At-home Silver Plating for Electrical Contacts

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nm9stheham

nm9stheham

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I am rebuilding the heat/defrost control for my '62 Dart and the issue was that the blower switch contacts inside the control corroded and got hot and made everything all 'melty'. I trimmmed out the plastic button control holes and made the mechanical action all good, but the brass contacts and associated berylium copper wipers needed some treatment for the corossion.

What I am trying for restoration is some silver plating powder called Coolamp from a company in Oregon that has been making this product for years. This is a simple treatment of rubbing the powder onto a burnished contact for 30-60 seconds with a damp rag. You get a thin silver plating as a result. Below is a picture showing the brass contact plates with the contact and connector areas plated, and one of the switch button wipers plated too beside one waiting to be burnished.

For switch grease, I used some silver loaded grease call Cramolin; I don't know if this is even made anymore under that name. My dad (RIP) used this regularly to restore burned relay and switch contacts and connections in high power AM transmitters for years.

After initial re-assembly, the switch contacts were all reading 0.1 ohm or 0.0 ohm on my Fluke digital meter. I'd have to pull out a better meter to get a truly accurate readings.

Coolamp and any silver loaded greases are expensive so this makes sense only if you have it for other things or are doing a a bunch of electrical parts restorations. Coolamp can be bought off of eBay for a lot less than new.
 

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I'm gonna havta tuck this one away in my mind..........
 
in the ARMY RESERVE in the 70s. i was shown a trick for testing the ignition points resistance. i hope i can remember it right. with points closed run voltage through them. cant remember if it was 12 volt or through the resistor. then test the volts across the points. i think if more than .10 - .50 volts the points have to much resistance. but now we have electronic ignition. just a history reff.
 
To Moe's post above....Once I get this back in the car, I will be testing the blower current by itself and then testing the voltage drop through this restored switch to see how well this works. That is a much more accurate way to measure low contact resistances with common field equipment.

Of course, the real question is how it will hold up over the years. To help this last longer, and since silver tarnishes readily, I'll be sure to put a good coat of something like Dow4 compound on all the connections where the 2 spade lugs go to stop/slow any tarnish, and make sure there is plenty of the Cramolin on the switch contacts.
 
After the climate push-buttons and the blower speed switches melted in my 65 Newport and 69 Dart, after replacing/fixing them I installed a 30 A relay so "blower hi" current came thru the relay. Otherwise, just a question of time before it melts again, unless you avoid the high position. BTW, my Newport had the rare 4-button pnuemo-switch (non-AC) so I had to rig a 5-button (AC) switch to work.
 
My dad was good with a torch. He used Sil-Fos high temperature silver solder to fix high current contacts. It only took a second, to heat and stab the silver. While he did the impossible to fix everthing, Bill's relay idea is better.
 
KitCarlson said:
Sil-Fos .
Click to expand...

As a former HVAC service guy, SiFos and other silver (hi temp braze) "solder" is some of the most under-rated products there are. There's all kinds of uses for them

One example was years and years ago when I worked for a big auto / truck parts outfit. We made all kinds of hydraulic hoses, and we kept getting requests for PS hoses that "nobody had." One day we got the idea to just whack off the metal tube ends, silver - braze them into a JIC (AN) fitting and make "a hose in between."

A friend of mine and I used to play with "big" amateur radio amplifiers. These are perfectly legal, unlike CB. We used to wind our own tank inductors, and silver-braze the taps on the coils. Used a propane torch tank on one for a winding form. No RF heating in those!!!
 
Both the fan motor and AC clutch windings are inductive. Turning ON, is not a problem, turning OFF is. Diodes can be used to freewheel or catch the current. The current is then consumed by the motor or clutch as the field collapses, for several mS. A 3A rectifier like 1N5404G is a good choice. Apply cathode (line mark at end) to positive lead of motor or clutch coil, other lead to ground. When ON the diode is reversed biased, so no conduction, when switched turned OFF, the diode conducts, carrying the current protecting the switch contacts.

Placing diodes close to motor and AC clutch is best for eliminating EMI. It also protects the temperature regulator contact too. That part is a PITA to replace at my age.
 
^^You'll know it if you get the diode in backwards, LOL

"Attention K mart choppers. EPA diode smoke cleanup on aisle 5"
 
Very true.
Caution polarity matters, wear safety glasses. :) They can go off like fire crackers, good for one time only.
 
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