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Author Topic: Big Trouble with White LEDs  (Read 1584 times)

Le Caux Deux

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Big Trouble with White LEDs
« on: January 22, 2011, 06:36:32 PM »

I'm having a problem with white LEDs, I think they must be High Intensity but where not sold as such.
When I try to incorporate them with 2 red LEDs as towing lights The 2 reds light but the 1 white does not. The single white works om its own but is very bright can I firstly get it to work with the reds and secondly can I reduce its intensity by incorporating an extra resistor in the circuit.

Mike
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tigertiger

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Re: Big Trouble with White LEDs
« Reply #1 on: January 22, 2011, 06:43:02 PM »

I am guessing you are wiring these in series.

The white and blue LEDs need at least 3v. Less than that and no light.
The other colours need 2v only.

My initial guess is you have a circuit of more than 2v but less than 3v.

LEDs are best wired in parallel with a separate resistor on each branch to drop the voltage to the required level.

But I am no expert
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malcolmfrary

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Re: Big Trouble with White LEDs
« Reply #2 on: January 22, 2011, 10:20:02 PM »

If they are wired in series, the white probably demands a lot more current, but, getting the same current as the reds, doesn't light.  The total required voltage might be more than the supply, as well, but that would likely stop any of them lighting.
If they are wired in parallel with just one limiting resistor for the lot, the white will probably need more volts than the reds.  In this case the reds will set the volts available from the resistor at their preferred level, so the white just sulks.
Like Tiger says, put the reds on their circuit, with the white on its own circuit, where its resistor can be chosen to give the required light level.
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wombat

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Re: Big Trouble with White LEDs
« Reply #3 on: January 22, 2011, 11:09:11 PM »

It depends on how you have connected the LEDs

My recommendation is that LEDs should always be set up with their own series resistor. The resistors should be sized so that each LED draws no more than 10mA.

Wom
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Le Caux Deux

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Re: Big Trouble with White LEDs
« Reply #4 on: January 23, 2011, 10:32:40 AM »

I'm no electrician but I guess they are wired in Parallel I've got a supply to each LED and then use the mast as earth (Made from brass tube, The supply is 12v. Yes I can get all the whites to light if I use a separate supply for the coloured and a another for the whites.
Do you think I can reduce the intencity of the whites by using higher value resistors?

Mike
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malcolmfrary

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Re: Big Trouble with White LEDs
« Reply #5 on: January 23, 2011, 11:56:09 AM »

Quote
Do you think I can reduce the intencity of the whites by using higher value resistors?
Yes.  Less current, less light output.
When I did my learning about LEDs, 10mA was a good current to aim for (even if they could stand up to 20mA), 1.9 volts was the number to calculate on.  Nowadays, careful study of the specs. is needed, as the colours that used to be "impossible" have been achieved using different internal arrangements at the cost of increased power requirements, both voltage and current having increased.
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boneash

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Re: Big Trouble with White LEDs
« Reply #6 on: February 17, 2011, 07:31:18 PM »

Hi
Le Caux Deux

Did you succeed with your efforts to equalize the light from the white LEDs and get them to work satisfactorily?

Cheers
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Le Caux Deux

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Re: Big Trouble with White LEDs
« Reply #7 on: February 17, 2011, 10:02:24 PM »

Hi Boneash
Yes I wire all white towing Lights separately and increased the resistor value so that the look something near the brightness of the other bulbs, Its never going to be perfect but its acceptable. Quite difficult to get the right impresion in a photo though The lights look blue compared to the red but they are white. Added an Extra resistor to Mast Head Nav Light since this picture

Mike,
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