# Thread: 8 or 6 AA With 3 LuxIII's?

1. ## 8 or 6 AA With 3 LuxIII\'s?

I want to use a fatman board to drive 3 LuxIII's, I want to make it dimmable by using a pot. I was originally going to use 2 3AA battery holders, but i guess 8AA will give a longer runtime. I have a couple of questions:

I seem to remember reading that NiMh AA cells have a larger diameter than alkie AA's. Will 8 AA NiMh fit in the 2D using an 8AA to 2D battery holder from the sandwich shoppe?

Will 3 LuxIII's run Ok using the fatman and 8AA NiMh? I am planning to use a high Vf luxeon (K or L) so that the battery voltage will be less than the toal Vf of the LED's since the fatman is a boost circuit. 8 NiMh = 9.6V / 3 LuxIII (T**K bin) = 10.5V-11.2V

Or, would it be a better choice to use 3 T**J LuxIIIs and 6 NiMh?

I also appreciate any suggestions.

2. ## Re: 8AA With 3 LuxIII\'s?

It depends on the brand of the cell and the mAH rating. They are bigger than alkies. You might have to bore the body of the mag out to fit certain ones.

Shane

3. ## Re: 8AA With 3 LuxIII\'s?

i do some loose math, check specs here
and sounds TIGHT but right.

and it sounds overall efficient use of, with higher voltage, there should be less drops through the different points of resistance , like the curcuit, the switch, the spring even, the wiring to all of the leds. Plus at that level the curcuit is acting efficient, as each voltage dropping is droping higher voltages a smaller percentage of the whole. meaning .5v loss at 3v is more than .5v loss at 9v.

some ni-mhys were so tight 4 wide in a mag body that it would scrape the insulation off, then also there is slight expansion when the pressure rises (older), which can also make differences in what does and doesnt fit.

there is at LEAST 2100s that will fit, the 2300 energisers BARELY fit, they were boring the mag bodies slightly , with 4 LINES of boring down the body, expanding only where the batteries would be located , to get ANY battery to go in.

havent done it, but just from reading sounds good, especially if you use ni-mhy and have a charge connect on the back , so if they fit tight, you dont have to drag them in and out, damaging the insulation.

4. ## Re: 8AA With 3 LuxIII\'s?

FMU, if you want maximum dimming capability (30mA) you'll need to use 6AA. The reason is when you drive the Luxeon so low the Vf will drop significantly (~2.6V/luxeon). So ~7.8V Vf, you'll need a Vin less than that, which means 6x1.3 should work perfectly ;D

If you want maximum runtime at high power then 8AA is the way to go. However if you got a stock mag you'll probably use the Raynovac 1800mA cause those Energizer 2500mA won't fit so your runtime gain will only be ~7-10%. If you bore the body then it'll be a nice 33% gain.

In any case, here are some runtime of different configuration, power output, and temperature test case. 90 minutes @ max power &amp; 52+ hrs on low is not that bad [img]/ubbthreads/images/graemlins/grin.gif[/img]

5. ## Re: 8AA With 3 LuxIII\'s?

Thanks modamag!

So, how do the 24/2500 mAh fit in the 3AA to D holders?

7. ## Re: 8AA With 3 LuxIII\'s?

Great! Thanks for the help. [img]/ubbthreads/images/graemlins/happy14.gif[/img]

Now, where do I find money...

8. ## Re: 8AA With 3 LuxIII\'s?

[ QUOTE ]
Former_Mag_User said:
Great! Thanks for the help. [img]/ubbthreads/images/graemlins/happy14.gif[/img]

Now, where do I find money...

[/ QUOTE ]

Not sure, If you find some tell me where. [img]/ubbthreads/images/graemlins/wink.gif[/img]

Shane

9. ## Re: 8AA With 3 LuxIII\'s?

