contact surface material

[malua mada!]

I made an exposed lid switch consisting of two mating pairs of flat brass stock about 1 x 1/2 inches. When I close the lid they make contact and 12VDC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was causing problems.
However, the contacts get dirty. They develop carbon scabs and get hot. THese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.
What would be better than brass? Would a coating of solder help? I also have sheet copper. And tin plated steel from a shielding cage.
I could also apply some GOLD perhaps? How?(I brought some home from the dentist , after carrying it around in my mouth for years)
Thanks for your insights

 

[Tom Biasi]

On 4/2/2017 11:03 PM, malua mada! wrote:

I made an exposed lid switch consisting of two mating pairs of flat brass stock about 1 x 1/2 inches. When I close the lid they make contact and 12VDC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was causing problems.
However, the contacts get dirty. They develop carbon scabs and get hot. THese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.
What would be better than brass? Would a coating of solder help? I also have sheet copper. And tin plated steel from a shielding cage.
I could also apply some GOLD perhaps? How?(I brought some home from the dentist , after carrying it around in my mouth for years)
Thanks for your insights

Yes the material is important but also is the contact design.Look at how
a relay closes it's contacts. Fast contact and a slide action called wipe.

 

[Rheilly Phoull]

On 3/04/2017 11:03 AM, malua mada! wrote:

I made an exposed lid switch consisting of two mating pairs of flat brass stock about 1 x 1/2 inches. When I close the lid they make contact and 12VDC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was causing problems.
However, the contacts get dirty. They develop carbon scabs and get hot. THese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.
What would be better than brass? Would a coating of solder help? I also have sheet copper. And tin plated steel from a shielding cage.
I could also apply some GOLD perhaps? How?(I brought some home from the dentist , after carrying it around in my mouth for years)
Thanks for your insights

Why not use a micro switch ??

 

[default]

On Mon, 3 Apr 2017 12:09:46 +0800, Rheilly Phoull
<rheilly@bigslong.com> wrote:

On 3/04/2017 11:03 AM, malua mada! wrote:
I made an exposed lid switch consisting of two mating pairs of flat brass stock about 1 x 1/2 inches. When I close the lid they make contact and 12VDC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was causing problems.
However, the contacts get dirty. They develop carbon scabs and get hot. THese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.
What would be better than brass? Would a coating of solder help? I also have sheet copper. And tin plated steel from a shielding cage.
I could also apply some GOLD perhaps? How?(I brought some home from the dentist , after carrying it around in my mouth for years)
Thanks for your insights



Why not use a micro switch ??

That would be my first choice too. Duh... Too easy maybe.

Plan "B" add a relay to switch the heavy current

Plan "C" would be to take the contacts from a relay or contactor.

Plan "D" would be to punch two silver slugs and braise them to some
steel stock.

 

[malua mada!]

Thanks all.
I am trying two problems with one stone, and creating a third. Wire fatigue has been a problem. Having a live wire grid attached to the lid is OK for me but the thing is an incubator with metal egg cradles . I would hate hearing of someone dropping a cradles' worth of expen$$ive eggs because of unexpected spark fun.
It may be a good idea to move the contacts from the hinge edge to the opposite side. I was leveraging switching speed for firm contact.
Tom, I don't recognize the slide action in the relays I have looked at. Looks like slam bang to me.
Thanks again

 

[John Larkin]

On Sun, 2 Apr 2017 20:03:20 -0700 (PDT), "malua mada!"
<fritzo2ster@gmail.com> wrote:

I made an exposed lid switch consisting of two mating pairs of flat brass stock about 1 x 1/2 inches. When I close the lid they make contact and 12VDC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was causing problems.
However, the contacts get dirty. They develop carbon scabs and get hot. THese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.
What would be better than brass? Would a coating of solder help? I also have sheet copper. And tin plated steel from a shielding cage.
I could also apply some GOLD perhaps? How?(I brought some home from the dentist , after carrying it around in my mouth for years)
Thanks for your insights

12 volts won't hurt anybody.

A mosfet or a relay would let you run the contacts at low current. You
could use a proper interlock switch.

Or maybe just buy an interlock switch rated for 5 amps.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Sjouke Burry]

On 03.04.17 5:03, malua mada! wrote:

I made an exposed lid switch consisting of two mating pairs of flat brass stock about 1 x 1/2 inches. When I close the lid they make contact and 12VDC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was causing problems.
However, the contacts get dirty. They develop carbon scabs and get hot. THese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.
What would be better than brass? Would a coating of solder help? I also have sheet copper. And tin plated steel from a shielding cage.
I could also apply some GOLD perhaps? How?(I brought some home from the dentist , after carrying it around in my mouth for years)
Thanks for your insights

A reed relay on the inside, and a small magnet glued to the
lid, gives you a 100% reliable safety switch.

 

[Tom Biasi]

On 4/3/2017 1:32 PM, malua mada! wrote:

Tom, I don't recognize the slide action in the relays I have looked at. Looks like slam bang to me.
Thanks again

If you look at the spring blades that hold the contacts you can see a
slight slide
as the spring blades push the contact down. It's only a little. If you
are looking at a heavy
duty contactor you will not see this.

