# Deal Extreme 5mm LEDs



## spencer (Apr 7, 2008)

Does anybody know the forward voltage on Deal Extreme's 14000mcd 5mm white LEDs? I think typical on most LEDs is around 3.4v on 20mA. Is that close? Also what would the forward voltage be at say 50mA? Could I drive the 5mm led at 50mA for any amount of time? I just had an idea that involves many LEDs and I'm just figuring out if it is even plausible.


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## MikePL (Apr 8, 2008)

I guess that all 5mm LEDs are produced according to a standard and all are driven at 20mA. The DX 5mm LEDs are the typical ones so don't expect much sensation when you buy them. They are bright but nothing special for these days.

I can recommend you LEDs from ebay sellers (actually they have stores and are producers). I bought a few times packs of 100 and they were really exceptionally bright.


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## Fallingwater (Apr 8, 2008)

MikePL: can you recommend the sellers to me as well? I only know jeledhk right now.


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## TorchBoy (Apr 8, 2008)

spencer said:


> Does anybody know the forward voltage on Deal Extreme's 14000mcd 5mm white LEDs? I think typical on most LEDs is around 3.4v on 20mA. Is that close? Also what would the forward voltage be at say 50mA? Could I drive the 5mm led at 50mA for any amount of time? I just had an idea that involves many LEDs and I'm just figuring out if it is even plausible.



A random sample from my 50 pack using 3 x AAA NiMH cells (4.01 V) and a 22 ohm resistor (just because I happened to have that stuff within reach):

22 mA @ 3.05 V
22 mA @ 3.07 V
24 mA @ 3.08 V
28 mA @ 3.02 V
23 mA @ 3.02 V

So just by chance the current figures are in the right ballpark to give you a rough idea of what to expect for Vf.

Disclaimers: I got them several months ago so I have no idea if the present ones would be similar, but I would expect so. Also, the current was jumping around a few milliamps so my methodology could likely be a tad better. Or maybe the multimeter I was using to measure the current is a bit wayward.

They don't seem very bright compared to the Crees I've been playing with recently but they're not bad. I'll get around to using them one day, either in an array or in a rope light to be run off a 12 V SLA.

So... is your idea plausible or busted?


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## spencer (Apr 8, 2008)

My idea is plausible. The LEDs don't need to be very bright because there will be 406 of them on a desk and very bright might blind you. I might do a little write up on it later.


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## spencer (Apr 8, 2008)

And would 406 LEDs at say 20mA need heatsinking? They would be all squeezed into a 30x60 inch area.


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## TorchBoy (Apr 8, 2008)

Don't know about squeezed - a quick calculation tells me you'd have them spaced at a bit less than two inch intervals.

BTW, flattening the tops of them will mean they emit light more broadly.


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## spencer (Apr 8, 2008)

Thanks for the tip on flattening the tops. I already knew that and was actually planning on doing that. And your calculation was a bit off. They would be exactly spaced at 2 inches. 14x29=406 LEDs with a 1 inch border around.


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## TorchBoy (Apr 8, 2008)

spencer said:


> ... with a 1 inch border around.


:thumbsup: Didn't think of that doing my quick calculation. (Apart from that, yay me!) I don't think any extra heatsinking would be required for that sort of thing running at a few milliamps.

I say go for it. We just don't see many 5 mm array projects around here, and this one sound quite cool. How will it be powered?


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## spencer (Apr 8, 2008)

I think I will go with the CCHIPO driver from the same guys who do the Maxflex driver. The LEDs will go in a desk. Maximum brightness is not the goal, rather a nice glow is the goal.


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## spencer (Apr 8, 2008)

Just thought of something else. Can anybody look at the specs of the CCHIPO driver and tell me what I should be using as an AC adapter? Since it is a boost driver, the input voltage obviously needs to be less than the LED voltage. I'm thinking that the minimum VOut from CCHIPO would be 19 volts (about 2.8 Vf (maybe minimum voltage at 2mA) x 7 = 19.6V) and up to 23 volts (3.2 Vf ish at 35mA x 7 = 23.1V). 23 volts would be the max because the CCHIPO driver can only do 45 watts. I'm thinking an 18 volt AC adapter at 2.5 amps and that will get me exactly 45 watts coming out of the AC adapter (I think I need that much coming out and I know little about electricity). Just wondering what you guys think.