It'll be our own little secret. [img]/ubbthreads/images/graemlins/yellowlaugh.gif[/img]

10. ## Re: 8AA With 3 LuxIII\'s?

somebody pointed out wisely that there is a direct circuit path through the fatman through an inductor and a diode... don't remember the voltage drop on the diode but that's your little added buffer.. nonetheless.. if you want full dimming.. you need to have the Vf higher than Vbat.. so sometimes using K bin or L bin emitters will help... i would pick the emitters.. and drive them with a fatman from an ad-hoc battery pack with 6 or 8 cells and measure the current (measure the mA from the LED- to ground and you'll get 1/10th the value of mA)...

6 x 1.2 = 7.8 and 8 x 1.2 = 9.6V..

(9.6V -.5)/3 = 3.08V... i think you'd be able to dim down almost to minimum even with an 8-pack of cells.. but with fresh batts might not.. but under load the VF will certainly be over 10-11V even with Jbin emitters.. but 8AA packs can be hard to fit into 2D lights.. when i sell my mods that will be this type of solution i'll be using 6AA-&gt;2D adapters because it's a total 'gimme' as far as fitting.. go look at fivemega's adapters they are unbeatable.

-awr

11. ## Re: 8AA With 3 LuxIII\'s?

only problem is that fivemega is out of the 6AA-2D [img]/ubbthreads/images/graemlins/frown.gif[/img]

Shane

12. ## Re: 8AA With 3 LuxIII\'s?

I'm running this exact configuration created by modamag (6AA + Fatman + 3xTWOJ + dimming knob). 6AA allows dimming and when I tried 8AA it was like the dimming function didn't even work.

I took an 8AA adapter and soldered a wire where one stack goes. I can use the biggest fattest AA rechargeables they can come up with.

Jeff

13. ## Re: 8AA With 3 LuxIII\'s?

yeah 8AA with a fresh charge and TWOJs... probably can dim to like 600mA which will barely look like it dims at all... i had the same problem running a single TWOJ from a single LiON.. dimmed down to 600mA.. i was really confused at first.. i had everything hooked up... it actually dawned on me that i had Vbat over Vf while i was falling asleep.

you'd actually have to try it to see if you can dim fully if you used 8AAs and Kbin emitters.. i'm using "L"s in my latest design and have full dimming with 4 emitters and 3 LiONs.

too bad about the supply of FM adapters.. i know i broke one of my 168 adapters and i can't even get a replacement part :-(.. fortunately.. it's so well designed it works broken... just uses the spring pressure from the mag to hold everything together.

-awr

14. ## Re: 8AA With 3 LuxIII\'s?

Thanks for the info andrewwyyn! That was a concern of mine, that the dimming wouldn't work with the higher volatage of 8AA.

Even if fivemeaga did have them, they are too expensive for me, \$35 [img]/ubbthreads/images/graemlins/broke.gif[/img]...I don't think so. I'll stick with my \$3.50 3AA to D adapters. [img]/ubbthreads/images/graemlins/tongue.gif[/img]
I checked his thread and it says that only the 3D adapters are out of stock, unless he hasn't updated his first post. [img]/ubbthreads/images/graemlins/icon3.gif[/img]

· --2D Mag-- Have It
· --Tri Sink--Have it
· 3AA to D Holders
· Fatman/Pot
· 3x LuxIII stars
· 3x IMS 20mm
· modamag Bi-Pin connectors
· 6x 2400 mAh AA
· AA NiMh Charger

Anything missing?

15. ## Re: 8AA With 3 LuxIII\'s?

For \$18, you can get an 8AA to 2D adapter from the sandwich shoppe and solder the wire in like I did. If you use 2 AA dummy batteries, you have the option of using 7 or 8 AA.

I like that setup better than the 3AA adapters.

Jeff

16. ## Re: 8AA With 3 LuxIII\'s?

Yeah, but the body needs to be bored out to use the 2400mAh NiMh with the 8AA battery holder. Unless I use lower capacity cells. [img]/ubbthreads/images/graemlins/thinking.gif[/img]

EDIT: I'll just stick to the 3AA-&gt;D adapters. SInce I will be needing 6AA for the best dimming capability and I'll save \$10! [img]/ubbthreads/images/graemlins/tongue.gif[/img]

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