Anyone know where I can find some capacity information on regular alkaline Cells? I have an MP3 player that eats the single AAA cell and want to know what I can gain by wiring an external AA, or C cell in.
Can't use NiMH types - dies at 1.2 volts.
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You can see capacity information on battery data sheets from the manufacturer. Most battery compamies can provide this stuff on the "comercial" or "industrial" sections of their web sites.
Here are some links to Panasonic Alkaline batteries for AAA, AA, and C size cells:
- mkaras
According to the Energizer Bunny:
AAA = 1250 mah AA = 2850 C = 8350 D = 20500
Since the C and the D cost the same, I would go with the D.
Tam
Do you think it could work with two of those plus a couple of large enough Schottkys?
-- Regards, Joerg http://www.analogconsultants.com
How's about a lithium-ion cell with a switching regulator?
Luhan
That would be the high-tech solution with a very good nerd factor ;-)
No idea what small Li-Ion cells cost but for the regulator there are a lot of modern and small footprint solutions available at TI, National etc. Could be a bit noisy though in case that MP3 player contains a radio.
-- Regards, Joerg http://www.analogconsultants.com
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I make it a point not to buy products that use AAA batteries. Capacity is propoertional to the square of the diameter, so using AA versus AAA is a big deal. Also, AA cells are quite cheap. Having done some capacity testing, get any alkaline. The difference between brands is small.
Generally the manufacturers will provide some information:
Of these, the first had the most straightforward list of nominal energies in batteries of different sizes. It should be plenty for the rough ratio of AA to AAA information you are looking for.
The short version cut-and-paste:
Type Amp-hours AAA 1.250 AA 2.850 C 8.350 D 20.500
As for the NiMH, you have tried it, and not based your conclusion about the voltage cutoff based on the fact that the Alkalines that come out show 1.2v when it says they're dead, right? An alkaline which shows
1.2v with no load will probably sag much lower when loaded than NiMH batteries would run.
Thanks for all the responses. It is looking like C may be my best option. This thing hangs from my neck in a hacked waterproof container for kayaking - the D size, unfortunately, won't fit.
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I'm right with you there - hate the AAA for most things. Cost of the player was a consideration, and I'll add an outboard battery holder.
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Yes I did try it. Considered two AA NiMH with some dropping diodes but that sounds wasteful too. At ~1.3 volts I hear an occasional thump after a loud passage - so I think it is borderline at 1.3.
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I try not to get too involved or pricey with this stuff - I've upset the kayak a few times, so anything that goes with me is disposable or nearly so.
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I'll try a C cell - it has to hang around my neck so light is helpful, and it might be nice if it floats.
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NiMH AAA is _quite_ adequate for 90% of flash mp3 player use.
I get about 10 hours from one cell.
I would not hesitate in returning a MP3 player that died at 1.2V - it gets maybe 20% (IIRC) of the energy out of even an alkaline AAA cell.
Modern NiMH AAA cells are quite good - I've got a torch that puts out 1W for >40 mins, on one AAA cell, and happily sits on my keyring.
Cheap and small.
Your MP3 player dies at 1.2V? If that is the case then it is a very poor design, and I'd suggest you get a different one! A good design will use up all the capacity in the battery, down to 0.8V for Alkalines (or at least 1V), and also have a selectable software setting for using NiMh cells.
Energizer & Duracell websites both have datasheets with capacity curves, like this:
In your case your MP3 player will use a DC-DC converter which will essentially be a constant power load, so use the constant power curve. A real test in the actual product is often the only way to get an exact figure though, but the graphs are good for ballpark stuff.
Dave :)
Agreed. There is a big market for the smaller size afforded by a AAA. If you don't like it you can always get a larger player that takes AA's.
I get 15 hours out of my Creative MuVoTX/FM
I don't know what voltage it dies at though, might have to measure it...
Dave :)
He is more than likely measuring the no load voltage. That is not to say that it is 1.2V when the thing is running. I just went through that with a camera. A 6V alk cell measured 6.0, but would not work the shutter. A new battery fixed it. (It is an SLR; no autofocuss, no flash, battery was 10 years old).
Tam
I once had the beer kayak and sure enough I rolled it. Took us almost an hour to save all those cans.
-- Regards, Joerg http://www.analogconsultants.com
Yep, it's called internal resistance ;-)
Dave :)
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