Power switch
 

Most of the old equipment has power supply switch problem. The contacts arc
by electric power and need to be replaced or sand down to refinish the
surfaces to prevent resistance build up. After the resurfacing surface, is
there any chemical can prevent the arc again and the oxidation coming back?
I am using the de-ox cleaner now, any other suggestions.

Thanks

Eric

One more thing I would like to mention, those power switches are coming from
audio equipment such as amplifier, CD player.

Thanks

Eric

"Eric" wrote in message
...
Most of the old equipment has power supply switch problem. The contacts
arc
by electric power and need to be replaced or sand down to refinish the
surfaces to prevent resistance build up. After the resurfacing surface,
is
there any chemical can prevent the arc again and the oxidation coming
back?
I am using the de-ox cleaner now, any other suggestions.

Thanks

Eric

One more thing I would like to mention, those power switches are coming from
audio equipment such as amplifier, CD player.

Thanks

Eric

"Eric" wrote in message
...
Most of the old equipment has power supply switch problem. The contacts
arc
by electric power and need to be replaced or sand down to refinish the
surfaces to prevent resistance build up. After the resurfacing surface,
is
there any chemical can prevent the arc again and the oxidation coming
back?
I am using the de-ox cleaner now, any other suggestions.

Thanks

Eric

Caig Labs DeoxIt product is excellent for oxidized switch contacts. I don't
use abrasives on any contacts (motor or relay contacts, or electronics
switches) because it degrades the surfaces.
I typically use a heavy paper such as file folder strips wetted with DeoxIt
to clean contacts.
Where the contacts are slightly rough or badly oxidized (or dirty) I'll use
the end grain of a hardwood swab stick or a pop-cicle stick cut with a long
tapered bevel.

Badly pitted contacts require replacement, particularly where they carry
larger currents in power applications. I don't put much trust in sandpapered
contacts, as they're reliability is questionable, likely to fail in ways
that could cause other problems.

Cheers
WB
..................

"Eric" wrote in message
...
Most of the old equipment has power supply switch problem. The contacts
arc
by electric power and need to be replaced or sand down to refinish the
surfaces to prevent resistance build up. After the resurfacing surface,
is
there any chemical can prevent the arc again and the oxidation coming
back?
I am using the de-ox cleaner now, any other suggestions.

Thanks

Eric

Caig Labs DeoxIt product is excellent for oxidized switch contacts. I don't
use abrasives on any contacts (motor or relay contacts, or electronics
switches) because it degrades the surfaces.
I typically use a heavy paper such as file folder strips wetted with DeoxIt
to clean contacts.
Where the contacts are slightly rough or badly oxidized (or dirty) I'll use
the end grain of a hardwood swab stick or a pop-cicle stick cut with a long
tapered bevel.

Badly pitted contacts require replacement, particularly where they carry
larger currents in power applications. I don't put much trust in sandpapered
contacts, as they're reliability is questionable, likely to fail in ways
that could cause other problems.

Cheers
WB
..................

"Eric" wrote in message
...
Most of the old equipment has power supply switch problem. The contacts
arc
by electric power and need to be replaced or sand down to refinish the
surfaces to prevent resistance build up. After the resurfacing surface,
is
there any chemical can prevent the arc again and the oxidation coming
back?
I am using the de-ox cleaner now, any other suggestions.

Thanks

Eric

On Mon, 13 Sep 2004 15:24:30 -0400, "Wild Bill"
wrote:


Caig Labs DeoxIt product is excellent for oxidized switch contacts. I don't
use abrasives on any contacts (motor or relay contacts, or electronics
switches) because it degrades the surfaces.
I typically use a heavy paper such as file folder strips wetted with DeoxIt
to clean contacts.
Where the contacts are slightly rough or badly oxidized (or dirty) I'll use
the end grain of a hardwood swab stick or a pop-cicle stick cut with a long
tapered bevel.

Badly pitted contacts require replacement, particularly where they carry
larger currents in power applications. I don't put much trust in sandpapered
contacts, as they're reliability is questionable, likely to fail in ways
that could cause other problems.

Cheers
WB
.......

Yes, excellent advice.

I don't know what the legal position is in other countries, but over
here you'd come un-stuck...

Power switches are classified as Safety Items and must always be
replaced by the correct item and never repaired. If - as does actually
happen, surprisingly often - the switch failed again and went on fire,
there would be legal and insurance implications. In the event of a fire
in apparatus I'd repaired for someone else, I'd be liable automatically,
whether it was a chargeable job or not; and in the case of equipment of
my own, it would open a large loophole in my insurance if the company
got wind of it.

I still keep my basic Public Liability Insurance up to date, just in
case...

TTFN



--
ajb

On Mon, 13 Sep 2004 15:24:30 -0400, "Wild Bill"
wrote:


Caig Labs DeoxIt product is excellent for oxidized switch contacts. I don't
use abrasives on any contacts (motor or relay contacts, or electronics
switches) because it degrades the surfaces.
I typically use a heavy paper such as file folder strips wetted with DeoxIt
to clean contacts.
Where the contacts are slightly rough or badly oxidized (or dirty) I'll use
the end grain of a hardwood swab stick or a pop-cicle stick cut with a long
tapered bevel.

