How many AAs or AAAs for runtimes as good as a single 18650?
- Thread starter Lumenato
- Start date
Help Support Candle Power Flashlight Forum
Wrend
Enlightened
Three NiMH AA or AAA cells in series should give you about the right voltage. The AA sized cells will typically be just a little lower in capacity. The AAAs would be much lower.
I don't use 18650 cells though, so I'm not as specifically knowledgeable about them as others here.
I don't use 18650 cells though, so I'm not as specifically knowledgeable about them as others here.
baterija
Flashlight Enthusiast
- Joined
- Feb 7, 2008
- Messages
- 1,053
It depends. There are a lot of variables (Serial or parallel, drive current to the LED, light resistances, etc) Probably a good way to get an idea is to look at what the AA based lights can give you in specific lights. You likely won't find the higher end of output till you get many AA cells because they just don't do well with high current.
hoongern
Enlightened
If you're JUST talking about equivalent energy, it's pretty easy.
An average 18650 (3.7V, 2900mAh) holds 3.7*2.9 = 10.73Wh of energy.
An average AA [eneloop] (1.2V, 2000mAh) holds 1.2*2 = 2.4Wh of energy.
An average AAA [eneloop] (1.2V, 800mAh) holds 1.2*0.8 = 0.96Wh of energy.
Thus, you'd need 10.73/2.4 = 4.5 eneloop AAs to equal the amount of energy a 2900mAh 18650 holds.
And you'd need 10.73/0.96 = 11.2 eneloop AAAs to equal the amount of energy a 2900mAh 18650 holds.
Of course, different circuits use energy in different ways depending on how they are regulated. *Generally*, most circuits will be more efficient at higher voltages (as long as they're designed to take the higher voltage)
(I forgot to add - keep in mind that the amount of energy you get from a cell always depends on the rate of discharge)
An average 18650 (3.7V, 2900mAh) holds 3.7*2.9 = 10.73Wh of energy.
An average AA [eneloop] (1.2V, 2000mAh) holds 1.2*2 = 2.4Wh of energy.
An average AAA [eneloop] (1.2V, 800mAh) holds 1.2*0.8 = 0.96Wh of energy.
Thus, you'd need 10.73/2.4 = 4.5 eneloop AAs to equal the amount of energy a 2900mAh 18650 holds.
And you'd need 10.73/0.96 = 11.2 eneloop AAAs to equal the amount of energy a 2900mAh 18650 holds.
Of course, different circuits use energy in different ways depending on how they are regulated. *Generally*, most circuits will be more efficient at higher voltages (as long as they're designed to take the higher voltage)
(I forgot to add - keep in mind that the amount of energy you get from a cell always depends on the rate of discharge)
Last edited:
mohanjude
Flashlight Enthusiast
Does anybody know the energy content of AA and AAA primaries (top Branded Alkaline)
thanks for your input.
thanks for your input.
Wrend
Enlightened
With alkaline cells it's even more relative to their discharged usage rate.
In very low drain rate devices (such as TV remotes), they'll have more usable energy than most NiMH cells. In higher drain rate devices (such as bright flashlights), they'll have less.
Just as a rough estimate from my experience with testing Eneloop and Energizer run times, I think they match up in effective capacity at a drain rate of about 250mA.
In very low drain rate devices (such as TV remotes), they'll have more usable energy than most NiMH cells. In higher drain rate devices (such as bright flashlights), they'll have less.
Just as a rough estimate from my experience with testing Eneloop and Energizer run times, I think they match up in effective capacity at a drain rate of about 250mA.
Thanks for the detailed reply! This is great. Sounds like I'll need a 4AA light to get similar energy from an 18650 then. HHmmmmm fenix LD40? sunwaymanM40a? jetbeam PA40,? zebralight q50? Any other 4AA lights out there?
random question here. why doesn't sanyo or any other company make a giant NIMH that has similar V and mAh as a 18650? That would be awesome as it's safe and has same specs. Any chance we may see one in coming years?
Wrend
Enlightened
The chemistry type of a cell determines its voltage. Hoverer, they could (more or less) just make a bigger cell to increase capacity.
To match the voltage as closely as possible, you'll want 3 NiMH cells in series. If you want higher capacity, something like the Eneloop XX 2500mAh cells would help some. I prefer the regular second generation ones though, because they have a significantly higher cumulative lifetime capacity potential.
I know for sure I'd buy some Eneloop true D sized cells, if they made them. At least 4, probably 8 or more.
Also, is the 2900mAh of an 18650 cell actually usable every cycle without damaging the cell? I know for my hobby Li-ion type cells you shouldn't use the full capacity to prolong cell life.
On a side note, I think the company that owns the rights to the NiMH cell won't allow there to be any cells made larger than D sized. Something to do with oil companies not wanting them available for electric cars. :shrug: (http://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteries)
To match the voltage as closely as possible, you'll want 3 NiMH cells in series. If you want higher capacity, something like the Eneloop XX 2500mAh cells would help some. I prefer the regular second generation ones though, because they have a significantly higher cumulative lifetime capacity potential.
I know for sure I'd buy some Eneloop true D sized cells, if they made them. At least 4, probably 8 or more.
Also, is the 2900mAh of an 18650 cell actually usable every cycle without damaging the cell? I know for my hobby Li-ion type cells you shouldn't use the full capacity to prolong cell life.
On a side note, I think the company that owns the rights to the NiMH cell won't allow there to be any cells made larger than D sized. Something to do with oil companies not wanting them available for electric cars. :shrug: (http://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteries)
Last edited:
