Total Watts in a AA NiMH?

[matrixshaman]

This is a somewhat theoretical question to help with some calculations I'm doing for an experiment. If you completely drain a AA NiMh battery dead how many watts could you get out of it? I think I'm asking this correctly versus how many watt-hours. Rough guesses gladly accepted if this is not a commonly known quantity Consider this a slow drain situation if that would affect the answer - say 24 hours.
And yes I've searched here for this answer and see Silverfox's threads on some watt-hour ratings but I don't think that's quite what I want as I don't know how long they last at that rating and I'm sure the watt-hour stats decrease as a cell is run down. I'll make a real rough guess here of maybe 20 to 30 watts? :shrug:

 

[leeholaaho]

This is a somewhat theoretical question to help with some calculations I'm doing for an experiment. If you completely drain a AA NiMh battery dead how many watts could you get out of it? I think I'm asking this correctly versus how many watt-hours. Rough guesses gladly accepted if this is not a commonly known quantity Consider this a slow drain situation if that would affect the answer - say 24 hours.
And yes I've searched here for this answer and see Silverfox's threads on some watt-hour ratings but I don't think that's quite what I want as I don't know how long they last at that rating and I'm sure the watt-hour stats decrease as a cell is run down. I'll make a real rough guess here of maybe 20 to 30 watts? :shrug:

Try allaboutbatteries.com

http://www.allaboutbatteries.com/Energy-tables.html

 

[mattheww50]

Depends upon how fast you want the power. The largest AA capacity is about 2700mah,
which means the batter capacity is somewhere around 2.700 x 3600 x 1.25 joules.
A Joule is 1 watt of power for 1 second (12150 joules).

Generally as you get past a current draw of about .5C (where C is the Amp hour capacity of the battery), the usable capacity falls rapidly due to I^2R losses within the battery.

So the answer is that useful capacity of a AA NiMh battery depends upon what the capacity of the battery is, and how fast you want to use that capacity.

If you want to only draw 1 amp (1.25 watts) or so, you will get about 2.5 hours, 100ma (125mw) , and you will probably get pretty close to 27 hours, want 4 amps (5 watts) and you may not get 25 minutes.

 

[jhellwig]

You have it backwards. Watts are what the power that the battery is producing at any given time. Watt-hours is watts produces for a given amount of time. If a battery produced one watt for one hour that would be 1 watt-hour. Given that an AA eneloop is rated at 2000mAh you would multiply that by the nominal voltage of 1.2v and you get 2.4Wh, granted, that is at the rated capacity. If you discharged that battery completely it could be more. Probably not much more though.

 

[matrixshaman]

jhellwig -- nice Avatar - one of my favorite people - Tesla!

I probably was not asking the right question as I didn't refresh myself on energy units and how to determine the total energy stored in a AA NiMH. Maybe Joules would be a better thing to look at since Watts are more time dependent. Based on the what matheww50 stated it may get around 12150 Joules although using extrapolation from the web site leeholaaho mentioned I think I come up with about 10800 Joules - still in the same ballpark. I just threw this question out earlier without a lot of thought and I believe Joules is really what I want. Thanks everyone for the help :thumbsup:

 

[Ragiska]

I probably was not asking the right question as I didn't refresh myself on energy units and how to determine the total energy stored in a AA NiMH. Maybe Joules would be a better thing to look at since Watts are more time dependent. Based on the what matheww50 stated it may get around 12150 Joules although using extrapolation from the web site leeholaaho mentioned I think I come up with about 10800 Joules - still in the same ballpark. I just threw this question out earlier without a lot of thought and I believe Joules is really what I want. Thanks everyone for the help :thumbsup:

as they are both quantities of energy, watt hours and joules are easily converted back and forth (they measure the same thing). silverfox's testing at various load rates are exactly what you asked for (although i am still not sure what you actually want).

best case scenario for a NiMH, 3 Wh = 10800 J

 

[TorchBoy]

Even though you had it backwards, if you had actually wanted watts, when you short an Eneloop I've heard it'll provide up to 17 amps, which at 1 volt would be 17 watts. But not for very long.