NOTE: I'm pulling the Vf figures out of the sky at any given number of mA


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## Calina (Apr 9, 2008)

spencer said:


> Thanks for the tip on flattening the tops. I already knew that and was actually planning on doing that. And your calculation was a bit off. They would be exactly spaced at 2 inches. 14x29=406 LEDs with a 1 inch border around.


 
That will leave a 2 inch border. If you want them 2 inches apart with a one inch border you'll need 450 LEDs (15x30). I'm not sure you realize how much light this will provide, with 406 LEDs at 20 mA you will have more or less 1200 lumens, that's a lot of light. You would likely have more than enough light with 50 LEDS, 6 inches apart with a 3 inch border. Try a couple of Fauxton to give you an idea of how many LEDs you'll need (take into account that Fauxton are over driven with fresh batteries).


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## TorchBoy (Apr 9, 2008)

Calina said:


> That will leave a 2 inch border. If you want them 2 inches apart with a one inch border you'll need 450 LEDs (15x30).


So I _was_ right? 



Calina said:


> with 406 LEDs at 20 mA you will have more or less 1200 lumens, that's a lot of light.


What sort of efficacy does DX's 5mm LEDs have?


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## Calina (Apr 9, 2008)

These particular ones, I don't know but good LEDs provide around 70 lm/W at 20 mA (that would be 3 to 3.5 lm/LED at 20 mA and 2 to 2.5 as much at 50 or 60 mA), the best ones do better. Check this thread by jtr1962 for more information on 5mm and 10mm LEDs: https://www.candlepowerforums.com/threads/89607&highlight=led+lumen+testing


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## spencer (Apr 9, 2008)

Calina said:


> That will leave a 2 inch border. If you want them 2 inches apart with a one inch border you'll need 450 LEDs (15x30). I'm not sure you realize how much light this will provide, with 406 LEDs at 20 mA you will have more or less 1200 lumens, that's a lot of light. You would likely have more than enough light with 50 LEDS, 6 inches apart with a 3 inch border. Try a couple of Fauxton to give you an idea of how many LEDs you'll need (take into account that Fauxton are over driven with fresh batteries).



And that right there is why this project will probably never happen. Man I can't believe I overlooked that.


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## TorchBoy (Apr 9, 2008)

I don't see what the problem is. You can drive them at 1 mA each for a total of less than 100 lumens and a total ~1.1 W. Or drive them at a few microamps each for a total of less than 1 lumen and a few milliwatts.


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## spencer (Apr 9, 2008)

I said the project will not happen because I overlooked something as simple as the LED spacing. 

In response to what you said: I don't think that I can use CCHIPO driver because it has a minimum of 30mA. In a string of say 10 LEDs: 10 x 3.2 = 32 Volts (really don't want to get too close to the maximum of 39 Vout) 10 LEDs at 30 mA is 3mA an LED which would still be pretty bright.

Can anybody suggest a different driver maybe?


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## TorchBoy (Apr 9, 2008)

spencer said:


> I said the project will not happen because I overlooked something as simple as the LED spacing.


 Why on earth would a difference of 3.6 mm kill the project?



spencer said:


> Can anybody suggest a different driver maybe?


What power supply?


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## space (Apr 9, 2008)

When you run a string of LED's as you say, they will be connected in series. This means that everyone will have same current going through them. Through the 1st, on to the 2nd and so on. (It is really happening all at once.) So when this string is running at 30mA, all LEDs in that string get 30ma.
 
What you easily could do is run multiple strings on the output of the driver. But then you will need a current limiting resistor in each string (they will ensure current sharing between the strings). (This is a normal practice.)

You could easy run 50 (yes 50) strings at 20mA on the driver you are talking about.


space


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## spencer (Apr 9, 2008)

So you are saying that + @20 mA --- LED --- LED --- - and both the LEDs get 20mA? 
What about:
+ --- LED --- LED -
| ..................|
| ..................|
----- LED --- LED

(ignore the periods, they are only there for spacing)
How many mA would each LED get if + = 20mA? 
My electronic knowledge is far from adequate. I'll have to do more research.


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## spencer (Apr 10, 2008)

Actually forget my example above. Lets take this real world to what I'm actually doing. I have changed my number of LEDs. I will have 60 parallel strings of 8 LEDs in series for a total of 480 LEDs. If the driver is putting out its minimum of 30mA, how much power will *EACH* LED be receiving?


