Three way 12v switches

[Diemjoe]

This may be overly lazy but I an wondering if it is possible to have both side porch lights be controlled from either side of the cabin. Two switches controlling a single 12volt LED. I am not really seeing anything that specifically says it is doable during my internet searches. The closest I have come is a DPDT Toggle Switch but I think that is two lights one switch. I am looking for 1 light two switches like in a 3way switch in the 120v AC world.
The reasoning is if the teardrop buddy wants to go for a roam in the middle of the night and would like the porch light on. Be nice to not have to reach across. And in the much more likely event, I am solo, I wouldn't have to reach ALLLLLL the way over to the other side of the cabin to work that sides porch light.

[Da'engineer]

This may be overly lazy but I an wondering if it is possible to have both side porch lights be controlled from either side of the cabin. Two switches controlling a single 12volt LED. I am not really seeing anything that specifically says it is doable during my internet searches. The closest I have come is a DPDT Toggle Switch but I think that is two lights one switch. I am looking for 1 light two switches like in a 3way switch in the 120v AC world.
The reasoning is if the teardrop buddy wants to go for a roam in the middle of the night and would like the porch light on. Be nice to not have to reach across. And in the much more likely event, I am solo, I wouldn't have to reach ALLLLLL the way over to the other side of the cabin to work that sides porch light.

Why not wire a momentary push button as a switch using a JK filp-flop IC then you can just wire a second button to the same inputs

[MtnDon]

1. IF used with very low amperage DC lights, like LED's, the 120 VAC three way residential switches are okay. AC switches should not really be used for DC but for very low current switching they will work a long time. A bit on the bulky side for TD use perhaps.

2. A pair of 12 volt DC rated SPDT switches will fulfill the three way function. Just have to think through the wiring. (North American three way switches are simply SPDT switches with the terminals clearly marked for the design purpose.)

3. Skip the three way idea and use a 12 volt remote control switch system. ebay search.

[Graniterich]

Number three, remote control from China, under four dollars

[GerryS]

MtnDon, why should you not use AC switches for DC? I've never heard this before....other than perhaps to avoid confusion....can you elaborate?

As long as you are not trying to pull x+1 when the switch is rated for x amps, I don't see what the difference is. Voltage also plays a part....but we are talking 12 vs 110 not 208 vs 110...

[bobhenry]

AC and DC switch contacts are manufactured with different materials in order to withstand the arcing that occurs, and the resulting degradation of the switch contacts. AC circuits typically break cooler than DC circuits because the current drops to zero 120 times per second, which means arcing stops at least by the time the current goes to zero. Current in a DC circuit does not drop to zero immediately when the contacts open when there is an inductive component in the circuit. In a DC circuit, the voltage will spike when the contacts open and the arcing will be significantly more than in the comparable AC circuit. This results in more rapid contact degradation through pitting from the high temperature arc. The voltage rating only talks about insulation factor. Current rating only talks about current capacity, neither of which is related to the other. So an AC switch is NOT equal to a DC switch.

This is really no big deal I installed the shallow blue electrical boxes and purchased the solid covers. I drilled the correct size hole for a dc rated switches and that was that. As the contacts are "harder" the dc switches CAN be used for ac applications. I liked the fact I was able to easily get two switches in the box ( I think 4 maybe 5 would be possible).
I added DC bulb sockets to all the selected AC fixtures and made each light dual useage......





I selected a rotary and a flip toggle when I installed Chubby's dual element lights. The rotary was DC and the toggle was AC. In the dark I could tell by feel which I was about to use.

[TheDrip]

3way switches on DC are quite easy to write up. Two SPDT switches. Single Pole Double throws switches have three poles/connectors. The center post on the first switch gets connected to 12V, the two outer posts get connected to the two outer posts of the 2nd switch, and the center post of the third switch gets connected to your light. Negative wire just goes straight without switching.

[Dale M.]

More details....





All you need is basically a single pole double throw (SPDT) switch on each side of cabin and a couple of "travelers" (wires)...

AC or DC, LED or Incandescent lights, its all the same...

Dale

[MtnDon]

bobhenry has the AC - DC switch difference correct. The contacts in a DC switch use much heavier metal in switches of comparable current capacity. Same thing is true for circuit breakers; AC breakers normally can not handle DC loads. DC breakers may even have a correct installation orientation, one end marked as being "up". This is for proper control of the DC flame arc that occurs when breaking a circuit. This can also be true of fuses, some AC designs being suitable for DC, others not.

[Diemjoe]

Thanks, I bought some DC switches and an LED bulb tonight. Will check this tomorrow.

[GerryS]

I can see where metallurgy etc would make a difference at high voltages... But for the sake of our conversations it seems overkill. I wouldn't use them because they are HUGE.

Now, breakers...different discussion . Rated 20A @120VAC means just that...

Learn every day I guess

[MtnDon]

It's not a difference in metallurgy as much as it is that the contacts use much more copper; thicker contacts. A DC switch also may use a spring driven snap action to break the contact more quickly; no silent switching as in a residential AC switch. The DC switch may also place the two contact points farther apart to increase the length of the arc to the point that it can no longer sustain itself.

It is possible to have the AC switch contacts weld together when the switch is used on DC. But as was said previously, low current switching should not be the disaster that high current switching would be.


To make the breaker situation more confusing some residential breakers that are 120 VAC rated are also approved for DC use. SquareD QO series breakers are code approved for DC circuits up to 48 VDC at the same amperage as the AC rating. They are frequently used in the low voltage sections of off grid PV solar systems. You may not see the markings on the breakers but the factory spec sheets have them listed.

Big DC breakers have magnets in them to pull the arc flame to one side.

[H.A.]

....

[Dale M.]

More details....

Dale

Now if you want to go real nutty about your lighting, place a '4 way' switch on your traveler wires.
Actually you can place as many 4way switches on the travelers as you wish...
Then flipping ANY of the switches will turn on-off your light !

Ahem...



Now to really squeeze your brain...



http://www.diychatroom.com/attachments/ ... t-6way.jpg

Dale

[Diemjoe]

Wow, That is some setup. Definitely a brain twister.