 

[jhellwig]

You want to use watts cause joules doesn't fit in p=ie . That right, there are joules in pie.:nana:

Watt-hours is mostly meaningless for everything except your electric bill.

 

[Benson]

Even though you had it backwards, if you had actually wanted watts, when you short an Eneloop I've heard it'll provide up to 17 amps, which at 1 volt would be 17 watts. But not for very long.

Yes, but if you had to short it, it's delivering 0V * 17A = 0W. You should get maximum power in the load somewhere in the vicinity of 0.6-0.7V (matched impedance means half the voltage), and about half the current, so maybe 5.5W.

Watt-hours is mostly meaningless for everything except your electric bill.

Unless, of course, you care about runtimes, particularly in the case of a switching power supply running a constant-power load (e.g. an LED driven with regulated current). Which pretty much describes any 1xAA or 2xAA flashlight with decent regulation.

 

[TorchBoy]

Yes, but if you had to short it, it's delivering 0V * 17A = 0W. You should get maximum power in the load somewhere in the vicinity of 0.6-0.7V (matched impedance means half the voltage), and about half the current, so maybe 5.5W.

Oh yeah. I was thinking of the loaded voltage with 10 A, as per SilverFox's test. That's 10 W then. They're better than you think.

 

[wapkil]

Yes, but if you had to short it, it's delivering 0V * 17A = 0W.

Yeah, because obviously you managed to short it with a zero resistance connection, additionally eliminating the battery internal resistance. Zero watts means zero power, as evidenced by the wire that slowly starts to glow from the heat :nana:

 

[Benson]

Oh yeah. I was thinking of the loaded voltage with 10 A, as per SilverFox's test. That's 10 W then. They're better than you think.

Alright then, in that case you could probably get better than 15W out if you really load it down, and I'll bet you'd see more than 30A in a dead short. But I don't think I'll try it, since my multimeter's only rated for 10A...

 

[matrixshaman]

I'll let you in on a bit of a chuckle as to why I started this thread. A guy is claiming he is getting over 9000 watts out of circuit running off a single AA NiMh battery ...
As much as I've researched alternate energy and I really want to believe it's possible I think this one will go down as a major boondoggle with very flawed measurement procedures. What he's doing is charging a 650 Farad (yes that's Farad not microfarad) Ultracapacitor with the AA and a special circuit. The capacitor has a short term burst capability of 3500 amps at 2.7 volts so that's that's where he's getting his 9000 plus watts (Ohms law states Power in watts = Amps times volts). In reality this Cap can't put out nearly that much and the charging is interesting but I'll have to see it to believe the AA can fully charge that Cap (takes over half a day) and only lose .005 volts. No replications of this have been possible so far so as I said I think there are some problems with measurement procedures.

 

[Mr Happy]

I'll let you in on a bit of a chuckle as to why I started this thread. A guy is claiming he is getting over 9000 watts out of circuit running off a single AA NiMh battery ...
As much as I've researched alternate energy and I really want to believe it's possible I think this one will go down as a major boondoggle with very flawed measurement procedures. What he's doing is charging a 650 Farad (yes that's Farad not microfarad) Ultracapacitor with the AA and a special circuit. The capacitor has a short term burst capability of 3500 amps at 2.7 volts so that's that's where he's getting his 9000 plus watts (Ohms law states Power in watts = Amps times volts). In reality this Cap can't put out nearly that much and the charging is interesting but I'll have to see it to believe the AA can fully charge that Cap (takes over half a day) and only lose .005 volts. No replications of this have been possible so far so as I said I think there are some problems with measurement procedures.

Well gosh, it's perfectly possible to get 9000 watts from an AA battery if you can squeeze the energy into a short enough time period.

Here's the calculation:

Approximate energy capacity of an AA cell = 1.2 V x 2 Ah = 2.4 Wh

If we want 9000 W the discharge time is 2.4 / 9000 = 0.00027 h = ~1 s

So if you could discharge all the energy in an AA cell with perfect efficiency you could obtain 9 kW for approximate one second. However, such energy conversions are rarely close to 100% efficient, so conservatively we might expect 9 kW for half a second.

