2xAA / 1000mA Driver?

KowShak

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Since nobody makes the light I want, I've decided to make my own. Right now I'm looking for a driver that'll run a Cree XR-E or a SSC P4 at 1000mA off a pair of NiMH batteries.

The one that seems to be the obvious choice at DX (sku.15880) seems to be on back order with no ETA and the not so obvious alternative (sku.7882) is on back order too. Does anybody know the SKUs at KD for something that'll do the same sort of job? Alternatively anywhere else thats competitively priced?

Thanks
 

Greg G

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With a 2AA NiMH setup I would limit current to about 700ma. There isn't much visible increase in light going from 700ma to 1000ma. You can get a Madmax Plus from the Sandwich Shoppe for 700ma current.

If you must have 1000ma, I'd probably go the Li-Ion route (14500), and use a good buck converter, like an SOB 1000, also from the Sandwich shoppe.

It will also help to have a good low Vf emitter. All of the Seoul U2SWOH emitters I've bought from Photonfanatic were low. If you want a low Vf Cree XR-E you'll have to buy a few and hand pick one by checking them on a power supply.
 

KowShak

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That sandwich shoppe driver looks like the sort of thing I'm after but its more than twice the price of the DX driver I was looking at and doesn't have the multi-modes. Efficiency looks good, I'm guessing that the cheaper step up circuits will have to rape the batteries to get 1000mA at the stepped up voltage because they're less efficient. I don't think that the 1000mA will be a problem if I get a multi-mode driver because I can always run in low mode to conserve battery life when I don't need the brightness.

I have two aims to the project, one is to be bright and throw as far as possible. The other aim is to use NiMH AA batteries that I've got a load of (and a charger for) and that I replace with alkaline if I get stuck.
 

Greg G

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I think you're asking for a lot out of a 2AA NiMH light, but I wish you the best of luck.

Keep us posted on your progress. :twothumbs
 

KowShak

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I've had a look around CPF and found some a thread about NiMHs, it had a link to a pdf document with discharge curves for some Energiser NiMH cells.

The thread
https://www.candlepowerforums.com/posts/2642382&postcount=24
The data sheet
http://data.energizer.com/PDFs/nh15-2000.pdf

According to that data, an AA NiMH cell will output 1000ma from the cells for 2 hours, or 2000ma for about 1 hour. To feed 1000ma to the emitter at lets say 3.6V would need 3.6W plus whatever power the boost circuit and regulator waste.

For a driver that is 66% efficient it will need 5.5W going into it to produce 3.6W out at the correct voltage. Assuming that the NiMH will produce a constant 1.2v over its discharge cycle (in reality it doesn't, the voltage sags as the cell discharges) it will need produce 2300ma of current at 1.2v to produce 5.5W. In reality the voltage will sag so the regulator would have draw more current from the cell to maintain a constant 1000ma to the emitter, the upshot of all this is that with reasonably good NiMH cells the runtime on full power would be perhaps 45 minutes.

Going through the maths for the Sandwich Shoppe Madmax, at 76% efficiency (worst case) and 88% (best case) means drawing between 1380ma and 1190ma which would give much better runtime at least double the runtime at 1000ma to the emitter. 1000ma to the emitter can be done but its going to kill the runtime compared to 800ma, which wouldn't be a lot dimmer. Unfortunately the Maxmax doesn't have the multiple modes I want and its expensive, I'm not in the US so postage on top is expensive too!

I still need a boost circuit, one that does 3W and has lots of modes to play with. Its going to have to be something cheap (and nasty) from DX or KD, I just need somebody to recommend me a SKU!
 

LEDninja

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Whoa!
Careful with your battery selection.

Look at these 2 output graphs:
Energizer 2300 mAh
EnergizerAA2300variousRates2.jpg


Eneloop
EneloopAA2000atVariousRates2.jpg


With 1000 mA at 3.6V output you need 1500 mA at 2.4V input.
The Energizer can not maintain 2.4V (1.2V/battery) even at 500 mA.
The Eneloop can maintain 2.4V (1.2V/battery) up to 2000 mA.
The Energizer might be fine for powering low end minimag drop-ins such as the SMJLED/Terralux TLE-20 but for what you are doing I would be more careful making sure the battery can provide the amps as well as the mAh.

Here are Silverfox's test results for NiMH batteries:
https://www.candlepowerforums.com/threads/79302
Check there before you buy your batteries!
 

KowShak

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With 1000 mA at 3.6V output you need 1500 mA at 2.4V input.

That assumes that the driver is 100% efficient, in reality its not going to be that efficient e.g. Sandwich Shoppe quotes two figures for efficiency for the Madmax, 76% efficiency at volts and 88% at 3.0 volts. I would guess that 2.4 volts would be somewhere between the two for efficiency, I've seen figures of less than 50% for some single AA drivers. 50% efficiency would mean I'd need to draw 3000ma from the cells and that would really be pushing the limits.

