(Topic ID: 119958)

Classic Bally/Stern HV overvoltage protection - sanity check

By Lindsey

9 years ago


Topic Heartbeat

Topic Stats

  • 16 posts
  • 7 Pinsiders participating
  • Latest reply 9 years ago by G-P-E
  • Topic is favorited by 3 Pinsiders

You

Linked Games

No games have been linked to this topic.

    Topic Gallery

    View topic image gallery

    Untitled.jpg
    shunt2.jpg
    Bally-Stern HV Over Voltage Protection.jpg

    #1 9 years ago

    This idea came up in another thread and I was thinking about posting it to pinwiki, but I wanted to get some more eyes on it to make sure there are no further gotchas that are going to pop up since I'm not planning to test it in a machine (I already drew it with the diode backwards once ).

    The complaint was that the fuse doesn't blow when the transistors in the voltage regulator circuit short out and the voltage goes over 200VDC. This is actually a really common problem. The fuse doesn't blow because that's an overvoltage condition and fuses are overcurrent protection, but we can add overvoltage protection easily by adding a zener diode.

    Like this:
    Bally-Stern HV Over Voltage Protection.jpgBally-Stern HV Over Voltage Protection.jpg

    #2 9 years ago

    This is good (yes - simple : ) idea, it can works, questionable is "only" about zenner dissipation ?

    ( "one shot protection" ?

    #3 9 years ago

    Will only work for a split second.
    With no current limitation, one quick rise above the zener threshold and that zener is toast. No easy way to put current limiting in there without affecting the clamping voltage.

    Unfortunately, there is no easy method to add voltage limiting onto this circuit as it is currently designed.

    #4 9 years ago
    Quoted from G-P-E:

    one quick rise above the zener threshold and that zener is toast

    Yes...that's what I mentioned about "one shot"....but, I'll try and see results
    (of course with "dummy load"

    #5 9 years ago

    Could a MOV be used instead of a zener diode, and be able to survive more than one hit? Or possibly a thyristor to cut power?

    Note: I'm a novice when it comes to electronics, so forgive me if these suggestions don't make sense.

    [edit]: If something won't fit on the driver board, would it be possible to come up with a daughter board that connects to the driver board's connector to provide overvoltage protection or a shutdown circuit?

    #6 9 years ago

    I'll defer to Ed as the expert on this one. I'm guessing that you're saying the diode won't conduct long enough before burning out to blow the fuse? What about with a big-ass diode?

    #7 9 years ago

    Yeah... they make 5w 200v zener? That would survive in reality at least a handful of times, no?

    I dont have any of that zener, but i ordered some from china. I am for sure going to try. Should be able to hit 200v via adjusting the POT.

    #8 9 years ago
    Quoted from ForceFlow:

    Or possibly a thyristor to cut power?

    You nailed same idea It works on Gottlieb (SYS1)...NOT on high voltage (+5v & -12v)

    Appropriate selection zenner diode, with current & delayed limits .... why not?
    (worth a try ! )

    #9 9 years ago

    If you want to save your zener...

    Mac

    shunt2.jpgshunt2.jpg

    #10 9 years ago

    The PNP transistor will shunt the current to ground instead of the zener taking it.

    #11 9 years ago
    Quoted from Sheprd:

    If you want to save your zener...
    Mac
    shunt2.jpg

    Nice one! I would like to try with just the zener first because it's easier for people to install but this is a great idea for plan B.

    #12 9 years ago
    Quoted from Sheprd:

    The PNP transistor will shunt the current to ground instead of the zener taking it.

    What PNP Transistor would you suggest? The NJW0302G is rated @ 250V.

    #13 9 years ago

    I took a brief look at digikey and there are lots of options for transistor. Just needs to be pretty beefy with a high enough voltage rating. The NJW0302G looks like a good option to me. 15A@250V should be plenty beefy enough.

    Might also just fry the E-B junction of the transistor with no current limiting. Some testing is definitely in order

    #14 9 years ago

    I am not able to try "any" idea in next 10 days, my workshop is "full" with Gottliebs and Laser War (which is "on work" )
    BUT...there is Fathom "near by", and I planed set-up him, after finishing Laser War.

    Anywhere , over voltage protection is nice idea

    #15 9 years ago

    You could alternatively place an NPN in series with the fuse, a bias resistor between collector and base, and the 190V zener from base to ground. This would effectively be placing a 190V regulator in series. It would normally be saturated and passing the input voltage (170V) through unless the voltage spikes above about 190V, then it will clamp it there, opening the transistor to take the drop from the maximum down to 190V. If you were clever, you could include an LED that would come on to tell you your primary regulator has bitten the dust and you are running on backup. Yes, overkill.

    #16 9 years ago

    By far the most common discrete overvoltage protection circuit out there is the zener/SCR combo.
    For an example -- see any Gottlieb System 1 or System 80 power supply.
    Set the zener voltage to where you want the trip voltage to be.

    Untitled.jpgUntitled.jpg

    Reply

    Wanna join the discussion? Please sign in to reply to this topic.

    Hey there! Welcome to Pinside!

    Donate to Pinside

    Great to see you're enjoying Pinside! Did you know Pinside is able to run without any 3rd-party banners or ads, thanks to the support from our visitors? Please consider a donation to Pinside and get anext to your username to show for it! Or better yet, subscribe to Pinside+!


    This page was printed from https://pinside.com/pinball/forum/topic/classic-ballystern-hv-overvoltage-protection-sanity-check and we tried optimising it for printing. Some page elements may have been deliberately hidden.

    Scan the QR code on the left to jump to the URL this document was printed from.