2AA vs. 2 consecutive uses of AA

Contemplating whether to buy a 2AA or a single AA light. In Urban landscapes I guess form factor is important and a AA light would be the best. But for hiking/camping a 2AA light would be good.

While that was my original reasoning, I then feel that if a 1AA light can help me pass a considerable amount of night time (assumption=>I won't need the light for the whole night), then the next day anyways I will be able to replace the cell and be ready for the next night.

And that makes me wonder, what are the differences (in running time, for instance) between a 2AA light and 2 consecutive uses of a 1AA light?
If these are negligible, then the 1AA would be the best choice, right?

:thinking:
thanks,

Seems like it is going to be an unfair comparison, at least in terms light output. The higher voltage on the 2AA light will beat the lower voltage on the 1AA light.
eg.: noticed that Fenix LD20/L2D boasts a max of 180 lumens while LD10 has a max of 120 Lumens.

So,
2AA:
Pros:
* Higher light output
* Longer running time without the need to swap the battery
Cons:
* Form factor

and the reverse holds good for the 1AA lights.

If you are contemplating buying a Fenix L2D/LD20 you can also purchase a L1D body that will accept the L2D/LD20 head, therefore effectively meaning you can have both an AA and a 2xAA light by swapping the head and tailcap. The LD20 and LD10 heads are identical.

All other things equal and given the same light output, 2xAA will have a runtime advantage over 2x 1xAA for two distinct reasons.

1) The voltage boost is more efficiency
2) By having double the voltage, you decrease the battery current draw, which enables you to draw more juice out of the available cells.

Looking at the LD10-LD20 lumen disparity, can it be generally assumed that a 2AA light will have more light power than a 1AA light?

Walden said:

Looking at the LD10-LD20 lumen disparity, can it be generally assumed that a 2AA light will have more light power than a 1AA light?

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If you look, only the brightness on turbo is different.

Another point to consider -- if you find that a 2AA light is too large to carry, you won't carry it and it will sit home on a shelf no matter how good it is.

Well if you want 2AA power but also want smaller size, you can go for a CR123 light. Same energy as a AA battery but at a higher voltage. Of course, they aren't exactly cheap if you don't buy online.

2AA will allow for a more efficient circuit, higher output and longer runtime, but size is larger too. If you don't need that much output and a smaller size is better then 1 AA is fine.

... or try getting both.
I have been edc'ing both an AAA and a 2xAAA lately. I get greater overall efficiency (less boost required) with the 2xAAA, so that gets the most use. My AAA is so small that it sits in a jacket pocket as backup. Best of both worlds.

Kestrel said:

... or try getting both.
I have been edc'ing both an AAA and a 2xAAA lately. I get greater overall efficiency (less boost required) with the 2xAAA, so that gets the most use. My AAA is so small that it sits in a jacket pocket as backup. Best of both worlds.

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ya, I guess to get the best of both worlds I should get a AAA and a 2AA light.


but i am still thinking about the 2AA vs 2 consecutive use of 1AA.

parnass said:

Another point to consider -- if you find that a 2AA light is too large to carry, you won't carry it and it will sit home on a shelf no matter how good it is.

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no, I have carried my existing 2AA (Rayovac 3watt) light on hiking trips, where I would invariably get late and would have to use my light.

Gunner12 said:

Well if you want 2AA power but also want smaller size, you can go for a CR123 light. Same energy as a AA battery but at a higher voltage. Of course, they aren't exactly cheap if you don't buy online.

2AA will allow for a more efficient circuit, higher output and longer runtime, but size is larger too. If you don't need that much output and a smaller size is better then 1 AA is fine.

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For the most flexibility get an AA light that can run on Li-Ion 14500s as well as alkalines and NiMh. Then your quest for the best AA light is over.

Take your time and look around on this site. You will find a number of choices. If you ask me, the right thing to do is spend a little more money for a light that will be flexible and reliable.

