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Q: How Much Current Can an 'AA' Battery Supply? ( Answered ,   6 Comments )
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 Subject: How Much Current Can an 'AA' Battery Supply? Category: Science > Physics Asked by: jjsonp-ga List Price: \$5.00 Posted: 26 Mar 2006 15:21 PST Expires: 25 Apr 2006 16:21 PDT Question ID: 712235
 I have 2 Energizer brand AA batteries, rechargeable NiMH type. 2500 milliamp-hours. They are labeled as 1.2 volt as well. Now, if put these two in series, I believe the voltage is additive. Also I now have 5000 milliamp-hours (or 5 amp-hours) of total usable energy, theoretically. My question is, how do I determine how many amps these two batteries can load at a given time? Is there a limit? For instance if I have 5 amp-hours available, can I run a 5-amp motor for an hour? Or a 10-amp motor for half an hour? Or is there some lower limit of the current draw of the motor, and determined by...what? If someone knows the answer, I'm assuming it's a quite simple, one- sentence answer. A link would be appreciated as well.
 Answer
 Subject: Re: How Much Current Can an 'AA' Battery Supply? Answered By: hedgie-ga on 26 Mar 2006 18:44 PST Rated:
 see at least two questions here: 1) Do capacity of the battery, and voltage add when you connect them in series? Yes. You will have now 5 amp-hours, and so you can run .1 A bulb for 50 h or .05 A bulb got 100h 2) Can you run 10-amp motor on a dry cell battery? No. Batteries have an inner resitance, which limits the current they can deliver. Those resistances add also, in series: One battery has upper limit V/Ri on current it will supply at short,and two baterries in series will have same max current limit 2*V / 2 * Ri. If you connect in parallel, max current will double. capacity http://en.wikipedia.org/wiki/Battery_(electricity)#Battery_concepts inner resistance http://www.dokidoki.ne.jp/home2/tohrus/battery/battest0E.html In general, for a load (e.g. a bulb) with resistance R, the current supplied by the battery is: I= V / (R + Ri) (Ohms law for equivalent circuit) Equivalent circuit is shown here ( our R.i is their r ) under heading: The emf of a battery: where it says: The equivalent circuit is shown on the left, where r is the internal resistance of the battery with emf E, connected to a circuit with resistance R. The voltmeter measures the potential difference across R and not the emf of the battery which is equivalent to the potential difference across (R + r). http://www.physchem.co.za/Current%20Electricity/Heating.htm Hedgie - rating appreciated Request for Answer Clarification by jjsonp-ga on 27 Mar 2006 11:45 PST Thanks hedgie. That clears things up somewhat. However, you did not provide a specific answer to my question: "...how do I determine how many amps these two batteries can load at a given time? Is there a limit?" Do I need to use a multimeter to measure the internal resistance, and then calculate the maximum current they can provide using the formula you mention (i=v/ri)? I still want to know exactly how to determine the maximum current 2 AA batteries can provide. Clarification of Answer by hedgie-ga on 28 Mar 2006 12:52 PST jjsonp-ga I do not recommend "using the formula you mention (i=v/ri)". as it requires shorting a battery and that is not a good idea (for several resons) which I will not elaborate (since I know the answer) and you are right, that: " If someone knows the answer, I'm assuming it's a quite simple, one- sentence answer. .." I suggest that you use the formula for equivalent circuit with a reasonable load I= V /(R + Ri) for two ( or several values of R ) (one, two, three, flashlight bulbs, in series and parallel ..) For each mesurement your get pait of values (R and I) (same V for all) You can then plot V/I vs R + Ri and get a line, roughly Ri is a constant (you get when you extrapolate V/I-->0 and do not forget that R.i will change somewhat over the life of a battery and with temperature. Rating appreciated Hedgie
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 Comments
 Subject: Re: How Much Current Can an 'AA' Battery Supply? From: isnraju-ga on 26 Mar 2006 19:37 PST
 The internal resiatance o the battery consumes power as seen by heating of the battery. so part of 5Ah is consumed inside especially aat higher loads. But baaery capacity is again deFined to a cell end voltage. There will be still some power after %Ah has been used. But this may not be adequate to run the equipment.
 Subject: Re: How Much Current Can an 'AA' Battery Supply? From: larryg999-ga on 27 Mar 2006 07:30 PST
 "I have 2 Energizer brand AA batteries, rechargeable NiMH type. 2500 milliamp-hours. They are labeled as 1.2 volt as well." If you place these two AA batteries in SERIES, the resulting voltage adds to 2.4 volts but the current capacity = 2.5 amp-hours (NOT 5.0 amp-hours). If you place these two AA batteries in PARALLEL, the resulting voltage = 1.2 volts and the current capacity = 5.0 amp-hours. This is a logical consequence of the fact that each AA battery has a fixed ENERGY-storage capacity = 6.0 volt-amp-hours = 6.0 watt-hours.
 Subject: Re: How Much Current Can an 'AA' Battery Supply? From: rracecarr-ga on 27 Mar 2006 14:48 PST
 larry is right. Connecting batteries in series will not give you more amp-hours. Also, the maximum current that can be supplied is the same with one battery or 2 in series. Only the voltage is doubled. There is no minimum current.
 Subject: Re: How Much Current Can an 'AA' Battery Supply? From: isnraju-ga on 05 Apr 2006 15:43 PDT
 also every battery has rating based on discharge rate. so you may get 5Ah at say 5hour rate of 1A but at 1 hour rate you dont get 5A.
 Subject: Re: How Much Current Can an 'AA' Battery Supply? From: bipolarmoment-ga on 13 Apr 2006 18:04 PDT
 isnraju is very correct. I did lots of research on different battery types (NiCad, NiMH, etc.) during an ASME design project. Discharge rates can vary by battery type, temperature and how much stored energy is left. Generally, for everyday batteries (A,AA,etc.) NiMH are the best in every respect compared to NiCad or Alkaline--though all three will vary between brand so be wary. Lithium Ion generally have crazy energy density but not as great at power discharge.
 Subject: Re: How Much Current Can an 'AA' Battery Supply? From: samatros-ga on 10 Jun 2006 18:46 PDT
 I'm not sure if you still need help, but Energizer keeps data sheets on their batteries, which might be of some use to you. In reference to battery nh15-2500 (An Energizer 1.2v 2500mAh rechargeable NiMH battery): "The internal resistance of the cell varies with state of charge, as follows: Cell Charged: 30 milliohms Cell 1/2 Discharged: 40 milliohms (Tolerance ±20% applies to the above values)" (http://data.energizer.com/PDFs/nh15-2500.pdf , 1) For other Energizer batteries, you can search on http://data.energizer.com/ with the appropriate category.
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