30 LED blacklight
EEYORE, Tue Jul 25 2006, 08:43PMOk, so i just got 30 UV LEDs on ebay...While i know these arent the best quality (30 for 3$) they do infact cause stuff to flouresce nicely. They are 1000mcd units...Cause my Autunite to glow brightly, as well as my uranium glass vacuum tubes...
So here is what I want to do. While 1 is nice, I would like to use all 30 of them. I have heard paralleling LEDs is bad, but since 30 in series would require a high voltage, I am stumped. Any ideas?If possible, Id like it to portable (able to run on batteries). Im thinking either rectified mains/dropping resistor, or some kinda boost converter?
Each LED is rated at 3.6volts, and im guessing 25mA.
Thanks!
Matt
Re: 30 LED blacklight
Marko, Tue Jul 25 2006, 08:59PM
I don't think paralleling is that bad, as 30 led's isn't really some huge number.
Bigger problem would be delivering enough current from ordinary batteries (3/4 amps!) they would work but loose brightness quickly as battery dies, and then various other effects would show, led's would stop to be equal in brightness and etc.
Marko, Tue Jul 25 2006, 08:59PM
I don't think paralleling is that bad, as 30 led's isn't really some huge number.
Bigger problem would be delivering enough current from ordinary batteries (3/4 amps!) they would work but loose brightness quickly as battery dies, and then various other effects would show, led's would stop to be equal in brightness and etc.
Re: 30 LED blacklight
ragnar, Tue Jul 25 2006, 09:05PM
If you use separate dropping resistors for each LED and run them at 20mA (or even 15), they should parallel nicely. I'm not sure rectified mains / dropping resistor is the best idea, use a transformer, regulator, and a dropping resistor if you're running off the mains.
If you use rechargeable cells, three in series, you'll get 3.6V, but it's still advisable to use a resistor of some description. Running off alkalines at 4.5V, you calculate your dropping resistor for each LED as such:
(Vin - Vdesired) / (currentdraw)
e.g. one LED (4.5V - 3.6V)/0.02A = 45 ohms. Remember that the discharge curves of alkaline cells suck, and rechargeable batteries have fairly nice, flat discharge curves.
ragnar, Tue Jul 25 2006, 09:05PM
If you use separate dropping resistors for each LED and run them at 20mA (or even 15), they should parallel nicely. I'm not sure rectified mains / dropping resistor is the best idea, use a transformer, regulator, and a dropping resistor if you're running off the mains.
If you use rechargeable cells, three in series, you'll get 3.6V, but it's still advisable to use a resistor of some description. Running off alkalines at 4.5V, you calculate your dropping resistor for each LED as such:
(Vin - Vdesired) / (currentdraw)
e.g. one LED (4.5V - 3.6V)/0.02A = 45 ohms. Remember that the discharge curves of alkaline cells suck, and rechargeable batteries have fairly nice, flat discharge curves.
Re: 30 LED blacklight
EEYORE, Tue Jul 25 2006, 09:07PM
How about this idea...3 LEDs per string, and 10 strings total, all paralleled. This will let me use 12 volts, no?Sorta MMC style
"Hurray tesla!"
Matt
EEYORE, Tue Jul 25 2006, 09:07PM
Firkragg wrote ...
I don't think paralleling is that bad, as 30 led's isn't really some huge number.
Bigger problem would be delivering enough current from ordinary batteries (3/4 amps!) they would work but loose brightness quickly as battery dies, and then various other effects would show, led's would stop to be equal in brightness and etc.
I don't think paralleling is that bad, as 30 led's isn't really some huge number.
Bigger problem would be delivering enough current from ordinary batteries (3/4 amps!) they would work but loose brightness quickly as battery dies, and then various other effects would show, led's would stop to be equal in brightness and etc.
How about this idea...3 LEDs per string, and 10 strings total, all paralleled. This will let me use 12 volts, no?Sorta MMC style
"Hurray tesla!"Matt
Re: 30 LED blacklight
dan, Tue Jul 25 2006, 09:08PM
You can parallel them you just need to get 30 220ohm-ish resistors. Put one resistor in series with each of the LEDs.. Then parallel all the resistor&LED strings.
I have made a large 321 blue LED array with 107 three LED strings and only used a 2ohm 20W resistor on the supply to limit the current. I have since had to replace a few of the weaker led's that fried but it does work well off of 12v and draws ~4A from a car battery. I did it that way because I didn't want to solder 321 resistors but I will probably recover the LEDs from the board and rebuild it the correct way one of these days.
p.s. If they are the cheap ones from some seller on ebay from hongkong do expect to loose a couple over time.. they aren't all made equal and there will be some that turn out to be duds. I find about 1 in 1000 dies after an hour or so.. an 1 in 100 after 10 hours. But what do ya expect for $0.01/led
dan, Tue Jul 25 2006, 09:08PM
You can parallel them you just need to get 30 220ohm-ish resistors. Put one resistor in series with each of the LEDs.. Then parallel all the resistor&LED strings.
