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Old 11-15-2016, 10:02 AM   #1 (permalink)
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Default leds in parralell, ran with voltage regulation. ok?

ok, so I'm back to night flying stuff again since winter is here. last year I successfully made blades and just used led strips on the rest of the heli.

this go around I'm doing it on a protos 380. much smaller than my previous setups so I don't want bulky led strips. my plan is to lay out patterns on my canopy and boom using copper tape (positive and negative running parralell to eachother), then I will apply single 0805 leds across positive and negative, all in parralell. To power it all, I'm I'm using a dc-dc adjustable converter to bring my flight pack voltage down to whatever I want. I have selected all leds with forward voltage of 3 to 3.2v.

anyone with experience know how well this will work? I know it's better to regulate current for an led rather than voltage, but I'm already looking at hours of soldering and adding a resistor to each will be a rediculous amount of extra work. im sure it will work fine, the only possible issue I see is variance in brightness from one led to another since forward voltage may not be precisely the same between them.
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Old 11-15-2016, 10:29 AM   #2 (permalink)
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Higher voltage will automatically create higher current and vice versa

You use a resistor because normally LEDs would operate on a fixed voltage and you must limit current with the resistor. But if your voltage is adjustable, you can just adjust the voltage until you have the right brightness (current).
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Old 11-15-2016, 10:43 AM   #3 (permalink)
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i understand that concept, what I'm not sure about is the consistency of the leds. I've heard that leds of the same kind can actually vary a bit in their actual forward voltage and that's why it's better to limit current so that each led has the same current, but might be varying slightly in voltage because of the slightly different forward voltages of each led. i realize i will be able to adjust voltage with the pot on the converter and in turn, they will pull more or less current/brightness. so the question is, will I likely notice differences in brightness between leds when running them all at an equal fixed voltage, and not limiting current individually with resistors. the main issue with leds is the voltage/current curve. no current flows at all up to a certain voltage, then there's a somewhat narrow band of voltage they will operate in, then any higher and they will blow. so a small difference in forward voltage could potentially give a significant difference in brightness. I guess I won't really know till I get them and test a string of them. I was just hoping maybe someone had tried this before and had a general idea of how well it works.
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Old 11-15-2016, 11:06 AM   #4 (permalink)
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What are the LED colors?
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Old 11-15-2016, 11:18 AM   #5 (permalink)
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haven't decided exactly what I'm gonna use, but I got white, blue, purple, green, all from the same manufacturer and all have a specified forward voltage of 3-3.2v. problem is, I don't know the consistency. if one led has a true forward voltage a few% different than another, it will pull more/less current and not have the same brightness, even if I'm feeding the same voltage to all of them.
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Old 11-15-2016, 11:20 AM   #6 (permalink)
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The only thing that would make a significant difference is different colors but only some are different, most are very close.

A couple % off will not be noticeable. Lots and lots of things run many LEDs in parallel.
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Old 11-15-2016, 11:27 AM   #7 (permalink)
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ok, thats what im hoping for. if one whole color is different in brightess, i can deal with that relatively easy by isolating the brighter color and adding a resistor to that parallel circuit. if its close to consistent within a color, ill be happy with that
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Old 11-15-2016, 11:33 AM   #8 (permalink)
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Yeah you won't notice. The Led strips you buy are almost always in parallel. Actually they are a mix of series in parallel (parallel sets of 3 leds in series). But you would never notice a difference in brightness.
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Old 11-15-2016, 11:49 AM   #9 (permalink)
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well, they usually have a resistor for each set of three. at least the ones I've had, but I've never seen a brightness difference within those 3 so probably be fine.
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Old 11-16-2016, 10:36 AM   #10 (permalink)
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Only thing I can offer is to use blue sparingly. I find it puts a fuzzy blue halo around my helicopter, and makes red look pink/purple. Plus at lower voltages you can eliminate the halo effect, but becomes very hard to see with contrasting colors. I just ordered soft white to swap out the blue color on my heli.

Your going to do a lot more work than just sticking some LED strips on a canopy. I would suggest doing a nighttime test with blue to see how your eyes can handle it. Just trying to save you some "redoing" work.

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Old 11-17-2016, 10:48 AM   #11 (permalink)
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What will you use to bring voltages down? I need same thing.. I did ordered some small voltage step-down boards, but I am kinda afraid will they work good to bring voltages down from 25 (6s) to 3V..
I am guessing you need same thing, from 25V (6s) to 3V?
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Old 11-17-2016, 12:08 PM   #12 (permalink)
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Quote:
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Only thing I can offer is to use blue sparingly. I find it puts a fuzzy blue halo around my helicopter, and makes red look pink/purple. Plus at lower voltages you can eliminate the halo effect, but becomes very hard to see with contrasting colors. I just ordered soft white to swap out the blue color on my heli.

