12v conundrum

[Divisiblemarlin]

Greetings to all! 

Im currently converting a van and looking for a puzzle piece of advice, ill try to be concise.

What I'm attempting to achieve is a lighting circuit that has a dimmer, and two switches.

Switch 1(spst) powers on and off the whole circuit.

Switch 2 (C/NO/NC, latching) when on, powers the dimmer. When off, bypasses the dimmer to still power the light.

All the pieces work independent, dimmer works with the light, ground is okay, but I've tried every conceivable connection with little success.

My guess is Switch 2 is the weak link, but i can't see how changing it for a dpdt would help, when in the latching switches' case would just double the c/no/nc terminals.

Should a relay be involved? 

Many thanks in advance for any help or advice you can offer! 

Marlin 

 

[Sharpend]

So you want the light on permanently but also controllable by dimmer- is that correct? 

 

[Divisiblemarlin]

Not quite, the light needn't be on permanently.

Switch 1 to control power to light and dimmer

Switch 2 to control power just to dimmer

So, (assuming switch 1 is 'on')

when switch 2 is in the off position, the dimmer is inactive and the light is on (full).

Switch 2 in the on position, light can also be dimmer controlled.

I hope this makes it a little clearer!

 

[Geoff1946]

As we are on 12volts I'm guessing that your dimmer is a simple resistive device, or if it is electronic only has two terminals.  Similarly that negative is vehicle bodywork. (If not give details).

Then :  Supply to common terminal of switch 1. 

NO terminal of switch 1 to common terminal of switch 2.  (Switch 2 being a two way )

Out terminal 1 of switch 2 direct to lamp.

Out terminal 2 of switch 2 to dimmer input terminal.  

Dimmer output terminal to lamp, 

 

[Divisiblemarlin]

Dimmer is a standard pwm deal, with 4 terminals, +/- v in & +/- v out

Aye, ground is chassis.

So switch 2 being a 2 way, is that a dpdt?

Would this one work and how would you connect it?

Thanks!

 

[Geoff1946]

With that dimmer, either its -ve input and -ve output need to be connected together internally, OR the -ve input will be the van chassis and the -ve output to the lamp isolated from the chassis.

A DPDT switch is just two independent double throw switches operated together.   Double throw is just another way of saying two way.

On the switch you picture the centre of each row of three is a common, switching between the two outer ones, (I think, it's hard to see the legends * ) The top and bottom single terminals are probably an led indicator. 

*  Switch legends.   NC = Normally closed   NO - Normally open    C= Common.

 

[Divisiblemarlin]

This has provided a lot of clarity, thank you.

Just to confirm then, theoretically, 

If Switch 2 is powered at the common terminal, connection to the light runs from NO, and connection to the dimmer runs from NC, so when the switch is not pressed, power still goes to the light, and when the switch is pressed, power diverts to the light via the dimmer

 

[Geoff1946]

Yes. I've sketched it out now. The first is as I tried to describe in words, OR you can put switch 2 on the output of the dimmer if you want, (like the top half of diagram 2) . It shouldn't matter.

The second diagram is if you have to use all four wires of the dimmer, i.e. the negatives are not simply connected together inside. 

 

[Divisiblemarlin]

I think its going to habe to be configuration 2, as config. 1 will either only use the dimmer for both of sw2 positions, or not use it at all, depending on the -ve layout. 

Cant test the dpdt config as i don't have the switches at the minute! Very frustrating!