SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Nobody ever manufactured anything to interconnect multiple controllers, as far as I know, even though the electronics are rather simple. Your idea is a "strictly at your own risk" one. The practical solution is to purchase the proper controller, and to resell the old one. That would be a kindness to the next homeowner.

In theory your idea might work. Then again it might not work. I've done some creative wiring in my day. I don't know how many extra wires you have but if you can keep from wiring anything together you'll be better off. Running a new wire might be the cheap way out. I'd say on the rain sensor it wont make a difference. But if you can keep the ground wires seperate from the two timers it will only work in your favor. I'm not saying it wont work if you wire them together. But Boots is right. Do this strictly at your own risk. As far as the master valve goes. Does that wire actually go anywhere? To a pump or master valve? If not disconnect that then you'll have a spare wire.
Good luck.

Taking the Master Value out of the equation for a moment, you should be fine using one rain sensor and connecting all the commons together.

The transformers powering the controllers should be electrically isolating the controllers from everything else. When you have two isolated electrical circits, you're always safe attatching a single wire from any point of circuit #1 to any point on circuit #2. The reason this is safe is because electrical current must flow in a loop. When there is only one connection point, no current can flow.

Now in the real world, you usally can not just randomly touch random points of two circuits together because most electrical circuits are not isolated. Usually some part of the circuit is grounded. When that is the case, ground acts as the return path to compete a loop and nasty electrical things happen. This sort of explains why birds are not hurt when they land on a live electrical wire. There is only one connection point between the bird and the wire... his foot. There's no way for any electricity to flow from the wire to the bird and therefore he remains safe.

Now when you throw the master valve into the equation, you begin connecting the two systems at more than one point, current can flow, and things can get damaged. It would take some sort of a relay controlling circuit to allow the master valve to be fired from either controller. I'm afraid you are going to have to either purchase a larger controller, disable the master valve, or get someone to build you the nessesary relay circuit.

I've done controller interconnections before the modern-day solid-state designs. There are ways for things to go wrong. There is a possibility of one controller feeding voltage/current/power into another controller with unpleasant results. It can still be done safely with solid-state controllers, but it requires you to assemble some solid-state circuitry of your own, in order to get the master valve operation you want.

I always wonder at home systems with more than a dozen zones, and wonder if things couldn't be simplified somewhere. Used currently-made controllers do have a resale value, so it isn't money completely lost.

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by davel</i>
<br />Yeah I can see that if the MV is on at both controllers by accident you could theoritically get a "pop" on one of the controllers from the additional amprage (or voltage) whoah it has been 10 years since my one circuits class in college so I don't remember. I'll probably end up buying a 16 valve controller but I just wanted to get away cheap...
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Having MV on at both controllers isn't as much of an issue as having both controllers directly connected to MV and only ONE of them being turned on.

If the controllers are identical (at least in voltage output) then when both of them are on at the same time, current won't flow between them because they are at the same voltage potential. Instead, the MV will just pull half of it's current from one controller and half from the other.

The real question is what happens if MV outputs from both controllers are connected together and one is "on" and the other is "off". It depends upon how the controllers are designed. If the controllers operate relays such that you have an open circuit when the valves are off, then everything is great and you only have interconnection issues when both are "on". But if the output is controlled by solid state circuitry, the two controllers might not play nice (again, it just depends upon the design of the controllers).

Although multiple controllers on one system aren't that uncommon in my area, I do not recommend them either. To many complications, variations and etc.. But if you still desire to go this route, this device here will simplify things.
www.transitionalsystems.com/isolator.htm
Of coarse the real chalenge is finding a distributor that caries these! Good luck!