Why 3x AAA batteries in stead of 1x AA battery?

Many LED flashlights have 3x AAA batteries. This gives the same capacity as 1x AA battery. What is the advantage of that compex battery system over LED flashlights with just simple 1x AA battery? The latter is simpler and saves time, weight, volume and battery cost IMO.

Same capacity~ but lower voltage. To drive a light at the same output with 1.5 vs 4.5 would be much more difficult.

bfayer said:

Same capacity~ but lower voltage. To drive a light at the same output with 1.5 vs 4.5 would be much more difficult.

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Thanks. But there are many 100 lumens flashlights that have 3x AAA batteries, while there are also 100 lumen flashlights with 1x AA battery.

Are those 1x AA flashights with 100 lumens more expensive to produce, than those 3x AAA flashlights with 100 lumens? Is that what you mean?

Yes. LEDs need around 3.6 volts to operate.

One AA battery will give you 1.5 volts. To get it up to 3.6V, it needs a boost circuit. This will have an inductor and chip (and some more little parts depending on quality) mounted on a circuit board. The cheapest unregulated boost circuit will be around 50 cents in bulk.

Three AAA batteries give you 4.5 volts. No need for any circuitry, just wire the LED right up to the battery. Practically free and almost impossible to get wrong. (Other than being a horrible practice to begin with, overvoltaging an LED is bad for it.) This is also why you see so many 3xAAA lights and 1x18650 lights at places like DX. For a single-mode light they don't have to do anything other than slap together a switch, LED and battery holder.

The 50 cents for a boost circuit might seem like nothing, but on a $3 flashlight that would wipe out any profit.

parametrek said:

Yes. LEDs need around 3.6 volts to operate.

One AA battery will give you 1.5 volts. To get it up to 3.6V, it needs a boost circuit. This will have an inductor and chip (and some more little parts depending on quality) mounted on a circuit board. The cheapest unregulated boost circuit will be around 50 cents in bulk.

Three AAA batteries give you 4.5 volts. No need for any circuitry, just wire the LED right up to the battery. Practically free and almost impossible to get wrong. (Other than being a horrible practice to begin with, overvoltaging an LED is bad for it.) This is also why you see so many 3xAAA lights and 1x18650 lights at places like DX. For a single-mode light they don't have to do anything other than slap together a switch, LED and battery holder.

The 50 cents for a boost circuit might seem like nothing, but on a $3 flashlight that would wipe out any profit.

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Thanks for your explanation.

3xAAA does NOT give the same capacity as one AA, (going off eneloop specs) 1AAA = 850mAh, since only the voltage adds up when in series the capacity of a 3xAAAs battery config is still only 850mAh, but voltage adds up to 3.6v. 1xAA is 2000mAh.

Now if the holder had the 3xAAA in parallel the capacity would add up making 2550mAh but most all of those 3xAAA lights are running their batteries in series, not parallel, and since running them in parallel would only be at 1.2v, the benefit of higher voltage would be negated, why add on the size/weight of 3xAAA over 1XAA? The added size/weight/parts to fail makes no sense for the additional 500mAh, you could just buy a 2500mAh or larger AA from the get go if you just going for capacity.

In short-
running batteries in series add the voltage but capacity is the same as one single battery.
Runnin batteries in parallel add the capacity but voltage is the same as one single battery.

Cereal_Killer said:

3xAAA does NOT give the same capacity as one AA, (going off eneloop specs) 1AAA = 850mAh, since only the voltage adds up when in series the capacity of a 3xAAAs battery config is still only 850mAh, but voltage adds up to 3.6v. 1xAA is 2000mAh.

Now if the holder had the 3xAAA in parallel the capacity would add up making 2550mAh but most all of those 3xAAA lights are running their batteries in series, not parallel, and since running them in parallel would only be at 1.2v, the benefit of higher voltage would be negated, why add on the size/weight of 3xAAA over 1XAA? The added size/weight/parts to fail makes no sense for the additional 500mAh, you could just buy a 2500mAh or larger AA from the get go if you just going for capacity.

