In article , "Dave Plowman (News)"
writes:

Got a switch story from my old car. The window switches control relays.
The exact same Lucas switch is used on other makes with no relays. On
mine, the switches need regular cleaning. In the high power use, not.

When switching relays, presumably it's breaking the supply to a
reactive load?

--
Mike Fleming

In article ,
Mike Fleming wrote:
In article , "Dave Plowman (News)"
writes:

Got a switch story from my old car. The window switches control relays.
The exact same Lucas switch is used on other makes with no relays. On
mine, the switches need regular cleaning. In the high power use, not.

When switching relays, presumably it's breaking the supply to a
reactive load?

Yes - although with only about 100mA flowing, not enough of a spark to
keep them clean.

--
*I stayed up all night to see where the sun went. Then it dawned on me.*

Dave Plowman London SW
To e-mail, change noise into sound.

In article , "Dave Plowman (News)"
writes:

In article ,
Mike Fleming wrote:
In article , "Dave Plowman (News)"
writes:

Got a switch story from my old car. The window switches control relays.
The exact same Lucas switch is used on other makes with no relays. On
mine, the switches need regular cleaning. In the high power use, not.

When switching relays, presumably it's breaking the supply to a
reactive load?

Yes - although with only about 100mA flowing, not enough of a spark to
keep them clean.

I was thinking of the high voltage arc as the field collapses causing
damage to the contacts.

--
Mike Fleming

On Thu, 21 Dec 2017 18:44:31 +0000, Mike Fleming
wrote:

In article , "Dave Plowman (News)"
writes:

In article ,
Mike Fleming wrote:
In article , "Dave Plowman (News)"
writes:

Got a switch story from my old car. The window switches control relays.
The exact same Lucas switch is used on other makes with no relays. On
mine, the switches need regular cleaning. In the high power use, not.

When switching relays, presumably it's breaking the supply to a
reactive load?

Yes - although with only about 100mA flowing, not enough of a spark to
keep them clean.

I was thinking of the high voltage arc as the field collapses causing
damage to the contacts.

The trick for the best switches is the wiping contact. Initial contact
and arc happens at one spot, then the blades slide across each other
and final contact is made at a clean spot. And the wiping action
ensures that oxidation is never a problem either. Those switches tend
to cost a bit more, though.

d

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

In article ,
Mike Fleming wrote:
In article , "Dave Plowman (News)"
writes:

In article ,
Mike Fleming wrote:
In article , "Dave Plowman (News)"
writes:

Got a switch story from my old car. The window switches control
relays. The exact same Lucas switch is used on other makes with no
relays. On mine, the switches need regular cleaning. In the high
power use, not.

When switching relays, presumably it's breaking the supply to a
reactive load?

Yes - although with only about 100mA flowing, not enough of a spark to
keep them clean.

I was thinking of the high voltage arc as the field collapses causing
damage to the contacts.

I'd imagine the window motor is an even bigger reactive load. ;-)

--
*If you can read this, thank a teecher

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Don Pearce wrote:
On Thu, 21 Dec 2017 18:44:31 +0000, Mike Fleming
wrote:

In article , "Dave Plowman (News)"
writes:

In article ,
Mike Fleming wrote:
In article , "Dave Plowman (News)"
writes:

Got a switch story from my old car. The window switches control
relays. The exact same Lucas switch is used on other makes with
no relays. On mine, the switches need regular cleaning. In the
high power use, not.

When switching relays, presumably it's breaking the supply to a
reactive load?

Yes - although with only about 100mA flowing, not enough of a spark to
keep them clean.

I was thinking of the high voltage arc as the field collapses causing
damage to the contacts.

The trick for the best switches is the wiping contact. Initial contact
and arc happens at one spot, then the blades slide across each other
and final contact is made at a clean spot. And the wiping action
ensures that oxidation is never a problem either. Those switches tend
to cost a bit more, though.

These switches are a pretty simple up and down copper to copper contact.
Nothing so sophisticated as a wiping action. Luckily, they are quite
simple to strip down and clean.

--
*I am a nobody, and nobody is perfect; therefore I am perfect*

Dave Plowman London SW
To e-mail, change noise into sound.

Once upon a time on usenet Phil Allison wrote:
Mike Fleming wrote:

-------------------


There are two major issues with large mains rated toggles when used
with less than mains voltages.

1. The contact material ( often plain brass) tarnishes with a non
conductive layer. Regular use at mains voltage usually prevents
this layer building up.

2. Grease applied to the moving parts of the switch migrates to the
contacts, hardens and stops conduction.

In case 2, a squirt of WD40 often restores good operation, far as
being a mains switch is concerned.


There's a third issue specifically with switches used on DC
circuitry, which is that current flow is constant and unidirectional
and so the arcing that occurs as a contact is made and broken will
always be in the same direction and will not be broken by the
alternation of the current, only by the contact gap getting large
enough.


** Switches have *distinctly different* voltage ratings for AC and DC
currents for exactly this reason.

240VAC switches ( and relays) are normally down rated to 24V or 32V
when used with DC current of the same magnitude.

https://www.mouser.com/blog/Portals/...ig1-Switch.png

Not much relevant, however, to our present topic.

Indeed. Knowing you I opened this post expecting to see an all-capitals rant
full of medical terms, mentions of bodilly waste products and genitalia and
threats of physical violence.

Strange....
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)