> I didn't know relays would wipe from normal current flow through them. I
> thought wiping was strictly a mechanical operation arising from the
> closing and opening of the contacts. How does it do this from normal
> current flow?
Different contact materials have different hardness and even
shapes. High current contacts are harder materials with wider
contact areas, while low current contacts are softer materials with
smaller contact areas.
High current contacts rely on a bit of voltage and current flowing to
"burn away" any film or non-conductive deposits, while low current
contacts have a softer surface of a material that doesn't
contaminate as easily. The pressure is also higher in a small area,
allowing mechanical wiping to have a larger effect.
This is a common problem with high current relays used to switch
receive lines, and why a few low power "hot switches" will clean up
a high current relay. Vacuum relays of course avoid these
problems.
The ideal amplifier open-frame relay would use low current small
surface area contacts on the receive side, with high current
contacts on the transmit side.
73, Tom W8JI
w8ji@contesting.com
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