Ok...what am I doing wrong this time? I just got my 1 watt luxeon in the mail. This is my first luxeon. I hooked up two freshly charged NiMhs that gave me a reading of exactly 3 volts on my meter. I hooked it up to the LED just to see the light...it's slighly less bright than a match. Why???
What am I doing wrong?
- Thread starter zmoz
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ufokillerz
Enlightened
max according to spec sheet is under 3.9 i believe. 3V from your 2 nimh is when it is under no load, when the luxeon draws from it, the Voltage drops alot, so its not getting much at all. I suggest 3 Nimh AA's or something else, when your running close to 3V, you get little light.
LED_ASAP
Enlightened
Noooo, please don't put 3 fresh-from-the-charger Ni-H's on a LS. You will fry it in no time. use some kind of resistor, or use 3 crappy "heavy duty" (non-alkaline) AA batteries.
Abe Furburger
Newly Enlightened
1. I test mine on a current/voltage regulated mains power supply.
2. Don't forget to heat sink it - it will fry & die...
Abe.
2. Don't forget to heat sink it - it will fry & die...
Abe.
I tried 2 fresh alkalines, slightly less than 4 volts. (I only have a 2 battery box right now) All I have to say is WOW. Right now I have that same feeling you get when you accidently see someone welding. /ubbthreads/images/graemlins/ooo.gif Ok...now I consider you people slightly less nuts... /ubbthreads/images/graemlins/wink.gif
Rothrandir
Flashaholic
as long as you are using adaquate heatsinking, and a medium to high vf luxeon, 3aa is fine /ubbthreads/images/graemlins/grin.gif
nihms will deliver a higher current, so the led could go boom.
nihms will deliver a higher current, so the led could go boom.
Rothrandir
Flashaholic
i know..i was going for dramatic /ubbthreads/images/graemlins/twak.gif
actually, it's kind of a sizzle...
actually, it's kind of a sizzle...
\"not wrong....mistaken\"
There seems to be lots of misunderstanding about how LEDs work. In what us electrical types call 'first order approximation' (simplified way of looking at a device that includes most important details) the LED is a device with known Vf and no internal impedance (resistance). It is an 'open circuit' (no current draw at all) to all voltages less than Vf, and a 'short circuit' (all the current the source can provide) to all voltages above Vf. This means go a tiny bit above the magic voltage, you draw huge currents and the device dies.
The reality is we need at least a second order approximation (adding the internal resistance, typically one ohm for the star) to the above, since it is all that controls the current in 'direct drive'. Cell and contact resistances add a fraction of an ohm, but it seems wise to only 'count on' a single ohm (unless you add some). FWIW third order approximations would include changes in Vf from current (goes up a bit with higher current) and temperature (goes down .002 volts per degree C).
Let's look at the second order direct drive? Let's assume Vf of say 3.3 Volts? 3 Volts means no current (since we're not yet to Vf). In reality, Vf is a bit 'soft', that is a very small current does flow at voltages just below it (causing the very weak glow seen). 4.5 Volts from our battery less 3.3 for Vf gives us 1.2 Volts 'across the resistor'. Ohms law sez 'current is Volts divided by Ohms'. 1.2 divided by one is 1.2 Amps! Over 3 times the "absolute maximum" rating from the maker. The numbers say that for direct drive circuits, .35 Volts in the battery is the total difference between 'no light' and 'full blast' (at least as far as maker's ratings go).
IMO, this is no way to build a reliable flashlight. Battery life is sure to suffer (it's a waste to drive it too hard), low temperature performance is poor to none (as battery voltage drops faster than Vf), light levels will dim constantly and we run a very real risk of destroying the LED with 'hot batteries', say fresh from the charger. CMG must agree as their 'direct drive' Reactor (marginal performance with two cells, 'needing' Lithium cells in most folk's opinion) picked up an extra cell *and a series 2.2 ohm resistor*. The difference between models is striking.
