[Milsurplus] [Heathkit] O.T. Dow Key Coaxial Relay

[Glen Zook]

After a while, even a relay designed for DC can magnetize.  The "cure" is to reverse the leads to the coil.  This may have to be done every few years depending on just how much the relay is used.

Glen, K9STH

Website:  http://k9sth.com


--- On Mon, 11/15/10, Kevin Ward <n2ie at arrl.net> wrote:

You can tell an AC coil from a DC coil if you can get the coil cover off (without ruining it) and get a look at the coil itself.  An AC coil has a D-shaped ring through the core at one end.  This keeps the relay from chattering as the coil voltage swings through zero.  A DC coil has no D-ring. 
 
Depending on the core material, running an AC relay on DC can magnetize the core.  The relay may then tend to hang in the energized position, or may be slow to drop out. 
 
If the relay tends to hum, buzz or chatter when run on AC, it probably has a DC coil.