JP's DIY LED Fixture

[jpccusa]

Kcress,

CONTINUITY TEST: All LED's lit up, individually, as expected.


Hard to see but the probes are touching the wire close to the adjacent LEDs solder joints.

SHORTED WIRE TEST: All LED's did NOT lit up when I switched the probes (independently) to the screws.


Initial position


Move red probe to screw


Move red probe back checking LED works


Move black probe to screw

It really took me less time to do both tests on all LEDs than it took you to write me the instructions. I really appreciate your help and time (same goes to FishMan and others) this far! Please stick around since I'm still not done. LOL

NOTE: I hope people find this thread ridiculously easy to understand and follow. I am taking advantage of the fact I am not knowledgeable in electronics/electricity to visually document all the steps of the entire process.

[kcress]

Damn! Someone who can follow instructions perfectly!

Excellent pics too. Bravo.

So. All tests done. All Passed.
This means NO assembly errors.

Is there still a problem?

[jpccusa]

The two white strings (red wires) work perfectly. Their measurement across the resistor is almost identical.

For the blues (green wires), there is a huge difference between the two strings. Please see post #69 for some numbers.

I am not sure I am measuring correctly in order to have the parallel strings balanced.

Fishman was helping as well, and he addressed the three questions from post #69.

I posted some results at the end of post #74 as well.

[Algaenot]

Kcress – Outstanding testing description. There are many of us that do not have the experience with electronics and having someone who is willing to describe the process at a very basic level is much appreciated. Your patience and willingness to take the time to help novices like myself should be applauded.

[Pro X]

Very good pics by jpccusa with very easy to follow instructions with what to expect and what's wrong if something else occurs by kcress. All this in the first 3-4 pages.......priceless.

[jpccusa]

Originally Posted by Algaenot

Kcress – Outstanding testing description. There are many of us that do not have the experience with electronics and having someone who is willing to describe the process at a very basic level is much appreciated. Your patience and willingness to take the time to help novices like myself should be applauded.

AMEN!!!

Originally Posted by Pro X

Very good pics by jpccusa with very easy to follow instructions with what to expect and what's wrong if something else occurs by kcress. All this in the first 3-4 pages.......priceless.

Thanks, and if you set your user controls to display more posts per page, that will make this thread only 2 pages long so far.

I must add that Kcress' instructions are not meant to correct something that went wrong. His instructions are meant to prevent something from going wrong.

I jumped the gun, didn't check for continuity and shorts, and ended up with one less LED. Do these tests before plugging the driver(s) into the electricity!

[kcress]

Algaenot, Pro X; Thanks for the kind words. Thanks for the.. thanks.

I will be pointing a lot of people back to this thread because jpccusa's pictures are perfect.

And yes! Do those tests before the first power-up. I do them before I even bother installing the drivers.

OK, so your blue strings are imbalanced. We can fix that. It seems about 1 in 4 builds has a notable imbalance that would need to be corrected.

Alrighty then. Some info on this. Keep in mind that the Vf of any LED is a function of the current thru it. So when you measure the Vfs of individual LEDs you can't really compare Vfs across two parallel strings - since they don't have the same current running thru them.

So lets look at your numbers jpccusa:

Originally Posted by jpccusa

Okay, I nervously got some numbers.

Line 1: (3.02)(3.04)(3.04)(3.03)(3.01)(3.03)(3.03)(3.01)(3.00)(3.10)(3.15)
Line 2: (3.02)(2.95)(3.02)(3.10)(3.04)(3.27)(3.20)(3.02)(2.95)(3.18)(3.04)

The above numbers were measured using adjacent LED's, multimeter dial on position 20 (at about 10 o'clock on dial). There are only 22 LED's because one burned. I removed one good LED from the other line so both lines have the same quantity.

Line 1: 655
Line 2: 404

The above numbers were measured across the resistors of each line, multimeter dial on position 2 (at about 9 o'clock on dial).

Measurements were taken with the system turned on and driver's internal potentiometer dialed to 650 on line 1 since that was the highest line.