I have made a large 321 blue LED array with 107 three LED strings and only used a 2ohm 20W resistor on the supply to limit the current. I have since had to replace a few of the weaker led's that fried but it does work well off of 12v and draws ~4A from a car battery. I did it that way because I didn't want to solder 321 resistors but I will probably recover the LEDs from the board and rebuild it the correct way one of these days.
p.s. If they are the cheap ones from some seller on ebay from hongkong do expect to loose a couple over time.. they aren't all made equal and there will be some that turn out to be duds. I find about 1 in 1000 dies after an hour or so.. an 1 in 100 after 10 hours. But what do ya expect for $0.01/led
Re: 30 LED blacklight
rupidust, Tue Jul 25 2006, 09:30PM
Decide on a working voltage, 5, 12, 24 and work from there on. If you decide 12v, use correct amount of Leds in series just under 12v and a low value current limiter resistor so that watts will not be wasted in the current limiter. Then make parallel strings of series leds.
To hell with what is heard. Have you had any problems yourself paralleling LEDs? The main issue is the effect of heat on Leds in close proximity for long periods of time. (30) 100 milliWatt Leds is 3 watts rather it be pure 30 in parallel or combinations there of. 3 watts is nothing. And of course using 30 current limiters is questionable because at 5v the limiter may waste 35 milliWatts each totaling 1.0 watts of heat but thats 1 watt over a large surface area; therefore making no difference for a one time non production product. Parallel strings of 12v (10.8v - 1.2v current limiter) may only waste 30 milliWatts per 12v string. There in lies the rational for using high voltage strings.
Paralleling large numbers of resistors with only ONE (1) current limiter may cause a problem because ONE limiter will not compensate if one or two leds were to not function causing the remaining leds to increase in current. This is not bad for large numbers because the increase is distributed across the remaining leds. If you were to have 5+ leds die on you, then you got other problems.
1000mcd are relatively weak comparted to common 5,000 and 20,000 these days. You might want to try some 5,000mcd Leds simply because the Led count will drop about 1/5 the total.
rupidust, Tue Jul 25 2006, 09:30PM
Decide on a working voltage, 5, 12, 24 and work from there on. If you decide 12v, use correct amount of Leds in series just under 12v and a low value current limiter resistor so that watts will not be wasted in the current limiter. Then make parallel strings of series leds.
To hell with what is heard. Have you had any problems yourself paralleling LEDs? The main issue is the effect of heat on Leds in close proximity for long periods of time. (30) 100 milliWatt Leds is 3 watts rather it be pure 30 in parallel or combinations there of. 3 watts is nothing. And of course using 30 current limiters is questionable because at 5v the limiter may waste 35 milliWatts each totaling 1.0 watts of heat but thats 1 watt over a large surface area; therefore making no difference for a one time non production product. Parallel strings of 12v (10.8v - 1.2v current limiter) may only waste 30 milliWatts per 12v string. There in lies the rational for using high voltage strings.
Paralleling large numbers of resistors with only ONE (1) current limiter may cause a problem because ONE limiter will not compensate if one or two leds were to not function causing the remaining leds to increase in current. This is not bad for large numbers because the increase is distributed across the remaining leds. If you were to have 5+ leds die on you, then you got other problems.
1000mcd are relatively weak comparted to common 5,000 and 20,000 these days. You might want to try some 5,000mcd Leds simply because the Led count will drop about 1/5 the total.
Re: 30 LED blacklight
Simon, Wed Jul 26 2006, 01:47AM
When people say paralleling LEDs is bad they mean directly parallel. Making an LED resistor circuit that lights up and putting it in parallel with another is fine.
Putting LEDs in parallel directly is problematic because they are very much non-ohmic in a drifting way. They don't have fixed voltage drop per unit current relationship, so there's no way you can expect the same current to flow through the two different LEDs.
Simon, Wed Jul 26 2006, 01:47AM
When people say paralleling LEDs is bad they mean directly parallel. Making an LED resistor circuit that lights up and putting it in parallel with another is fine.
Putting LEDs in parallel directly is problematic because they are very much non-ohmic in a drifting way. They don't have fixed voltage drop per unit current relationship, so there's no way you can expect the same current to flow through the two different LEDs.
Re: 30 LED blacklight
EEYORE, Wed Jul 26 2006, 01:54AM
Well im done with it...Works really good!So bright though...I can see stuff florescing all around, but alot is drowned out by the visible part. Any way to filter out the visible spectrum?
