(Topic ID: 123070)

Can you drive an EM coil with DC power?


By PhilGreg

5 years ago



Topic Stats

  • 30 posts
  • 12 Pinsiders participating
  • Latest reply 5 years ago by SYS6
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    #1 5 years ago

    Hi,
    from what I've read it would seem like it would be possible and not-damaging to do this as long as you add a diode like on SS or DMD games, but would it be practically feasible to drive non-holding Gottlieb EM coils with 24V DC power (as opposed to the normal 28V AC).

    Cheers!
    Phil

    #2 5 years ago
    Quoted from PhilGreg:

    Hi,
    from what I've read it would seem like it would be possible and not-damaging to do this as long as you add a diode like on SS or DMD games, but would it be practically feasible to drive non-holding Gottlieb EM coils with 24V DC power (as opposed to the normal 28V AC).
    Cheers!
    Phil

    Yes, I did it too my Gottlieb '58 woodrail pop bumpers, used an individual bridge and diode on all 5 pops. Gives them a nice kick.

    #3 5 years ago

    Thank you sir.
    Also since DC gives more kick I figure going down 4V from 28V AC to 24V DC should be ok?

    #4 5 years ago
    Quoted from PhilGreg:

    Thank you sir.
    Also since DC gives more kick I figure going down 4V from 28V AC to 24V DC should be ok?

    I don't see why not. Try one and post your results.

    #5 5 years ago

    They will pull more current with the dc your giving them. The voltage for the ac divided by square root of 2 would give you the equivalent dc voltage. I dont know if it matters. I would try it and feel the coils to see how hot they get.

    #6 5 years ago
    Quoted from Det_Deckard:

    They will pull more current with the dc your giving them. The voltage for the ac divided by square root of 2 would give you the equivalent dc voltage. I dont know if it matters. I would try it and feel the coils to see how hot they get.

    Bear in mind that I did this with pop bumpers only, which are on for brief bursts. I wouldn't recommend this mod for coils that are on for longer lengths of time, such as flippers, and definitely not for hold coils.

    #7 5 years ago
    Quoted from wayout440:

    Bear in mind that I did this with pop bumpers only, which are on for brief bursts. I wouldn't recommend this mod for coils that are on for longer lengths of time, such as flippers, and definitely not for hold coils.

    I played with using some buck-boost converters ebay to change the dc fed to some pinball motors to get the correct speed.with non standard motors. They are cheap and you can get.ones with numeric voltage displays for less than 10dollars.if you wanted to play around with the voltage.

    #8 5 years ago

    Yes, you can operate AC coils on DC. However, on coils driving things like slingshots, pop bumpers, hole kickers, etc you need heavier duty switch contacts. The higher momentary surge will burn up regular contacts. This is where you'd need tungsten contacts for longevity.

    #9 5 years ago

    Ok, my DigiKey order is in the mail, I'll let you guys know how that turns out.

    Cheers
    Phil

    #10 5 years ago
    Quoted from KenLayton:

    Yes, you can operate AC coils on DC. However, on coils driving things like slingshots, pop bumpers, hole kickers, etc you need heavier duty switch contacts. The higher momentary surge will burn up regular contacts. This is where you'd need tungsten contacts for longevity.

    On my '58 Gottlieb the pop relays already have the larger heavy duty tungsten contacts in the pop bumper solenoid firing circuit, while on the same relays there are also sets of smaller silver contacts for ringing the bell and scoring.

    #11 5 years ago

    Plenty of EMs are already running DC coils from the factory.

    -1
    #12 5 years ago

    You don't need diodes for an EM application.

    #13 5 years ago
    Quoted from jrpinball:

    You don't need diodes for an EM application.

    The diodes are used to save the bridge from damage when the coils magnetic field collapses, so I absolutely recommend them ...sure the game is an EM, but you just added a solid state component.

    #14 5 years ago

    Hey I'm not saying I want to modify my EM, I want to drive EM coils with DC power for a different application, so I do want to use diodes.

    #15 5 years ago
    Quoted from PhilGreg:

    Hey I'm not saying I want to modify my EM, I want to drive EM coils with DC power for a different application, so I do want to use diodes.

    I understand. Regardless of your application, the coil is a current operated device. It doesn't care what voltage (AC or DC) is impressed on it as long as the voltage level does not exceed the voltage rating of its magnet wire insulation. As such, you can apply a DC voltage to an AC coil. To get the AC coil to work on a DC system requires a sufficient DC voltage be impressed on the coil so that the same amount of current is drawn as when the coil is operated on AC.