In short-
running batteries in series add the voltage but capacity is the same as one single battery.
Runnin batteries in parallel add the capacity but voltage is the same as one single battery.

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I don't see it:

A single AAA is 850 mAh times 1.2 volts = 1020 mWh.
Three AAA give 850 mAh times 3.6 volts = 3060 mWh.
One AA is 2000 mAh times 1.2 volts = 2400 mWh.

If the lights are designed for the correct voltage, the 3 X AAA will out-run the 1 X AA. And that's not including the losses in the up-converter.

Power is measured in watt hours.

Amp hours stays the same in series, but watt hours still go up. The power available in 3 850 AAAs is not much different than a single 2500 AA.

So yes "capacity" as measured in amp hours is not more with 3 AAAs, but the intent of this post is actually about available power.

You can only compare amp hour capacity between batteries or packs of the same voltage.

georget98 said:

I don't see it:

A single AAA is 850 mAh times 1.2 volts = 1020 mWh.
Three AAA give 850 mAh times 3.6 volts = 3060 mWh.
One AA is 2000 mAh times 1.2 volts = 2400 mWh.

If the lights are designed for the correct voltage, the 3 X AAA will out-run the 1 X AA. And that's not including the losses in the up-converter.

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You assume a 2000 AA, run the same numbers with a 2500 AA.

The original post did not specify battery capacity, hence my ~ symbol. If you don't know the variables you have to talk generalities.

bfayer said:

Power is measured in watt hours.

....

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power (energy per unit time) is measured in Watts ( joules / sec, MKS). Energy is the time integral of power, approximated as noted above as Watts x hours, abbreviate Watt-hour or Whr. [ That's why your electricity bill (energy use) is in "kWh", or kilowatt-hours. A spinning meter integrates the current consumption and assumes a constant voltage. I don't know if electronic meter includes voltage or power factor. ]

Electrical power transfer is calculated P = E x I or voltage times current.

So, with 3 x AAA (series connected), you can supply three times the power because your voltage is three times greater. The series connection means you have each cell discharging at the same rate. So, the energy (power over time) you have available is 3 times the single cell.

You can spend this energy in either making your run time longer (keep the same brightness, or light energy) or making your LED shine more (make more light energy).

First order, it's factor of 3 going from one cell to three, assuming no losses in whatever control is required (that is, regulator) to achieve your goal.

Forgot to factor in something: voltage sag due to internal battery resistance as well as multiple contact resistance. The more connection points between the cells and the load, the more power loss exists. AAAs sag in voltage almost immediately while AAs are a bit more resilient. I'd say the nominal working voltage of AAAs is around 1V.


Take Duracell coppertops for example
http://www.duracell.com/media/en-US/pdf/gtcl/Product_Data_Sheet/NA_DATASHEETS/MN2400_US_CT.pdf


The discharge curve is non-linear across different current loads.
Say the LED cumulative load is 500mA, a coppertop AAA has only 0.65AH compared to an AA which at 500mA load current performs on average 2AH.
Say if both cells manages to sustain 1.2V working voltage during the load time.


3AAA in series would yield 0.65AH at 3x1.2 = 3.6V or about 8424 joules.
1AA at 2AH with 1.2V nominal voltage is equivalent to about 8640 joules.


However, if its under a 50mA load,
AAA: 1.15AH 3S = 3.6V 14904 Joules
AA: 2.8AH 1S = 1.2V 12096 Joules


As you can see, AAAs are designed primarily for low drain applications, 50mA is two properly driven 5mm LEDs. Very few companies past Ccrane does this. Most comes in 7 LEDs, which will run anywhere between 140mA all the way up to 180mA. Anything higher than 150mA, its no place for AAAs. They will be tortured to death, then murdered.

bfayer said:

You assume a 2000 AA, run the same numbers with a 2500 AA.

The original post did not specify battery capacity, hence my ~ symbol. If you don't know the variables you have to talk generalities.

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With a 2500mAH AA, you're up to 3000 mWH. This is still a little shy of the 3060 mWH figure using three 850 mAH AAA batteries. Of course, if we're going to step the AA up to 2500 mAH, we could also step the AAA up to 1000 mAH for 3600 mWH. And none of this takes into account driver losses resulting from the fact a 1xAA light needs a boost driver.

