Antique Arcade Game AC Coil problem
Antique Arcade Game AC Coil problem
(OP)
An arcade game from the 1940s uses a small 120 VAC coil to pull in a latch that releases a power switch. The coil present in the game was fried and seems impossibly small --a medium gage wire (I forget the # turns, but maybe .75" diamater). I rewound the coil with the same gage wire and approximate overall size, but it only has a few ohms resistance. In operation, the coil is only on ong enough to pull in the plate and release all power, but the switch contacts arc badly.
On top of this, a 250VAC 0.1MFD cap was wired IN PARALLEL with the coil. I've seen this setup before but the cap is always across the coil switch contacts to minimize arcing, not across the coil itself.
When I apply power to the coil the switch arcs terribly as I've mentioned. I don't know if the cap is any good as it's ancient as well.
So...
Could this be correct that such a low-ohm coil would be used with a high voltage, and was the original coil something other than the one I found in the machine?
What would be the purpose of a cap across the coil (and was the original configuration having the cap across the contacts)?
Keith
, but only a few ohms resistance.
On top of this, a 250VAC 0.1MFD cap was wired IN PARALLEL with the coil. I've seen this setup before but the cap is always across the coil switch contacts to minimize arcing, not across the coil itself.
When I apply power to the coil the switch arcs terribly as I've mentioned. I don't know if the cap is any good as it's ancient as well.
So...
Could this be correct that such a low-ohm coil would be used with a high voltage, and was the original coil something other than the one I found in the machine?
What would be the purpose of a cap across the coil (and was the original configuration having the cap across the contacts)?
Keith
, but only a few ohms resistance.





RE: Antique Arcade Game AC Coil problem
RE: Antique Arcade Game AC Coil problem
Keith
RE: Antique Arcade Game AC Coil problem
RE: Antique Arcade Game AC Coil problem
else wise the cap discharge current is massive and will help destroy the contacts it is intended to protect.
You can get a ready potted CR suppressor which has a suitably rated capacitor for this duty from most electronic catalogue suppliers look for contact arc suppressors.
RE: Antique Arcade Game AC Coil problem
The voltage generated across the inductor is V = L x dI/dt
where L = inductance of coil, dI/dt is the rate of
rise for the current. In other words, the steeper the change in current the bigger the voltage which would cause
arcing. The other thing: coils and latches usually have iron housing that completes the magnetic circuit. The coils generate magnetic flux which goes through the latch and comes around the housing and back to the latch again. This gives it more inductance. The more inductance, the slower the time constant which also is related to impedance. More impedance would limit the current spike. So, if there is a housing, it should be used with the coil and latch.
If not, more coils is needed to bring up that inductance.
The resistor idea suggested by the gentleman, might work in limiting the current spike from the cap but not from the 120VAC source unless you add resistance there too.
RE: Antique Arcade Game AC Coil problem
RE: Antique Arcade Game AC Coil problem
I didn't mention that there is a 3 amp 120VAC motor running when the contacts that energize the coil that pulls in the latch that breaks the contacts to the whole machine.
But in any case, the original circuit did not have a resistor and had simply the coil and cap.
Also, I tested the cap and it has rated capacitance and 35 microamp leakage at 200V -- does that sound good?
RE: Antique Arcade Game AC Coil problem
Is that DC? I've rebuilt a few old magic eye capacitor testers and even back then they thought 9uA was really bad. It's not your problem, but this is not a good cap to have across the line. I for one love light bulbs. A 15W 120V lamp may be just what you need. A low resistance for a quick pulse and the resistance will increase about 8 times that if the situation persists. That will protect the solenoid from burning up.
RE: Antique Arcade Game AC Coil problem
Rereading your post again, I think the cap is just for filtering and does not really contribute much to the arcing.
It may be that the arcing was always an issue and the reason for the fried coil. You could try using an
MOV [metal oxide varistors] ones rated for 250VAC - 500VAC [experiment]. It will clamp the high voltage spike generated by the coil. Put it across the coil.
The real solution would be to use an SCR or TRIAC to replace the large switch contacts. You'd still need to use a smaller switch to trigger the TRIAC. Solid state switches do not arc. Of course, this might be more design
engineering than you want to do.
RE: Antique Arcade Game AC Coil problem
Thanks for all the help.
RE: Antique Arcade Game AC Coil problem
Dan - Owner

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