Hi,
Is there any way to know how many AMPs are comming out of a battery? Most batteries purchased at the shops dont tell you.
I have a voltmeter here but that only (you guessed it) shows volts!
Thanks in advance.
Amps is a rate of current flow. It depends on the load for a particular voltage. The battery will have a maximum rating which is determined by the physical makeup of the battery. You need the specs on your battery. Tom
That's because it depends upon the load connected to the battery.
If you know something about the load, like its power consumption or its resistance (assuming a resistive load), then you can work out the current being supplied at a given voltage. Otherwise, purchase an ammeter and measure the current!
--- The amount of current a battery can deliver into a load depends on the battery voltage, the internal resistance of the battery and the resistance of the load.
If you had an ammeter you could connect it in series with the load and measure the current.
If the load resistance was fixed and you knew what it was, or if you had an ohmmeter and could measure it, you could divide the load resistance into the battery voltage and get amps as the quotient.
If you have neither an ammeter nor an ohmmeter you might be pretty much shit out of luck.
Except...
You could get a very small valued resistor (a 'shunt') and put it in series with the load and the battery, then measure the voltage drop across the shunt.
Your circuit would look like this: (View in Courier)
+--------+ | | | [LOAD] |+ | [BATTERY] +
^^^^^^^ charge :-)
-- John Fields Professional Circuit Designer
I'm going to take a different take on the question. Perhaps he's asking how many amps the battery can supply at maximum load (lowest circuit resistance).
Batteries are "current limited" by the size of the internal electrodes affected by the chemical process.
A "AA" battery could source up to .5 Amps, "C" battery 1 Amp, and "D" cell up to 1.5 Amps. Two "D" cells in series is still 1.5 Amps. but two in parallel would be 3 Amps.
A five pound lead-acid battery might source up to 20 Amps and a forty pound one perhaps 100 Amps as the larger battery has bigger lead electrodes.
-- Not true. The internal resistance of a battery is due mainly to the resistance of the electrolyte.
OK John.
Well, OK..I was primarily considering the internal components of the battery. But even then, you're referring to the internal resistance vs current sourcing capacity. A small nuance of difference, but its all part of the big picture.
This is like asking how much water comes out of a garden hose. The answer is - as much as you want or need, up to a point. Two things determine how much water will flow from the hose - the valve or faucet setting, hose length and hose diameter (resistance) and the water pressure (voltage). As I open the valve more water will flow (current) and if my water pressure increases more water will flow.
Batteries usually show only the pressure (voltage) they provide because the current delivered by the battery depends on the load or application. Battery or cell types such as D, C, AA, etc are selected based on the current requirements for a particular application.
NEVER measure current like you would measure volts. A current measurement must always be done with the meter leads in series with the load. Meters have a very low resistance on the current (A) setting, to minimize the meters effect on the measurement. You can ruin a good meter by putting it on the current (A) setting and putting it across a battery. At best you'll blow a fuse.
Dorian
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