Maximum current from a battery

Click For Summary

Discussion Overview

The discussion revolves around the maximum current that can be drawn from a battery, specifically considering the effects of internal resistance and the implications of connecting resistors in parallel. Participants explore theoretical limits, practical considerations, and the behavior of batteries under different conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that a battery with 1 ohm internal resistance and 9 V can produce a maximum current of 9 amps when connected to wires with zero resistance.
  • Another participant argues that connecting a 0.5 ohm resistor in parallel does not allow for surpassing the maximum current, as the internal resistance limits the current.
  • Some participants propose that the maximum current can be calculated as voltage divided by internal resistance, but this may not account for all factors.
  • A later reply questions the simplification of internal resistance, noting that higher loads can affect the battery's emf due to temperature changes from power dissipation.
  • Participants mention that batteries are rated for short circuit current, but they are not designed to be short-circuited.
  • Discussion includes the behavior of PV cells, which are characterized by open circuit voltage and short circuit current, with some participants noting that high currents can be managed in specific applications.

Areas of Agreement / Disagreement

Participants express differing views on the implications of internal resistance and the behavior of batteries under load. There is no consensus on whether the maximum current can be exceeded or how internal resistance should be interpreted in practical scenarios.

Contextual Notes

Limitations include the assumption that internal resistance can be treated as a simple series resistance, and the discussion does not resolve how temperature affects emf in batteries under high current conditions.

abdo799
Messages
168
Reaction score
4
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?
 
Physics news on Phys.org
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.
 
So basically maximum current = voltage/internal resistance and i can never surpass it
 
Yep.
 
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.
 
Yup...i got it
 
abdo799 said:
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.
 
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.
 
sophiecentaur said:
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.
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 105 ·
4
Replies
105
Views
12K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 32 ·
2
Replies
32
Views
5K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 14 ·
Replies
14
Views
6K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 57 ·
2
Replies
57
Views
13K
  • · Replies 11 ·
Replies
11
Views
2K