DIY LED lights

[Nexogen]

if is LZ4-00R210 Red 10 Watt 655-670nm you can adjust the Voltage between min 8.2V and Max 11.4V (TC = 25°C)

[ALToronto]

OK, thank you. David, that looks really good. I can just see a Rube Goldberg contraption of pipes and t-joints with lights shining out of the open ends of the t's. Do you really need such a huge heat sink, though, if you're putting the diodes into a larger pipe arrangement?

So, back to voltage and current calculations. If each 5 W LED draws 15-17.5 V, this means that the current has to be around 300 mA, correct? At 17.5 V I get 286 mA, at 15 V I get 333 mA. So with constant current, a 75 W driver should put out somewhere around 250 V, correct? I was exaggerating about arc welder voltage, but it's enough to throw a person a few feet.

Now moving a little further - if the driver does not put out sufficient voltage, does this mean that it puts out excessive current, and I will over-drive the LEDs and burn them out faster? Or does it mean that they will be under-powered?

[DavidCampen]

Originally Posted by ALToronto

So, back to voltage and current calculations. If each 5 W LED draws 15-17.5 V, this means that the current has to be around 300 mA, correct?

That calculation is correct assuming that the LED is consuming 5 watts of power (5 W / 15 V = 333 ma) but when an LED is called "5 W LED" that is, at most, only an indication of the maximum amount of power it can draw without being destroyed. You need the datasheet so that you can look at the current versus forward voltage curve.

Originally Posted by ALToronto

At 17.5 V I get 286 mA, at 15 V I get 333 mA. So with constant current, a 75 W driver should put out somewhere around 250 V, correct? I was exaggerating about arc welder voltage, but it's enough to throw a person a few feet.

You are unlikely to find a driver that puts out 250 v but, yes, if you did then that is a dangerous voltage. In my designs, I like to keep the maximum output voltage below 36 v.

Originally Posted by ALToronto

Now moving a little further - if the driver does not put out sufficient voltage, does this mean that it puts out excessive current, and I will over-drive the LEDs and burn them out faster? Or does it mean that they will be under-powered?

The drivers have a maximum voltage that they will put out, you need the datasheet for the driver that you use. The driver that I have used supplies a constant current of 1050 ma at between 12 and 36 volts.

[Nexogen]

For ALToronto;

I don't know what led or device you use but in example with LZ4-00R200 or LZ4-00R210, if is not minimum 8.2V is no light or flicking and current for 8.2V is approximately 110mA and for 11.4V is 1A

[DavidCampen]

Originally Posted by ALToronto

Do you really need such a huge heat sink, though, if you're putting the diodes into a larger pipe arrangement?

To a first approximation, thermal conductance is proportional to surface area. The surface area of the copper pipe is much less than that of the heat sink so its thermal conductance will be much less. The thermal conductance of the heat sink alone is about 0.2 watt per degC so to dissipate 10 watts the heat sink will be 50 degC above ambient. My guess would be that the pipe would add only another 0.05 watt/degC. LED efficiency decreases significantly with increasing temperature and I prefer to not use forced air cooling.

[DavidCampen]

Originally Posted by ALToronto

OK, thank you. David, that looks really good. I can just see a Rube Goldberg contraption of pipes and t-joints with lights shining out of the open ends of the t's.

I don't much care for the Rube Goldberg allusion. Here is a photo of a 16 x 10-watt LED light bar that I built.

[lepetitmartien]

Originally Posted by naoki

Shenzhen Fedy claims to have one in 680-690nm range:
Epistar 3w 660nm led, View Epistar 3w 660nm led, FEDY Product Details from Shenzhen Fedy Technology Co., Limited on Alibaba.com

But most of deep red diodes seem to be around 660nm.

Alla, I don't know what current you are going to drive 5W diodes, but that seems to be pretty weak for the area you want to cover. Most commercial ones seem to be driving 5W diodes at 2-3W.

There was 690nm leds until some weeks ago (I'm keeping an eye on this), I don't see them anymore in my european/japanese webshops of reference. But there's still LEDEngin LZ1-00R205 655-670nm listed.

If it can help, 1.023world - has a simulator for the leds they sell. Check in the left column. (you can change the langage to English in the simulator, bottom left option menu)