[AMRadio] Reduce relay contact arc

[ARS W5OMR]

I've got a job ahead of me, replacing the power switch on my Drake L-7.
Same reason. Years of arcing A.C. voltage.

I burned up a set of relay contacts after I converted a Viking II to PTT,
then connected it to a computer to operate the rig via remote (from the
bedroom to the shack, on the local lan). Made about 3 transmissions, and it
quit keying up. Upon forensic investigation, the relay contacts were MIA.

That was DC, and in hindsight, a 1kV capacitor across the relay contacts
would have prevented that loss.

A.C. voltage is a different animal.

-Geoff/W5OMR



On Wed, Jun 13, 2018, 11:13 Rob Atkinson <ranchorobbo at gmail.com> wrote:

> I went through this a few years ago.   The usual solutions are
> snubber, inrush limiter with a resistor, or a thermistor.   The all
> work to some degree but in different ways and circumstances.  A
> thermistor works, but runs hot and won't do anything if the relay is
> closed and opened repeatedly before the thermistor can cool down to
> recycle.   All these methods may or may not prevent arcing on break.
> I wound up using a solid state hocky puck SPST circuit.
>
> 73
>
> Rob
> K5UJ
>
> On Wed, Jun 13, 2018 at 9:08 AM, CL in NC via AMRadio
> <amradio at mailman.qth.net> wrote:
> > If you have a relay that is switching line voltage or higher AC voltage,
> is there any way to reduce the arcing?  You might suggest a snubber, but if
> you use the snubber formula to calculate component sizes, the capacitor
> allows enough AC to pass such that your transformer is making volts.  You
> put it on the primary of say a HV B+ PS, and you will get some amount of B+
> on the secondary, and if you put it in the secondary HV line, you will leak
> AC into the rectifiers and still make B+.  Any solutions other that
> something like a .01 across the contacts and live with it?
> >
> > Charlie, W4MEC in NC
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