We Dont Need No Stinking Resisters

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**DONOTDELETE**

Guest
I have a few questions that somone here may have already learnt.

how many LEDs (assume white nitchitas) can be placed on 3 alkiline AA batteries w/o any resisters by using the internal resistance of the battery. In other words, how many does it take so the batteries cannot put out enought current to blow the array from overcurrent?

then the same thing for 4 AAs is it possible to have say 40 white leds on 4 AAs and not need current limiting?

Along those same lines, if the battery is being torqued to 3.8v say from its original of 4.5, it probably isnt going to last long eh?

the reason i ask is because the photon works great at its 6v little batteries for a usefull lenght of time, and a lexeon star can run off of 3AAs without toasting.
so if we had volume formulas for internal battery resistance, instead of formulas for loosing power out a resister that isnt outputting light, then we "dont need no stinking resisters"

is there any such substance that is completly reflective (mirror/foil) without being conductive? the purpose being to use it on the back of a array pcb , without fighting it to keep from shorting stuff.
Mylar is conductive unfortunatly, and most of the metal paints are also.

I performed a TOUCH light conversion this week, i had a touch light make me angry so i tore it open and tossed in a bunch of old hacked up leds that should have been in the trash. the touch lite uses 6v 4AAs.
in this case i combined 2.4v leds (red redorange yellow) with 3.6v leds (white turquoise) 2.4+3.6=6 :)
the array has about 26 leds in it and puts out the same volume of light through the heavy difusion for 1/2 the power of the incadescent.

so using this same idea take like a amber or redorange and tie a cyan to it, and you get a spectum that will show most colors and instantally work with 6v, use 2 banks and you get 12v , simplicity & reduced componentry is like building a pyramid instead of a skyscraper :)
 

jeff1500

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Somewhere I saw a website where someone was running an led at 100 mA just to see how long it would last. I think it was some kind of survival equipment site.

I think at higher current flow all the electricity just gets wasted anyway. They make mostly light up to 20 mA then after that the light output stays about the same but then they start making lots of waste heat.

You could put a bunch of leds in parallel and then just use one resistor to adjust the current to the whole batch. Then you just got one stinkin' resistor.
 
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**DONOTDELETE**

Guest
he he
but surely there is an ammount of 5mm whites that can be put on 3 alkaline AA batteries and have them running at about 20-40ma each

sombody must know, once i saw a chart somone had on the battery internal resistance, to much math for me, but it might help.

untill then i will keep using the perfectally matched voltages of the NMHY batteries, with the leds.
 

LED-FX

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"is there any such substance that is completly reflective (mirror/foil) without being conductive? the purpose being to use it on the back of a array pcb , without fighting it to keep from shorting stuff.
Mylar is conductive unfortunatly, and most of the metal paints are also."


Haven`t worked out the quptes thing on this board yet.....anyone care to explain?

Reflective film, you`ll be wanting Radiant Mirror Film from 3M:
http://www.3m.com/about3M/technologies/lightmgmt/product s_solutions/tech/visible_mirror_tech/visible_mirror_tech.jhtml

They do a sample kit with some of this in it.
Its non conductive and ,I think, the most reflective substance available beating glass mirror.

And guess this should have gone in under your thread about your Video light but could you tell me a bit more about the colour balance with white leds, noticed you had to add other colour to balance it to white?

Adam
 

php_44

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Apr 4, 2001
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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Video Guy:
I have a few questions that somone here may have already learnt.

how many LEDs (assume white nitchitas) can be placed on 3 alkiline AA batteries w/o any resisters by using the internal resistance of the battery. In other words, how many does it take so the batteries cannot put out enought current to blow the array from overcurrent?
.....
so if we had volume formulas for internal battery resistance, instead of formulas for loosing power out a resister that isnt outputting light, then we "dont need no stinking resisters"
<HR></BLOCKQUOTE>

If you don't put the resistors in yourself - you're using the battery as a resistor. Batteries as resistors are very messy and unpredictable. If interested read on...

A while back I did some research on a few battery web sites. I had a different idea in mind - I was designing a conversion with a switching power supply and wanted to choose the number of batteries to minimize size/cost and maximize life. I plowed through pages of discharge graphs for AA cells from different manufacturers, and different cells from the same manufacturer.

