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Capacitor size to actuate 2 latching solenoids

Discussion in 'General Electronics Discussion' started by eem2am, Oct 12, 2010.

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  1. eem2am

    eem2am

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    Aug 3, 2009
    Hello,

    We are wanting to utilise two latching solenoid valves in our domestic water system.

    We wish to switch both of them in one second, i.e., switch one , then the other one, within one second.

    **************************
    We wish to assert which is the lowest value of capacitor that we can use for actuation like this…..but the datasheet of the latching solenoid does not appear to help us…………….
    ***************************

    Anyway, we must actuate these valves using the energy in a capacitor initially charged up to 12V by a SEPIC converter with a 5V(in) input.

    I.e.
    We charge the cap up to 12V, ‘hit’ one solenoid, then charge the cap back up to 12V, then ‘hit’ the other solenoid……
    …we can’t have the SEPIC charger running while the solenoid coils are actually being actuated.

    Solenoid actuation circuit:
    Xxxxxxxxxxxxxxxxx
    http://i55.tinypic.com/1z3nz9e.jpg

    Here is the part of the latching solenoids datasheet that concerns electrical parameters
    Xxxxxxxxxxxxxxxxxxx
    http://i53.tinypic.com/jg5v1i.jpg


    The datasheet does not give the DC coil resistance, but we measured it at 30R.
    The datasheet does not give the coil inductance, but we put a step input of 12V into it, and measured the rise of current………….from this test, we calculated that the coil inductance was 43mH….but we are unsure if this test is bogus?.......because doesn’t the inductance of solenoid valve coils vary widely throughout the actuation process?



    Power source
    The power source that we have for valve actuation is provided by using power from our 5V rail which we already have in our product.
    (i.e. we have a 5V rail present which is provided from a 5W Buck converter.)
    Our SEPIC charger uses this 5V as its input)

    Anyway,
    We are thinking if sizing the energy storage capacitor so that it can maintain a voltage across the latching solenoid coil of above 6V over a 20ms actuation period.

    Is this correct?
     
    Last edited: Oct 12, 2010
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