Switch Considerations

[Atomic_Sheep]

Hi guys,

Have a few questions regarding switches, namely what considerations are important when selecting a switch?

1.) I noticed there are ebay sales of 40 switches for a total price of 5 dollars and then other places where you would be paying 3 dollars per switch (Panasonic switches) but still, why the discrepancy? Is it worth paying the extra? Does the age old adage of you get what you pay for come into play here?

2.) What about the electrical specifications? I've got very basic knowledge about electronics (just experiments at school etc and some other minor things) so I don't quite know what to look for when it comes to selecting an appropriate switch. Granted! I need to provide a circuit diagram for more specific advice, which I don't yet have, but was wondering what initial impressions people had about something like this:

Actuator Type Lever
Contact Configuration DPDT-2NO/2NC
Contact Current Rating 0.2 A @ 14 V dc
Maximum Operating Temperature +80°C
Minimum Operating Temperature -30°C
Switch Operation Latching
Terminal Type Solder

Is the 0.2A current the max current that this switch can take and same goes for voltage? 0.2 seems small, no?

3.) What about the pins? There are usually 6 from what I see. Where can I find what each pin does? Can't seem to find anything on this.

This circuit diagram on page 2 looks completely nonsensical to me:

**broken link removed**

 

[alec_t]

Is the 0.2A current the max current that this switch can take

Yes.

What about the pins?

It's usually obvious with a resistance/continuity check. If in doubt, download the datasheet for a particular switch.

 

[jpanhalt]

That switch to which you link is for signals. Hence its low current rating.

What's not obvious about that? It is a push button, not lever switch. It's double "pole". The center contact (pin) is connected to the Normally Closed (N.C.) contact/pin in one position. When pushed, the center pin connects to the N.O. contact, and the connection to the N.C. contact is broken. The other pole (#2) works concurrently and the same way electrically.

John

 

[KeepItSimpleStupid]

In a few words it kinda impossible to define a switch.

Some of the more important things are:
1. Switches are rated for AC or DC or both. If you don't head the rating, the contacts can weld.
2. Some switches have an inductive or horsepower rating.
3. Some, rare, must not switch a current carrying circuit.
i.e. the switching current capacity can be much lower (including 0 Amps) than the on capacity.
4. Switches that switch low current have special plating such as gold
5. Switches can be designed to remove the oxide of the contacts mechanically.
6. Some switches can have arc suppression.
7. There may be a wetting current specified. A minimum recommended current to switch,

Now, there is a pole designation or how many contacts move.
SP (1P), DP (2P), 3P, 4P; single pole, double pole/2 pole, 3 pole etc.

And there is a throw designation.
ST, DT for single pole; Double thow

So, you get things like SPST and DPDT

That isn't enough to specify a switch.

DPDT (on)-off-on is a way to specify that one side is momentary (), there is a center position, and the other side is on
DPDT on-none-on does not have a center position,
Both switches would have 6 wires.

There is one switch that doesn't follow these rules and it;s used in control panels.
and that's the SPST - 1NO/1NC switch

An SPST switch normally has 3 wires. a 1NO/1NC switch has 4 wires.
Two contacts break before another two contacts make.

The NO and NC mean Normally Open and Normally Closed. This nomenclature is seen with relays as well. You might see "1 NO AUX contact"

or One Normally Open Auxiliary Contact

Furthermore, some switches are "make-before-break (shorting) or "break-before-make (non-shorting). The former was used in audio applications to eliminate pops. So, for an instant, all of the switch contacts are shorted.

Switches and relays can be called "Definite purpose". Examples are "A reversing switch" and a "Lighting Contactor".

I'll stop here and let stuff digest a bit. I did "mention" some similarities between relays and switches.

An example of a switch that's really common in a lot of households is the reversing switch on a ceiling fan. It is not supposed to operated when the fan is on.

 

[Atomic_Sheep]

Thanks so much guys, excellent explanations. Much appreciated.

 

[eTech]

Hi Atomic

Probably a better approach would be...."know the problem you are trying to solve, then find the solution."
Not the other way around

If you have a circuit that needs a switch, then you can zero in on an appropriate switch. Otherwise, you'll run the risk of buying something you may never be able to use.

Btw...I don't think lever switches are used much any more, except maybe in industrial systems.

Just my 2 cents...

eT