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12v circuit question

daz

By daz
in DIY Astronomer

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daz

daz

Posted
Posted

I am in the process of building an all-in-one power box for my obsy, and the circuit is as follows:

  • From +ve terminal of the transformer , to +ve side of an ammeter
  • From the -ve side of the ammeter to a 12v red illuminated switch (to act as a total on/off for the 12v circuits)
  • From the switched side of the main switch to a 5-way fuse board
  • From the other side of the individual fuses to 12v red illuminated switches
  • From the switched side to the red terminals of a 4-way phono connector board
  • From the white terminals of the phono board to the -ve of the transformer

Nothing too technical and it all works OK with the exception of the illuminated switches......

If I have nothing switched on, the main switch does not light. If I switch one of the four switches (and have a load on the circuit) then the switches illuminate. However, depending on the load, the brightness is variable. What I really want is the main switch to be on - regardless of load - and the individual circuits to be when in the on position - again, regardless of load.

I think I have worked out that I need to provide an additional connection to the -ve terminal from each switch, but it needs to have a resistor in-line that is greater than than the maximum resistive load for each circuit. So, when in the on position, but no load applied, the current will flow through the resistor and light the switch. When in the on position and load is applied, the current will flow through the circuit because it is a less resistive load than the in-line resistor.

Does my logic and thinking sound correct, or is there something obvious I have missed??

Much thanks all :)

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Psychobilly

Psychobilly

Posted
Posted

Yes you have to provide a negative connection for the switch to illuminate... If they are 12V then they may still be a bit bright so you can put a resisitor in series with the negative wire to dim them... If they are 240V "neons" then you wont get anyhting...

Peter...

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yesyes

yesyes

Posted
Posted

The answer is in the "customer questions" at the bottom of the maplins page:

Q)

How are the terminals connected? Are 1 and 2 the switch terminals, and 3 the second connection for the illumination?

A)

1 is live in 2 is live out 3 is ground.

Q)

Do you have to have the ground cable in for the LED to work, if so what does it connect to? (not on the switch, but where on the other end)

A)

you do have to connect the ground leg to allow the led to work. You can wire this to anything that is used as an earth.

So pin 1 of the switch should go to the power supply +ve

Pin 2 is the output

Pin 3 is ground (should go to -ve on the power supply)

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Psychobilly

Psychobilly

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The +ve of the light is connected to the switched +Ve internally.. the logic about the current only flowing through the loads is how can i put this politely.... OK nonsense...

The 12V is applied across both the load and the light each "path" will draw the current required... the only reason you might need a resistor in series with the -Ve connection of the switch is to dim it if its to bright...

Peter...

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yesyes

yesyes

Posted
Posted

As far as I can tell it should be connected like the diagram below.

If you need to put a resistor in, put it between pin 3 of the switch and ground (not in the +ve lines). Otherwise it will also have an effect on the voltage to your connected devices.

post-14790-133877470599_thumb.jpg

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