Your numbers 655 and 404 should actually be 0.655 and 0.404. They represent 655mA and 404mA when measured across a 1.0ohm resistor.

Once you've made your list of the individual LED Vfs examine both lists. In the high string (655mA) find the lowest recorded Vf. That will be the "3.00" one. This represents the LED doing the most to increase the current in this string.

In the low string find the highest Vf. "3.27" This represents the LED that is doing the most to reduce the current in this string.

Of course power down...

Remove and swap these two LEDs. This will automatically cause the high current string to draw less current and the low current string to draw more current. It will drive the two string currents together.

Please give it a shot and let us know how that one swap changes the currents.

If the current imbalance is still more than 50mA refer back to your two lists and take the next low/high pair and swap them in the same direction. Then re-check. There is no way to calculate this, you have to do single pair swap and checks.

Don't forget to do the Continuity Check and the Short Check on the two LEDs you swap each time. You don't want to have a bad solder job blowing LEDs or fuses.

[Algaenot]

Agree on the excellent pics. jpccusa must have a forehead mounter camera.

[jpccusa]

Kcress: Will do. I thought that was the correct way of doing it, but the math in my head was not making sense.

Was the multimeter settings right to make the LED and strings measurement? I thought to find the mA I would need to use the DC Amps (2 to 5 o'clock on the dial). Will I ever use those functions?

Algaenot: I have a helper who holds the probes while I take the pictures.

[kcress]

To use the DC amps to measure the current you must change the lead plugin on the meter and break the wires and insert your meter. A real pain in the butt and not without risks. You measure the voltage across the resistors that you should have installed with the fuses.

[jpccusa]

Alright, more pictures...

First I unsoldered and removed both (3.27) and (3.00) from their strings.



Then I reapplied thermal compound and reattached the LEDs, making sure I swapped their positions.


This is the thermal compound. If you are going to do parallel, I recommend something that won't set (glue) your stars down. Screws and this worked perfectly. And this compound was cheap too (I will put a price list together once I am completely done).


Anyway, checked for continuity and short. All good.

Powered on and measured both strings across the resistors:
Line 1: 485
Line 2: 574

A little better, but still too far apart.

Repeated the process with the next highest and lowest pair, which was (3.20) from line 1 and (3.01) from line 2.

Checked for continuity and short. All good.

Powered on and measured both strings across the resistors:
Line 1: 543
Line 2: 516

Adjusted the driver's internal pot to about 650 using line 1 as measurement (highest of the two).

Final measurement:
Line 1: 663
Line 2: 630

Powered on the whites and measured across the resistors:
Line 1: 649
Line 2: 643

The difference on the whites is 6mA and 33mA on the blues. I think I'm DONE!!!!


(Kcress? Am I?)

[kcress]

No! Your fixture is useless on the floor, you have to hang it...










Congrats! Well done!


One more bit of data, that would be really nice for my research, would be to crank up the current all the way and measure the two string currents.
(Don't forget to put it back!)

I'm trying to get a feel for how high the MWs will go if we aren't pushing the voltage limit at the same time.

The data sheet sez 1.3A but I always seem to see much higher than that.

Hey! What are you taking your pictures with and what are you doing to them if anything?

[jpccusa]

Originally Posted by kcress

No! Your fixture is useless on the floor, you have to hang it...

Congrats! Well done!

Thank you. It would be almost impossible to do this project if I didn't have the support here.

Originally Posted by kcress

One more bit of data, that would be really nice for my research, would be to crank up the current all the way and measure the two string currents.
(Don't forget to put it back!)

I'm trying to get a feel for how high the MWs will go if we aren't pushing the voltage limit at the same time.

The data sheet sez 1.3A but I always seem to see much higher than that.

This is not a joke, right? I can turn the MW internal pot all the way up (pass specification), make some measurements, and turn it back down without the risk of damaging anything?

Originally Posted by kcress

Hey! What are you taking your pictures with and what are you doing to them if anything?

I'm taking my pictures with a Canon PowerShot SD750

The pictures are on a Picasa web album (PM sent).