Get both would be my answer. A 2xAA thrower for outdoor activities where range is important. 1xAA flooder for more close up activities which serves as backup to your 2xAA.

Walden said:

ya, I guess to get the best of both worlds I should get a AAA and a 2AA light.
but i am still thinking about the 2AA vs 2 consecutive use of 1AA.

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I just meant, both using the same battery format, AA in your case.

Toaster said:

Get both would be my answer. A 2xAA thrower for outdoor activities where range is important. 1xAA flooder for more close up activities which serves as backup to your 2xAA.

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... Thanks. Like that. Easier to feed.:thumbsup:

You might want to check out the Photon Proton Pro. The secondary red LED is useful for outdoor activity if you want to maintain your night vision for late night bathroom runs, not waking other people, or hiking by moonlight.

Otherwise, the NiteCore D10, D20, and NDI are also excellent choices for their ability to be both very bright, and have a good low mode.

Bottom line up front - I just ran some numbers that show close to a 20% runtime hit if you run 2 single cells, versus a 2AA light with other things equal. They aren't "real" numbers...just ballpark assumptions to illustrate the effect.

If you have a 2AA and a 1AA light that both have a 3.6 Vf with a constant current driver pushing 333 ma with cells at 1.2 volts (all reasonable if not typical numbers and they make the math easy for me .) For now we will assume the boost driver is 100% efficient. We'll use the eneloop data in Silverfox's NiMh shootout to determine watt hours at the appropriate loads.

The 1 cell light is then pushing 1.0 amps from the battery and the 2 cell light is pushing 500 ma. Looking up the data in the shootout the eneloop gives 2.445 Wh at 500ma and 2.320 Wh at 1 Amp. That's about a 9% loss in power capacity running them one at a time vs together in the 2AA light.

(Interestingly the drop between 1A draw and 2A draw also rounds to 9%, and the same with 2A versus 4A. So each doubling of draw seems to cost an additional 9% of power capacity.)

Anyway that's a 9% loss just from the battery issue. Drivers aren't perfectly efficient and boost converters tend to be more efficient when input voltage is close to output. Finding the data for a micropuck it shows 70% efficiency for 1V input and 85% for 2.5 volt input. Probably safe to assume that between 1.2V and 2.4 V the efficiency hit is at least 10%.

Power consumed by resistance is also related to the square of current. While that number is probably pretty small, doubling the current loses 4 times as much power. That might be good for another percent or so loss in efficiency. So let's call the overall efficiency side loss (including drive loss) 11%

Bottom Line
So 91% of the power capacity of the 2AA times 89% of the efficiency in using that power and we are at about 81%. Given 2 lights with the exact same drive current to the LED we are looking at about 19% less runtime in the 1xAA with 2 cells used, versus a 2xAA. Putting it another way...

If the 1AA give you 2:00 total runtime with 2 cells an identically driven 2AA gives you about 2:28 in runtime.

Baterija:
Great post!!:twothumbs Will take my time and digest the data that you provided.

thanks!

I suggest you get one of each. 1 AA for EDC and 2AA for outdoors. That's what I do, and I like it.

LightScene said:

For the most flexibility get an AA light that can run on Li-Ion 14500s as well as alkalines and NiMh. Then your quest for the best AA light is over.
...

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+1 !

The main disadvantage of 2x AA (and any other 2x light) is that you will virtually never find two equal cells. Consequently, one of the two will deplete earlier and the output will suffer it not cease.

Rather soon than later the less capable cell will die, leaving you with x-1 cells, which usually will be an odd number of cells. So, what will you do with the other, good cell ? Place on the shelf until another cell dies and you have an even number of cells again ? Great....:duh2:

I have a whole bunch of AA and AAA cells, each with a different age and capacity, which I can easily use in my 1x lights with no hassle.

+1000 for any 1x light ! :thumbsup:

baterija said:

If you have a 2AA and a 1AA light that both have a 3.6 Vf with a constant current driver pushing 333 ma with cells at 1.2 volts...

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That's a really good analysis, thanks.
K