On Sun, 19 Aug 2007 14:39:50 +1000, Peter Dettmann
wrote:

On Sat, 18 Aug 2007 03:16:00 GMT, Ross Herbert
wrote:

On 17 Aug 2007 19:58:41 -0400, Sam Goldwasser
wrote:


You will usually find a copper "shading ring" wrapped around the
end
of the
pole piece. The current induced in the shading ring delays the
decay
of the
magnetic field long enough to smooth it out between cycles. There
is
no
diode or smoothing cap!


In the telephony industry these are known as "slugged" relays. Such
relays have a solid copper slug of a specific length - eg. 1/2" or
1"
depending on delay period required - the same diameter as the coil
itself. The slug could either be at the armature end or the heel end
of the coil depending upon whether a predominantly slow operate or
slow release was required. For ac operation it hardly matters which
end is slugged and if pushed for a part you could use a relay with a
spare winding on it and simply short circuit this winding to produce
a
"slugging" effect.

No there is a difference here Ross, in the AC relay, the "slug" does
not cover the whole of the magnetic iron path, it is typically only
applied to about a quarter of the iron circuit. The process is to
delay the decay of flux in that slugged path so that there is a
useful
magnetic pull during the time that the un-slugged path has zero flux,
(and therefore zero magnetic pull). Using the DC relay slug is not
really useful for the AC case as it covers the whole magnetic path.

Peter Dettmann


Hi Peter, there is NO difference.

The principle is exactly the same even though the use of telephony
relays is predominantly DC usage. However, they also were used in AC
applications such as the detection of ringing voltage in ring trip
circuits before the advent of semiconductor rectifiers. A relay which
would chatter in response to 16-2/3 c/s ringing would not be very
effective as a ring trip relay so the slug performed the same function
as in modern AC relays at 50 or 60 Hz.

In the telephone type relay I was referring to the slug does NOT cover
the full length of the winding bobbin either. As I said the slugs are
in different lengths eg. 1/2", 1", 1-1/2". The winding bobbin length
is always a fixed length for the relay type and the slug was located
either at the armature end or the heel end. A typical ring trip relay
would have a 1" armature end slug.

Here is a typical 3000 type telephony relay as used in UK and
Australia in SxS. http://www.britishtelephones.com/autorel.htm

In fact this particular picture appears to show the winding bobbin
with a copper front cheek which is the smallest armature end slug of
all. In normal "donkey" relays the front cheek is always bakelite.

For further study of the BPO 3000 type relay data see
http://www.samhallas.co.uk/repositor...k_complete.pdf
WARNING: Over 3MB. It will take some time to download.