Your going to do a lot more work than just sticking some LED strips on a canopy. I would suggest doing a nighttime test with blue to see how your eyes can handle it. Just trying to save you some "redoing" work.

Dave
yep, I remember that about blue. very fuzzy look without much definition to shapes. I'll probably stay away from it. mostly white and red.
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Old 11-17-2016, 12:11 PM   #13 (permalink)
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What will you use to bring voltages down? I need same thing.. I did ordered some small voltage step-down boards, but I am kinda afraid will they work good to bring voltages down from 25 (6s) to 3V..
I am guessing you need same thing, from 25V (6s) to 3V?
yep, I found some cheap dc converters on ebay. 10 of them for 8 bucks. I'm also a little concerned about the large voltage step down but I'm assuming if it's within spec, it should work ok. I'll do some long term testing on the bench to see how they hold up. the ones i got are rated for 3a and only weigh 2 grams each, so I decided I'll just use one for each color so I can adjust brightness of each color individually.
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Old 11-18-2016, 03:58 AM   #14 (permalink)
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Then probably same like mine..
http://www.ebay.com/itm/191947837264...%3AMEBIDX%3AIT
I am still waiting for some things, but almost ready to start my build..
Will watch your thread to see how these will do.. Or whoever use them first..
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Old 11-18-2016, 09:01 AM   #15 (permalink)
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yep, that's the one. originally I ordered a larger one rated for 5a but it's pretty big and weighs 16 grams. those smaller ones should show up today or tomorrow. last night I got 50 leds soldered and tested with the 5a convertor. worked flawlessly. about one full turn on the pot to go from fully dimmed to bright as hell. I'm sure the smaller converters will work just as well. definately the perfect way to power these leds. also the converter had no issues stepping down from 6s to 3v. left the 50 leds powered for about an hour and I didn't feel any heat at all.
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Old 11-19-2016, 12:56 PM   #16 (permalink)
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Quote:
Originally Posted by Che Che View Post
What will you use to bring voltages down? I need same thing.. I did ordered some small voltage step-down boards, but I am kinda afraid will they work good to bring voltages down from 25 (6s) to 3V..
I am guessing you need same thing, from 25V (6s) to 3V?
Why, instead of stepping the voltage down, you don't power the LEDs from the balance plug, so that you can directly get the voltage you need?

Never did it for LEDs, but did it to power a small fan to cool the ESC down, in that case the impact on the single cells you are pulling from was really small.
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Old 11-19-2016, 01:20 PM   #17 (permalink)
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A single LiPo cell will blow up LEDs. LEDs run on 2.5-3V. A full cell is a lot more than that. Not only that but they would be extremely bright. LEDs at full brightness are way too bright to fly with... I know from experience. I ran my night rig on 2s LiPo with LEDs made for direct 3s LiPo because 3s was blinding. A step-down lets you fine tune the brightness.
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Old 11-19-2016, 01:32 PM   #18 (permalink)
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A single LiPo cell will blow up LEDs. LEDs run on 2.5-3V. A full cell is a lot more than that. Not only that but they would be extremely bright. LEDs at full brightness are way too bright to fly with... I know from experience. I ran my night rig on 2s LiPo with LEDs made for direct 3s LiPo because 3s was blinding. A step-down lets you fine tune the brightness.
You mean a single LIPO cell will blow up THOSE LEDs. Since then you say you could run LEDs on 3S ))))

Me, I run them on 2S with a brushed motor ESC commanded from the TX so I can dim them how much I want (canopy and tail differently, actually, with two channels and two ESC s)
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Old 11-19-2016, 02:19 PM   #19 (permalink)
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Me, I run them on 2S with a brushed motor ESC commanded from the TX so I can dim them how much I want (canopy and tail differently, actually, with two channels and two ESC s)



What brushed ESC? I tried that, but it made the LEDs flicker, even at full power.
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Old 11-19-2016, 02:23 PM   #20 (permalink)
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You mean a single LIPO cell will blow up THOSE LEDs. Since then you say you could run LEDs on 3S ))))

Me, I run them on 2S with a brushed motor ESC commanded from the TX so I can dim them how much I want (canopy and tail differently, actually, with two channels and two ESC s)
The LEDs I had were in series to run on 12. 3v x 3 LEDs x 3 resistors = LED strips able to run on 12v...
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