Here's what I discovered about alkaline cells - particularly "AA" types.
<UL TYPE=SQUARE><LI>Cell resistance for fresh cells can be as low as 0.08 ohm to as high as 0.5 ohm depending
on make and manufacturer (ie- duracell (regular, ultra, etc), energizer, rayovac, radio shack, etc).
<LI>Cell resistance increases quickly as cells discharge, does not increase linearly, varies by manufacturer,
and depends highly on how fast you discharge the cell (worse at higher discharge). This is exactly why LED lights without switching power supplies look great for a short amount of time, spend a long time at a drooping mediocre brightness, then run for a very long time at low light levels. In this mid life mode - cells can have 0.1-0.85 ohms of cell resistance that is continually rising.
<LI>Cell Capacity (how many amp-hours you can wring out of a cell) is MUCH higher when you discharge the cells at a reasonable rate (like 2.8AH@25mA, 1.6Ah@300mA, or 1AH @ 1000mA).
<LI>You get the most life for your money by taking the cell down to at 0.8V or lower at which point the cell resistance is in the ballpark of 0.7-3 ohms at a draw of 100mA or so.
<LI>If you need to discharge the cell at a high rate (like 500mA+) then Lithium cells offer the most capacity while suffering the least amount of capacity loss in this situation - though you pay for it in $$ spent. You can begin to justify rechargables (like NiCd or NiMH) but they have less than half the capacity of alkaline or Lithium.
[/list]

Basically - I came to the conclusion that I'd get the most for my money by mostly using a AA cell at around 150mA feeding a switcher to supply constant current to the LEDs till the cells were too dead to run the switcher. This is how the ARC or ARC-LS, and several home built lights from folks in this forum work. My 2-cell AA aluminum body light, and my 4-AA cell 12 LED (turtle light style) dimmable light both have boost style switchers. I run my LEDs at 20-35mA and they stay at the same brightness till the AA's are nearly dead then drop off rapidly (my warning to replace the batteries). My two cell boosted light runs the LED at 35mA, gets used every day for a half an hour+, and goes a half a year+ on AA's.

Running my LEDs this way will allow them to last their predicted lifetime with little degradation in performance. As MrAL pointed out - LEDs like to be fed current not voltage (because a LEDs operating voltage varies with LED color/chemistry, temperature, production batch, how much current you're running through them, etc).

Here's what I discovered about rechargable cells - "AA" types.<UL TYPE=SQUARE><LI>Internal resistance of NiMH AA cells is about 0.03 ohms charged and about 0.04-0.05 ohms 1/2 discharge, rising rapidly near full discharge when the cell voltage drops like a rock.
<LI>Internal resistance of NiCd AA cells is about 0.02 ohms charged and about 0.03-0.04 ohms 1/2 discharge, rising rapidly near full discharge when the cell voltage drops like a rock.
<LI>Mostly - NiCD and NiMH cell capacity is not affected by how fast you discharge them as long as you are not drawing >2-3 amps.
<LI>You quickly and permanently loose capacity if you over discharge these cells, or if you grossly or habitually over charge them.
[/list]

Bottom line - Build a switcher!!!!!
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PS - Duracell specifically recommends that their alkaline cells perform best in constant power discharge (switching supply) where the initial current is low and increases as the battery voltage dives toward 0.8 or lower.

PS - for those making switchers - the above data clearly shows why NiMH or NiCd's do not require an input capacitor while Alkalines benefit quite a bit due to their higher internal resistance.
 

remuen

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by jeff1500:
I think at higher current flow all the electricity just gets wasted anyway. They make mostly light up to 20 mA then after that the light output stays about the same but then they start making lots of waste heat.<HR></BLOCKQUOTE>

Sorry Jeff, that's not correct in this way. Driving a LED with a higher current will give a higher light output. But the light is not proportional to the current. I don't have excact figures but if you increase the current eg. from 20mA to 40mA (= 100% increase of the current) the light output will increase only about 50%.

But in the other point you're absolutly right: Some of the additional energy (in this example the 50% 'unused' increase of the current) will only cause heat and then you have to take the thermal runaway in account.

Conclusion: 2 LED's driven with 20mA are brighter than 1 LED with 40mA = higher efficiency.
 

remuen

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by jeff1500:
I've always wondered what the maximum safe current level is. I've got dimmer working but I don't know what to set the maximum current value to. I've been limiting it to about 25 mA.

Here's a good graph of light output (luminous intensity) vs. current.
http://www.ResurgentSoftware.com/Perfect_LED_Light.html
<HR></BLOCKQUOTE>

Some really good technical informations about LED's ....!

I think you can go up to 40mA without any problems. I set the current in my LT1613 prototype to 33mA. With this current the LED's get a bit warm but not hot.
 
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**DONOTDELETE**

Guest
great PHP that was the info i seeked.
looks like the "internal resistance" isnt very high ever, much lower than i expected.

so i still dont know HOW MANY whites does it take to get to the center of a battery?
ahh math i knew it would come to that.


the batteries sure prefer to be discharged at slow rates, even the lithium, course the Nimy's love it :)

some of the stats we have though are based on for some reason running the flashlight for days, and my uses arent like that, they are more akin to an alkiline, use it for a while, then let it sit, then use if for a while.
and
A light that slowly decreases and therfore uses less power would be an advantage for a lot of situations that flashlights are used. the human goes into a more conservative use, eyes have adjusted to the darkness and of course the always occuring somebody left the darn thing on :)

gotta think of all the positive sides :)

but i gotta agree that running the led at Optimum currents is the most efficient, and more leds run slower is better,and the heat is usually the waste product.

by the time they actually BURN out though , somehow I guarentee that we will know of a new wizz bang version of them :)
 
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**DONOTDELETE**

Guest
Hey led thanks for the link
and the "sample" pack looks like its actually affordable this time :)

I will plug it into the wall socket for the first trial and make sure it isnt conductive :)
 

LED-FX

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Jul 23, 2001
Messages
630
Location
Edinburgh UK
Its definately non conductive,used it myself in couple of appliactions directly over pcb,cut crosses for LEDs to poke through.

