[Q] basic electronics: Batteries

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.

Thanks. Bear with me next time. ;-)

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

Here is a web page that lists some independent test results for various cells and batteries:

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:

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

So a bare bear would be furless?

Bill

The appropriate question is, will he help you bear your burden?

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

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

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:

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:

and you can lookup data sheets here: