# LED Question - low output issue...



## edwood saucer (Aug 21, 2006)

Okay - made my first successful 6 light spot light...

But that's not what this thread is about...

I made a 2 light array for my witch.

I followed the wiring diagram provided from the LED wizard site.

It said I need one resistor - then one light then the other.

And it works - HOWEVER - the output on the second light is poor.

I tried rewiring and resoldering them and have the same result.

This is just a guess - but in between the lights (and I did this to aid in threading them into the wig form) I have a splice.

The wire I am using in between and on both ends to connect to the battery is one side of an extension cord wire that I cut down the middle. I had no idea what guage to use.

Anyway - does anything jump out as wrong? I even put a new light on that side with the same result.

The project isn't at a total stand still as I can gouge eye sockets out of frankestein - but I am stalled on the lights.

Any help is appreciated.

EWS


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## gmacted (Jan 18, 2006)

Edwood,

What are the parameters of the circuit? What is the supply voltage, forward voltage and forward current of the LED?

I saw in an old post made by you that the LED had a typical forward voltage of 3.2V and a forward current of 20 mA. I'm assuming you used a 12V supply and wired them in series.

Here's the formula of the circuit.

R = (12 - 3.2 - 3.2)/ 0.020

The resistor should be ~280 ohms or slightly larger. A standard 330 ohm resistor would give you a current of about 17 mA. 

If the resistor, and the two LEDs are wired in series, the current through all the devices will be the same. That's ohms law (kind of like gravity, you can't change it).

You said you used extension cord wire between the LEDs, but this will have little to no effect on the total circuit. If the LEDs are wired in series, then the current through both LEDs will be the same and will result in the same brightness.

What your saying doesn't agree with simple electronics. It should work. Could you post a picture so I could take a look? Otherwise, you've got me stumped.


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## edwood saucer (Aug 21, 2006)

I can post the circuit diagram - but can't the actual wire-up because our digi - camera has died...

http://www.fizzcreative.com/haunt/images/2LEDArray.jpg


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## edwood saucer (Aug 21, 2006)

I will go to Radio Shack tomorrow and get proper gauge wire... something is awry here.

I will create a new circuit and see if the problem duplicates.

Like I said - I had success with 6 lights on a 6 volt - I can't believe I'm having problems with 2 lights on a 9 volt.


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## Brad Green (Jul 29, 2004)

OK, this may be too obvious, but still worth asking. Are you sure the LED's are wired in series (cathode to anode)? LED's typically have a flat side and a round side, for over simplification, it should be flat tied to round to complete the series (sorry, can't think of any other reason that hasn't already been looked at)


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## edwood saucer (Aug 21, 2006)

I will double check when I tear it apart - I was very careful about it though (atleast I thought I was)

The thing is - is that the second in the series does light - it's just dimmer. And I thought that if you didn't go cathode to anode - it wouldn't work at all.


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## edwood saucer (Aug 21, 2006)

And a follow up to that - they are both wired seperately - so I have complete control over what wire connect to what as I have a splice in the middle.

I did this to prevent stuffing them in the head being too difficult. So I can say with relative certainty that they are wired correctly if the above comment holds true - of them NOT lighting when they are cathode to anode.


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## gmacted (Jan 18, 2006)

edwood saucer said:


> I can post the circuit diagram - but can't the actual wire-up because our digi - camera has died...
> 
> http://www.fizzcreative.com/haunt/images/2LEDArray.jpg


This should work just fine. If you wired it like this you should have no problems.


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## gmacted (Jan 18, 2006)

edwood saucer said:


> I will double check when I tear it apart - I was very careful about it though (atleast I thought I was)
> 
> The thing is - is that the second in the series does light - it's just dimmer. And I thought that if you didn't go cathode to anode - it wouldn't work at all.


You are correct. If you wired the LED backwards, it would not work at all.


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## edwood saucer (Aug 21, 2006)

Quick update - 

Rewired with smaller gauge, tried to do a cleaner job and everything worked just fine.

Thanks all!


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## MansionHaunter (Sep 20, 2006)

Just for future reference: hooking up LEDs in series will work well for LEDs that are of the same type and manufacture, since they'll have the same forward voltage drop and the same photoptic output per unit current flow. 
If you're using several different LEDs, particuarly if you're using different colors, it's better to pair them up with their own dropping resistors to ensure that each gets the current it was designed to carry. 
Most high brightness LEDs these days want about 10 to 15 mA running through them, thought older makes may take more or less depending upon their own specs.
Over-driving an LED will turn it into an NED - a Noise Emitting Diode. BANG!


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## edwood saucer (Aug 21, 2006)

Thanks MH


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## Zombie-F (Apr 12, 2004)

Just curious, what guage wire were you using? The guage of the wire shouldn't matter much at all with these circuits because we're only drawing milliamps with even large arrays.

My thought would have been that you used the wrong sized resistor again. The ohm value for a 3 LED array would definitely be different from the ohm value needed for just two.


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## edwood saucer (Aug 21, 2006)

It may or may not have been the gauge - it was half an extension cord.

I'm just chalking it up to a ghost in the machine. Made three sets of lights since that all work perfectly.

Finishing the sets of spots will be next.

I do appreciate everybodies help though.

EWS


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## Zombie-F (Apr 12, 2004)

You're using extension cord wire? That seems a bit large to be soldering to tiny LED leads. What are you attaching the other end of the wire to for power?

The best wire I can find to use for LED spotlights and eyes is 24 guage 2-conductor power wire from Jameco. You can get a 100' spool of it for $5.59. It's the same wire that's used with wall AC adapters, so it's pretty flexible.

You can see it here:
http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=100280


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## edwood saucer (Aug 21, 2006)

I picked up smaller gauge wire at Radio Shack - then things began to work well.


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