[ARC5] Keying suggestions

[Dennis Monticelli]

There is an industry standard way of clamping that inductive spike and
still allowing for rapid release of coil energy.  You simply put a
zener in series with the clamp diode.  When the diode engages, the
total clamp voltage is 0.7V plus Vzener.  The value of the zener is
not critical.  I would suggest something in the 10 to 20V range with a
current rating equal to or greater than the coil current.  A zener in
that voltage range would dissipate the relay coil engery approx 15
times faster than just using a diode while clamping the max voltage at
a predefined safe level.  To get the same benefit from an RC snubber
would require some experimentation of values.

Dennis AE6C


On 4/9/06, J. Forster <jfor at quik.com> wrote:
> I looked at the suggested schematic and it's NOT a good thing IMO. What happens
> when the circuit opens is undefined. Yes, it does make sense to isolate the
> relays from each other, but there is nothing, other than the reverse breakdown
> of the diodes, to prevent huge voltage spikes across the relay coils. That
> circuit will cause either the diodes or coils to fail sooner or later.
>
> IMO, you need a snubber across the relay coils, and if you are intent on doing
> the diode isolation, you need a snubber across each coil.
>
> -John
>
>
> Mike Hanz wrote:
>
> > There are *two* ways to employ a spike diode - one *across* the relay
> > coil, and the other *in series* with it.  See Steve Williams'
> > interesting keying relay experiments on a complete 274N set at
> > http://aafradio.org/docs/docs.html , under SCR-274N relay timing notes,
> > for a lot of good information.
> >
> > I'm a little puzzled by the original question, though.  K-53 isn't
> > designed well for keying purposes unless you intend to send fairly
> > slowly, and keying the MO at the same time isn't conducive to
> > stability.  An external relay in the B+ line like the original design is
> > actually easier to rig up than the effort needed to modify the
> > transmitter wiring, reversible though that might be.  Just a couple of
> > data points to think about....
> >
> > Best 73,
> > Mike
>
>
>
> _______________________________________________
> ARC5 mailing list
> ARC5 at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/arc5
>