# [Q] basic electronics: Batteries

Discussion in 'Electronic Basics' started by [email protected], Sep 2, 2005.

1. ### Guest

Hi all,

I have a couple of basic questions on batteries. I only know very
silly questions.

There AA, D, C batteries in the market (Duracell, etc). Does anyone
know what amphare (current) for these batteries give?

If I have 1.5V AA battery, and for an example, it gives 50mA. (I have
no idea if it gives 50mA.) If a circuit needs 1.5V, but 100mA, what do
I need to do?

Thanks!

2. ### John PopelishGuest

I haven't gotten dressed, yet, but I will try to help.
Batteries are rated for some product of current and time, usually the
small ones use units of milliampere hours. Peak current possible is
usually thought of as short circuit current, but you get no voltage
under that condition. The short circuit current is the unloaded
voltage divided by the internal resistance. Smaller cells have higher
internal resistance. A practical maximum current would include a spec
for how low the cell voltage can sag (how much of the available
voltage is consumed as the current passes through the internal series
resistance).
That question might be better stated, "I have a 1.5V (no load) AA
battery, and for an example, it gives 50mA. with the voltage sagging
to no lower than 1.25 volts for an hour. If a circuit needs at least
1.25V, but 100mA for an hour, what do I need to do?" The answer is
that you either need to parallel 2 or more of these AA cells (not a
good idea unless you are sure all are equally fresh and from the same
batch) or you change to a larger size cell that has at least twice the
volume and half the internal resistance.

Here is a web page that lists some independent test results for
various cells and batteries:
http://www.zbattery.com/zbattery/batteryinfo.html
Does this data make sense in light of my explanation?

3. ### BobGGuest

Since he doesnt know much about electricity, maybe the water analogy
would help. Volts is like pressure, current is like gallons per minute,
and resistance is like the size of the hose. Also ohms law is fairly
simple.... E=IR... volts=current*ohms and Watts=volts*amps. That much
and some algebra will get you right up there with the engineers with
batchelors degrees.

4. ### WK2Guest

Thanks. Bear with me next time. ;-)

5. ### Bob MonsenGuest

AA batteries can give peak current of 10A or more. However, if you do that
you will quickly exhaust them. The capacity of batteries is usually
measured in 'amp hours' (or milli-amp hours). For example, assume your AA
cell is 1000 milliamp-hour. That means that if you draw 1A for 1
hour, or 100mA for 10 hours, or 10mA for 100 hours, you will exhaust the
battery. Unfortunately, the rate at which charge is pulled out (the
current) affects the actual amount of charge you can get. Generally, the
more current, the less total charge can be obtained.

Current also affects the voltage, since the battery can be thought of as
a resistor in series with a voltage source. As a cell discharges, it's
internal resistance increases. Thus, it's voltage goes down...
example, it gives 50mA. (I have no
There are different kinds of AA cells. Alkaline cells are the main kind of
'primary' cell, which basically means non-rechargeable. "secondary" cells
are rechargeable, and come in various tasty flavors, like nicad, nimh,
liion, etc. nicad and nimh cells are both 1.2 volts nominal, whereas liion
cells are 4.2V. They come in different 'capacities', amp hours. So, you
can get a 1700 mAH nimh cell, or a 3000mAH nimh cell. They are both 1.2V,
but one will last longer given a particular current requirement. Some
cells are also constructed to have different maximum current capabilites.
For RC aircraft use, for example, you want to have high max current,
because the electric motors take large currents. For a tape player, you
may only want 100mA, so a battery that lasts longer, but doesn't allow
larger max currents can be used.

You can find out more by going to the duracell site, and looking at the
battery specifications.

Look here: http://www.duracell.com/oem/

--
Regards,
Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
Thomas Henry Huxley, 1877

6. ### redbellyGuest

And those voltages are not fixed numbers either. A freshly charged
NiMH cell has about 1.4 to 1.5 V, which slowly drops during use.
I've measured close to 3.2 V on brand new "3V" lithium coin cells.

Mark

7. ### Bill GrayGuest

So a bare bear would be furless?

Bill

9. ### Jasen BettsGuest

look at the lamps used in torches (US:flashlights) an AA powered torch will
typically have globe that uses upto 500 mA etc...

from a list in a catalogue I get the following

AA 500mA
C 600mA
D 750mA

these figuures depend somewhat on the batteries involved,
AA size NiCd cells can produce 2 or 3 amps quite readily, but it's nore real
good fo them...

unfortunately the makes of primary (non rechargable) baatteries don't seem to
publish their technical specifications...

at 500mA an AA cell isn't going to last real long (hours?)

Bye.
Jasen

12. ### Nikolas BrittonGuest

At 0.5A your typical AA alkaline battery will be dead well before the 3
hour mark.

*Motors: NiCd, non-rechargeable lithium's, alkaline's.
*Moderate ~ High drain solid state devices: Li-ion and NiMH
rechargeables.
*Low drain devices: Any type, rechargeable Li-ion and NiMH cells should
not be used with simple, analog, resistive loads such as lamps and
motors because they can potentially damage the cell if you let the
device completely drain it, not good for NiMH cells.
*Flashlights, smoke alarms, pocket radios, TV remote controls: Alkaline
or other non-rechargeables that have a *long* shelf life. All batteries
self discharge but rechargeable batteries have a very high self
discharge rate, NiMH's have the highest self discharge rate at around
1% per day, logarithmic decay. This self discharge can be slowed by
storing batteries in the fridge, but not the freezer!

Rechargeable lithium ion cells work at 3 ~ 3.6V, so, you won't find
them in AAA, AA, C, or D format because those are all 1.2 ~ 1.6V cell
formats, the next best thing to Li-ion's are nickel metal hydride
(NiMH) cells. These things are perfect for today's high drain digital
devices because... well, this guy puts it in better words then I can:
http://dpfwiw.com/batteries.htm#alkaline2 Also they have no "memory
effect" and with a good smart, "microprocessor controlled", charger the
batteries can last 500 - 1000 charge/discharge cycles.

Also check out this site, pay attention to the "Watt-hours" column in
the battery table and note that the Alkaline cells are all the way at
the bottom: http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM

and you can lookup data sheets here: http://data.energizer.com/ and buy
NiMH/NiCd stuff here: http://thomas-distributing.com/