Help! Why don't these LED's work!

[Roady]

Hi guys, I have a very poor understanding of electronic principles but why don't these work?!

I spliced an LED onto another cable with a LED to try and drive 2 LED's for HDD activity lights from my mobo. Only one of them lights up! Fixable (change to 'lower power requirement' LED's) or give up what I'm trying to do?!

 

[Roady]

No resistors, they're these so listed as 3.3v

Nowhere could I found the actual voltage outputted by motherboards front panel LED headers, very few list it, the ones which do list it as 2.2v, 5v and 3v!

They came pre assembled, I assumed they'd be the same so matched white to white, blue to blue!

 

[Roady]

Just double check you have the cathode and anode legs the right way around. positive to the long leg, ground to the short leg. If you don't have the different size legs to check the anode (+) will be the smaller part that angles down inside the led.

Thanks cypto, will check that later!

All the LEDs are the same product but you've hacked into them to join them?

So if you've not rewired the LEDs directly and just joined their wires blue to blue and white to white there should be nothing stopping them working. Unless there is no resisstor and Lamptron assume that all front panel headers are below the Vf of the LED, which seems unlikely.

Yup just hacked into them to splice them together, soldered and then heatshrink... Was quite impressed with my work until it came to test them lol!

I can't see any evidence of a resistor on the cables or the LED side, is there some way to determine the voltage of the LED's so I can buy some resistors? Or easier to start again and buy LED's & resistors to suit?

 

[Roady]

Thanks Tony, pretty sure my LED's don't have those, I'll 'reverse engineer' one of them this weekend and see if I can spot a resistor hiding somewhere!

will connect my multimeter to my mobo header to see what I'm working with, I'll be very surprised if it's not a standard 3.3v or such?! So I probably need to look at a pair of 1.5v LED's with resistors? Any idea what rating I'd need?

 

[Roady]

As always Tony, many thanks for your help and for sharing your wealth of knowledge!

I just about follow what you're saying so I'll be putting it to the test this weekend! Wish me luck!

 

[Roady]

Only just getting back to this (too many other things to do! )

Measured the voltage as 1.55v which doesn't sound right... Not sure how I measure amperage with the multimeter I have either!

Although I think that would explain why only 1 of the 3v LED's lit up?