Matt
EEYORE, Wed Jul 26 2006, 01:54AM
Well im done with it...Works really good!So bright though...I can see stuff florescing all around, but alot is drowned out by the visible part. Any way to filter out the visible spectrum?
Matt
Re: 30 LED blacklight
Bjørn, Wed Jul 26 2006, 05:42AM
Bjørn, Wed Jul 26 2006, 05:42AM
1000mcd are relatively weak comparted to common 5,000Those numbers says nothing about the amount of light it outputs so it is a fairly useless comparison unless you have other information,
Re: 30 LED blacklight
Conundrum, Wed Jul 26 2006, 09:43PM
I've had failures in el cheapo white LED's. Unfortunately it caused overcurrent in the remaining diodes causing them to also fry :(
repaired the torch as best i could (the LED's cost over £40) and so far it looks OK.
But I am going to add a failsafe and also a temp activated fan to keep things cool.
-A
Conundrum, Wed Jul 26 2006, 09:43PM
I've had failures in el cheapo white LED's. Unfortunately it caused overcurrent in the remaining diodes causing them to also fry :(
repaired the torch as best i could (the LED's cost over £40) and so far it looks OK.
But I am going to add a failsafe and also a temp activated fan to keep things cool.
-A
Re: 30 LED blacklight
HV Enthusiast, Wed Jul 26 2006, 11:55PM
I'd try a simple boost converter. (control IC, inductor, and MOSFET, and a few caps) You can monitor current through one string and use it as feedback for current regulation. Any boost design should work fine for this.
HV Enthusiast, Wed Jul 26 2006, 11:55PM
I'd try a simple boost converter. (control IC, inductor, and MOSFET, and a few caps) You can monitor current through one string and use it as feedback for current regulation. Any boost design should work fine for this.
Re: 30 LED blacklight
Marko, Fri Jul 28 2006, 11:02PM
I used to paralell LED's without resistors many times actually and had no visible differences in output power or greater current missharing.
Those were lower power normal led's altough, but I don't think you are really going to have trouble with paralelling a bunch om similar led's.
Different led's paralleled together without resistors usually cause problems. I once put a led damaged by heating paralel to about ten others (wich seemed alright) and it was noticeably dimmer.
Marko, Fri Jul 28 2006, 11:02PM
I used to paralell LED's without resistors many times actually and had no visible differences in output power or greater current missharing.
Those were lower power normal led's altough, but I don't think you are really going to have trouble with paralelling a bunch om similar led's.
Different led's paralleled together without resistors usually cause problems. I once put a led damaged by heating paralel to about ten others (wich seemed alright) and it was noticeably dimmer.
Re: 30 LED blacklight
Sulaiman, Fri Jul 28 2006, 11:44PM
For white led's I've used a (very) simple boost convertor
which worked well.
I made a 'blacklight' illuminator for my handycam and used 'constant current'
which works very well and is very simple and quite efficient
more importantly it gives constant light/uv output.
D1 to D6 are uv leds
Q1 any pnp
Q2 any npn
R1=R2=(Vled-Vbe)/Iled
OOPS ! D1 to D3 on the right should be D4 to D6
This circuit will give constant led current for 11volt supply and above
Sulaiman, Fri Jul 28 2006, 11:44PM
For white led's I've used a (very) simple boost convertor
which worked well.
I made a 'blacklight' illuminator for my handycam and used 'constant current'
which works very well and is very simple and quite efficient
more importantly it gives constant light/uv output.
D1 to D6 are uv leds
Q1 any pnp
Q2 any npn
R1=R2=(Vled-Vbe)/Iled
OOPS ! D1 to D3 on the right should be D4 to D6
This circuit will give constant led current for 11volt supply and above
Re: 30 LED blacklight
Steve Conner, Sun Jul 30 2006, 06:33PM
I like that circuit Sulaiman! It's pretty sneaky
Steve Conner, Sun Jul 30 2006, 06:33PM
I like that circuit Sulaiman! It's pretty sneaky
Re: 30 LED blacklight
Marko, Sun Jul 30 2006, 09:28PM
hm, ''many diodes make constant-current source work''.
If i'm asked, I would simply put all LED's in paralell and power them from 3x 1,2V nicd (3,6V).
I wouldn't care a lot if I have 3mcd brightness difference between two of them (for the sake of simplicity and compactness of the system).
Marko, Sun Jul 30 2006, 09:28PM
hm, ''many diodes make constant-current source work''.
If i'm asked, I would simply put all LED's in paralell and power them from 3x 1,2V nicd (3,6V).
I wouldn't care a lot if I have 3mcd brightness difference between two of them (for the sake of simplicity and compactness of the system).
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