[ARC5] Backwave

[Roy Morgan]

On Oct 26, 2015, at 6:48 PM, Jay Coward via ARC5 <arc5 at mailman.qth.net> wrote:

> 
> Hello Everyone,
> I always thought back EMF diodes were wired across the coil, not in series. Maybe at +28V it doesn't matter?

Do not be confused by there being two different phenomenon going on.

The posted URL:

http://aafradio.org/docs/Relay_timing_issues_-_SCR-274N.html

Talks about solving a problem where one or more relays affected other relays that were in parallel with it/them. This situation apparently caused some of the relays to act badly.  The diodes in series with the coils isolated the relays from affecting each other.

The more normal situation where a relay has a diode installed backwards ACROSS its coil is done to cause the relay to open as soon as possible after the coil voltage is removed, or to reduce transient voltages that would otherwise be generated.  This second reason is the case especially where the relay is being driven by a solid state device.

I don’t think the voltage in the case of the SCR-274 transmitters was the important factor.

Roy

Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958