[Milsurplus] A relay transient suppression circuit.....?

[hwhall at compuserve.com]

Interesting!  Seems to my recollection I've seen diodes used across a coil or an RC pair across a coil but not both.
 

 Wayne
WB4OGM

 

-----Original Message-----
From: Hubert Miller <kargo_cult at msn.com>
To: tetrode <tetrode at googlegroups.com>; 'Milsurplus' <milsurplus at mailman.qth.net>
Sent: Sun, Feb 21, 2016 7:18 pm
Subject: [Milsurplus] A relay transient suppression circuit.....?



Going thru some manuals today, deciding which to keep and so on, i find one for a keying ‘control panel’ by RCA. It says this: 
“Each relay has an RC circuit in series with a diode across the coil to provide transient suppression. This RC circuit lowers the maximum keying
rate to about 80 WPM based on a standard word equal to 25 centerholes of Morse tape.”  
 
The relays are provided with a -12 dc. The relay coil has connected to this hot -12 end, a diode 1N459 anode ( reverse biased ); the diode
other end ( cathode ) goes to a paralleled 10kR and 2.2 uF connected reverse to the operating voltage across the relay. Is that RC to 
prevent damage to the diode by the reverse EMF of the coil, on break (opening ) the relay circuit ( by ungrounding the cold +12 end of the
coil, where a hand key or auto keyer is connected ? And probably the delay effected by the capacitor discharging slows the coil release? 
Why the capacitor at all? The diode and resistor should do the job, i would think, and the inrush current into the charging capacitor ( by
the reverse coil EMF ) i would think, puts a big initial current spike thru the diode? 
What think?
thanks-
Hue Miller 

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