Badly pitted contacts require replacement, particularly where they carry
larger currents in power applications. I don't put much trust in sandpapered
contacts, as they're reliability is questionable, likely to fail in ways
that could cause other problems.

Cheers
WB
.......

Yes, excellent advice.

I don't know what the legal position is in other countries, but over
here you'd come un-stuck...

Power switches are classified as Safety Items and must always be
replaced by the correct item and never repaired. If - as does actually
happen, surprisingly often - the switch failed again and went on fire,
there would be legal and insurance implications. In the event of a fire
in apparatus I'd repaired for someone else, I'd be liable automatically,
whether it was a chargeable job or not; and in the case of equipment of
my own, it would open a large loophole in my insurance if the company
got wind of it.

I still keep my basic Public Liability Insurance up to date, just in
case...

TTFN



--
ajb

Thanks for the suggestion and I am some confuse on the inrush current
limiter. On the switch, do I use a PTC instead of NTC since I need to block
the high current first turn on and let the switch conduct fully.
Is the inrush current limiter is solder on the two connectors of the switch?
Thanks

Eric


"Ross Herbert" wrote in message
...
On Mon, 13 Sep 2004 10:08:12 -0500, "Eric"
wrote:

|Most of the old equipment has power supply switch problem. The contacts
arc
|by electric power and need to be replaced or sand down to refinish the
|surfaces to prevent resistance build up. After the resurfacing surface,
is
|there any chemical can prevent the arc again and the oxidation coming
back?
|I am using the de-ox cleaner now, any other suggestions.
|
|Thanks
|
|Eric
|
There are products such as De-Oxit and Stabilant 22 (very expensive)
which will prevent oxidation of switch contacts, but this doesn't
appear to be the main problem in your situation.

It seems that your problem is caused by arcing at the contacts which
results in pitting and carbonising deposits to form which can cause
erratic and unreliable contact switching. There is no "magic spray"
which can prevent arcing, and you will continue to have this problem
unless some means of reducing the heavy switch-on/switch-off surges is
employed.

Here is a brief explanation;

http://www.machinedesign.com/ASP/str...tedArticle.asp

Items such as high power audio power amps employ massive filter
capacitors and often use toroidal transformers. Toroidal transformers
inherently produce higher switch-on currents than conventional
laminated E-I core transformers and the large capacitors appear as a
near short circuit at the moment of switch-on. In order to reduce the
switch-on current you should have a surge limiting device such as a
PTC inrush current limiter or a power resistor in series with the
mains input to the transformer. In the case where a power resistor is
used a relay is used to short circuit the resistor several seconds
after switch-on.

To minimise arcing during switch-off you should have a "snubber" or
resistor of say 27 ohms in series with a capacitor of say 220nF (X2
rated or 270VAC) or thereabouts (the values will depend on the
magnitude of the surge currents) connected directly across the switch.
Note that the capacitor will have approximately 14K ohms impedance so
some minute current will flow through the transformer primary when the
switch is in the off position.

Here is an explanation;
http://www.allaboutcircuits.com/vol_4/chpt_4/2.html

Thanks for the suggestion and I am some confuse on the inrush current
limiter. On the switch, do I use a PTC instead of NTC since I need to block
the high current first turn on and let the switch conduct fully.
Is the inrush current limiter is solder on the two connectors of the switch?
Thanks

Eric


"Ross Herbert" wrote in message
...
On Mon, 13 Sep 2004 10:08:12 -0500, "Eric"
wrote:

|Most of the old equipment has power supply switch problem. The contacts
arc
|by electric power and need to be replaced or sand down to refinish the
|surfaces to prevent resistance build up. After the resurfacing surface,
is
|there any chemical can prevent the arc again and the oxidation coming
back?
|I am using the de-ox cleaner now, any other suggestions.
|
|Thanks
|
|Eric
|
There are products such as De-Oxit and Stabilant 22 (very expensive)
which will prevent oxidation of switch contacts, but this doesn't
appear to be the main problem in your situation.

It seems that your problem is caused by arcing at the contacts which
results in pitting and carbonising deposits to form which can cause
erratic and unreliable contact switching. There is no "magic spray"
which can prevent arcing, and you will continue to have this problem
unless some means of reducing the heavy switch-on/switch-off surges is
employed.

Here is a brief explanation;

http://www.machinedesign.com/ASP/str...tedArticle.asp

Items such as high power audio power amps employ massive filter
capacitors and often use toroidal transformers. Toroidal transformers
inherently produce higher switch-on currents than conventional
laminated E-I core transformers and the large capacitors appear as a
near short circuit at the moment of switch-on. In order to reduce the
switch-on current you should have a surge limiting device such as a
PTC inrush current limiter or a power resistor in series with the
mains input to the transformer. In the case where a power resistor is
used a relay is used to short circuit the resistor several seconds
after switch-on.

To minimise arcing during switch-off you should have a "snubber" or
resistor of say 27 ohms in series with a capacitor of say 220nF (X2
rated or 270VAC) or thereabouts (the values will depend on the
magnitude of the surge currents) connected directly across the switch.
Note that the capacitor will have approximately 14K ohms impedance so
some minute current will flow through the transformer primary when the
switch is in the off position.

Here is an explanation;
http://www.allaboutcircuits.com/vol_4/chpt_4/2.html