The most practical way to achieve this energy conversion is indeed to charge up a capacitor from the cell and then discharge it quickly. That is how camera flashes manage to produce a light vastly brighter than the sun from small batteries (how many watts is the sun?). A camera flash is about a thousand (a million?) times brighter than the brightest, most wicked hotwire ever seen on this forum.

Edit: I just did a quick check. As a rule of thumb, a camera flash has a power output in the order of 100 kW.

 

[Benson]

I'll let you in on a bit of a chuckle as to why I started this thread. A guy is claiming he is getting over 9000 watts out of circuit running off a single AA NiMh battery ...

Now if he'd said over 8000 -- or over 10000 -- I'd have believed him. Are you sure you haven't been trolled?

As much as I've researched alternate energy and I really want to believe it's possible I think this one will go down as a major boondoggle with very flawed measurement procedures. What he's doing is charging a 650 Farad (yes that's Farad not microfarad) Ultracapacitor with the AA and a special circuit. The capacitor has a short term burst capability of 3500 amps at 2.7 volts so that's that's where he's getting his 9000 plus watts (Ohms law states Power in watts = Amps times volts). In reality this Cap can't put out nearly that much and the charging is interesting but I'll have to see it to believe the AA can fully charge that Cap (takes over half a day) and only lose .005 volts. No replications of this have been possible so far so as I said I think there are some problems with measurement procedures.

Well, 2.4kJ is roughly a fourth of the total capacity of a NiMH battery, so charging that cap is definitely doable, and it shouldn't take all day, either. Now remember, for NiCd/NiMH, voltage isn't a reliable state-of-charge metric), so maybe, perhaps because of spending all day about it, the actual voltage recovers to within 5 mV (still seems pretty unlikely to me), but that doesn't change the fact that it's at least a quarter drained, and probably more like half drained.

 

[TorchBoy]

(how many watts is the sun?)

I think I remember a thread about that. Or it might have been about how many lumens it produces.

 

[Mr Happy]

If you measure it at sea level on a clear day at an angle perpendicular to the sun's rays the solar radiation is about 1000 W per square meter.

 

[matrixshaman]

Well gosh, it's perfectly possible to get 9000 watts from an AA battery if you can squeeze the energy into a short enough time period.

Here's the calculation:

Approximate energy capacity of an AA cell = 1.2 V x 2 Ah = 2.4 Wh

If we want 9000 W the discharge time is 2.4 / 9000 = 0.00027 h = ~1 s

So if you could discharge all the energy in an AA cell with perfect efficiency you could obtain 9 kW for approximate one second. However, such energy conversions are rarely close to 100% efficient, so conservatively we might expect 9 kW for half a second.

The most practical way to achieve this energy conversion is indeed to charge up a capacitor from the cell and then discharge it quickly. That is how camera flashes manage to produce a light vastly brighter than the sun from small batteries (how many watts is the sun?). A camera flash is about a thousand (a million?) times brighter than the brightest, most wicked hotwire ever seen on this forum.

Edit: I just did a quick check. As a rule of thumb, a camera flash has a power output in the order of 100 kW.

Mr Happy, I appreciate your input. However do you really think you can get that 9000 watts for even the theoretical ~1 second? You are going to need to push over 7000 Amps out of that battery at 1.2 volts. A dead short just isn't going to see that much current out of a AA. Even that monster UltraCap with it's half-inch diameter bolt ends isn't going to do that much.
I do see now though how one could arrive at such numbers in the slow charge being done with this battery. It is surprising how much energy can be available in a AA.
I'm more inclined to think this device is using a nuclear boost though

 

[TorchBoy]

And the surface area of a sphere with a radius of 150,000,000,000 m is... what?

 

[matrixshaman]

If you measure it at sea level on a clear day at an angle perpendicular to the sun's rays the solar radiation is about 1000 W per square meter.

And people say there is no such thing as 'free energy' They forget the energy from Sun light is not only free but the visible light is only part of what it radiates. Now if I could only figure out how to capture all that energy for free. I'd even be willing to pay a few bucks for it

BTW here is a pic of the circuit and battery (missing in the pic). This is not my circuit build. The claim is that a single AA will power the LED, charge the Capacitor and I think even light the incandescents part of the time all while barely using any battery power. I want to say 'pipe dream' ...