I need to control a bi-stable motorized valve. I hesitate between two types of wiring:

  1. Inverse polarity of 2 wires to open or close: I can do it with two coupled relays. Does it hurt to do it with two relays with an intermediate state at ground for both contacts?

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  1. 3 wires and still 2 relays

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Is there a best solution between both and why? Pros and cons?

  • 2
    Good question - but it has nothing to do with the Raspberry Pi. Perhaps another stackexchange might be more appropriate.
    – joan
    Commented Feb 20, 2022 at 17:24
  • 1
    You need to define the problem better, I am assuming you are using a RP for control. Either would work under most conditions but what happens when you lose power? I use NC (Normally Closed) valves. Since I am not on batteries the current the valve draws while on is negligible. To a battery that would be a problem. That way the valve closes in the event of a power failure putting everything in a known state. Generally keeping it as simple as possible is the best solution.
    – Gil
    Commented Feb 20, 2022 at 20:51
  • @Gil, 1) I use NC for filling the tank. I have tried direct control NC for drip watering, around 2 hours openned per day, the electrovalve was very hot - it was a cheap one around 25€. 2) For watering, if I lose power, I want watering to go on, then a bistable valve is alright for my usage. 3) I use a RP.
    – lalebarde
    Commented Feb 21, 2022 at 7:45
  • @joan: shall I move it? Which one do you recommand?
    – lalebarde
    Commented Feb 21, 2022 at 7:46
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    @lalebarde: Gardening & Landscaping, or Home Improvement might do it. You can see the entire list of SEs by clicking the 'hamburger stack' in the upper RHC of the page here.
    – Seamus
    Commented Feb 22, 2022 at 7:48

1 Answer 1


I do drip watering with NC valves as well and they do get hot. Mine are in direct sun and I cannot hold on to them after they have been on about an hour. They have been that way for about 10 years and yes I bought the cheapest ones I could find. They are 24VAC. I am on a city water system which continues to supply water even when the power fails so they must shut off if the system loses control. You can check the voltage to the valves, it may be high. In your case I would not worry about the valves, they normally will get warm, sometimes too warm to comfortably hold on to.

  • Thanks for your useful feedback, but my question is on wirering
    – lalebarde
    Commented Feb 24, 2022 at 6:47

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