2x switches for 1x Bulb

[zuzullo]

SEE PHOTO attached: On 12v system I have a group of lamps that are tryggered by switch n1 and another group connected to switch n2. But I need a 3rd group that turn ON whenever either switch 1 or 2 is ON.

Which device do I need to do this?

 

[Hedges]

For DC, you could connect diodes so each switch can energize the 3rd group. It will get 0.7V less. But neither will backfeed the other.
Alternatively, could have each switch energize a relay. Two switches, two relays. Both relays connect 12V to 3rd group.

You can get DPST switches. One contact enables group 1 and the other enables group 3. Second switch, one contact enables group 2 and other enables group 3.

 

[Jim Burrow]

Most hardware stores carry two-way switches. You see these switches in hallways in homes for example. Enter the hallway at one end and turn the hallway light off at the other end. -

 

[zuzullo]

For DC, you could connect diodes so each switch can energize the 3rd group. It will get 0.7V less. But neither will backfeed the other.
Alternatively, could have each switch energize a relay. Two switches, two relays. Both relays connect 12V to 3rd group.

You can get DPST switches. One contact enables group 1 and the other enables group 3. Second switch, one contact enables group 2 and other enables group 3.

Thank you Hedges.
The diodes seem to be the cheaper solution, right?

 

[Hedges]

Diodes probably cheaper than relays, and can be connected downstream without adding wires from switches.
Oversize appropriately; they dissipate heat. Perhaps more likely to fail for heavy motor loads.

Multiple pole switches shouldn't be terribly expensive and are a simple, robust solution.

For me, would depend on the load to be driven and what I happened to have on hand.

 

[chops728]

It depends if you want to be able to turn it on by one switch and off with the other also

 

[Hedges]

True.
Boolean logic.
Create a truth table, a Karnaugh map.
We have methods to reduce and optimize.
Note that some physical implements of logic elements are bidirectional, while others are not.
Develop a test methodology. Ensure there are no test escapes, and that any defects don't merely cause internal bit flips, but there is a sensitized path so their state is visible to the outside.
Does it accept synchronous inputs, or must it be operated with a "Grey code" to avoid race conditions and propagation of a transient unintended state to the output?
If system is updated in the future, perform regression testing to ensure this functionality didn't change.

 

[zuzullo]

Diodes probably cheaper than relays, and can be connected downstream without adding wires from switches.
Oversize appropriately; they dissipate heat. Perhaps more likely to fail for heavy motor loads.

Multiple pole switches shouldn't be terribly expensive and are a simple, robust solution.

For me, would depend on the load to be driven and what I happened to have on hand.

Diodes works best in this configuration, thanks. I am buying 3A diodes to put them through ~2A loads. Do they burn and cause fire in case the rated amperage is exceeded? Or do they just stop working?

 

[Delmar]

DPST switches are the most reliable, and flexible to rewire for future requirements.

 

[Delmar]

Another option

 

[Hedges]

Diodes works best in this configuration, thanks. I am buying 3A diodes to put them through ~2A loads. Do they burn and cause fire in case the rated amperage is exceeded? Or do they just stop working?

Typically, diodes fail by shorting. Before shorting, they have a voltage drop of 0.7V or so. That is from the PN junction plus IR drop.
After shorting, would likely be lower voltage and somewhat reduced power dissipation, so would probably be cooler than the 150C or higher junction temperature which caused failure. But no guarantees how a failed part operates.

Do not assume that a "3A" diode could actually carry 3A, or that a "60V" diode could hold off 60V reverse voltage.
Specsmanship varies. As a minimum, specs mean this is the maximum instantaneous current it can carry, and the peak instantaneous voltage without causing immediate breakdown.

You need to analyze thermal situation. At both ambient temperature and if junction is at maximum allowed, what is the power dissipation of the diode at your maximum forward current, and at maximum reverse voltage?

Given datasheet specs and your thermal environment, would that power dissipation cause junction to sustain or rise above maximum allowed temperature? If so, it is overstress and will cause failure.

Some diodes are reasonably usable within their specs, if you provide the thermal environment described (e.g. a certain amount of copper PCB area.)
Others are not. You have to read the spec and analyze your design.

I would be more inclined to use a 10A or larger diode for 2A.