Ohm's Law

I am having issues with a calculation-

If a AA battery has is 1.5V, 3 AA would be 4.5V.

If a AA battery has is 2.3 Amps, 3AA would be 6.9 Amps.

If I am using a 10 ohm resistor the it comes out to 69Volts.

If I=Volts/ Ohms I get either .45 or 6.9 Amps.

What am I doing wrong?

The batteries combine to 4.5V only if they are in series, and the total capable amperage combines to 6.9A only if the batteries are in parallel. They can't be both.

Well, if you have three AAs in series, you can't just add the currents together. The current should be the same through each battery. I think what you want to do is look at the total voltage across the batteries, and using the resistance you apply across that voltage you can determine the current. However, I think that batteries can be limited in the amount of current they can supply, so you might not actually get that amount of current through them if the resistance is too low. Hopefully someone will correct me if what I say is wrong.

DanielJ said:

If I am using a 10 ohm resistor the it comes out to 69Volts.?

Click to expand...

The fact that you are calculating 69 volts from a battery combo that you already know to be 4.5v tells me that you are doing something wrong. Im not sure what to tell you other than your math is incorrect.

Three 1.5V @ 2.3Ah AA batteries in series = 4.5v @ 2.3Ah
Three 1.5V @ 2.3Ah AA batteries in parallel = 1.5v @ 6.9Ah


Three 1.5v AA batteries in series (4.5v) through a 10ohm resistor = 0.45A
Three 1.5v AA batteries in parallel (1.5v) through a 10ohm resistor = 0.15A

Thanks Seth. I feel so stupid doing these simple equations incorrectly.

DanielJ said:

Ohm's Law

I am having issues with a calculation-
If a AA battery has is 1.5V, 3 AA would be 4.5V.
If a AA battery has is 2.3 Amps, 3AA would be 6.9 Amps.
If I am using a 10 ohm resistor the it comes out to 69Volts.
If I=Volts/ Ohms I get either .45 or 6.9 Amps.
What am I doing wrong?​

Click to expand...

WOW,
now this is REALLY totally wrong ...


as has been typed:
when You put the cells in series, the voltage adds together,
when You put the cells in parallel, the mAh add together.

Now to ohms law:
R = U / I
... that leads You the resistor value for a current that is given.

Example: You have three cells in series --> 4,5 V
You have a red led (2.5 V) You want to drive with 20 mA ...
You have "too much" voltage and have to get rid of the excess ...
R = U / I
R = (4.5-2.5) / 0.020
R = 100 Ohm