    When you apply a voltage to a coil is creates a magnetic field. When you remove the voltage the magnetic field collapses and creates a reverse polarity voltage and can be many times the value of the original applied voltage. This creates a transient voltage pulse that can damage other components in the circuit that are not rated for this polarity or the higher voltage created, things like semiconductor bridge rectifiers have a maximum voltage limit and breakdown if exceeded. Having a reversed biased diode across the coil allows the diode to conduct for reverse polarity voltages and creates a 'short circuit' across the coil that allows the pulse to be dissipated in the resistance of the coil wiring.

    #16 5 years ago

    Hi Phil
    the schematic of "Fan-Tas-Tic" shows the DC-Wiring for the bumpers (and for the Delay-Relay used for the Roulette-Wheel): At the end of the schema, End-22 and 23. Here: http://www.ipdb.org/machine.cgi?id=820 -> down to 1 MB PDF Schematics. I cannot have a look at the schema directedly - I must copy it (down) to my Personal-Computer: I click on the PDF with "Right-(Handside)-Mouseclick" -> make a copy on my PC -> I open my copy ... Greetings Rolf

    #17 5 years ago

    Thanks guys, I did try to activate the coil with 24V DC with a diode and no problemo.

    #18 5 years ago
    Quoted from wayout440:

    The diodes are used to save the bridge from damage when the coils magnetic field collapses, so I absolutely recommend them ...sure the game is an EM, but you just added a solid state component.

    I thought the diodes were added to protect the driver board and MPU board from back EMF damage in solid state games. I don't think EMs with DC have diodes on the coils, do they?

    #19 5 years ago
    Quoted from jrpinball:

    I thought the diodes were added to protect the driver board and MPU board from back EMF damage in solid state games.

    This is correct. In a solid state game, what are you protecting on the driver board? Transistors. In an EM game, If modifying an AC coil to use DC by using a semiconductor based bridge rectifier, it is also desirable to add the flyback diode. (transistors and bridge rectifiers are solid state devices)
    http://en.wikipedia.org/wiki/Flyback_diode

    #20 5 years ago

    OK, but do EMs using DC have diodes on the coils? I'm not sure, but I don't recall seeing them on the DC EMs I've encountered. Maybe there's a single diode installed at the bridge rectifier which serves the same purpose?

    #21 5 years ago
    Quoted from jrpinball:

    but do EMs using DC have diodes on the coils?

    Gottliebs do.

    #22 5 years ago

    Shopped out and sold a nice "Golden Arrow" last year. I replaced one of the bumper coils which was fried, but don't recall seeing diodes on any of the coils. I've only seen them on SS games.

    #23 5 years ago
    Quoted from jrpinball:

    Shopped out and sold a nice "Golden Arrow" last year. I replaced one of the bumper coils which was fried, but don't recall seeing diodes on any of the coils. I've only seen them on SS games.

    Golden Arrow doesn't use any (it's not DC). Hit the Deck does (seven of them, for example).

    #24 5 years ago

    In AC there is reactance and resistance that yields impedance. DC only resistance. IMHO the flyback diode needs to be there. The collapsing field will result in a reverse EMF that can damage your solenoid drivers. Just some stuff from work and a HMO I am far from an expert on these machines. I deal with 250 VDC controls at work. If a flyback diode fails it get ugly.
    Sputnik

    #25 5 years ago

    there are no "solenoid drivers" in an em machine...

    and fortunately for many of us, no 250vdc either... 110vac is plenty to get my attention...

    #26 5 years ago
    Quoted from DirtFlipper:

    Golden Arrow doesn't use any (it's not DC). Hit the Deck does (seven of them, for example).

    Didn't know "Golden Arrow" wasn't DC. I thought they used DC exclusively after the first one (which was?...). I think Williams was using DC in their EMs all the way back to "Granada" and "Spanish Eyes" iirc.

    #28 5 years ago

    Nice find, Dirtflipper!

    #29 5 years ago
    Quoted from jrpinball:

    OK, but do EMs using DC have diodes on the coils? I'm not sure, but I don't recall seeing them on the DC EMs I've encountered. Maybe there's a single diode installed at the bridge rectifier which serves the same purpose?

    I've had several Williams games with DC bumper via the bridge rectifier. No diodes on any of them.

    #30 5 years ago

    If you sketch out the circuit of a bridge rectifier converting ac to dc for a coil you can see that the bridge ends up with an arrangement that is two series diodes and the pairs of series diodes are in parallel. My ascii art isn't up to drawing this, but you end up with an "equivalent" circuit that is how a normal diode is wired across a coil.

    In a solid state circuit the back emf diode protects the switching device - the transistor, but in an EM I don't think you need to protect anything.

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