A "general" question ??

Hi All,
I need some help in thinking this out, by yous guys what is better educated then Iz, in electrical theory--I will describe my reason for this question, and my answer, later, as I do not wish to influence your thinking.
Think of a "plunger and coil" set-up, such as was used by WurliTzer, for the latch bar "solenoid", or Seeburg's 100 select, "Pin Bank", "pin cancel" coil/plunger, or Seeburg's early "credit add coil/plunger", in a CCU--( all "spring loaded" return). The switch MAY have a cap across it, or not--
IF power is applied and removed prior to the plunger going "all the way" into the coil housing, ( plunger MAY be "blocked", or just "sticky") will it draw a larger amount of current across the switches, then normal ?
Could this be the reason the switches become "dirty", and/or "pitted" very rapidly ?
TIA, Ron Rich

Hi Ron,

You could may be correct, take for example pinball fipper coils and the open switches that controlled them we always had to keep replacing these when we used to operate pinballs.

On jukeboxes the caps across the contacts did help surpress arcs but the contacts would get pitted as you say, back in the day when I worked on Seeburgs the reversing switches and the switches on the mechanism needed a lot of work.

Regards
Alan

Alan Hood
ami-man
UK

In a coil, when voltage is induced, then removed, a certain peak "surge" is created - hysteresis effect.
This voltage can be several times the average voltage applied, but only momentarily.
Once the coil is activated it settles down.
The surge voltage basically is what enhances the chance for contacts to "spark" and pit.
The capacitor (if used) across the contacts absorbs some of this energy, reducing or eliminating the spark.

Now to address Ron's question - There is the chance for difference in spark energy as related to plunger action - most of the sparking is caused mainly by the coil involved - though the inductance is different depending on the plunger's position.
If A.C. powered, the spark energy is dependant on where in the A.C. cycle the current is made/broken.
If D.C. powered, surge-reducing diodes across the coil can help eliminate the surge by absorbing the surges. - these are used to protect the transistor drivers. (diode cathode end to positive side)
If switch-controlled DC coils, best to use the blocking diodes to help prevent arcing, as well as capacitors across the switch contacts to quell the sparking.

Thanks All--I should have noted that this is a 25 vac cap protected circuit--
Short story is--
A Seeburg M100B, (made in 1949) that I operate, came up with the complaint that it was stealing quarters about the first of the year. I rebuilt this machine about 12 years ago, and have had no problems other then "kids" sticking "toothpicks" in the coin slot till now--So I cleaned the coin switch contacts, ran some coins thru it and left--about a month or so later--same complaint. So I installed a new cap, and re-cleaned the switch--that lasted about another month or so, and the complaint came back. At a loss of what to do now, I changed the coin coil, and once again cleaned the switch--I know that I should "keep my mouth shut"--but it seems to have ended my problem. The old cap was good and the resistance measurements on the coils were : Old, 47.3 ohms--new ( I checked several) 46.1 or 46.2--not enough of a difference, IMHO to affect anything--I'm guessing that the plunger was binding, at times--
Ron Rich

With age some contacts will loose its silver plating and the brass under it will tarnish quickly .
Blade contacts usually have at least one side a solid silver round contact pad . In general it depends on the amount of voltage & current on the contacts . Along with that it matters how hard or soft the contacts make contact ...and... the condition and treatement of the contacts themselves .

A cleaned contact that was not treated the right way along with not contacting hard enough will cause a slight arc causing it to dirty up fast . Contacts need to be carfully cleaned ( not just sprayed with some cleaner or hit with alcohol ) With problem contacts they need to be filed down past any pitting then polished off as shiney as can be and aligned correctly .

Some people will run fine sandpaper on contacts . That will make the contacts rough and arc in some cases .

Ken,
Agree--on "sandpaper", I say NEVER use it as it tends to embed sand into the silver. Always use a burnishing tool !
Spraying "something", I find is only useful for contacts that rotate, as any spray that leaves residue, of any type attracts dirt--real fast in "blade type" contacts, which can be cleaned, prior to burnishing if oily, with a "safety solvent"--watch where the spray goes, as some of them will destroy things such as "plastic". Ron Rich