Advise Re diodes for irrigation times

Hi guys,
As I'm new to the whole forum set up I hope I've come to the right place for some assistance.

At present I have one irrigation timer used to control a 220V pump via a relay.
I now want to connect a second irrigation timer to the same relay, using the same coil input contacts.
As each timer will have its own 220V / 24Vac power supply transformer I'm concerned that there will be a back flow of power between the two irrigation timers.

One option would be to install a second 24Vac/220V relay, (this will will involve some major digging work)
A Second option would be to install a diode in both the timer output cables.

I'm I correct with the idea of fitting diodes or what would you recommend.

The irrigation timer out put source is 24Vac - 300 mAmp.
What type & size diode must I install?

Thanks

I don't believe a diode is the solution. A diode would half wave rectify the 24 VAC control signal to the relay controlling the pump motor. My guess is the timer circuit uses a small relay to send the 24 VAC to the pump motor relay. That said, if you were to parallel another timer with the first it should work. However, the phasing must be the same. Using an identical timer with the output configured exactly the same in parallel should work.

Ron

Thanks, Ron

I'd recon you are correct the timer would use an output relay, Basically only one timer will be in operation at a time.
My concern is if someone activates the manual watering mode on both timers at the same time.

To ensure the phasing is 100% correct, I could use the same power supply transformer for both timers.
The instruction manual for the timers mention the timer can be used to simultaneously activate two station solenoid valves at once.
So in this case should some one activate both timer manual modes at once the transformer should be able to handle the load.

Theo

Hi Theo

If I take a mains to 24 VAC transformer and parallel it with a mains to 24 VAC transformer maintaining the output phase nothing will happen. I will end up with a greater current capacity and that is about it. I could make a diagram if it would help you understand it. Even if someone used manual override on one of the timers when the other was already on it wouldn't matter. That was what I based my post on. The pump relay could be operated by either timer in parallel and if both were on at the same time nothing would happen other than the pump running. The pump would run till both timers were off.

Ron

I went ahead and made a little cartoon of what I was getting at as far as transformer outputs. It shows a correct and wrong way.

Ron

I suggest that you use a 24 Vac relay on one timer to disconnect the 24 Vac from the other timer.

Hi, Ron

I'm with you now, thanks for the drawing
So basically I've got nothing to worry about other than ensuring the phasing is correct.

Thanks a million for your assistance

Theo

Hi Theo

You are welcome. You could configure as Diver 300 suggest but my suggestion would be just to parallel the timers as we covered.

Ron