Well done, Wolfgang.
You bring up an important point about using relays, the so-called "wetting
current" required.
https://en.wikipedia.org/wiki/Wetting_current?useskin=vector
When I worked at Tesla some years ago now, every physical switch in the
body (doors, dash, steering wheel, etc) had to have a certain amount of
current flow through it precisely to adhere to this 'wetting current'
requirement. I believe it was OK to have the current on make or break --
that is, normally open is OK, as long as the current flows during make.
Usually about 10 ma. Generally, tho, sometimes you want current flowing
through some important switches all the time because you want to know if
they fail/error -- and that means running the wetting current all the
time. There weren't too many of these. And of course if a different
switch mechanism is used (magnet / coil, reflected light, etc, etc) this
wetting current does not apply.
(Gosh, I remember running 60 ma through the loop magnets on my teletype
machine, at around 150V! Nice sparks when you typed on the kbd in local
loop...)
One would think relays would be 'fairly simple' devices, but here Omron
gives a good set of relay properties:
https://www.ia.omron.com/support/guide/36/explanation_of_terms.html
73,
Mike K6THZ
p.s. These Coto 8401-12-100 relays do seem to still be available:
https://octopart.com/search?q=Coto+8401-12-100+relay¤cy=USD&specs=0
but yes only Quest (says they) have them for $ 13.52 USD each + tax/ship.
On Wed, Mar 8, 2023 at 10:11 AM Wolfgang Peringer <dk7cy@bingo-ev.de> wrote:
> The problem for the loss of sensitivity in receive mode was K3 on the
> input board. It is a Coto 8401-12-100 relay which is no longer available
> or very expensive nowadays. Contacts were dirty and i could measure a
> resistance between the closed contacts which caused the loss of
> sensitivity. As i didn't have a substitute at hand I used the KB relay
> (same 8401-12-100) which is normaly used to switch in a resistive pad
> to avoid a overdrive condition as substitute for the K3 relay. The
> defective K3 is now in the position of the KB relay. Whenever a
> overdrive situation occurs the KB relay will be activated and the RF via
> the contacts on its way to the resistive pad will clean the contacts, hi.
>
> vy 73
>
> Wolfgang
>
> dk7cy
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|