Protecting horn switch contacts against arcing damage
Nik Rim
The contacts seem to have lost whatever protective plating they had. If I
clean them up they work well for a week or so and then oxidise up and become
intermittent.
Any suggestions on some sort of protective gel I can apply. I've the usual
contact cleaners etc but nothing for protecting contacts switching a
reasonably large current.
thanks.
ian field
"Nik Rim" <que...@kbd.com> wrote in message
news:9pmdnazlvMmkbbfW...@westnet.com.au...
For some time I've had a problem with the front brake light switch on my
motorcycle, it is exposed to rain and the contacts corrode - up to now the
only solution has been to carry a spare.
The nearest I've found to a barrier lubricant is Elvolube electrical contact
grease, but I only have a battered - nearly empty tube and web searches have
drawn a blank.
The next best thing is GT85 - its like WD40 but with PTFE.
The previous 2 replacements I ordered fared no better than the one fitted
when I bought the bike, when each brake light switch fails I clean it in
solvent (cellulose thinners) then burn the contacts clean by switching 2x H4
bulbs with both filaments connected.
When I got down to my last switch, I ordered 3 more - the first of those I
fitted has lasted the winter so far, but I'm still thinking of modifications
just in case.
The first suggestion is to use an automotive style relay between the switch
and load, if contact oxidation is your problem, the back emf from the
inductance of a relay coil may produce a spark that punches through the
oxide layer.
Try it with the filed contacts for as long as it lasts, if that fails try it
with new contacts and see if they do any better.
Nik Rim
"ian field" <gangprob...@ntlworld.com> wrote in message
news:GFDWm.34874$iW....@newsfe30.ams2...
I've got both WD40 & some teflon spray. I wonder if white silicone grease
would help. Looks like I may have to visit a couple of auto shops.
The circuit already has a relay. I think the problem is usage - because of
its application the vehicle horn is used a few times each day and it's now
15 years old.......
ian field
In theory, any arcing will turn silicone into its dioxide which will
insulate the contacts - silicone is best for repelling water and not much
else.
kreed
If you are concerened about them arcing, (which is then pitting,
burning and damaging the contacts) try a 1-2UF poly capacitor across
the contacts.
IF they are switching a logic circuit, or something that draws
virtually no current (not enough to "burn" through any crap that
accumulates), you could try adding a 1k resistor across the load. (ie
- if the contacts switch the load to earth, then add the resistor
between the contact that doesn't go to earth, and 24v supply.
ian field
"kreed" <kenre...@gmail.com> wrote in message
news:38cc9707-de8d-4779...@u1g2000pre.googlegroups.com...
> On Dec 18, 1:00 pm, "Nik Rim" <que...@kbd.com> wrote:
>> Well it's half on topic....horn switch contacts in a 24V vehicle.
>>
>> The contacts seem to have lost whatever protective plating they had. If I
>> clean them up they work well for a week or so and then oxidise up and
>> become
>> intermittent.
>>
>> Any suggestions on some sort of protective gel I can apply. I've the
>> usual
>> contact cleaners etc but nothing for protecting contacts switching a
>> reasonably large current.
>>
>> thanks.
>
>
> If you are concerened about them arcing, (which is then pitting,
> burning and damaging the contacts) try a 1-2UF poly capacitor across
> the contacts.
That's a good way to make a capacitor discharge spot welder, put a low value
resistor in series with the cap to limit the instantaneous discharge
current.
kreed
wrote:
> "kreed" <kenreed1...@gmail.com> wrote in message
You probably should add a resistor to make life easier for the cap if
nothing else, but my experience in switching 48v @ 8A DC inductive
loads, there wasn't a problem with this method (capacitor, no
resistor) which was used for years in this application, with hundreds
of switch activations a day.
2uF and The spark was reduced from a substantial "flash" to almost
nothing. Contact burn / pitting and erosion was dramatically reduced.
I considered the very small discharge of the cap into the contacts as
being good for helping keep the contacts clean, whether I was right or
not I don't know.
ian field
Capacitance on its own dramatically subdues any back emf from any inductive
component in the circuit (unless you're lucky enough to hit resonance) so
reducing the voltage rise and the ability to punch through crap on the
contact faces.
For the motorcycle brake light problem I mentioned elsewhere in the thread,
I'm considering deliberately introducing inductance in the series circuit to
cause a "punch through" back emf.
who where
>The circuit already has a relay. I think the problem is usage - because of
>its application the vehicle horn is used a few times each day
are you italian? or mustering stock?