Illum said:

Forgot to factor in something: voltage sag due to internal battery resistance as well as multiple contact resistance. The more connection points between the cells and the load, the more power loss exists. AAAs sag in voltage almost immediately while AAs are a bit more resilient. I'd say the nominal working voltage of AAAs is 1.0V

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A AA battery certainly does have lower internal resistance. But it's also going to have to supply about three times the current of 3 AAA batteries. And a AA certainly doesn't have only a third of the internal resistance of a AA (at least with NiMH). Also, although contact resistance is a factor in a 3xAAA battery holder, so is the aforementioned driver loss with 1xAA. I would be willing to bet you're not losing the 15-20% typical of a boost driver through the battery holder contacts.

Is there a technical reason for the "3xAAA -> 9 led" format being so massed produced?

edpmis02 said:

Is there a technical reason for the "3xAAA -> 9 led" format being so massed produced?

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Well, the three AAA batteries came about because this is the lowest number of cells that can provide th voltage necessary to power a typical LED with a simple (ie cheap) direct drive setup. Basically, all that is needed is a resistor to limit the current. As for nine 5mm LEDs, there's nothing magical about that. Perhaps manufacturers have found that this is the minimum number required to meet the typical expectations as far as light output.

My head hurts.

Flask said:

My head hurts.

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+1...

I look at the analysis a bit simpler, the AAA option is 2-3x:
- more costly if you like to buy
- more hassle if you like to charge
- more difficult to share batts with other devices

One possible benefit is in higher efficiency of input/output conversion of the circuit (if there is one), as the total voltage will be much closer to the LED Vf.

But that of course doesn't make up for the large decrease in power/size ratio going from AA to AAA.

Here's how I see it. Both 1xAA and 3xAAA have their advantages. The advantages of 1xAA are as follows:


- Doesn't require batteries in multiples of three (which is always awkward, since batteries are typically sold in twos and fours)
- No potentially unreliable battery holders to worry about
- MUCH easier to change the battery on the run
- 1xAA lights are generally more compact
- Extra batteries are easier to carry
- Although a 3xAAA light need not be low quality, quality 1xAA lights are easier to find


Advantages of 3xAAA


- Simpler, cheaper, and more efficient drivers can be used
- Due to higher voltage, lower driver losses, and fewer cost constraints resulting from high driver current requirements, higher power is possible
- Lower current requirement from batteries, even in comparison with internal resistance (which is about .05 ohms for a NiMH AA and about .08 ohm for a NiMH AAA).


So there you have it. Interestingly, all of the advantages I see with 1xAA are convenience related, while the advantages of 3xAAA are performance related. Keep in mind, though, that not all lights of a particular battery configuration necessarily take advantage of these. This is particularly true with 3xAAA lights (which often tend to be cheap, low performing lights).

When I see 3 AAA, I immediately put my hand over my wallet, and don't remove it until I see definitively that the light is regulated, and not simply a direct drive. So many of the lights one sees that are 3AAA are cheap, direct-drive ones with maybe a resistor to help control current. I personally have progressed beyond them, until I get rich enough to be able to afford to give them away as freebies instead of fauxtons.

parametrek said:

Yes. LEDs need around 3.6 volts to operate.

One AA battery will give you 1.5 volts. To get it up to 3.6V, it needs a boost circuit. This will have an inductor and chip (and some more little parts depending on quality) mounted on a circuit board. The cheapest unregulated boost circuit will be around 50 cents in bulk.

Three AAA batteries give you 4.5 volts. No need for any circuitry, just wire the LED right up to the battery. Practically free and almost impossible to get wrong. (Other than being a horrible practice to begin with, overvoltaging an LED is bad for it.) This is also why you see so many 3xAAA lights and 1x18650 lights at places like DX. For a single-mode light they don't have to do anything other than slap together a switch, LED and battery holder.

The 50 cents for a boost circuit might seem like nothing, but on a $3 flashlight that would wipe out any profit.

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What he said.

That's why all the el-cheapo supermarket lights are 3 x AAA.