Calling out to Weezard for LED advice

[DreadedHermie]

Blue#1: 15.2V gave 1.5A, 14.7V gave 1.2A
Blue #2: 15.6v gave 1.5A, 15.1V gave 1.2A

A .48 ohm resistor in series with Blue #1 would have balanced the two emitters in parallel at 15.1 V.

Weezard, how did you arrive at this? As I said before, I'm not sure which terms to plug into the equation.

[Weezard]

Weezard, how did you arrive at this? As I said before, I'm not sure which terms to plug into the equation.

The answer is quite simple.
I screwed up.
Must have been too early.:stoned:
Happens alla time.
Sorry.

So, let's see if I can still figger.
Um.

R = E/I
So, .4/1.2 = .334 Should be .33 ohms. .34 is close enough and can be cobbled from 2 .68 ohm resistors in parallel.

Here's where I got bumfoozled.
P = E x I .4 x 1.2 = .48 W
A couple 1 or 2 Watt .68 ohm should run cool enough.

Let that be a lesson to ya.
If ya want math done right, yer gonna have to DIY.
There is no "I" in Weezard.

Oddly unabashed,
Wee Zard

[DreadedHermie]

It's posted stuff I was just trying to preview a couple times. When I tried to finish the previous post, it got eaten. :wtf:

Anyway, I'm back at it. Got new leds epoxied to the sink. Wired up and measured a couple reds, both of 'em almost "in the crack" between 2 voltages. About 10.6 and almost 10.9 for the other. Maybe not a problem, I may run 3 leds each on separate power supplies. That kinda depends, and I had calculated a question:

1.2A x 10.8V = 13W.
13W x 4 leds = 56 W.

NOW I read somewhere Mean Well likes 30% extra headroom (130W. of driver to push 100W.of leds) So 4 reds on that PLN 60-12 is close to full 5A load, any way you figure it. Trying to run 6 reds per light means a big-ass driver ($) or 2 x 3. My original plan was to run 4 reds per driver, with one driver split lighting the 2 "extra" leds on both lights.

How much headroom do they really need, is I guess what I'm asking.

These Mean Wells are very nicely made, BTW. :thumbsup: The trim pots that adjust voltage and current feel smooth, like a nice full size pot, and the taper is great, real smooth changes; easy to dial in.

The 12V adjusts from 10.61V to 13.27V (exactly, every time, measured with a Fluke 87) and the 15V goes from 13.21V to 16.55V.

Gonna try and post this now so I don't lose it.

[DreadedHermie]

R = E/I
So, .4/1.2 = .334 Should be .33 ohms. .34 is close enough and can be cobbled from 2 .68 ohm resistors in parallel

I get it! :clap: I was trying to "run the equation backwards" with .48ohms plugged in. I wasn't seeing any of the niumbers I was expecting....

Sorry, I'm leapfrogging posts.

If I run blues @ 15.1V:

1.2A x 15.1V= 18.12W each blue

3 x 18.12 = 54.36W

54.36W x 1.3 = 70.67W

Is that how you figure it? Is the PLN 60-15 just marginal to drive 3 blues, or are they just being real conservative?

[DreadedHermie]

Weezard, the 15.1V scenario is just hypothetical. I fried the leds that measured this way. I just wanted to know how to invoke The Law.

I've got the replacements glued on but haven't wired 'em yet. Been up all night (common problem) and I'm 6 hours ahead of you. No touchee $$$ leds till later! :stoned:

Anyway, suppose I've got a happy voltage dialed in for my blues, let's suppose these next ones want 14.8V to draw 1.2A. Here's the question: if I want to dim the blues, can I leave the voltage set where it is and just dial down the current limiter? (That way I could just eyeball the changes and not have to measure.) Or is the proper way to do this by dialing down the voltage?? Does it matter? Would one way create any more waste heat, or stress components more than the other way?

[Weezard]

Weezard, the 15.1V scenario is just hypothetical. I fried the leds that measured this way. I just wanted to know how to invoke The Law.