F Murtz
redundant in this day and age. Try this, next time you hear a horn take
note and you will find it has been used illegally or it is after the event
Nik Rim
"who where" <no...@home.net> wrote in message
news:u96oi5lh0f3nrf30e...@4ax.com...
:)
Neither, it's a commercial vehicle, needs to "honk" @ each a dozen pickup
points twice per day.
F Murtz
Mr.T
"F Murtz" <hag...@hotmail.com> wrote in message
news:4b2c8bcc$1...@dnews.tpgi.com.au...
> > Neither, it's a commercial vehicle, needs to "honk" @ each a dozen
pickup
> > points twice per day.
> >
> That is illegal, a horn is only to be used for an emergency.
On public roads yes, perhaps his "pickup points" are on private property
though. Then there is a question of noise regulations of course :-)
MrT.
petrus bitbyter
"Nik Rim" <que...@kbd.com> schreef in bericht
news:l8adnTWec9uukbbW...@westnet.com.au...
Guess replacing the switch by a new one is the most simple and cheap
solution because you will be ready for another 15 years. Even if the thing
does a 150 bucks, it's only some cents a day.
petrus bitbyter
Nik Rim
"petrus bitbyter" <pieterkral...@enditookhccnet.nl> wrote in message
news:4b2cd8b1$0$9529$e4fe...@dreader29.news.xs4all.nl...
True - I considered that approach, the vehicle has 6 months to go before it
will be replacee. The steering wheel hub is one of the contacts, replacing
the whole assembly will be $$$$.
thanks
David
horn relay - you can buy a push button switch for a few $$ from an auto
parts or electronics supply shop, and wire it in instead of the one in
the steering wheel
If you cannot access the original horn relay just fit another one and
wire it up to the horn and the new switch
Just mount it anywhere convenient, and Marys your aunty
David
In article <-N-dnaKGwvpzQLHW...@westnet.com.au>,
Nik Rim
"David" <post...@REMOVE-TO-REPLYconfidential-counselling.com> wrote in
message news:postings-B7DABE...@news.bigpond.com...
> The easiest solution is to just fit an alternative switch to drive the
> horn relay - you can buy a push button switch for a few $$ from an auto
> parts or electronics supply shop, and wire it in instead of the one in
> the steering wheel
>
> If you cannot access the original horn relay just fit another one and
> wire it up to the horn and the new switch
>
> Just mount it anywhere convenient, and Marys your aunty
>
> David
>
>
Good idea. Thanks
aussiblu
http://westsidedelivers.com/kopr_shield.asp I've used it with
success with terminals and alternator slip rings and the like
but not relay contacts. I buy mine from Eastwoods:
http://www.eastwood.com/ but they don't seem to stock it
anymore.
--
Regards
Blue
Remove ZX from email address to reply directly.
aussiblu
http://www.jgthomas.com.au/files/resourcesmodule/@random4765c5acc02ef/1197852611_01.pdf
ALMINOX
" Recommended for aluminium to aluminium bolted or
compression connections. Alminox contains sharp,
conductive zinc granules suspended in a viscous petroleum
base. Under pressure these granules make high pressure
contact points with the parent metal to effect a sound
electrical connection, whilst the base material seals the joint
to prevent further corrosion. Catalogue number ALM325G,
supplied in 325g squeeze tubes. "
aussiblu
why I was thinking relay contacts.
Nik Rim
"aussiblu" <zxaus...@bigpond.net.au> wrote in message
news:dKrXm.63565$ze1....@news-server.bigpond.net.au...
Thanks, I'll see if Coventrys has it.
ian field
"aussiblu" <zxaus...@bigpond.net.au> wrote in message
news:dKrXm.63565$ze1....@news-server.bigpond.net.au...
Sounds like it might be similar to copper slip, last time I got that on
switch contacts it produced a whisp of smoke as the metal particles formed a
leakage path between contacts.
aussiblu
Ease) I know is just a high temperature anti seize grease see
http://www.molyslip.com/products/anti-seize-assembly-compounds/copaslip-anti-seize-compound/
aussiblu
coppaslip.
http://www.lawson-his.co.uk/scripts/details.php?cat=Anti-Seize%20Compounds&product=25277
aussiblu
than greasy so I doubt it will smoke the switches.
aussiblu
http://old.nabble.com/Re:-Kopr-Shield-p21613980.html ie.
Kopr -Shield only needs to be applied sparingly and will not
form a conductive path unless compressed.
aussiblu
may be GB (Gardner Bender) Ox-Guard. See
http://www.gardnerbender.com/pdf/products/wire_connectors.pdf