IMO every experimenter should get a modest DMM and use it to read the actual current he's using. The meters are simple to use and cheap and are the only real way to make informed decisions. You should also keep some external resistance in circuit to keep things under control until you're sure what's going on. It's easy enough to do. A simple way is to wrap the small value resistor in tape until it's about the same diameter and length as a AA cell (with the wire leads coming out the ends), then fold the leads over so they make contact when it's inserted in the battery holder in the place of a cell. Using a 4 cell AA holder, this allows you the possibility of 3 cells (two if you put a 'dummy' in one place).
A last thought, remember that current meters themselves have resistance, and since they're in series to be used they automatically *lower* the current in direct drive and resistor only systems as they make the reading, the real current (with them removed) will be higher still.
Or so I see it.
Cheers.
Doug Owen
There seems to be lots of misunderstanding about how LEDs work. In what us electrical types call 'first order approximation' (simplified way of looking at a device that includes most important details) the LED is a device with known Vf and no internal impedance (resistance). It is an 'open circuit' (no current draw at all) to all voltages less than Vf, and a 'short circuit' (all the current the source can provide) to all voltages above Vf. This means go a tiny bit above the magic voltage, you draw huge currents and the device dies.
The reality is we need at least a second order approximation (adding the internal resistance, typically one ohm for the star) to the above, since it is all that controls the current in 'direct drive'. Cell and contact resistances add a fraction of an ohm, but it seems wise to only 'count on' a single ohm (unless you add some). FWIW third order approximations would include changes in Vf from current (goes up a bit with higher current) and temperature (goes down .002 volts per degree C).
Let's look at the second order direct drive? Let's assume Vf of say 3.3 Volts? 3 Volts means no current (since we're not yet to Vf). In reality, Vf is a bit 'soft', that is a very small current does flow at voltages just below it (causing the very weak glow seen). 4.5 Volts from our battery less 3.3 for Vf gives us 1.2 Volts 'across the resistor'. Ohms law sez 'current is Volts divided by Ohms'. 1.2 divided by one is 1.2 Amps! Over 3 times the "absolute maximum" rating from the maker. The numbers say that for direct drive circuits, .35 Volts in the battery is the total difference between 'no light' and 'full blast' (at least as far as maker's ratings go).
IMO, this is no way to build a reliable flashlight. Battery life is sure to suffer (it's a waste to drive it too hard), low temperature performance is poor to none (as battery voltage drops faster than Vf), light levels will dim constantly and we run a very real risk of destroying the LED with 'hot batteries', say fresh from the charger. CMG must agree as their 'direct drive' Reactor (marginal performance with two cells, 'needing' Lithium cells in most folk's opinion) picked up an extra cell *and a series 2.2 ohm resistor*. The difference between models is striking.
IMO every experimenter should get a modest DMM and use it to read the actual current he's using. The meters are simple to use and cheap and are the only real way to make informed decisions. You should also keep some external resistance in circuit to keep things under control until you're sure what's going on. It's easy enough to do. A simple way is to wrap the small value resistor in tape until it's about the same diameter and length as a AA cell (with the wire leads coming out the ends), then fold the leads over so they make contact when it's inserted in the battery holder in the place of a cell. Using a 4 cell AA holder, this allows you the possibility of 3 cells (two if you put a 'dummy' in one place).
A last thought, remember that current meters themselves have resistance, and since they're in series to be used they automatically *lower* the current in direct drive and resistor only systems as they make the reading, the real current (with them removed) will be higher still.
Or so I see it.
Cheers.
Doug Owen
Gimpy00Wang
b0rk, b0rk, b0rk
- Joined
- Mar 12, 2003
- Messages
- 841
Re: \"not wrong....mistaken\"
Quite the plethora of electronic information! Good going!
- G!mpy
[ QUOTE ]
Doug Owen said:
There seems to be lots of misunderstanding about how LEDs work. In what us electrical types call 'first order approximation' (simplified way of looking at a device that includes most important details) the LED is a device with known Vf and no internal impedance (resistance). It is an 'open circuit' (no current draw at all) to all voltages less than Vf, and a 'short circuit' (all the current the source can provide) to all voltages above Vf. This means go a tiny bit above the magic voltage, you draw huge currents and the device dies.
