Comparing LED brightnesses (prob a simple question)

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guest
 
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Joined: Fri Feb 17, 2006 5:35 am

Re: Comparing LED brightnesses (prob a simple question)

Post by guest »

at 360mA you should be ok
but there might be some of those start up issues
with a 300mA wallwart

one thing that makes the problem even worse
is that the x0x uses a voltage doubler at the input
so one half of the waveform makes the 5v rail
and the other half makes the 12v rail
so you really only have 300mA for half of the time
which averages to 150mA

luckily these ratings dont mean all that much
and they can usually do much more than that

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paradigm x
 
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Re: Comparing LED brightnesses (prob a simple question)

Post by paradigm x »

Thanks.

What i dont get is why the greens need so much current to match the blues. Prob the low mcd rating. others seems to have mulitcoloured x0xen with no issues. Oh well.

I think ive wasted far too much time on this already and just going to put blues everywhere except maybe tempo and done. My other x0x has white everywhere and ive managed to use it.

THanks for all your help luap and guest.

:)

guest
 
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Joined: Fri Feb 17, 2006 5:35 am

Re: Comparing LED brightnesses (prob a simple question)

Post by guest »

i wouldnt worry about it too much
throw in what you want
and see if it works

another reason for requiring higher currents
is if the led has a wider beam angle
it will look less bright at any particular point

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paradigm x
 
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Re: Comparing LED brightnesses (prob a simple question)

Post by paradigm x »

Yeah, i know, its largely irrelevant. Its more a noob learning as much as anything. Ive got a nice colour combo which adds up to around 292mA so ill see how it goes.

Im just a bit worried/rubbish at desoldering so want to try and ensure it will work first time. no point putting in 600mA worth of LEDs for example.

cheers tho, been very useful and interesting.

Im going to get on with it now :)

guest
 
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Re: Comparing LED brightnesses (prob a simple question)

Post by guest »

best of luck

one last thing
its also good to measure the current
in addition to using calculations
this is pretty easy
just set one up and measure the voltage across the resistor
then divide that by the resistor value

ive found that led voltages can vary a lot
for example
the datasheet will say 2v but it turns out its 1.2v

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paradigm x
 
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Re: Comparing LED brightnesses (prob a simple question)

Post by paradigm x »

well i got a couple of hours to play with this today;

A layout that calculations indicated would take 282 mA seemed to take 310mA when i measured the current as you showed. Damnit!

My second option is around 272 measured/246 calculated.

Good job you suggested measurement, it actually came out higher.

So now i need to decide whether to risk my number 1 option or take the second option.

On the plus side i can read resistors an awful lot better now :lol: :roll:

Still think it was a useful excercise, despite wasting lots of time.

Cheers

guest
 
Posts: 3155
Joined: Fri Feb 17, 2006 5:35 am

Re: Comparing LED brightnesses (prob a simple question)

Post by guest »

i find i spend a lot of time
doing things very tangential to a project
but end up learning a lot from

you can always get a 500mA supply
so i wouldnt worry about it too much

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paradigm x
 
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Re: Comparing LED brightnesses (prob a simple question)

Post by paradigm x »

Thanks Guest.

Feel a bit better now :lol:

Im going to go for my number one option - it is my baby after all. :P

I dont like the wall wart ive got anyway, its one with a number of different connections at the end, which plug in, and are a bit flaky. I could always chop the end off and solder a connector on if theres no problems i guess. But for a few pounds might as well get a proper one, with 500mA rating.

Many thanks again

Ben

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