Using AC with LEDs (Part 4) - The New Technologies

Step 5 Another lighting test

And here, the first picture under a 15-W fluorescent.

The second with the 3-watter, using the same exposure.

Comments

[turbonut48]

I've been looking for this type of info for a long time. Your explanations are really good. I've got the parts on order and can't wait to build something. Probably start out with a small nightlight for an extremely dark hallway at night.

[qs]

I'm sure you will have lots of fun doing it! Good luck, and keep us posted!

[arirang777]

WHOAAAA!! So the amount of light between the 8x100mlA and the 1X700mlA is practically the same? of course as you pointed out, eight LEDs have better heat dissipation and light dispersion than just one. Will these particular LEDs used in your project fade after some usage? As long as you match the rate of 700mlA of this converter, you could use any LED type (red. green, etc) in its given quantities, right? I HAVE SEEN THE LIGHT!! :-)

[qs]

As far as the light output goes, more sources tend to give more even illumination - like the different between a 'naked' bulb and a frosted one. There will be a slow reduction in light output - the 10- or 100,000 hour life is based on the point at which light output is exactly half of when it is new. Most of this is caused by heat, so make sure everything runs cool and you'll get the service you expect from LEDs.

[qs]

No - in parallel circuits you cannot mix your LEDs. Each LED has to share an almost exact percentage of the total, and, if the Vf of one is substantially lower than the others, it will 'hog' all the current and basically self-destruct.

[arirang777]

Alright, I won't do that. Let me see if I understand the basic then: in this project's case, you used 8 matching LEDs to fulfill the converter output. Why 8? because that's the needed number according to their own power requirements to fully cover the 700 mlA of the converter. Now, if I get other color LEDs, green, red, amber, superbright white, etc, their own power requirements changes, but if I use ONE type of color only (all red, all green, all amber, etc) using your formula I will get a number of LEDS to fully cover the 700 mlA of the converter. I guess I should have made clearer my question by adding that as long as I fully cover the output (mlA) of the converter, I could use any number of the SAME LEDs on the array safely. Not different LEDs within the same array, but different color arrays instead. (thanks for the warning, though ;-] ) What could be your considerations in the following case: -Let's say you want to place the converter in the middle of a room, but you want to place the LEDs around the corners of such room. Distance between converter-LED will increase of course, therefore its internal resistance. You will have to consider the length/diameter of LED wires, but where this r (ohm) value fits within your formula? Thank you, qs, for your explanations and this instructable. I fave'd it. Cheers!!

[qs]

Yes, as long as the 8 (or 9!) LEDs share the same electrical requirements, and add up to 700mA, or MORE, then you should be fine.

The advantage of splitting up 700mA into smaller 80mA lights is that the current loss is 100 times less (Ploss = i*i*R), so thinner wires may be possible. Probably #26AWG wire if the distance between lights is under 10-ft.

[stp715a]

Nice instructable. Thanks.

When you say "add up to 700mA, or MORE" does that mean greater than 9 superflux LEDs? Can 20 superflux LEDs be used on the single controller?

Thanks

[qs]

In essence, since the device is Current-limited and the LEDs are connected in parallel, you can have any number of LEDs which can handle at least 700mA. With 9 LEDs, the current going through each will be about 78mA. Although this doesn't sound like much, remember that for LEDs, light output per amp goes up as the current goes down. In other words, light production is more efficient if we drive it with a lower current.

[stp715a]

Thanks for the response.

Do you think I could use your AC design connecting (4) of these in parallel?
http://www.bigclive.com/happy.htm

Thanks

[googolplex]

No - the two are not compatible! The design you indicated is meant for a constant voltage source, like from a fixed output wall-wart. It uses resistors to burn up power which will otherwise over-drive the LEDs.

[arirang777]

Supercool! QS FOR PRESIDENT! (after Obama, of course.) Thanks again and keep the great work man!