Adjustment of Variable Resistance in an automobile battery

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Discussion Overview

The discussion centers around the adjustment of variable resistance in automobile batteries, exploring whether this adjustment is mechanical (using potentiometers or rheostats) or electronic, and the implications of these configurations. Participants also touch on the role of potentiometers in automobiles beyond audio volume control.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that automobile batteries do not have variable resistance, providing a constant voltage and delivering current based on the load connected to them.
  • There is a suggestion that the term 'load' refers to the electrical accessories connected to the battery rather than a rheostat or potentiometer.
  • Some participants argue that using potentiometers or rheostats in automobile circuits would be inefficient due to heat production with large currents.
  • A question is raised about whether the alternator and battery should be treated as separate sources of emf or as a single system, with responses indicating that it depends on the context of the design being considered.
  • One participant mentions the internal resistance of a battery, comparing it to a thermistor that changes resistance with temperature.

Areas of Agreement / Disagreement

Participants generally agree that automobile batteries do not have adjustable variable resistance and that the load is determined by the connected accessories. However, there is no consensus on the treatment of the alternator and battery as separate or unified sources of emf, indicating ongoing debate.

Contextual Notes

Some assumptions about the definitions of terms like 'load' and 'variable resistance' may not be fully clarified. The discussion also reflects a lack of resolution regarding the practical applications of potentiometers in automotive contexts.

saadm
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TL;DR
Adjustment of Variable Resistance in an automobile battery
How is the load (variable resistance) adjusted in an automobile battery? Mechanically (potentiometer, rheostat) or electronically

(digital potentiometer) or are both configurations possible.Can the load in a automobile battery be a three terminal divider (potentiometer) or is it almost always a rheostat?

Besides adjusting audio volume, what else is a potentiometer useful for specially in an automobile?

Please let me know if I should start a new thread for this. I included the questions here because of their relevance to the topics discussed in this thread.

Thanks,
 
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saadm said:
How is the load (variable resistance) adjusted in an automobile battery?

Batteries don't have have a variable resistance in them. In normal operation, a battery simply provides a constant voltage (ignoring the effects of internal resistance).

The battery delivers current according to whatever the total load happens to be. E.g. if you turn the lights on, the battery delivers more current.

Maybe you are confusing this with a simple laboratory setup, where a battery and potentiometer or rheostat are used to perform experiments. That's not what happens in a automobile circuit.

saadm said:
Can the load in a automobile battery be a three terminal divider (potentiometer) or is it almost always a rheostat?
The 'load' just means whatever is connected to the battery, e.g. lights, starter motor, radio, wiper motor. It is never a rheostat,

Also, potentiometers and rheostats would be very wasteful because of the amount of heat they produce with large currents.

saadm said:
Besides adjusting audio volume, what else is a potentiometer useful for specially in an automobile?
Have you tried typing "automobile potentiometers" into a search engine? What did you find?

Edit - typo's corrected
 
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An automobile battery does NOT have an adjustable variable resistance.
The battery voltage remains reasonably fixed, usually near 12 volts.
The load current drawn from the battery by electrical accessories is determined by the individual accessories.
The battery is charged by an alternator. The voltage and charging current are regulated by changing the alternator field current.
 
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Baluncore said:
An automobile battery does NOT have an adjustable variable resistance.
The battery voltage remains reasonably fixed, usually near 12 volts.
The load current drawn from the battery by electrical accessories is determined by the individual accessories.
The battery is charged by an alternator. The voltage and charging current are regulated by changing the alternator field current.
Great minds think simultaneously!
 
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Steve4Physics said:
Great minds think simultaneously!
Great minds think alike, fools never differ.
 
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Great, thank you to Steve4Physics and Baluncore for the answers. One more question, the alternator and the battery are to be treated as two separate sources of emf or a single whole system of emf source?
 
While the engine is running, the alternator supplies all the accessories, and charges the battery.
When the engine is not running, the battery must supply the accessories.
The battery terminals are common to all circuits.
 
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saadm said:
... the alternator and the battery are to be treated as two separate sources of emf or a single whole system of emf source?
That depends on what you are trying to do. For example:

If you are designing a car’s charging-circuit, you would need to treat the battery and alternator as 2 separate sources of emf.

But if you are designing the car’s audio system, you would effectively treat the battery and alternator as a single unit – a ‘black box’ which always supplies 12V; you don't care how the 12V got there!

Also,did you find uses for potentiometers by doing a search?
 
saadm said:
TL;DR Summary: Adjustment of Variable Resistance in an automobile battery

How is the load (variable resistance) adjusted in an automobile battery? Mechanically (potentiometer, rheostat) or electronically

(digital potentiometer) or are both configurations possible.Can the load in a automobile battery be a three terminal divider (potentiometer) or is it almost always a rheostat?

Besides adjusting audio volume, what else is a potentiometer useful for specially in an automobile?

Please let me know if I should start a new thread for this. I included the questions here because of their relevance to the topics discussed in this thread.

Thanks,
If you are referring to the internal resistance. of a battery....
The internal resistance acts like a Thermistor....The resistance changes quickly with heat ..
 

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