It also increases apparent brightness of GID pigments coated over it.

Its a very thin material similar to alumninised mylar.

And its rated as the most reflective substance in the world,makes my day :)

Any more info on colour balance of white LEDs used for video,even in another thread?

Thanks

Adam
 
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**DONOTDELETE**

Guest
Led
oh thats right i was getting to that.

these are observations, i use no meters.

as we all know a "white" Led is a blue led with some yellow phosphors.
this leaves a slight color hole in the cyan and the red parts of the spectrum, this can be seen on the wavelenght spectrum for the whites.
a specturm chart is available on the link that jeff supplied , along with the current voltage vrses output specs (thanks jeff love that big one :)
the chart might not be the same Numbers for all the whites but the same basic pattern exists.

The cameras i am trying to light for actually use 3 dichromatic(whatever that means) filters and 3 tubes, so in reality it sees 3 colors red green blue.

course you take into acount that at least twice the whole system of recording and making it to a vhs tape uses YUV which is kinda similar to the controls on your television hue level of color and brightness levels, which is actually green/blue & red adjustment capacity, ok that just about complicates it :)

so i try (note try as i am on hands experimentor) to balance out the deficiencies of the blue by adding cyan (which the bright cyans are Lots of green)
and by adding red, the red also counters the green. so you end up with a total white light (well still kinda blueish)
which works out great to balance with outdoor lighting.

then comes trying to match indoor lighting, which is excessivly yellow, almost like a yellow led in total, and very much like the yellow phosphors in the whites.

it seems like countering the blue with the yellow is very hard in the design i am working on, i can see that almost 2 for one is going to be nessisary, as the Output levels of the yellow arent reallly up to par for the rest of the advancements, WHO really wants a super bright yellow? they want a super bright AMBER for turn signals and all.

which brings up how much red is in amber to the camera, as we all know most of the ambers have that red ring almost like they are red leds that are side tossing the red.
the ambers punch so much red into the red tube, that it oversaturates the red quickly , without adding much yellow.

what the heck is yellow to an rgb camera , mabey i need to think about that.


then it brings up the fact that red and blue on the camera are not used for luminescence the green is, and the red and blue is so dark to the chips that i would bet they are not driven as hard at all, and that it is boosted or compensated for in its combining circuitry.
an example of this is seperating out the 3 in photoshop you will notice that the blue and the red usually have the worst picture in them, its kinda dark and grainey.

but i am not altering the cameras, just working with what is there.

so the whites are way to blue, but are lots of LIGHT (the only reason for concidering it) one could potentially use RGB lighting but rgb never had the output level of the whites.
and rgb is not as easily balancable for the different types of light, running simple blues with the holes in the spectum filled could fill light spilling from outdoors, and lowering that as a WHOLE and adding loads of yellow in (not amber or yellow green) could potentailly set it for incadescent.

oops what was the question :)

doggone now i ran out of time
why i am not using rgb, cause the rgb leds are 9$ and the whites were supposed to be white right ?? and that is what got me roped into it, the smooth foreward 20* pattern of the whites, as the camera views about 20* foreward, made a great light.
add that to the horrible patterns that are in most leds.

but after writing this i am thinking that seperate interleaved rgb banks of 30* good optical lights might just do the trick.

How would i make YELLOW from rgb to balance for incadescent , Ahh that was and still is the problem, a rgb system would still need 5 leds, how would you make rgb more yellow when them 3 leds dont have much yellow spectrum in them.
so some of it was because i thought i could do it with 2 the Whites and the yellows.
i would bet i still can.

then there is yellowing the wonderfull whites, something else i tried base on some cool ideas here, using the top of turtle wax container and solventing its phosphorus plastic, then diping the head of the white into it, made the white more yellow, but of course the pattern is still more yellow on the edge blue spot in the center.
but in large banks this might just work.

then out of frustration and out of time, the design that you saw has a flip down hood on it, that offers some diffusion, because its to spotty when the camera is full wide, and a slight yellow filter ( the floral wrap stuff from the craft store) to fix it quick and to be able to use it on the job i had that week.

that is why i come here, i want everyone to fix it for me, so i can just put in what they say and have it magically work the first time, poor leds have been through the solder wringer.

also diffusion NEXT to the leds, stopped the heat from flowing out the front of the leds, and toasted them at the high drive levels i was runnign them at, so the flip down hood NOW is a whole inch away from the face of the led, running at the same level they dont overheat.
 
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