Lighting help

[chris1984_99_99]

Hi guys, I like to think of myself as a fairly competent builder, but when it comes to electronics I'm anything but! So, on that note I'm having some issues with a recent circuit I built. It's 10x5mm flickering LEDS wired in parallel connected to a rocker switch and a 9v battery for power. Simple and it works, the problem is the power in the battery is being drained even when switched off! I drew a very simplistic drawing of the setup to help, any assistance would be much appreciated! Its not an issue disconnecting a battery when not in use and just connecting when it is, it's just anoying! Thanks!!

http://i181.photobucket.com/albums/x123 ... 5d275f.jpg

[Ant]

You've got some fairly serious issues with that circuit!

Firstly, the switch is basically short-circuiting the battery when it's on (which will give you the impression it's off because the rest of the circuit will get no current). You need to put the switch between one pole of the battery and one leg of the circuit.

Secondly you cannot wire LEDs in parallel like that without a current limiting resistor for each one.

Taking a forward voltage of 2v (mid range of quoted figure) and 20mA current, you'll need (9-2)/0.02 = 350 ohm resistor in series with each LED. Closest standard value would be 360 ohms.

So using terrible ascii art the circuit should look something like this

Code: Select all

 (+)----0___0------WWW---|>|----------(-)
                |               |
                 --WWW---|>|----
                |               |
                 --WWW---|>|----
                |               |
                 --WWW---|>|----
                |               |
                 --WWW---|>|----

WWW is a 360 ohm resistor, |>| is a LED and 0___0 is the switch

Hope this helps!

[chris1984_99_99]

Thanks for the reply Ant, you have helped, I think I was basically bypassing the switch, i've rewired it and we will see in the morning if it is still draining the battery, hopefully not. I have the switch wired into the positive wire only now and it seems to be working.

Thanks again! I really need to get clued up with electrics!

[Tracy White]

For future reference, a good parallel LED array calculator can be found here.

It'll even sorta draw things out for you