What's happening to my minipac??

[supafraud]

Hi guys, so for those not aware I've created a software engine for a EM pinball machine. Unfortunately I'm stuck with a strange problem. The way that I have the targets and such hooked up to my software is with a minipac that is wired to the various drop targets, roll over targets etc. This works great until I start firing off solenoids. After a few solenoids fire off, for example if I just hit the flippers a few times, the minipac "disconnects" and is not detected and stops giving me input. Sometimes if I wait a few moments windows detects it again. At first I thought it was a wiring problem so I rewired the entire playfield (not awesome) only to have the same problem. It's not the driverboard because I have the same problem when it is dissconected and I am just hitting the flippers which are hardwired to a seperate power supply. In fact everything at this point is totally seperate from the computer with the minipac on it and the minipac itself. It's not vibration from the solenoids because i have moved it from having any contact with the playfield. I'm not sure how but I think it's some kind of electro magnetic thing going on. Does anyone have any ideas because this is driving me nuts! All I can think of is trying to shield the minipac with something but I think it's possible that the wiring harness would have to be shielded too. Please let me know if you have any ideas, the flippers are running 50volts AC from the original 1975 Bally transformer. The transformer itself is at least 3 feet away from the minipac and the closest solenoid is about 2-3 feet away currently. Obviously the wiring harness is only a few inches from the various solenoids but nothing is touching. So confused.

 

[BobA]

You might be inducing spikes into the ipac input wiring by having some of the wires running close to each other.  Can you separate all the ipac input wires from the selenoid wiring?  Can you use a diode across the flipper coils to damp the spike they create when the field collapses?   A 1n4004 diode placed across the coil of the flipper in reverse will damp the spikes.

[WindDrake]

You might be inducing spikes into the ipac input wiring by having some of the wires running close to each other.  Can you separate all the ipac input wires from the selenoid wiring?  Can you use a diode across the flipper coils to damp the spike they create when the field collapses?   A 1n4004 diode placed across the coil of the flipper in reverse will damp the spikes.

Bob beat me to it. I'd bet the solenoids are making the Minipac go into overvoltage shutdown from the Back-EMF out of the Solenoids. Diodes or Optoisolation will fix ya' up.

[supafraud]

thanks fr the replies. I actually happen to have a few 1n4004 diodes that were soldered to some switches i ordered. These little guys can handle to 50v 10 amps? also on the flippers there is the hold coil and the firing coil, how would that get hooked up?2 diodes?

[BobA]

I think the best way is 2 diodes as there are 2 coils making spikes on each flipper.

[danny_galaga]

Definitely voltage spikes. It's exactly how a car coil makes thousands of volts, from 12V. Give it 12V, and you get a strong magnetic field, when you disconnect, the collapsing field multiplies the voltage. The solenoid isn't designed to do that, instead using that magnetic field to convert electricity into mechanical force, but I'd still reckon you are hitting the minipac with hundreds of volts! What I don't understand is that pinball machines from what? the late seventies onwards have plenny electronics in them. How were THEY preventing the same spikes? I would have assumed there would be diodes built in to the solenoids. I guess they appear elsewhere in the circuit instead...

[supafraud]

OK, so I soldered on 2 diodes with the stripe facing the positive ends (as I found with googling) and the one connected to the hold coil got blown straight to hell when i activated the solenoid. It was a 1n4004. Any ideas?

Also in response to Danny, this is an old EM machine that did not have any diodes on any coil as there were no SS parts.

[robe_uk]

You said your circuit was 50v AC so sounds like you connected the diode across the supply, when the AC switched direction your diode basically created a short circuit hence blowing itself.  Usually the diode protection is across a DC circuit.   

Maybe try ferrite rings on your wiring which can damping emf noise, or as suggested before optoisolated your ipac inputs, hard the help over the net but good luck

[BobA]

+1 on ferrite rings around you lines.  Physical isolation of the lines maybe your only other option or wrapping them in conductive foil and grounding the foil.  Many multiconductor data lines and audio lines use a shield to help reduce interference.  Only ground the shield at one end so a loop is not created. Sorry did not notice the voltage to coils was AC.  The diode trick only works on DC. 

[MTPPC]

Install Relays to activate the flippers and use a bridge rectifier to create DC current to activate the relays. Then use a small diode to shunt the flyback voltage from the relay's coil.

[WindDrake]

Install Relays to activate the flippers and use a bridge rectifier to create DC current to activate the relays. Then use a small diode to shunt the flyback voltage from the relay's coil.

^ That. If you're working with 60/70's-era AC-Drive sources, that's the way to do it. Just make sure to use Solid-State Relays, as they are faster then Mechanical, and you don't want flipper lag.

[danny_galaga]

Oh, I didn'trealise you are using a complete EM pinball machine! I thought you were just scavenging parts! I don't understand what the software is for then, how would it be any different to how it was built in the first place? Off topic, but I don't think I geddit...