Best power source for LED array? - Page 2 - Overclock.net

Ionimplant · 05-27-09

This is what you would build:

Because the diode voltage varies from 3.2 to 3.4 and the battery will vary as well, you will have variation on lumen output. Maybe that is OK for your application and it is just a homebrew anyway!

EntropyTTU · 05-27-09

Quote:

Originally Posted by Boris4ka

Ok so you're saying that I need to:

Use the 7.2v 3000nimh battery
Wire one 200ohm resistor to each LED
Wire all the LED's in series

No, parallel.

Quote:

But since I have 7.2v, I can use two parallel LED's in series, no? 3.4v x2 = 6.8v, 6.8v < 7.2v.
If this is true, does that mean I use a different resistor, and only 25 of them?

No, if you drop to 25, you will need to divide by 2, or use a 100 Ohm.

I am saying a 2x25 array (2 parallel, 25 series). Makes sense? Or am I wrong again? Seems it would be easier to do this way if it's possible.

[/quote]

I think I see what you are saying. To make things simple, you want to run 25x2 leds, and use only 25 resistors obviously. So, yes, you could do this, however, you will need to half the resistance going to each set of leds, otherwise, you will cut the current in half, and your leds, will only be half as bright (approx, half, as led brightness is not linear).

The thing is, you need to wire them in parallel.

In regards to your original post.....

Yes, you could do this, using a 4 Ohm resistor, however, just make SURE to run them in parallel.

**Boris4ka** · 05-27-09

Quote:

You have to ballast the LEDs!! They are not perfectly matched. You never NEVER put two pn junctions in parallel!

I have no idea what that means.

Entropy, I think I mixed up series and parallel. I meant parallel the whole time. Are you saying I'd need one 4 Ohm resistor and that's it? Not one per LED or per 2 LED's?

I'm just getting more confused

Here's a diagram I made, is it what you're saying?

EntropyTTU · 05-27-09

Quote:

Originally Posted by Boris4ka

I have no idea what that means.

Entropy, I think I mixed up series and parallel. I meant parallel the whole time. Are you saying I'd need one 4 Ohm resistor and that's it? Not one per LED or per 2 LED's?

I'm just getting more confused

Here's a diagram I made, is it what you're saying?

Yes, kind of. Working on picture to show you, if I can get it to upload.

**Boris4ka** · 05-27-09

Quote:

Originally Posted by EntropyTTU

Yes, kind of. Working on picture to show you, if I can get it to upload.

If it's not uploading you can email it to me, it's my username @gmail. Thanks for all the help

Ionimplant · 05-27-09

Here is your diagram repeated:

It is a bad idea because diodes are not matched.

Here is a similar idea:

It too is a bad idea for the same reason.

Here is the correct way even though you have more components.

**Boris4ka** · 05-27-09

What do you mean the diodes are not matched?

EntropyTTU · 05-27-09

Ionimplant:

Are you talking about the LEDs flickering, because they are not balanced, I am confused as well.

I have an idea, to put the 50 in parallel, and simply run them as a one load, and then just use one resistor feeding this one load.

Do you see problems with this, because of what you are refering to?

[/IMG]

Boris:
Lol...This is the best I could come up with, I can't run my circuit simulation program in Linux, so I drew it, and snapped a pick for you.

THe problem is Boris, either way you cut it, no matter what the set-up , you will be pulling 1 AMP just from the LED,s this is going to SERIOUSLY drain your battery.

You might want to consider some higher powered leds, but much less in number.

Edit:Also --> See "Not Good". At 1 amp flowing through your resistor, you will need a 4watt resistor, with a LOW tolerance. It will be BIG, and expensive.

**Boris4ka** · 05-27-09

Quote:

Originally Posted by EntropyTTU

Ionimplant:

Are you talking about the LEDs flickering, because they are not balanced, I am confused as well.

I have an idea, to put the 50 in parallel, and simply run them as a one load, and then just use one resistor feeding this one load.

Do you see problems with this, because of what you are refering to?

[]http://i576.photobucket.com/albums/ss201/EntropyTTU/DSCF0954.jpg[/IMG][/IMG]

Boris:
Lol...This is the best I could come up with, I can't run my circuit simulation program in Linux, so I drew it, and snapped a pick for you.

THe problem is Boris, either way you cut it, no matter what the set-up , you will be pulling 1 AMP just from the LED,s this is going to SERIOUSLY drain your battery.

You might want to consider some higher powered leds, but much less in number.

The drawing shows what I was asking in the first post - using just one resistor. Thanks for going through all the trouble

However, why is 4 watts and 1 amp not good? The 7.2v battery is for RC cars, which can draw 30 amps and 300W, and that lasts 15 minutes. How bad of a drain do you think it'll be?

EDIT: I posted after your edit. So these are bad for the resistor huh. There's no other way? The reason I'm using 50 of these LED's is because they're $5 shipped and I already know how incredibly bright they are. To use a smaller more powerful LED would require a heatsink, driver, etc and would cost at least 10 times more.

EntropyTTU · 05-27-09

Quote:

Originally Posted by Boris4ka

The drawing shows what I was asking in the first post - using just one resistor. Thanks for going through all the trouble

However, why is 4 watts and 1 amp not good? The 7.2v battery is for RC cars, which can draw 30 amps and 300W, and that lasts 15 minutes. How bad of a drain do you think it'll be?

30 AMPS, WOW

You should be good to go then, I had no idea the battery had those specs. What size (physically) is the battery, btw?

Quote:

EDIT: I posted after your edit. So these are bad for the resistor huh. There's no other way? The reason I'm using 50 of these LED's is because they're $5 shipped and I already know how incredibly bright they are. To use a smaller more powerful LED would require a heatsink, driver, etc and would cost at least 10 times more.

In that case, you might want to go with the big resistor. I am so used to thinking in terms of circuit design, in regards to size, and especially cost, and its first nature to avoid things like that. However, for a bike light system, and if you're ok with the cost, and size, it should be no problem.

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Best power source for LED array?

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