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What's happening to my minipac??

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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.

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