Led help

[eliteph33r]

Hi i'm a little new to electric circuits and wiring and all that, so go easy on me plz. But anyway i was hoping someone could help. I have wired some batteries, LEDS, and resistors together to get some basic lighting and i can't seem to get them to light up.

diagram is as follows

[- 9v +]----[- 9v +]----[- 9v +]------(R 100Ω)--(R 100Ω)--(R 100Ω)-----[+ 3.5vLED -]-----(nextline)

[+ 3.5vLED -]-----[+ 3.5vLED -]------[+ 3.5vLED -]------[+ 3.5vLED -]------[+ 3.5vLED -]------[negative of 1st 9v]


While trying to troubleshoot i used the voltage meter and this is what i've found, but not sure what it means:


[- 9v +]----[- 9v +]----[- 9v +]-^28.8v -(R 100Ω)--(R 100Ω)--(R 100Ω)-^28.8v-[+ 3.5vLED1 -]-^22.2v-(nextline)

[+ 3.5vLED2 -]-^4v-[+ 3.5vLED3-]- ^1.2v-[+ 3.5vLED4-]------[+3.5vLED5-]------[+3.5vLED6-]------[negative of 1st 9v]


I'm Getting a very significant Voltage Loss inside LED#2

And an elevated Voltage loss at LED1, because it is only a 3.5v LED and It's losing 6.6v

If anyone can help it will be greatly appreciated

 

[vne147]

The circuit you have depicted should work and allow 20 mA through the LEDs which is about normal. It's interesting that there is no voltage drop across your 3 current limiting resistors. There should be 6V there. Have you tested each resistor and LED individually to see if you've got a bad component?

Edit: the fact that there is no voltage drop across the 3 resistors could indicate a short across them. If there was a short, you could have easily burned out some of teh LEDs.

 

[eliteph33r]

well with my voltage checker it shows me resistance... and it says theres 297 resistance after them, but no voltage drop. So i dont know.

 

[vne147]

well with my voltage checker it shows me resistance... and it says theres 297 resistance after them, but no voltage drop. So i dont know.

So you measured resistance between where I've inserted points A and B and the resistance is 297Ω?

[- 9v +]----[- 9v +]----[- 9v +]---A--(R 100Ω)--(R 100Ω)--(R 100Ω)--B--[+ 3.5vLED -]-----(nextline)

[+ 3.5vLED -]-----[+ 3.5vLED -]------[+ 3.5vLED -]------[+ 3.5vLED -]------[+ 3.5vLED -]------[negative of 1st 9v]

 

[eliteph33r]

That is correct

 

[vne147]

Interesting. Well, that means there is no short across the resistors or at least there isn't one now. You might have a bad LED. I'd focus my attention first on LEDs 1 and 2 because the voltage drop is higher than normal. With LED 2 especially. Test each LED individually one by one like this:

[- 9v +]----(R 100Ω)----[+ 3.5vLED -]----[negative of 9V]

Can you post a picture of you circuit?

 

[eliteph33r]

Thanks for your help...

I think i ended up making an amature mistake somewhere along the line and doing something silly like soldering one of the negative sides of an LED to another negative of an LED, thank you for help though. I am still interested why the resistors were not showing any voltage drop. I ended up just tearing the whole setup apart and changing power supply so that resistors were not necessary.

Thanks

 

[audioguru]

The resistors did not show a voltage drop because the backwards LED did not conduct. The backwards LED might be damaged by the reverse voltage higher than the max allowed reverse voltage of 5V.
If you eliminate the resistors then nothing limits the current and the LEDs will instantly burn out, or the resistors can be replaced by a current-regulation circuit.