[AMPS] Relays hanging up

[Norman Hockler]

It's called "contact wetting"  Wetting can be obtained in two ways.  1. A 
difference of potential greater than about 8 volts across the contacts will 
break down the surface film and current will flow.  2.  A nobel metal 
(gold, silver, pladium, etc) will allow current flow when the DOP is lower 
than about 8 volts.  This is why you see contacts plated with gold when 
small signals are to be passed across a relay contact.  Wiping action can 
be physical or implied wetting for low level signals

de Norm N8NH



At , you wrote:

>Hi guys,
>
>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?
>
>73  Steve   WD0CT
>
>
>
>----- Original Message -----
>From: Tom Rauch <w8ji@contesting.com>
>To: <amps@contesting.com>
>Sent: Friday, August 11, 2000 5:03 PM
>Subject: [AMPS] Relays hanging up
>
>
> >
> > I've never seen a DC relay hang up from residual magnetism.
> >
> > The reason is the core material is intentionally a type that does not
> > retain magnetism. If it is magnetized, it will simply magnetize again.
> >
> > The reason most relays hang-up is because they weld into position
> > from hot switching.
> >
> > Lack of receive is more commonly caused by high resistance in
> > the contacts, which is generally caused because the contacts are
> > high current contacts designed to wipe when normal current
> > passes through the contact. Running a 20 ampere relay at nearly
> > zero amperes will almost certainly insure the relay will become
> > unreliable over a period of time.
> >
> > That is a constant fight when using conventional high current relays
> > to switch receiving lines.
> >
> >
> > 73, Tom W8JI
> > w8ji@contesting.com
> >
> > --
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> >
> >
>
>
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