Switch Contact Ratings & gold or silver contacts.

[Screech]

Ultra-miniture toggle switch with Gold contacts.
Technical specifications
Suitable for low level switching.
Contact Rating 25 VDC 25mA
Electrical Life 5*(10^4) operations.


Can i use more then 25 mA thru this switch safely?
and If I do, does that meen That the Electrical life operations are reduced?
The switch will be mainly in the one positon (mode selector).
It will conduct around 25 mA constantly thru it.

also,
whats better, Gold or silver or chrome?
doesn't silver tarnish?

Thanks

 

[Nigel Goodwin]

Can i use more then 25 mA thru this switch safely?
and If I do, does that meen That the Electrical life operations are reduced?
The switch will be mainly in the one positon (mode selector).
It will conduct around 25 mA constantly thru it.

There are a number of things to consider, mainly the current handling capacity of the contacts - too much current through them will cause them to over heat. The other main problem is current 'breaking', when you turn the switch OFF it will spark across the contacts, DC is far worse than AC for this (as AC goes to zero every few milliseconds) - the higher the current, the stronger and longer the arc - which destroys the plating on the contacts.

A 'reasonable' overload won't do much harm, but is likely to reduce the number of operations in it's life expectancy.

also,
whats better, Gold or silver or chrome?
doesn't silver tarnish?

Gold contacts are usually best - I've never heard of switches using chrome contacts?, I suspect they wouldn't be much use?, it's not a terribly low resistance material (is it?).

 

[JimB]

Generally, gold contacts are used in low current circuits (a few mA) such as inputs to a micro-controller or PIC.

Silver contacts are used for high current (a few amps) such as switching power.

Gold is used because it does not tarnish and works well in "dry" circuits, ie very little current.

Silver is used because it has a very low resistance. It does tarnish, but when switching a load, the current is able to "burn through" the tarnish to give a good contact.
Silver contact switches, when used in low current circuits will soon give problems of bad contact.

Chrome contacts? never heard of it.

JimB

 

[Oznog]

It also matters just how inductive the load is. If you break a relay coil for example and there's no flyback diode, you get a lot of high voltage that makes an arc that takes longer to break and has a stronger chance of pitting the contact surface.

While the obvious solution there is to install a diode, other things like long wire runs are less obvious.

 

[audioguru]

For microphone switching, I have always used switches with gold contacts and have never had a problem. I won't allow a switch with silver contacts anywhere near a microphone circuit. :lol:

Many switches with gold contacts have two power handling ratings. They have a very thin and "focussed on the contact area only" gold plating that costs very little for low power, and a heavier silver plating underneath for higher power. Use them with either rating but don't use it for low-level circuits after it has been operated at its higher rating.