The reality is we need at least a second order approximation (adding the internal resistance, typically one ohm for the star) to the above, since it is all that controls the current in 'direct drive'. Cell and contact resistances add a fraction of an ohm, but it seems wise to only 'count on' a single ohm (unless you add some). FWIW third order approximations would include changes in Vf from current (goes up a bit with higher current) and temperature (goes down .002 volts per degree C).
Let's look at the second order direct drive? Let's assume Vf of say 3.3 Volts? 3 Volts means no current (since we're not yet to Vf). In reality, Vf is a bit 'soft', that is a very small current does flow at voltages just below it (causing the very weak glow seen). 4.5 Volts from our battery less 3.3 for Vf gives us 1.2 Volts 'across the resistor'. Ohms law sez 'current is Volts divided by Ohms'. 1.2 divided by one is 1.2 Amps! Over 3 times the "absolute maximum" rating from the maker. The numbers say that for direct drive circuits, .35 Volts in the battery is the total difference between 'no light' and 'full blast' (at least as far as maker's ratings go).
IMO, this is no way to build a reliable flashlight. Battery life is sure to suffer (it's a waste to drive it too hard), low temperature performance is poor to none (as battery voltage drops faster than Vf), light levels will dim constantly and we run a very real risk of destroying the LED with 'hot batteries', say fresh from the charger. CMG must agree as their 'direct drive' Reactor (marginal performance with two cells, 'needing' Lithium cells in most folk's opinion) picked up an extra cell *and a series 2.2 ohm resistor*. The difference between models is striking.
IMO every experimenter should get a modest DMM and use it to read the actual current he's using. The meters are simple to use and cheap and are the only real way to make informed decisions. You should also keep some external resistance in circuit to keep things under control until you're sure what's going on. It's easy enough to do. A simple way is to wrap the small value resistor in tape until it's about the same diameter and length as a AA cell (with the wire leads coming out the ends), then fold the leads over so they make contact when it's inserted in the battery holder in the place of a cell. Using a 4 cell AA holder, this allows you the possibility of 3 cells (two if you put a 'dummy' in one place).
A last thought, remember that current meters themselves have resistance, and since they're in series to be used they automatically *lower* the current in direct drive and resistor only systems as they make the reading, the real current (with them removed) will be higher still.
Or so I see it.
Cheers.
Doug Owen
[/ QUOTE ]
Quite the plethora of electronic information! Good going!
- G!mpy
[ QUOTE ]
Doug Owen said:
There seems to be lots of misunderstanding about how LEDs work. In what us electrical types call 'first order approximation' (simplified way of looking at a device that includes most important details) the LED is a device with known Vf and no internal impedance (resistance). It is an 'open circuit' (no current draw at all) to all voltages less than Vf, and a 'short circuit' (all the current the source can provide) to all voltages above Vf. This means go a tiny bit above the magic voltage, you draw huge currents and the device dies.
The reality is we need at least a second order approximation (adding the internal resistance, typically one ohm for the star) to the above, since it is all that controls the current in 'direct drive'. Cell and contact resistances add a fraction of an ohm, but it seems wise to only 'count on' a single ohm (unless you add some). FWIW third order approximations would include changes in Vf from current (goes up a bit with higher current) and temperature (goes down .002 volts per degree C).
Let's look at the second order direct drive? Let's assume Vf of say 3.3 Volts? 3 Volts means no current (since we're not yet to Vf). In reality, Vf is a bit 'soft', that is a very small current does flow at voltages just below it (causing the very weak glow seen). 4.5 Volts from our battery less 3.3 for Vf gives us 1.2 Volts 'across the resistor'. Ohms law sez 'current is Volts divided by Ohms'. 1.2 divided by one is 1.2 Amps! Over 3 times the "absolute maximum" rating from the maker. The numbers say that for direct drive circuits, .35 Volts in the battery is the total difference between 'no light' and 'full blast' (at least as far as maker's ratings go).
