On Tue, 21 Aug 2007 22:41:21 +1000, Peter Dettmann
wrote:
SNIP
If a discussion on 3000 type relays were involved, I have my well
worn gram balances, contact adjusters, and armature bender at hand.


My initial post was to simply add a comment so that other readers
would not gain the impression that the only type of AC relay was one
with a "shading ring". It is only because of responses to my initial
post that I added further comments to expand on it or to correct those
responses but I did not plan for the thread to specifically become one
about BPO relays. If no one had cared to respond then it wouldn't have
gone further.

You are right that the 3000 style as an AC type is rare, as there are
much better designs used for AC, but still using the same principle
of the divided magnetic path as Ron described.

Actually, I haven't found any description on AC relays which refers to
a "divided magnetic path", or anything remotely resembling this term,
so I doubt that it means anything at all. What I did find is a
description of the various types of shading ring (as refered to by Ron
and others) which might be found on AC relays and/or contactors meant
for 50/60 Hz operation. See page 36.
http://books.google.com/books?id=gES...sKmenpcNVhKamU

While operating on the same principle, the solid copper slug as used
on the BPO 3000 type relay is far more effective for operation at
lower than 20Hz while also allowing the tailoring of the delay period
by varying the length of the slug.

AC relays commonly used today are not necessarily "better designed"
for use on AC than the 3000 type (and similar) relays. The AC relay of
today only has to operate on 50/60Hz where the slugging effect of a
relatively small shading ring is adequate, thus making the design much
simpler and less costly to implement than for the 3000 type relay. In
many cases the addition of semiconductors simplifies the design of
relays used for AC applications so that shading rings aren't required.

I might add that every relay manufacturer in the world making relays
for telephony applications, would have produced similarly slugged
relays of a perhaps a slightly different mechanical design - it wasn't
just the BPO 3000 type which used this principle. In closing, this
type of slugged relay would have been far more common than any other
type of AC relay used in any other industry then, and even today.
Every final selector in every strowger based switching system the
world over used one. They had to be reliable and good for millions of
operations.

I don't have an armature bender but I do have the pressure gauges and
spring adjustment tools.....