There are several real strong 2 AA lights on the market now.

There are several lights that throw really well and run on 2AA cells but to get a really small and intense hotspot you need a bigger diameter reflector than almost all 2AA lights have and of course this is the "Homemade and Modified" section after all!
 

Essexman

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I have good news and bad news.......

First the good - this question has been asked before, here, here, here, and you may find this thread a good read.

now the bad - you may have trouble finding what you want! Let us know how you get on.

If you are looking to use a larger dia reflector what host do you plan to use ?

I was thinking of something similar a while ago. I looked at this DIY kit from DX. Instead of 3 CR123 you could use 2 AA's (almost the same length by chance!), nice big reflector. You just need to find a suitable driver ...............
 

KowShak

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you may find this thread a good read.
Thanks for that, I think that thread pretty much answers all of the questions I haven't thought to ask yet!
If you are looking to use a larger dia reflector what host do you plan to use ?

I've got a couple of potential choices at DX. Sku 14972 takes 3AAs but has a removable extension that looks like its about the length of an AA. It'll get an LED upgrade and of course an uprated driver. The reflector and lens are big and deep (50mm diameter) but probably plastic but they can be replaced if required.

sku 7613 is a 2x18650 light with an extension that can be removed to make it take 3xCR123A which would take it down to target length but the reflector isn't as large as sku 14972. Reflector is not as big as above (40mm diameter perhaps) and has a flat area at the rear which I don't really like.

I've definately got some possibilities but I'm open to any sensible suggestions too! There are quite a few single 18650 lights that I'm tempted by but I'd need some sort of "universal" CR123a extension for them.
 
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HarryN

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If you like the AA format and are a bit open to non-traditional thought, there is another option - change the light color.

White is certainly what we first think of when talking about flashlights, but from an eye sensitivity and power efficiency viewpoint, red/orange (about 615 - 620nm IIRC) will just blow it away. There is a really good reason why traffic lights (red/orange) switched to LED so quickly, and white general lighting has not - the power savings were just enormous.

A very simple setup that is just amazingly efficient is
- 2 x AA NiMH
- About 1 - 2 ohms resistor
- Lumileds Lux III Red / Orange (the K2 is ok, but the Lux III is brighter)

Photon Fanatic made up a more sophisticated light for me in the past with a buck / boost circuit and 2 x 123s and the R/O - just crazy bright. But - you don't really need this fancy shmancy circuitry if you use NiMH AAs.

The Lux III R/O can handle 1.5 A IIRC, so there is a lot of margin, and with the low Vf of r/o compared to white - makes life easy.
 

KowShak

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If you like the AA format and are a bit open to non-traditional thought, there is another option - change the light color.

White is certainly what we first think of when talking about flashlights, but from an eye sensitivity and power efficiency viewpoint, red/orange (about 615 - 620nm IIRC) will just blow it away. There is a really good reason why traffic lights (red/orange) switched to LED so quickly, and white general lighting has not - the power savings were just enormous.

A very simple setup that is just amazingly efficient is
- 2 x AA NiMH
- About 1 - 2 ohms resistor
- Lumileds Lux III Red / Orange (the K2 is ok, but the Lux III is brighter)

Photon Fanatic made up a more sophisticated light for me in the past with a buck / boost circuit and 2 x 123s and the R/O - just crazy bright. But - you don't really need this fancy shmancy circuitry if you use NiMH AAs.

The Lux III R/O can handle 1.5 A IIRC, so there is a lot of margin, and with the low Vf of r/o compared to white - makes life easy.

Kind of drifiting away from the topic here but there are two reasons why traffic light bulbs are inefficient and LED bulbs are so much more efficient.

First is that the bulbs are turned on and off constantly (turning a bulb on and off, heating and cooling is a good way to shorten their lives) and have to last a long time. Long life bulbs are inefficent, long life bulbs that have to be turned on and off constantly are even more inefficient.

Second, a coloured filter is put in front of the bulb, that stops all wavelengths of light other than the colour you want (e.g. red or orange), which means a lot of the inefficiently produced light doesn't leave the light housing.

LEDs don't mind power cycling, you can also get coloured LEDs that produce only one colour of light, i.e. all the light they produce is seen.

Here in the UK we have a lot of low pressure sodium street lights, the streets are generally not brightly lit and I always associate that sort of coloured light with badly lit streets, so although the orange LED is nice thinking I really would prefer a white LED.

How efficient are red / orage coloured LEDs anyway? Do they compare with a Cree?
 

HarryN

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Here is a link to the Lumiled's web page with all of the technical info for the Lux III red / orange.

http://www.philipslumileds.com/products/luxeon/luxeonIII

There is no doubt that most users prefer white light vs the r/o, but you might surprise yourself. I find that the switch back to dark adjustment for my eyes is much faster for r/o that for white.