IMO, this is no way to build a reliable flashlight. Battery life is sure to suffer (it's a waste to drive it too hard), low temperature performance is poor to none (as battery voltage drops faster than Vf), light levels will dim constantly and we run a very real risk of destroying the LED with 'hot batteries', say fresh from the charger. CMG must agree as their 'direct drive' Reactor (marginal performance with two cells, 'needing' Lithium cells in most folk's opinion) picked up an extra cell *and a series 2.2 ohm resistor*. The difference between models is striking.
IMO every experimenter should get a modest DMM and use it to read the actual current he's using. The meters are simple to use and cheap and are the only real way to make informed decisions. You should also keep some external resistance in circuit to keep things under control until you're sure what's going on. It's easy enough to do. A simple way is to wrap the small value resistor in tape until it's about the same diameter and length as a AA cell (with the wire leads coming out the ends), then fold the leads over so they make contact when it's inserted in the battery holder in the place of a cell. Using a 4 cell AA holder, this allows you the possibility of 3 cells (two if you put a 'dummy' in one place).
A last thought, remember that current meters themselves have resistance, and since they're in series to be used they automatically *lower* the current in direct drive and resistor only systems as they make the reading, the real current (with them removed) will be higher still.
Or so I see it.
Cheers.
Doug Owen
[/ QUOTE ]
Re:
My personal recommendation is the Constant Current driver Mr. Al suggested some months back. I've built quite a number of them lately, with no problems found. Using a LM 334, a PNP transistor 3 resistors and a small capacitor. Properly set up, these have a drop out of less than .1 volt over Vf of the LED.
For reasonable Vf values (say under 3.5 Volts), this gives us very high efficiency (typically 90%) and nearly full capacity from 3 NiMH cells. The one I have waiting for my 5 Watters (come on Wayne!!) is set up for six cells for a nominal 7.5 volts. While a bit more complex than a simple single additional resistor it provides full features (constant light output, safe operation, long run time, etc.) an efficiency unmatched by (almost?) any other setup.
Otherwise the 2.2 ohms used by CMG in the updated reactor limits maximum current to safe (enough) levels with 3 NiMH or Alkaline cells. Not optimum, but serviceable.
Cheers.
Doug Owen
My personal recommendation is the Constant Current driver Mr. Al suggested some months back. I've built quite a number of them lately, with no problems found. Using a LM 334, a PNP transistor 3 resistors and a small capacitor. Properly set up, these have a drop out of less than .1 volt over Vf of the LED.
For reasonable Vf values (say under 3.5 Volts), this gives us very high efficiency (typically 90%) and nearly full capacity from 3 NiMH cells. The one I have waiting for my 5 Watters (come on Wayne!!) is set up for six cells for a nominal 7.5 volts. While a bit more complex than a simple single additional resistor it provides full features (constant light output, safe operation, long run time, etc.) an efficiency unmatched by (almost?) any other setup.
Otherwise the 2.2 ohms used by CMG in the updated reactor limits maximum current to safe (enough) levels with 3 NiMH or Alkaline cells. Not optimum, but serviceable.
Cheers.
Doug Owen
tvodrd
*Flashaholic* ,
Re:
Doug,
WOw, for some of us with a *little* electronics comprehension, cutting through the BS, and getting to the "real world" /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif
Larry
Doug,
WOw, for some of us with a *little* electronics comprehension, cutting through the BS, and getting to the "real world" /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif
Larry
Re:
[ QUOTE ]
Doug Owen said:
My personal recommendation is the Constant Current driver Mr. Al suggested some months back. I've built quite a number of them lately, with no problems found. Using a LM 334, a PNP transistor 3 resistors and a small capacitor. Properly set up, these have a drop out of less than .1 volt over Vf of the LED.
For reasonable Vf values (say under 3.5 Volts), this gives us very high efficiency (typically 90%) and nearly full capacity from 3 NiMH cells. The one I have waiting for my 5 Watters (come on Wayne!!) is set up for six cells for a nominal 7.5 volts. While a bit more complex than a simple single additional resistor it provides full features (constant light output, safe operation, long run time, etc.) an efficiency unmatched by (almost?) any other setup.
Otherwise the 2.2 ohms used by CMG in the updated reactor limits maximum current to safe (enough) levels with 3 NiMH or Alkaline cells. Not optimum, but serviceable.
