is anyone familiar with the innards of modern irrigation controllers? Mine is a Hunter m/n PHC-2400I, 24 zones, 24 Vac wall wart. It switches 24 Vac to the valves. The problem is random overcurrent fault events that cause the controller to stop in the middle of a cycle. There is no pattern to which zones (valves) cause the faults. It is within warranty, so a tech came out and swapped it out for a new one. The new one does the same thing.

While the guy was installing the new one, I opened up the old one. Because the daughter card (with zones 13-24) is ***hard soldered*** to the main board, I couldn't see part numbers. What was clear is one TO-220 3-pin device per zone.

My theory is that because I have *two* master valves, both connected to the one MV terminal, the total current for three valves is very close to the overcurrent trip point. I have whatever it takes to build a small driver circuit that is controlled by the MV output (24 Vac) with a beefy output stage. But I would like some insight into the original circuit. Are they using MOSFETs to switch the valves? There is an optocoupler per zone, so that could work.

Appreciate any insight / advice.

ak

A very simple test will be to disconnect one of those master valves and see if the problem stops. Then you would know that was the problem, or if it was not the problem.
It may also be that you have an intermittent short circuit in the wiring, which I am presuming is rather extensive, if you have zones 13 thru 24.
An entirely different source of the problem could be an occasional disturbance on the mains supply, since it seems that the problem is rather random.