hi guys,

I've knocked up an led circuit as I intend to replace my rear lights with nice bright Led ones, however on testing my battery went from 12,4V to about 7 the second time I tried to light the circuit?!? What's going on?!

The circuit I've created is 4 red LEDs wired in series, with a forward voltage drop of 2.6V each, rated at 20mA each. I've used an 82 ohm resistor wired in before the LEDs, also in series. 

A very simple circuit for all intents, but on initial connection to my battery only two of the leds lit, so I disconnected it. Check they were all the right way round, and tried again. And now they're almost off they're that dim. So I checked my battery and its down to 7.x voltage?!

Edit: point to note - I only had the circuit connected for about 5-10 seconds. 

Help anyone! Haha

I FIXED IT. 

Sort of. I have no idea why the voltage drop existed, but it was that of the cables I was using, the battery voltage was fine.

Key learning point - measure the battery voltage, not the voltage from some cables. 

I now have a prototype LED brake light ready to be made! (And yes, I have used more than just 4 LEDs haha. That was just one leg of the circuit

Which cables?  Are you talking about the battery cables on the bike, or your meter's test leads?  Not sure I understand what you found.

Point-Seven-five wrote:Which cables?  Are you talking about the battery cables on the bike, or your meter's test leads?  Not sure I understand what you found.

Sorry,

I meant I attached two cables from the battery to my circuit to test. And for some reason they ceased to carry voltage. Might have something to do with them being 10m long? I'll put some photos up of the LED conversion once in finished

It's the simple things that catch you out invariably! Looking forward to the pics.