Cheers.
Doug Owen
[/ QUOTE ]
Where might I find plans for one of those? /ubbthreads/images/graemlins/smile.gif
[ QUOTE ]
Doug Owen said:
My personal recommendation is the Constant Current driver Mr. Al suggested some months back. I've built quite a number of them lately, with no problems found. Using a LM 334, a PNP transistor 3 resistors and a small capacitor. Properly set up, these have a drop out of less than .1 volt over Vf of the LED.
For reasonable Vf values (say under 3.5 Volts), this gives us very high efficiency (typically 90%) and nearly full capacity from 3 NiMH cells. The one I have waiting for my 5 Watters (come on Wayne!!) is set up for six cells for a nominal 7.5 volts. While a bit more complex than a simple single additional resistor it provides full features (constant light output, safe operation, long run time, etc.) an efficiency unmatched by (almost?) any other setup.
Otherwise the 2.2 ohms used by CMG in the updated reactor limits maximum current to safe (enough) levels with 3 NiMH or Alkaline cells. Not optimum, but serviceable.
Cheers.
Doug Owen
[/ QUOTE ]
Where might I find plans for one of those? /ubbthreads/images/graemlins/smile.gif
Time to fess up....
I guess it's time to let ya in on a bit of a secret, I've taught this good stuff (part time) for more years than I care to confess to.....
Al's circuit is here on CPF, somewhere, and while I'm not at all good at such stuff, I'll try to find it. Perhaps a search on "LM 334"?. Anyway it's taken directly off the spec sheet for the device (always a good place to go, the maker wants engineers to use his parts, he makes it easy......). You can see the sheet on the Jameco web site (highly recommended for mail order parts, BTW) at: <http://www.jameco.com/Jameco/Products/ProdDS/23739.pdf> . Go to page 8, the "typical applications" section (always interesting IMO) and check out the 'higher output current' example. 2.2 ohms for R(set), 1,000 for R1 and .1 micro farad for C1 have worked super for 30 mA drive on 'Supor White 5 mm LEDs', The LED goes instead of the line connecting C1 and R(set) (in series with the transistor collector). I've been changing the transistor to a slightly higher capacity part (2N4918, 19 or 20 also from Jameco for under half a buck) and a hand wound R(set) made of about 2 feet of 30 AWG wire wrap wire for Luxeon LEDs. You can start long and 'cut and try' it until you get the current you want. For margin I tend to set it at 320 or so mA,
The LM 334 comes as a 'TO-92' case part, a small 3 lead transistor package, the same as the 2N3906, making the entire circuit easily 'sugar cube size' or smaller. Total parts cost is under $2, exclusive of LED and battery.
Paying attention to the possible need to add a heatsink to the transistor, cutting the R(set) wire in half and raising the cell pack to 6 (nominal 7.2 Volts) or perhaps even 7 depending and you're 'good to go' with 5 Watt Stars if they ever get here (come on Wayne!).
The neat thing about this circuit is the transistor makes up sort of a 'smart resistor' that changes it's effective resistance as needed (according to the IC regulator, LM 334) to maintain the proper current in the LED no 'matter what the battery voltage'. In reality, too high a voltage is a waste and only heats the transistor, and the circuit 'runs out of gas' when the battery gets very close to the voltage the LED needs (properly done this is less than .1 Volt). NiMH cells are a great fit here. Since at reasonable current draw then can easily stay above 1.15 volts until the bitter end, this means we can support a 3.35 Vf LED at almost 100% efficiency. At this point, a higher Vf diode will still get almost full current, probably not possible to detect the difference by eye.
Works a treat as the Brits would say, give it a lash.....
Cheers.
Doug Owen
I guess it's time to let ya in on a bit of a secret, I've taught this good stuff (part time) for more years than I care to confess to.....
