Hi Doug and AMD List Readers,

On Fri, 16 Aug 1996 07:18:29 +0000 Doug Helfman asked of John Grant:

> John,
>     With all this discussion on the digest regarding old switches,
> I'm wondering if I should be worried about my Welte.  I assume I
> still have the original switch, even though you replaced the motor.
> What do you think?
>
>                                             Doug

Doug,

I took the liberty of forwarding your message on to the AMD List as
I believe my response will be of general relevance there as well.

As strongly implied by Craig Brougher, Terry Smythe, and perhaps others,
the question of electrical switch longevity is not a particularly
difficult one to answer.  Switches usually fail mechanically simply
because most were never designed or engineered for more than a few
thousand cycles, particularly when they are asked to break the highly
inductive loading of the typical fractional hp motors that are found in
reproducers.  The electrical arc which is generated under these
conditions is HIGHLY destructive of the not-very-robust internal
components typically found in these switches.

My recommendation to you, and others similarly situated, (i.e., whose
switches are currently functional), would be the addition of a solid
state relay (SSR) to take over the switching of the main motor current.
The relatively small (typically a few milliamps) of current required to
oper se devices will ensure that no further destructive arcing takes
place at the contacts.  Of course, the switch will STILL be wearing
mechanically, but its ultimate failure should be delayed considerably.
Solid state relays typically operate on an input control voltage
anywhere between 3-32 VDC.  A simple wall transformer with DC output
will work for this application.  (Some suggested sources for these
components is included at the end of this message.)

Even if the original switch has failed and you are forced to engineer a
replacement, it would still be advisable to have it operate an SSR since
it will still last longer, and will allow you to use a lower-rated
(hence smaller) switch in the limited mounting spaces available for
them.  Addition of these components can always be done in a sensitive
and reversible way so as to protect (and respect) the historical design
of the apparatus.  You should make sure, of course, that the relay
contacts are in series with the "hot" side of the line, not the neutral.
This in turn necessitates a polarized plug on the line cord or
(preferably) a plug with integral safety ground for reasons previously
discussed here.  SSR's with a rated capacity of 20-25 amps should be
selected to allow for the start-up surge of the motors.

Catalogs from the following five companies are "must haves" for the
confirmed gadgeteer.  All have large selections of electrical switches
of various designs, ratings, and mounting arrangements.  They also have
solid state relays and the wall transformer/DC power supplys to operate
them.  Most have a selection of obsolete, end-of-production run,
surplus, and just plain hard-to-find stuff.  The American Science &
Surplus catalog also makes entertaining reading as most of the item
descriptions have clever, humorous write-ups.

        R & D Electronics
        Electronic Surplus Inc.
        1224 Prospect Ave.
        Cleveland, OH 44115
        (Can't find phone number right now, write for catalog or call
        directory assistance in Cleveland)

        All Electronics Corp.
        14928 Oxnard Street
        Van Nuys, CA 91411
        (800) 826-5432

        American Science and Surplus
        3605 Howard Street
        Skokie, IL 60076
        (708) 982-0870

        Herbach and Rademan Co.
        18 Canal Street
        Bristol, PA 19007
        (215) 788-5583

        Hosfelt Electronics, Inc.
        2700 Sunset Blvd.
        Steubenville, OH 43952
        (800) 524-6464

Doug, I will get some current prices on recommended components and
get back to you.

-- John Grant