solenoid driver circuit help

Discussion in 'The Projects Forum' started by minkey01, Jul 23, 2014.

  1. minkey01

    Thread Starter Member

    Jul 23, 2014
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    Hi. My project is almost complete, but I have this one circuit left that needs designing.

    I would like to drive a solenoid with a switch. My Solenoid is rated 100V and 1300 ohm. It had a cap already attached to it. Pics attached.

    The power supply I am using is 75V. I have the pdf for this if you need it. I also have the pdf of the old schematic from where the solenoid came from if you need it.

    Right now I just have the switch and solenoid directly hooked up to the power supply. It does activate, but from reading I hear you don't want or need to hold at this high voltage and it needs to come down after the initial trigger to eliminate heat and power wasting. Also I need a safety diode?

    Anyone familiar with these solenoid driver circuits that could sketch it up for me?

    Thanks so much!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Assuming this is a DC coil a BEMF diode could be used in place of the capacitor, you do not necessarily need a cap even if the DC supply is non-smoothed, the diode will help with this also.
    Usually coils are rated for continuous use, you can if you wish use a method to reduce the voltage after pick up, but not usually recommended if using the unfiltered DC approach.
    Do you intend switching with relay or solid state device?
    For S.S. you just require a suitably sized Mosfet.
    Max.
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
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    @ MAX +1


    I'll add this in case someone finds it useful.

    I had some dc drill clutches that wouldn't quite pull in with half wave 120vac.

    Full wave overheated them.

    I used this circuit.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    You can place a resistor in series with a cap to lower the hold voltage , this reduces the current through the coil, try different values for the resistor to suit the minimum hold current.
     
  5. minkey01

    Thread Starter Member

    Jul 23, 2014
    171
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    i am using a dc power supply. this one (pdf attached).

    i will be using a manual switch.

    this is the circuit it originally came from (see attached pic).

    i guess i would be happy activating this solenoid just like they did in the old schematic. could anyone interpret and isolate just the solenoid activation circuit from this schematic that i could use? give me a little circuit sketch pic?

    thanks! i really appreciate it. this is the last hurdle to my project.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The primary appears to be operated in a auto transformer mode, and the half wave DC for the brake and capstan Sol. is taken off one of the primary windings?
    The orientation of transformer connections appear to be on the opposite side to normal.
    Why the modification, is the circuit no longer used as shown?
    Max.
     
  7. minkey01

    Thread Starter Member

    Jul 23, 2014
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    Yes, no longer used as shown.

    I just ripped the solenoid out of that old machine, because I needed it for another project. So I only have the solenoid by itself.

    What do you think would be the best circuit to operate it. With a manual switch and my new power supply?

    Thank you! Drawn circuits really help as I am a bit of a noob to this.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You need to obtain the true operating voltage of the coil, it could be done with a variac, but I assume you do not have one?
    Preferably apply a varying level DC to the coil and detect the point it picks up with no delay, also operates any small load that you wish to use it for.
    A manual switch will operate it if that's all you need.
    Max.
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
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    A switch activated by the solenoid is often used, when more power is need for pull in, than can be safely handled for long periods.

    A resistor across the switch limits the holding current.
     
  10. minkey01

    Thread Starter Member

    Jul 23, 2014
    171
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    ok thanks max. sounds like the manual switch and one cap or diode for safety draining is all i need. you said continuous use is standard and i don't need to lower the voltage after the activate so i'll just stay with this simple setup.

    one last concern here. look at the solenoid pic. does the winding have electricity going through it that is now touching the metal box solenoid housing? if this is screwed to my main metal housing is that now connected to the power? a little paranoid.

    thank you for the help!


    oh...ps: i will do what you advised and vary the voltage during testing and find the min voltage to activate and hold during load. thanks for this tip!
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There should be no connection from the coil terminals to the metal frame?
    The .1μf capacitor in the pic is almost touching the coil frame.
    Max.
     
  12. minkey01

    Thread Starter Member

    Jul 23, 2014
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    all that yellow i see is probably a coating on the outside of the winding then? that yellow stuff does rest on the housing.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Usually taped then varnished.
    Max.
     
  14. minkey01

    Thread Starter Member

    Jul 23, 2014
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    shoot! got it all hooked up, but there is a problem.

    it does not have enough initial strength to pull in attached arm with spring tension. see attached pic.

    i can use my finger to help push the metal plunger in and then it will bottom out and the magnetism has no problem holding the metal plunger locked all the way in the solenoid giving the right pressure at the other end of the spring. it just can't pull it all the way in without help.

    is there anything i can do to give it more strength during the initial activation?
     
  15. inwo

    Well-Known Member

    Nov 7, 2013
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    Do you have 120vac available?

    See post 3.
     
  16. minkey01

    Thread Starter Member

    Jul 23, 2014
    171
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    120 VAC, it's just the wall AC right? Yes, this machine has a plug from the wall outlet.

    So this circuit would work with my solenoid? You saw the picture and ratings on my solenoid?

    Would I have to remove my big cap already on it? And then clutch + and - in your circuit is my solenoid connects?

    Thanks for the help! I'm so close to finishing this project. It always seems like the last problem takes forever. ha. I really appreciate the help.
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Leave the cap, it is only a small value anyway.
    Try a full wave bridge off of 120vac, if it is still reluctant to pull in, use a ~200μf capacitor across the bridge output.
    Max.
     
  18. inwo

    Well-Known Member

    Nov 7, 2013
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    Like Max said, try the full wave bridge. If it pulls in and doesn't overheat, you're good to go.

    The circuit I used drops it down to half wave for holding. Not needed in most cases.
     
  19. minkey01

    Thread Starter Member

    Jul 23, 2014
    171
    0
    Ok, just feel it for heat?

    Does anyone have a circuit schematic picture for the full wave bridge with part values rated to go with this solenoid?

    I'm inexperienced with designing the full wave bridge circuit. Sorry. Excuse my noobness. ;)
     
  20. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
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    Use four 2N4004 or a packaged bridge.

    Isolation transformer would be a good idea, and may be required for circuit discussion on this forum.
    Certainly a small line fuse as diodes often fail shorted.

    [​IMG]
     
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