Al's circuit is here on CPF, somewhere, and while I'm not at all good at such stuff, I'll try to find it. Perhaps a search on "LM 334"?. Anyway it's taken directly off the spec sheet for the device (always a good place to go, the maker wants engineers to use his parts, he makes it easy......). You can see the sheet on the Jameco web site (highly recommended for mail order parts, BTW) at: <http://www.jameco.com/Jameco/Products/ProdDS/23739.pdf> . Go to page 8, the "typical applications" section (always interesting IMO) and check out the 'higher output current' example. 2.2 ohms for R(set), 1,000 for R1 and .1 micro farad for C1 have worked super for 30 mA drive on 'Supor White 5 mm LEDs', The LED goes instead of the line connecting C1 and R(set) (in series with the transistor collector). I've been changing the transistor to a slightly higher capacity part (2N4918, 19 or 20 also from Jameco for under half a buck) and a hand wound R(set) made of about 2 feet of 30 AWG wire wrap wire for Luxeon LEDs. You can start long and 'cut and try' it until you get the current you want. For margin I tend to set it at 320 or so mA,
The LM 334 comes as a 'TO-92' case part, a small 3 lead transistor package, the same as the 2N3906, making the entire circuit easily 'sugar cube size' or smaller. Total parts cost is under $2, exclusive of LED and battery.
Paying attention to the possible need to add a heatsink to the transistor, cutting the R(set) wire in half and raising the cell pack to 6 (nominal 7.2 Volts) or perhaps even 7 depending and you're 'good to go' with 5 Watt Stars if they ever get here (come on Wayne!).
The neat thing about this circuit is the transistor makes up sort of a 'smart resistor' that changes it's effective resistance as needed (according to the IC regulator, LM 334) to maintain the proper current in the LED no 'matter what the battery voltage'. In reality, too high a voltage is a waste and only heats the transistor, and the circuit 'runs out of gas' when the battery gets very close to the voltage the LED needs (properly done this is less than .1 Volt). NiMH cells are a great fit here. Since at reasonable current draw then can easily stay above 1.15 volts until the bitter end, this means we can support a 3.35 Vf LED at almost 100% efficiency. At this point, a higher Vf diode will still get almost full current, probably not possible to detect the difference by eye.
Works a treat as the Brits would say, give it a lash.....
Cheers.
Doug Owen
Mr. Al\'s circuit
It turns out it's on a different forum, the electronics one...makes sense.
Anyway the thread is called "votage regulation question" back in December. Try <http://www.candlepowerforums.com/ub...ber=94719&page=&view=&sb=5&o=&fpart=all&vc=1> .
Cheers.
Doug Owen
It turns out it's on a different forum, the electronics one...makes sense.
Anyway the thread is called "votage regulation question" back in December. Try <http://www.candlepowerforums.com/ub...ber=94719&page=&view=&sb=5&o=&fpart=all&vc=1> .
Cheers.
Doug Owen
LEDmodMan
Flashaholic*
Re: Mr. Al\'s circuit
Doug,
What you have said is great information, thanks for posting it. I haven't been out of college for too long, and I remember my EE 2 and control theory courses pretty well. When I was first thinking about modding some lights, I was all about taking the theoretical approach like you have and building the electronic controllers, regulators, and such. These are great and certainly have their place (I love my MadMax) for constant current or voltage delivery over the life of the batteries. However, direct drive mods with the LS don't tend to behave quite like one would expect. You can 'direct drive' overdrive a 5 watt LS on 9 volts to about 10 watts without any problems as long as you heatsink it well enough (maybe sacrificing life, but that's yet to be seen). I thought I would just post here that I agree fully with everything you have said here, but that sometimes not everything behaves like you'd initially expect.
Doug,
What you have said is great information, thanks for posting it. I haven't been out of college for too long, and I remember my EE 2 and control theory courses pretty well. When I was first thinking about modding some lights, I was all about taking the theoretical approach like you have and building the electronic controllers, regulators, and such. These are great and certainly have their place (I love my MadMax) for constant current or voltage delivery over the life of the batteries. However, direct drive mods with the LS don't tend to behave quite like one would expect. You can 'direct drive' overdrive a 5 watt LS on 9 volts to about 10 watts without any problems as long as you heatsink it well enough (maybe sacrificing life, but that's yet to be seen). I thought I would just post here that I agree fully with everything you have said here, but that sometimes not everything behaves like you'd initially expect.
