Connecting 7 UV Leds into 5V or 12V circuit

Thread Starter

flashinstinct

Joined Sep 10, 2019
6
Trying to get 7 leds to light up on a 9V battery. Running them in parallel with resistors on each light. I'm a complete newb but was trying things out after reading a few articles. Clearly I am doing something wrong because the last two leds in the circuit don't light up.

The battery is emitting 9.49V so I know that's good. The 2 leds that don't turn on have been tested independently and work.

Led specs are 3V/20ma.

I used the R= (9V-3V)/0.02 = 300.

I used 330ohms resistors.

What am I doing wrong?

test.jpg
 

Thread Starter

flashinstinct

Joined Sep 10, 2019
6
are my values good? just so I know I made the calculations correctly. I've never used a bread board so this would be a real rookie mistake about the split between row 29&30.
 

ericgibbs

Joined Jan 29, 2010
9,354
hi,
I would suggest that 20mA is a little high, have you tried say 12mA or 15mA, this reduction in current would give you a longer battery life.
E
BTW: my BB's are the same as yours the power rails are not connected across the non coloured gap, you need to link them.
 

Thread Starter

flashinstinct

Joined Sep 10, 2019
6
These are just test on the battery. They will run on a plugged in 12V circuit. The leds do say the recommended amp are .15 to .18, so perhaps adjusting that will make them shine a bit brighter.
 

ericgibbs

Joined Jan 29, 2010
9,354
These are just test on the battery. They will run on a plugged in 12V circuit. The leds do say the recommended amp are .15 to .18, so perhaps adjusting that will make them shine a bit brighter.
Hi flash,
Recalculate the resistors for a 12Volt supply as opposed to the present 9V battery.
E
 

SamR

Joined Mar 19, 2019
1,634
It's not only rookies who get caught by that from time to time :oops:
No and it doesn't help that some come full rail and others split. It has probably happened to most of us. I also like to add jumpers from top to bottom rails unless using dual voltages.

Also the 20mA for LEDs may be the PDF rating but as long as you can see it is on and not dim it has enough mA's. So I tend to go HI on the resistors IE 330Ω even @ 5V. FWIW
 
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Thread Starter

flashinstinct

Joined Sep 10, 2019
6
Yeah, I could but just feel it would be more of a headache in the small space that I have. I will create two clamps and just bunch the wires up at each end and solder them all together with the source (+/-) wires. I'm getting the leds prewired with the resistor already attached. Less soldering on my end in the long run.
 

Thread Starter

flashinstinct

Joined Sep 10, 2019
6
You didn't measure the voltages on the terminals of the LEDs that weren't lighting. That would have directed you to the missing jumpers.
Again I knew the voltage was 0, but I had never used a breadboard before so consider it a real rookie mistake LOL. I was thinking my resistance was off and that the battery wasn't dispersing enough load to get to the 6th led. Live and learn.
 

dl324

Joined Mar 30, 2015
9,601
I was thinking my resistance was off and that the battery wasn't dispersing enough load to get to the 6th led. Live and learn.
The resistor would have needed to be off by more than an order of magnitude. And it's easy to swap a known good resistor with one that you suspect to be bad.

Battery dispersing... The current and interconnect resistance are much too low for that to be a factor.

If you had measured voltages and didn't find 9V where you expected it, that would have quickly lead you to the open on 9V. After correcting that, you might have noticed that you needed a similar jumper on ground. If not, standard troubleshooting techniques would have led you to it.
 
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