How about wiring a capacitor across the points to absorb the inductive kick?
Bill Huff
At 2/18/201201:17 PM, Eastern Sierra Adjustment Svc wrote:
This pic is captioned:
Here you can see that one side of the upper point is completely
worn away. You can also see where the lower point actually started
wearing away the armature after eating through the side of the point.
The unused side of the point is in very good condition. (It should
be, since it wasn't used.
The points must be realigned to get the clock running again, no
matter what. That's the hard part to do properly. You cannot just
"bend" the armature. But if we do realign the point, and if we then
filed them down, the clock would be operable again. The problem is
that then you have about half the point surface area you should
have, so the points will wear themselves down
again prematurely. That solution would be perfectly ok if you did
not want a 24/7 365 operation.
The challenge here is 1) to realign the points without doing any
other damage to the clock, and 2) then protect the points to
minimize the effects of future wear.
And:
Your friend's point is well taken, but the reason it won't work in
our case is that the clock coils represent a highly inductive load,
which generates a very high back EMF voltage across the points when
the points open. The coils in these clocks would typically be about
10 mH, which results in an arcing EMF of about 3000 volts. That's
why the points here are not made of copper in the first place. The
better clocks, like Borg, used tungsten points so they could stand
up to the inductive load. Even if we could resurface the points
with copper I'm afraid they would fail in a matter of only a few
weeks. The difference in the central office, of course, and the
reason copper points worked there was the absence of inductive
loading on the voice circuits.
Ron Water's idea about installing an on-off switch might be good,
but, I've already got a lot of wiring going on under the dash, with
the auxiliary starter, the rear speaker fader switch, and the FM
converter's wiring.
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