Why does a battery die when connected on prallel?

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Discussion Overview

The discussion revolves around the behavior of a 9V battery connected in parallel with a 2.kΩ resistor and a multimeter during a lab experiment. Participants explore the reasons for the battery overheating and becoming unusable, as well as the implications of measuring current incorrectly in such a setup.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant observed that the battery became hot and unusable, suggesting a potential short circuit.
  • Another participant proposed that the high initial current reading could indicate a short across the battery terminals.
  • Some participants questioned the configuration of the multimeter, suggesting it may have been incorrectly set to measure current in parallel rather than in series with the resistor.
  • There is speculation that the actual current could have been much higher than the reported 30mA, with estimates suggesting it could be around 300mA.
  • Concerns were raised about the accuracy of the multimeter reading, with suggestions that the participant may not have been using a digital meter or may have misread the scale.
  • One participant referenced a document indicating that a typical 9V battery could briefly deliver around 4 amps, raising questions about the internal resistance and power output of the battery in this scenario.
  • Another noted that some digital multimeters have a separate socket for high current ranges, which could lead to misreadings by a factor of 10 or more.

Areas of Agreement / Disagreement

Participants generally agree that the multimeter was likely misconfigured, leading to incorrect current readings. However, there is no consensus on the exact nature of the circuit's behavior or the implications of the readings, as multiple competing views remain regarding the interpretation of the measurements and the battery's performance.

Contextual Notes

There are unresolved questions regarding the assumptions made about the multimeter's settings, the interpretation of the current readings, and the internal resistance of the battery. The discussion reflects varying levels of understanding about circuit configurations and measurement techniques.

polaris90
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During one of my labs we were using circuits. I connected a 9V battery in parallel with a 2.kΏ resistor and a multimeter. I meaured the current across the circuit and noticed it went really high at the beginning (about 30mA) and then it slowly went down and the battery became really hot and unusable. Why did that happened? I've been trying to find why the battery would get hot and stop working. Any help?
 
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Because you created a short across the battery terminals.

It would be like connecting a light bulb to the battery. Depending on the wattage of the resistor, it may have gotten hot as well.
 
polaris90 said:
During one of my labs we were using circuits. I connected a 9V battery in parallel with a 2.kΏ resistor and a multimeter. I meaured the current across the circuit and noticed it went really high at the beginning (about 30mA) and then it slowly went down and the battery became really hot and unusable. Why did that happened? I've been trying to find why the battery would get hot and stop working. Any help?

The battery is obviously shorted.

What two devices were in parallel exactly? The resistor and the multimeter (as an ammeter)? What setting was the multimeter on?
 
polaris90 said:
During one of my labs we were using circuits. I connected a 9V battery in parallel with a 2.kΏ resistor and a multimeter. I meaured the current across the circuit and noticed it went really high at the beginning (about 30mA) and then it slowly went down and the battery became really hot and unusable. Why did that happened? I've been trying to find why the battery would get hot and stop working. Any help?

It sounds like you had a short circuit.
9 volts / 2000 ohms = 4.5 ma
This would occur if you connected your multimeter in parallel with your resistor while in the amps mode. It should be placed in series with the resistor when measuring current.
 
OmCheeto said:
This would occur if you connected your multimeter in parallel with your resistor while in the amps mode.
Yeah. That's where I was going too.
 
he did say ""I meaured the current across the circuit .."" and got 30 ma, presumably not through 2K..

Polaris, go to "Electrical Engineering and read this thread :

"" why must ammeter be connected in series?""
 
Last edited:
polaris90 said:
During one of my labs we were using circuits. I connected a 9V battery in parallel with a 2.kΏ resistor and a multimeter. I meaured the current across the circuit and noticed it went really high at the beginning (about 30mA)
The current was much higher than 30mA. You were not reading the right scale. I surmise that you were not using a digital meter? 300mA possibly.
 
NascentOxygen said:
The current was much higher than 30mA. You were not reading the right scale. I surmise that you were not using a digital meter? 300mA possibly.

no, as Jim hinted at, I bet he was trying to read the current in parallel across the cct instead of in series and the poor meter was shortcircuiting the battery

Dave
 
davenn said:
no, as Jim hinted at, I bet he was trying to read the current in parallel across the cct instead of in series and the poor meter was shortcircuiting the battery

Dave

I think the current would have to be much higher than 30 ma with a short circuit. That would mean the internal resistance is 330 ohm, and only 0.27 Watt of power would be produced in the battery.
 
  • #10
davenn said:
no
yes

I bet he was trying to read the current in parallel across the cct instead of in series and the poor meter was shortcircuiting the battery
That premise was fundamental to my reply. That the meter was shorting the meter is not in question, a 9v battery is not going to get hot powering either a 330Ω load, or delivering 30mA.

Not only was the meter incorrectly connected to the resistor, but OP has not interpreted the meter reading correctly, regardless of whether it was digital or analog. That 30mA was not 30mA, maybe it was 300mA.

I suggested analog, simply because I find it difficult to see how a digital reading could be misread too low by a factor of 10. Maybe there was a blob of solder on the readout and this was mistaken for a decimal point?
 
Last edited:
  • #11
here's short circuit tests on the common 9 volt 1604 "transistor radio battery" . Looks like they are capable of ~ 4 amps, briefly.

friedrichengineering.com/web_documents/9volt%20Battery.pdf
 
  • #12
Quite a few (cheap) digital multimeters have a separate socket for an unfused 10A range. You have to plug and switch range, so a misreading of a factor 10 (or even 100) is definitely possible.
 

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