Switch wiring help...

[flyeyes]

Hi all.

I thought I understood how to wire switches, but they're not behaving as expected so I'm obviously missing something.

I try to keep all my switches separated by function, with different locations and switch types to help identify the functions once learned.

I'm wanting to use some of the swoopy looking lighted push button switches available from mpja for some functions, but I'm having trouble getting the behavior out of the switch that I want.

There are two switches (and various colors) available, a SPDT that fits in a .75" hole and a DPDT that fits in a 5/8" hole.

So far, I have wired and mounted the larger SP switches as master and aux batttery master and they behave as expected. I wired a jumper between the "common" terminal and the ground for the LED, a wire from the contactor to the "normally open" terminal, and a wire from the common terminal to ground. There is a lighting bus feed to the LED positive terminal.

These switches light up when the bus is powered as expected.

My problem is the smaller DPDT switches. I'm having trouble getting the LED to light only when the switch is active. They have a total of 8 contacts, two for the LED, and three for each side of the switch (common, NO and NC). How do I need to wire these? I though I knew but I'm clearly wrong :/

 

[az_gila]

Hi all.

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My problem is the smaller DPDT switches. I'm having trouble getting the LED to light only when the switch is active. They have a total of 8 contacts, two for the LED, and three for each side of the switch (common, NO and NC). How do I need to wire these? I though I knew but I'm clearly wrong :/

Assuming the LEDs are set up for 12 volts.

One LED lead to the switch out wire that is powering the item under control.

The other LED wire to ground.

The LED wires are polarized so the connections need to be correct. Probably red/black, in which case black goes to ground.

Does the switch correctly control the device?

 

[flyeyes]

I haven't wired the switches into the airplane yet, but I'm using a VPX, so they're essentially connecting to ground to close a solid state relay. negliglible current.

There are two contacts apart from the others, 12v supply and GND, connecting a battery across these lights the LED as expected.

There are two rows of three contacts labeled NC, NO, and C. I presume that stands for "normally closed, normally open, and common." With the switch up, there is continuity between NC and C. with the switch depressed, there is continuity between NO and C.

My thinking was to use one side of the switch to take the VPX switching line to ground, and use the other side to switch the LED using power from the hot side of the lighting dimmer to the NO contact, and a jumper to the LED +12V, then Jumper from the C terminal to the LED ground and connect both of those to ground.

when I do this, the LED lights with the switch in either position.

 

[Mike S]

My problem is the smaller DPDT switches. I'm having trouble getting the LED to light only when the switch is active. They have a total of 8 contacts, two for the LED, and three for each side of the switch (common, NO and NC). How do I need to wire these? I though I knew but I'm clearly wrong :/

Sounds like you could do it with a jumper from the NO side of one switch half to the + side of the LED. Do not feed power directly to the LED.

You may need a diode in the jumpers to prevent current backflow depending how the rest of the circuit is wired.

 

[krw5927]

Assuming the switch has a built-in current-limiting resistor for the LED and is safe to hook up straight to the dimming bus, try the following:

 

[flyeyes]

Thanks for the replies. Normally this kind of stuff just makes sense to me, but for whatever reason it's not clicking.

 

[Bevan]

If you're still puzzled, think of it this way. The switch has three components. There's two SPDT switches in there and a LED with it's own terminals. You can hook them up any number of ways depending on what you want to do. The diagram in post # 5 correctly shows how you want it in this case.

Bevan

 

[krw5927]

Did that work for you, James?