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

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.


For completeness I should have added that we did extensively use
relays on AC fed from a full wave bridge rectifier, and without
capacitor for smoothing. This gave a tendency to chattering as there
is still a pulsating current to the relay, however this chattering was
overcome by the use of an armature end slug (as you describe) which
was only about 1/16" long.
A longer slug could be used, but fast operating speed was critical.

Peter Dettmann