My observation (given the large number of silver cadmium relay contacts
I've seen at large contest stations, as well as more limited use at my
little station) is that the large amounts of power being put through the
relays helps blow the contacts clean in real life and prevents
"intermittent receive" from happening on contact pairs that are also
recently used for transmit.
Tim N3QE
On Fri, Oct 10, 2014 at 8:29 AM, Tom W8JI <w8ji@w8ji.com> wrote:
> I have built four or five "stack matches" using these relays and have been
>> quite pleased with them.
>>
>> http://www.mouser.com/ProductDetail/TE-Connectivity/T92S11D22-12/?qs=%
>> 2fha2pyFadujQKxyiQ9QJsU9gOmzykpctnwthD3xoZjoJPHbNrun4hw%3d%3d
>>
>> 73...Stan, K5GO
>>
>
> If you look at the contact material, it is the wrong material type for our
> applications. Those relays are hot switch relays for high current
> applications with Silver Cadmium Oxide. From an engineering bulletin on
> selecting relay contact materials:
>
> Silver Cadmium Oxide
>
> Silver cadmium oxide contacts have long been used for switching loads
>
> that produce a high energy arc. Silver cadmium oxide contacts are less
>
> electrically conductive than fine silver contacts, but have superior
>
> resistance to material transfer and material loss due to arcing. They do
>
> exhibit greater interface resistance between mated contacts, and also a
>
> slightly greater contact assembly heat rise. The minimum arc voltagerating
>
> of silver cadmium oxide is 10 volts and, like fine silver contacts, the
> silver
>
> in this alloy will oxidize and sulfidate. Therefore, an arc is necessary to
>
> keep these contacts clean.
>
>
> This doesn't mean they won't work and will go up in smoke. It does mean
> they are subject to contact sulfidation which causes intermittent receive.
> They have silver, a hard base material, and large contact area that does
> not wipe well. They also are the type of relay that is subject to contact
> derating from skin effect because of constant resistivity.
>
>
> 73 Tom
>
>
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