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Maximum current from a battery

by abdo799
Tags: battery, current, maximum
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abdo799
#1
Dec21-13, 05:14 AM
P: 98
If we had a battery with internal resistance 1 ohm and 9 V.
If we connected to just wires ( resistance 0) i will produce a 9 amps current. Is this the maximum current? If we connect to this battery a 0.5 ohm resistor (in parallel ) the total resistance will be lower than one, will the current produced be greater than 9 amps?
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K^2
#2
Dec21-13, 05:33 AM
Sci Advisor
P: 2,470
You can't connect a resistor so that it's in parallel with internal resistance of battery with respect to the voltage drop of the battery. So yeah, you get maximum current if you just short the battery out.
abdo799
#3
Dec21-13, 05:43 AM
P: 98
So basically maximum current = voltage/internal resistance and i can never surpass it

mikeph
#4
Dec21-13, 06:57 AM
P: 1,212
Maximum current from a battery

Yep.
CWatters
#5
Dec21-13, 10:14 AM
P: 3,143
If we connected to just wires ( resistance 0) i will produce a 9 amps current. Is this the maximum current? If we connect to this battery a 0.5 ohm resistor (in parallel ) the total resistance will be lower than one...
The total resistance will be higher than one.
abdo799
#6
Dec21-13, 11:47 AM
P: 98
Yup...i got it
sophiecentaur
#7
Dec22-13, 10:03 AM
Sci Advisor
Thanks
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P: 12,157
Quote Quote by abdo799 View Post
If we had a battery with internal resistance 1 ohm and 9 V.
If we connected to just wires ( resistance 0) i will produce a 9 amps current. Is this the maximum current? If we connect to this battery a 0.5 ohm resistor (in parallel ) the total resistance will be lower than one, will the current produced be greater than 9 amps?
The idea of 'internal resistance' is not that simple. What actually happens inside batteries cannot necessarily be reduced to a simple series ohmic resistance when the load gets higher and higher. Any power dissipated inside the case will raise its temperature and this can alter the emf produced by the chemical process. Batteries are sometimes rated by their short circuit current (for a brief, specified, time) but they are not designed with a short circuit in mind.
Otoh, interestingly, PV cells are usually characterised in terms of open circuit volts, short circuit current and maximum power output (at specified temperatures). Continuously taking near-short circuit current is not too harmful for PV cells I believe.
CWatters
#8
Dec22-13, 10:37 AM
P: 3,143
Very true. Model aircraft and car racing competitors carefully control the temperature of their battery packs to get the best out of them. It's possible to get very high currents out of some quite small cells if you know what you are doing.
Borek
#9
Dec22-13, 02:12 PM
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Quote Quote by sophiecentaur View Post
Any power dissipated inside the case will raise its temperature and this can alter the emf produced by the chemical process.
http://en.wikipedia.org/wiki/Nernst_equation

Basically voltage is directly proportional to the temperature.


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