 

sci.elec.basics- contact surface material
John Larkin wrote:

On Sun, 2 Apr 2017 20:03:20 -0700 (PDT), "malua mada!"
fritz...@gmail.com> wrote:

I made an exposed lid switch consisting of two mating pairs of flat brass stock about 1 x 1/2 inches. When I close the lid they make contact and 12VDC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was causing problems.
However, the contacts get dirty. They develop carbon scabs and get hot. THese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.
What would be better than brass? Would a coating of solder help? I also have sheet copper. And tin plated steel from a shielding cage.
I could also apply some GOLD perhaps? How?(I brought some home from the dentist , after carrying it around in my mouth for years)
Thanks for your insights

12 volts won't hurt anybody.

12v? Under water even 4mv is dangerous, i'd say.

 

[rickman]

malua mada! wrote on 4/3/2017 1:32 PM:

Thanks all.
I am trying two problems with one stone, and creating a third. Wire fatigue has been a problem. Having a live wire grid attached to the lid is OK for me but the thing is an incubator with metal egg cradles . I would hate hearing of someone dropping a cradles' worth of expen$$ive eggs because of unexpected spark fun.
It may be a good idea to move the contacts from the hinge edge to the opposite side. I was leveraging switching speed for firm contact.
Tom, I don't recognize the slide action in the relays I have looked at. Looks like slam bang to me.
Thanks again

-------o--------v--
-------o--------^--



-------o.
-------o.`-.
`-.`-.
`-.`L.
`^.

This very crude and a bit hard to read, but you can see the contact points
move as the contacts are bent. If you contacts move enough there will be
some wiping which helps to remove the crud.

I think you will be better off with a sealed commercial switch. It is easy
to mount the switch on the box and have the lid press the actuator. Are you
familiar with micro-switches? They aren't necessarily small as the name
would seem to imply.

Or is this intentionally a home brew project that you want others to be able
to build as cheaply as possible? Home made switches aren't always a good
idea for the reasons you are finding. Some aspects of switches aren't
immediately obvious.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[Cursitor Doom]

On Wed, 01 Nov 2017 02:57:16 -0700, bruce2bowser wrote:

> 12v? Under water even 4mv is dangerous, i'd say.

Nope!




--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

 

Cursitor Doom wrote:

On Wed, 01 Nov 2017 02:57:16 -0700, bruce2bowser wrote:

12v? Under water even 4mv is dangerous, i'd say.

Nope

Then, at least 5 millivolts could be.

 

[Andy Bennet]

On 04/11/2017 15:04, bruce2bowser@gmail.com wrote:

Cursitor Doom wrote:
On Wed, 01 Nov 2017 02:57:16 -0700, bruce2bowser wrote:

12v? Under water even 4mv is dangerous, i'd say.

Nope

Then, at least 5 millivolts could be.

It's current that kills, not voltage.
If you are surrounded by conductive water the current will go around you
rather than through you.

 

[default]

On Thu, 9 Nov 2017 10:08:33 +0000, Andy Bennet <andyb@andy.com> wrote:

On 04/11/2017 15:04, bruce2bowser@gmail.com wrote:
Cursitor Doom wrote:
On Wed, 01 Nov 2017 02:57:16 -0700, bruce2bowser wrote:

12v? Under water even 4mv is dangerous, i'd say.

Nope

Then, at least 5 millivolts could be.


It's current that kills, not voltage.
If you are surrounded by conductive water the current will go around you
rather than through you.

In a perfect world perhaps. I flooded the bilge of my boat where the
battery compartment is and I could feel the 12 V when trying to save
the batteries from salt water. It was damned uncomfortable but only
for the cuts and abrasions on my hands.

Current may kill but voltage pushes the current along and overcomes
resistance. They told us in school that it takes ~100 milliamps to
kill, and that is through the skin and in a path with vital organs
(like arm to arm).

One of the linemen on a job I worked on took a jolt of ~5KV through
his arm. HT power line on distribution pole; flash of light, sounded
like a loud gunshot or cannon, he was slumped over in his harness out
cold, and his arm was still smoking... he lost the arm, but lived, and
has no memory good or bad of the accident.

 

[rickman]

Andy Bennet wrote on 11/9/2017 5:08 AM:

On 04/11/2017 15:04, bruce2bowser@gmail.com wrote:
Cursitor Doom wrote:
On Wed, 01 Nov 2017 02:57:16 -0700, bruce2bowser wrote:

12v? Under water even 4mv is dangerous, i'd say.

Nope

Then, at least 5 millivolts could be.


It's current that kills, not voltage.
If you are surrounded by conductive water the current will go around you
rather than through you.

Absolutely not correct! People swimming near docks where a power line leaks
current into the water have died. You are not supposed to jump in to help
such a person because you will also die.

I mentioned this to my neighbor who has 110 volts on his dock and couldn't
remember if they had a GFCI on that line. I told him if it didn't and
someone died, he would be in a lot of trouble. He ignored me. It is
unlikely for a short to develop, but if it does it can and does kill people.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998