[jpccusa]

PRICE LIST

* 50 LEDs + 8 fuses + 8 resistors + 8 terminal blocks + 2 drivers + 1 wall wart + 2 pots = $275.90 shipped (Group buy)
* Multimeter = $20 shipped (Ebay)
* Thermal Compound = less than $10 shipped (can't find the receipt)
* 2 Computer Fans + 12v wall wart = $15 (Ebay + Fry's)
* 18 ft. Aluminum Channel = $20.55 (Industrial Metal Supply Co.)
* 90 ft. #22 wire (3 colors) + Soldering Iron + Solder + Desoldering Braid = ~$25.00 (RadioShack)
* Hardware = ~$20.00 (HomeDepot)

Total Cost = ~$386.50 spent along ~ 6 months (my first purchase was the multimeter back in October of 2010)

[chris023]

Great job!!!

I am getting close to this point in my build and was wondering if a picture/clear explanation of "measured across the resistors of each line" is done.
I understand that it is to measure the forward voltage of a string, but am not sure where to put the probes?

appreciate it, thanks.

[jpccusa]

Hello Chris023,

Here is a picture


After you make that measurement, move both probes to the other string (above string in the picture) and make the measurement.

Good luck with your build.

[chris023]

great, thanks... doesn't matter which sides the probes go on right?

[jpccusa]

Originally Posted by chris023

great, thanks... doesn't matter which sides the probes go on right?

I don't think so, but when in doubt, do like the picture. The current was going from the right to the left.

[kcress]

Originally Posted by jpccusa

Thank you. It would be almost impossible to do this project if I didn't have the support here.



This is not a joke, right? I can turn the MW internal pot all the way up (pass specification), make some measurements, and turn it back down without the risk of damaging anything?


I'm taking my pictures with a Canon PowerShot SD750

The pictures are on a Picasa web album (PM sent).

Thanks for the info. That PowerShot continually impresses me.

No! Not a joke. If you're using ELN60s you can't get much over 650mA per string with two in parallel. That's according to the data sheet. But, I always see 700mA or 800mA because the ELN actually seems to put out more like 1.5A not 1.3. I want to know if yours do the same thing.

It won't hurt anything. Just put your meter across the higher string and crank up the pot. Don't force it AT ALL. As soon as there is the slightest turning resistance stop. Note the current and then note the other string's current. Then turn it back down where you want it.












chris023; It doesn't matter which probe goes on which side of the resistors. HOWEVER one way will give you a negative number and the other a positive. Just ignore the sign as it only tells the direction of the current. which matters not in this case, since it flows only one way - the way that lights the LEDs.

[Isayso]

Hi Jpccusa
are those U channel still 3/4" or did you switch for the 1" ones
thanks..
PS:
nice built I need to be kicked in the arse and start mine LOL

[jpccusa]

Those are 3/4" u-channels, identical to the HomeDepot ones from the beginning of this thread.

Report on Temperature: Yesterday I left the LEDs on for over 2 hours, same position as in the picture above (no convection on the channels), and I was still able to touch the aluminum for an indefinite amount of time. I bet once they are hung and with the two fans blowing, they will be barely warm.

Great thing I got talked out of the heavy and expensive heatsinks. They do an excellent job dissipating heat, but in my case, they would be overkill. Heck, even my fans I am thinking are overkill now.

Thanks for the compliments and GET YOUR PROJECT GOING (and don't forget to take pictures)!

[Isayso]

Hi thanks for the answer
I found 3/4" 1/8 and 3/4" * 1/8 thickness. ..any preference?
Or they are all the same
Thanks again

[jpccusa]

IIRC, thicker is better.

[chris023]

Thought I would post this question here, as there is so much good info on meters/testing.

I have a different meter (pic below), and am wondering which settings to use for testing forward voltage of individual LEDs, as well as string (from resistor). I believe 20 (individual) and 2 (string) were used on jpccusa's meter, and there is no 2 on my meter.

Thanks.

[jpccusa]

I believe 2000m is the same as 2 (the m I believe means milli, or 1000)