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Auto reversing polarity after a few milliseconds (for solenoid control)

Discussion in 'General Electronics Discussion' started by Adam Rendek, Sep 4, 2016.

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  1. Adam Rendek

    Adam Rendek

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    Sep 4, 2016
    Hello All,

    I came across mcasey's post about reversing polarity for a latching solenoid valve (here).

    I have very similar challenge where I have a latching solenoid valve (6 VDC) that would need reversing polarity to be turned on and off. I'm planning to control the valve with a capacitive pouch sensor (also 6 VDC). I tested them separately and the sensor works great and the valve works great too if I manually switch the polarity with the wires. Now I would need something in-between that would reverse the polarity automatically after every actuation.

    Essentially, the touch sensor would send a signal to the valve through that in-between device, which would switch to neutral after a few milliseconds AND switch the polarity. Then it would wait for the same signal from the sensor to forward it in reverse polarity to the valve to turn it off and the same cycle would repeat again.

    Here is the valve: https://ussolid.com/3-8-female-npt-magnetically-latching-solenoid-valve-dc-6v.html
    and here is the capacitive touch sensor switch: http://www.xkitz.com/touch-switches-c-1/capacitive-touch-switch-xcts1m-p-2.html

    Do you have any recommendations?

    Thanks in advance,

    Adam
     
  2. Bluejets

    Bluejets

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    Hbridge.......but there will be other considerations you probably haven't thought about.....inductive reactance ....time for solenoid to physically move being just a couple....i doubt the armature will get very far in a few milliseconds
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    CDRIVE likes this.
  4. AnalogKid

    AnalogKid

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    1. Any idea what the steady state current through the solenoid coil is?

    2. There is nothing in the valve description that mentions having to reverse the current through the coil. Are you sure this is necessary?

    ak
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yeah, I read those specs too and there's absolutely nothing in the description that so much as hints that reverse polarity is required or is even relevant for its operation. In fact the description indicates a typical "Pulse On - Pulse Off" logic. Unfortunately the specs fail to specify the required minimum pulse width to change states. o_O

    Chris
     
  6. Adam Rendek

    Adam Rendek

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    Sep 4, 2016
    Thank you All for responding. Indeed, there is not a lot of description for the solenoid valve and the manufacturer hasn't gotten back to me yet. What I know from experience is that if I touch the wires briefly one way to the batteries (6 V) it opens. If I touch them briefly again, it doesn't do anything, but if I reverse the wires and touch them briefly, it closes. I was even able to wire up the touch sensor and connect it to the valve AND successfully open it with a touch, but I have to manually reverse the wires to close it with a subsequent touch again.

    You may represent a deeper knowledge on this forum than what I'm ready to take on. I was hoping that there is a ready-made circuit (like the touch sensor I bought) that I could buy instead of designing/ building a circuit myself. Can you point me to any website that might have one by chance?
     
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    You could use 2 simple single pole momentry changeover switches(microswitch for example)
    Other than that the H bridge I mentioned in #2 if you plan to run a microcontroller for some such reason.
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I googled your valve's PN and got quite a few hits. Unfortunately the ones I read describe its operation identical to the link you provided; Pulse Open - Pulse Close.
    http://www.plumbingsuppliesexpress.com/item/5933559/

    Since your empirical tests prove otherwise just sit tight and wait for solutions from EP's membership. One of us will undoubtedly provide you with the most practical solution. Are you looking for a total DIY or are we to limit our suggestions to 'Plug & Play - Off The Shelf' solutions?

    Update: I was just about to click "Post Reply" when I decided to read the reviews in the link I provided above. The first reviewer describes the valve's operation exactly as you do.
    https://www.amazon.com/dp/B00YVIE9LI/?tag=leo-lk-20&ie=UTF8#customerReviews

    Sorry for inferring that you're misunderstanding its operation but the product description is rather sparse and obviously in error. Since none of us has your valve we have to rely on what the supplier or manufacturer specifies.

    Chris
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
  11. Harald Kapp

    Harald Kapp Moderator Moderator

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    Not even the manufacturer himself has any better information on his website.:(
     
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Frustrating, isn't it? I've bounced this around in my head to the point of getting a headache. Perhaps we're missing something? I've noted that the users (like Adam) have made their test 'dry'. The specs indicate it's a unidirectional valve which might hold the answer. Is it possible that the latching mechanism might require fluid or air pressure to operate properly? IE, without reversing polarity?

    I tried sketching an electromechanical circuit that would mimic this action but it just makes my headache worse. Besides, too much brain strain violates item (1) on my retirement 'Don't do' list.

    Chris
     
  13. Alec_t

    Alec_t

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    The valve is described as a magnetic latching type, which suggests its function is like that of a single-coil latching relay. Such relays require energisation pulses of ~10mS, the 'reset' current being the reverse of the 'set' current. Because the valve armature inertia is greater than that of a typical relay I would guess the valve pulses might need to be >10mS.
     
  14. Bluejets

    Bluejets

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    Taken from the specs........
    Magnetically Latching 2 Way 2 Position Solenoid Valve
    ACTUATION: A short 6 Volt pulse lasting only 50ms can open/close the valve

    As for whether or not it requires reversing the coil power, it would depend on the internal mechanism.
    I remember the old "bed lamp switch" which is press for on and press again for off.(latching)
    Maybe this has a similar mechanism internally.

    Also there is this.....
    Direct Operated/ Pilot Operated:.......Semi-Direct
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    The review I read on Amazon stated that the seller advised pulse times about 50mS.
    https://www.amazon.com/dp/B00YVIE9LI/?tag=leo-lk-20&ie=UTF8#customerReviews
    Chris
     
  16. Alec_t

    Alec_t

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    From scratching around on the web it seems the power requirement for a similar valve is ~2.2W, implying a coil resistance of ~15Ω (but unknown inductance). The touch sensor spec says the output switch provides an output voltage equal to the supply voltage at up to 10A and can be configured as a toggle (i.e. one touch for on, one for off).
    Based on those figures and an assumed coil inductance of 100mH, this simple circuit should do the trick. C1 might need to be a tad higher value.
    SolenoidToggle.JPG
     
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  17. Alec_t

    Alec_t

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    My post 16 circuit relies on the output switch of the sensor being a push-pull type with the ability to pull down to ground. If, instead, the switch is a normally-open high-side-only type, then that circuit won't work and something along the following lines would be an option :-
    SolenoidToggle3.JPG
     
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  18. Adam Rendek

    Adam Rendek

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    Sep 4, 2016
    Hello All,

    Thank you very much for looking into this. This is a great group and I'm impressed how helpful you all are to an "outsider". Work has kept me away from this project, but I haven't given up of course. Harald and Alec_t's solutions look comprehensive, but I'm too much of an amateur and get lost in those diagrams (I even more appreciate you engaging in a conversation with me because of that though). I'm looking for that old lamp push button solution (one push on, one push off) and I can solder parts together, but I wouldn't venture selecting actual products based on the diagrams. So I'm still trying to decipher your solution diagrams and find actual products that I can order from online to do the job.

    Adam
     
  19. Bluejets

    Bluejets

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    Oct 5, 2014
    When I quoted the old type bed lamp switch it was a means to describe what might be going on inside the valve. Was not meant that you should use it as a switch for your device.
     
  20. Adam Rendek

    Adam Rendek

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    Sep 4, 2016
    I got you Bluejets. Thanks for the clarification. It's a good analogy though, instead of a push button, I'd like to use to touch sensor and the valve in a similar way.
     
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