Illuminated push switch problem

[Paul1971]

Hi all, I am building my own control panel for my pond, it will switch lights, pumps, heaters etc.

I have today bought myself several Illuminated locking push switches.

Maplins N05AR.
**broken link removed**

I am a little baffled. There are 4 conections on the back of the switch, 2 are for the 240ac in and out, but two smaller ones for the LED inside the switch.

It states that the LED 2ill come on at 2.4v DC.

How an earth do i wire these up? do i have to have a seperate power supply for the LED or what? It seems a little strange that a switch would have a seperate power supply for the led.

Anyhow, Im not silly when it comes to electrical knowledge but this switch has got be baffled.

If someone would please take the time to explain how this switch is wired in basic terms I would be most grateful.

Thankyou.
Paul

 

[crutschow]

You can power them by putting a diode and resistor in series with each LED to the 240AC (the diode is to block the reverse voltage). For a typical 20mA LED current this would require a 12kΩ resistor. The resistor power dissipation is rather high so it needs to be rated at least 2.5W.

 

[Reloadron]

My take is this based on their Q&A:

Q- I''ve noticed on the switch there is 4 connectors at the back. What does each set of connectors do? Is one power for the LED and the other set for the circuit switch? Many Thanks - Rich T

Answer- Exactly that.

Tells me two terminals are switched by the switch and the remaining two terminals power the LED (LED 2.2Vdc 25mA). I get the impression the LED is not switched but just illuminates the switch button. The LED is illuminated anytime power is applied to the LED terminals of the switch.

As to powering the LED? If you wanted to power the LED off for example a common 5 VDC supply place about a 100Ω resistor in series with it and 1/4 watt would be fine.

Just my guess
Ron

 

[Paul1971]

Thanks for the replies, I would be happier to illuminate them, when the switch is in the ON position, so im thinking (crutschow) idea may work better.

Is there any chance of a small wiring diagram crutschow?
It would help me understand the set up alot easier.

Im sure getting hold of the resistors and diodes would be easy, Is there any particular diode i need?
So I understand, its ok to use the 240V supply on the switch to power the led as long as i have a resistor and diode in series to the led? Do i need a diode on both sides of the led or just the + side?

Sorry for the questions, maybe a diagram would be easier to understand.

Thankyou for your help so far
Paul​

 

[Boncuk]

I guess that's what Carl meant:

T1 through T4 are the connections of the switch. AC passes the switch from T1 and T2 supplying the AC load (R2). When "L" leaves T2 it splits into the load and the diode-resistor-combination to supply the built in LED. Return path for both, load and LED is "N".

Boncuk

 

[Paul1971]

Thankyou very much for you quick reply, The drawing is great.

I now have to source the resistors and Diodes from a UK source, any ideas?

Thankyou so much. I shall probably be asking you many more questions in the future.

Paul

 

[crutschow]

I believe you can get those from Maplin where you bought the switch.

 

[Paul1971]

Hi, Thankyou, I have now sourced the diodes and resistors. Thankyou for all your help.

One more question is there a tutorial on how to recognise which way around the diodes and resistors go. I know which is first and second in line but they look very similar either way around. i.e If I was to flip the resistor it would look similar. Just the coloured lines slightly different.
Hope you understand what im getting at.

Ohh a second question, If i want to fuse the 240V circuit, does the fuse go before the switch or after it, nearer the load. I personally think its well before the switch, can someone confirm this for me.

Paul

 

[Boncuk]

Hi Paul,

a resistor is a non-polarized component. Orientation is up to you. (Good practice is mounting them with the colour code reading the value from left to right (tolerance colour ring silver or gold (sometimes brown or red) to the right side and top to bottom on printed circuit boards. Arabic electronic engineers mount them from right to left. )

Since you will certainly solder the parts directly to the switch it doesn't matter.

Diodes are polarized components. Orientation depends on the circuit design. The attached drawing shows a diode, left hand side the part and right hand side the schematic symbol. The bar represents the bar stamped on the diode body and indicates cathode.

Fuses should always used "in front" of the circuits to protect the entire circuit. In your case the fuse should be placed before T1

 

[Paul1971]

Thankyou very much for that diagram, very useful.

Im trying not to drag this subject out for too long but have one more question.

Do these components get hot? Am I ablt to heat shrink some sleeving over the top of them or is this a no-no in this scenario? Ok two questions..

Regards
Paul

 

[smanches]

FYI, they make switches that will light themselves directly from the AC. I think they usually have small neon lamps in them. Unless they were considered not "green" enough and have since been discontinued.

Just something to think about for the next time.

 

[crutschow]

Since the resistor is dissipating several watts it will get hot. You should mount it in free air with no sleeving. The diode will stay cool and can have sleeving over it.