In any event, if you don't like the effect, you haven't lost much - this is a hobby and hobbies cost a little to play. :grin2: If your lights are just like everyone else's from Walmart - what is the point ?

Anyway, back to the physics. The energy of a photon of light is Energy = ( 1 / wavelength) x plank's constant.

Red / Orange = 617 nm
White = blue (460nm) + yellow (about 550 ish nm) + red (about 630nm)

More or less this means that no matter who makes a white LED, it will nearly always be much less efficient than just about anyone's red led. In the case of Lux III vs K2, the Lux III die is just massive, so it can take a lot of current and make a heck of a bunch of light. - typical is 190 lumens at about 3 watts.

You are comparing Vfs of about 2 - 2.5 Volts to Vfs of about 4 volts at similar currents.

On top of that, you don't have all of that circuit complexity.
 
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KowShak

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The data sheets quote 190 lumens at 1400ma for the red/orange Luxeon III. The forward voltage for 1400ma is quoted as 2.95 (typical).

Doing the maths, 190 / (2.95 * 1.4) = 46 lm/watt.

The luxeon rebel can be bought in orange, but the calculations put it in the 60 lm/watt ballpark.

luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light
http://en.wikipedia.org/wiki/Lumen_(unit)

Given that the lumen is corrected for the sensitivity of the human eye, the numbers would suggest that there is no advantage to using an orange LED instead of a white one, given that the white XR-E R2 can achieve 100 lumens per watt.

I could of course direct drive an orange LED off NiMH but 2.4 volts would not produce a whole lot of light!
 

HarryN

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Hi KowShak - I hope you are enjoying an open and friendly technical merits discussion about LEDs and flashlight use as much as I am. :twothumbs

I have become a bit spoiled by Lumileds and their really excellent binning specs, esp. when it comes to Vf. If you are using a real constant current driver, Vf largely does not matter from a "making it run" perspective. I hardly ever use "real" drivers, so Vf is a big deal for me.

The downside of my approach, is that it limits which LEDs I am able to really use, as knowledge about the Vf (and some games I play to lower it even more) are not really available to me with Cree and SS parts. I don't make so many flashlights that it really matters, so for my use and limitations - restricting my LED use to LL and highly binned LEDs is not a big deal. (I am too lazy to repeat all of my prior work for optics, heat sinking, etc.)

A useful example is the much maligned Lux V. If you look at the "typical specs", you would conclude that this part is more or less of limited value - 5 watts to make 120 Lumens is non - competitive. OTOH, reality is quite different, as it is possible to obtain XWOS binned Lux Vs. In other words, a phenominal color bin, about 200 Lumens (rated) at 700 ma, with a REAL Vf around 7.5 V @ 700ma. This is one heck of a light thrower and working with them on a bench is nearly blinding.

The R/O Lux III is similar - you can get some amazingly bright, low Vf parts that are dramatically different than the tyical part. Look for Photon Fanatic in CPF marketplace and search around a little.

I will admit that I have not personally tested the absolute latest LEDs from Cree and SS, but my prior testing of their parts (and LL parts) was that very little more light was gained driving them above 75% of rating - especially if you have limited battery power like a 2 x AA supply. Even with good heat sinking, efficiency falls fast with added power. You might see the "super bright start- up event" for 10 - 15 seconds, but after a couple of minutes - forget it.

The lumens per watt numbers from all suppliers need to be taken with a grain of salt IMHO. Those numbers usually come from an "insta test", sometimes at very low currents.

I should dig out a light that photon fanatic made for me - with a Lux III r/o and find an SF L4 to compare it to. This would probably work, but I am not sure that I know anyone with off the shelf lights around here. :crackup:

In any event, I think you will find that a well binned Lux III R/O will be about 60% of the Vf of a "typical" Cree white at 1000 ma.
 

KowShak

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From the Cree Data sheet, XR-E Q5 bin (R2 is better but the numbers aren't on the datasheet I have).

Forward voltage: 3.3v for 350ma
Brightness: 107lm @ 350ma

Doing the maths, that gives a typical 92 lumens/watt for a Q5.

The numbers above compare with the numbers I was quoting for the Red/Orange Luxeon, they're at 25C junction temperature and no doubt represent "insta-flash" performance, i.e. no warm up. Well, the numbers compare except for one difference, the Cree is quoted at 350ma and the Luxeon is quoted at 1400ma. There is a graph on here with R2 lumens / watt for different currents and I think by the time the R2 gets to using 4 watts its efficiency will have dropped but it will still be ahead of the Red/Orange LED.

I haven't done maths for any Cree Red/Orange LEDs.... they may well be more efficient than a Luxeon 3.
 

HarryN

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The nice thing about LEDs (especially now), is that they are cheap enough to play with on a bench. This will let you find out the "reality" vs "paper".

AFAIK, the Lux III r/o is the only LED bright enough to use as a single LED rear auto tail light on the market.

I would really enjoy reading about your testing and final selection.

Harry
 
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