I've got the replacements glued on but haven't wired 'em yet. Been up all night (common problem) and I'm 6 hours ahead of you. No touchee $$$ leds till later! :stoned:

Gettin a little gun shy?

Anyway, suppose I've got a happy voltage dialed in for my blues, let's suppose these next ones want 14.8V to draw 1.2A. Here's the question: if I want to dim the blues, can I leave the voltage set where it is and just dial down the current limiter? (That way I could just eyeball the changes and not have to measure.) Or is the proper way to do this by dialing down the voltage?? Does it matter? Would one way create any more waste heat, or stress components more than the other way?

Changing the current WILL change the voltage as long as the load is relatively constant. So 6 of 1...
But with a current limit supply, it's best to vary the voltage because the current limit will keep the voltage "capped".

I'll need more coffee to respond to your earlier posts.

Solar powered 'Zard

[denialisback]

[FONT=Book Antiqua]

Solar powered 'Zard

haha no way dude tell me you aren't providing your led electricity via solar panels, because something there would seem 'just outright wrong' lol.

feds, make some do the craziest of things, I guess lol even the smart ones haha


Peace,
Denial

[Weezard]

It's posted stuff I was just trying to preview a couple times. When I tried to finish the previous post, it got eaten. :wtf:

Boards flakin' again.
Good idea to highlight and hit control-C every 5 lines or so.

Anyway, I'm back at it. Got new leds epoxied to the sink. Wired up and measured a couple reds, both of 'em almost "in the crack" between 2 voltages. About 10.6 and almost 10.9 for the other. Maybe not a problem, I may run 3 leds each on separate power supplies. That kinda depends, and I had calculated a question:

1.2A x 10.8V = 13W.
13W x 4 leds = 56 W.

NOW I read somewhere Mean Well likes 30% extra headroom (130W. of driver to push 100W.of leds) So 4 reds on that PLN 60-12 is close to full 5A load, any way you figure it. Trying to run 6 reds per light means a big-ass driver ($) or 2 x 3. My original plan was to run 4 reds per driver, with one driver split lighting the 2 "extra" leds on both lights.

How much headroom do they really need, is I guess what I'm asking.

That would depend on the stability of the input, but 10% should be sufficient because your load is constant.

These Mean Wells are very nicely made, BTW. :thumbsup: The trim pots that adjust voltage and current feel smooth, like a nice full size pot, and the taper is great, real smooth changes; easy to dial in.

The 12V adjusts from 10.61V to 13.27V (exactly, every time, measured with a Fluke 87) and the 15V goes from 13.21V to 16.55V.

With a resistive load?

Gonna try and post this now so I don't lose it.

Seems to have worked.

Aloha,
W.

[Weezard]

I get it! :clap: I was trying to "run the equation backwards" with .48ohms plugged in. I wasn't seeing any of the niumbers I was expecting....



Sorry, I'm leapfrogging posts.

If I run blues @ 15.1V:

1.2A x 15.1V= 18.12W each blue

3 x 18.12 = 54.36W

54.36W x 1.3 = 70.67W

Is that how you figure it? Is the PLN 60-15 just marginal to drive 3 blues, or are they just being real conservative?

They are more likely to run at 12.6V or so at 1.2A.
You'll be lucky to get close to 15W. ea.
Since you are not going to get more than 45W. into 3 blue leds, the PLN60-15 will be just peachy.

45W. X 1.3 = 58.5W.

Next time I score some surplus cash, I'm gettin' acouple of those Meanwells.

Just beginning to get vertical.
Weezard

[Weezard]

haha no way dude tell me you aren't providing your led electricity via solar panels, because something there would seem 'just outright wrong' lol.

feds, make some do the craziest of things, I guess lol even the smart ones haha


Peace,
Denial

Howzit, D.?

Photovoltaics are on my wish list for the whole grass shack, someday.

But, in this case, I was referring to my personal limitations.
Like my li'l green buddies, I'm slow, stiff and creaky until I warm up a bit.
Coffee helps the brain, but the carcass is gettin' old.
Takes me an hour in the hot tub and a medicine pipe to stifle my sniveling in the AM.

Regards,
Wee Ancient 'Zard