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## HKJ (Apr 10, 2008)

spencer said:


> Actually forget my example above. Lets take this real world to what I'm actually doing. I have changed my number of LEDs. I will have 60 parallel strings of 8 LEDs in series for a total of 480 LEDs. If the driver is putting out its minimum of 30mA, how much power will *EACH* LED be receiving?



If the driver can supply enough volt and your have a series resistor (with a correct value) in each string your will get 30mA/60 -> 0.5mA for each led.

The purpose of the series resistor is to compensate for small differences in Vf, with eight led in a string I would say that 1 volt for the series resistor is enough.


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## TorchBoy (Apr 10, 2008)

spencer said:


> My electronic knowledge is far from adequate.





HKJ said:


> The purpose of the series resistor is to compensate for small differences in Vf, with eight led in a string I would say that 1 volt for the series resistor is enough.


HKJ, you might have to explain that in a bit more detail.


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## HKJ (Apr 11, 2008)

TorchBoy said:


> HKJ, you might have to explain that in a bit more detail.



Leds do not have the exactly same Vf. This is a problem when running them in parallel, because the different Vf would cause different current to flow in them and thus give different light levels.

Using a resistor in series with each led (or string of leds) will compensate, to some degree, for this difference in Vf.

A large voltage over the resistor will compensate very well, a small voltage over the resistor will not compensate to well. The problem with the large voltage is the power loss in the resistor. With the 8 leds in series, I would guess that 1 volt over the resistor would be amble compensation for any Vf differences.

I hope this explains it.


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## spencer (Apr 12, 2008)

I changed it again. I'm going for 75 strings of 6. What value of resistor would I need and how many watts should it be 1/2 watt? 1 watt?


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## HKJ (Apr 12, 2008)

spencer said:


> I changed it again. I'm going for 75 strings of 6. What value of resistor would I need and how many watts should it be 1/2 watt? 1 watt?



Your are running 75 strings og 6 leds on a 30mA constant current driver?

That gives your 0.4 mA for each string.
With only 6 leds I would reduce the voltage for the resistors to 0.7 volt, that gives a 1750ohm resistor, the nearest standard value is 1k8 (1800ohm).

The power in the resistor is 0.000288 watt, i.e. your can uses the smallest 1k8 resistor your can find.


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## spencer (Apr 12, 2008)

Maybe I wasn't quite clear. The driver would do 30mA minimum but up to 2 amps or something. To get the full 20mA to each LED is the driver would have to do 1.5A.


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## HKJ (Apr 12, 2008)

spencer said:


> Maybe I wasn't quite clear. The driver would do 30mA minimum but up to 2 amps or something. To get the full 20mA to each LED is the driver would have to do 1.5A.



What current range are your going to use?
And is is a constant current driver?

The resistor has to be calculated for the maximum drive current and then your will have to accept if there are any differences at the lower drive levels.


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## warlord (Apr 12, 2008)

I would say screw the driver and go with an unused DC output wall wart. You probably have one or two you don't need laying around the house somewhere. Take the output voltage of the wall wart and plug it into this:

led array wizard

It'll lay out the best led configuration for your pupose and also tell you how much current is drawn from the wall wart. Make sure this number doesn't exceed the WW specification and you'll be fine.

It's also nice because it'll tell you how much current in mA is dissapated by the leds and resistors.

But that's just me.


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## TorchBoy (Apr 12, 2008)

warlord said:


> You probably have one or two you don't need laying around the house somewhere.


Hm, now that you mention it, I think I have an unused 24V supply. I'm getting a few ideas... :thumbsup:


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## spencer (Apr 12, 2008)

That wouldn't be overly hard to do. The only problem is that I wanted to have some dimming functionality. The CCHIPO driver has some nice places for me to attach a potentiometer for dimming. How would I do that with a wall wart?
BTW: I like that array wizard. Nice. Thanks.


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## TorchBoy (Apr 13, 2008)

For two modes, you could just have an extra resistor of a suitably high power rating that can be shorted by a simple single-throw switch. You'd still have the balancing resistors for each chain of LEDs, of a value which would give you your high mode. With the extra resistor in series with everything you'd have a low mode also.


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## warlord (Apr 13, 2008)

I wouldn't add the whole "dimming" thing to the equation. 

I would suggest a SPCO switch (ON-OFF-ON) with one wired to power all the lights and one wired to power half the lights or so. You should get a better low light setting without any funny color change or PWM. If you want multiple settings just use a single pole rotary switch.


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