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Godcer

Stupid question about batteries

14 hours ago, Godcer said:

This might be in the wrong subforum, but it was the closest I coul find. I don't know much about electronics, so this might be a really stupid question.

I know that batteries have a rated voltage, like regular AA batteries are rated at 1.5 volts and li-ion batteries are typically at 3.6-3.7 volts. The battery's voltage drops during use, and a dead AA battery is around 1.2 volts. Let's say that I have a device that requires 1.5 volts to operate, but how does it even work at all? I know this sounds dumb, but I just can't get it, because the battery's voltage drops when it is used, so how can it still work when the voltage is lower?

When a circuit is designed. the designer of that circuit is aware of these things and other things you're not even aware of.

 

Here's for example some things you might be interested about, and what designers usually keep track of when designing something

 

The voltage of a battery will vary depending on the battery's chemistry.

A regular alkaline battery you find in stores will have around 1.65v when fully charged and as you take energy out of it, you'll find the battery will still give a reasonable amount of energy up to as low as around 1.3v

However, a rechargeable alkaline battery because the chemicals inside are different, they'll have a peak voltage when fully charged at around 1.35v but as soon as you start taking energy from them, the voltage will quickly lower to around 1.25v and the battery will still give reasonable amount of energy down to as little as 1..1.1v

Also, more recently, companies have started to manufacture non-rechargeable batteries using Lithium, and you can easily find in stores lithoum AA batteries which will have a "fully charged voltage" hovering at around 1.8v and they'll slowly discharge down to maybe around 1v

 

A website tested a bunch of these AA batteries - and I'm proud to say I actually sent a bunch of batteries to the person that owns the website - and you can see how three different chemistries behave when something uses them (in this case, think as if the batteries are in a flashlight or something that uses a small constant amount of energy) :

 

Website : http://batteryshowdown.com/results-lo.html

Image :

 

curve-200ma-135.png

 

So designers are aware that the maximum voltage of the batteries may vary a lot but they mostly care about the lower threshold, where the batteries may no longer be able to output the minimum amount of energy the circuit requires. So for example, a designer may check the battery from time to time and, if the battery voltage goes below let's say 1.1v, the circuit may turn itself off on purpose even through there may still be some amount of "juice" in the batteries. They do this simply because below that threshold, the circuit may behave erratically and that's something that may make the product look bad.

Designers also have to keep in mind the temperature range where the product would be used. Most batteries are sensitive to cold, and the voltage of such batteries will be lower when batteries are cold and the energy will have a harder time coming out of batteries - think for example a person using a walkman or a cd player in the winter in an outside pocket of the jacket - the batteries' voltage may prematurely go below the minimum voltage and you may think the batteries are low, but as you go inside the house and the batteries warm up, they'll start working again.

 

The maximum voltage is not that critical, though there are electronic components like transistors or mosfets that are sensitive and can be damaged by big voltages.

 

In general, because of different techniques and manufacturing processes, in products using low voltages, the point where there's a risk of damaging integrated chips or components is generally at around 5.5v..6v

A smaller percentage of integrated circuits and components are more sensitive and can tolerate only about 3.3v to 3.6v

 

Some products aren't that sensitive to voltage, think for example clocks, or remote controls..

If a product requires a minimum voltage or a maximum voltage lower than what is provided by batteries, the product may have a circuit which converts that voltage into the desired voltage. You can have either a buck (step-down) regulator, which takes for example 2 x 1.5v down to let's say 2.5v , or you may have a boost (step-up) circuit which takes voltage from a couple of AA batteries and makes sure the voltage is raised to 3.6v or 5v or whatever is required by some components inside the product.

 

A minimum voltage is usually required by microcontrollers (tiny processors in products). Some microcontrollers can function with very low voltage up to certain speeds, for example let's say 1 Mhz with as little as 1v, but if you want more processing speed like 4 Mhz you may need at least 1.2v and if you need 8 Mhz you may need at least 1.8v and if you need 16 Mhz you may need 2.5v

So you could probably make a simple remote control or a clock using a microcontroller running at 1 Mhz but if you need something more complex that does a lot of calculations, you may want to add a step-up circuit to raise the voltage to the minimum the processor requires to function at 8 Mhz or 16 Mhz

 

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Posted · Original PosterOP

This might be in the wrong subforum, but it was the closest I coul find. I don't know much about electronics, so this might be a really stupid question.

I know that batteries have a rated voltage, like regular AA batteries are rated at 1.5 volts and li-ion batteries are typically at 3.6-3.7 volts. The battery's voltage drops during use, and a dead AA battery is around 1.2 volts. Let's say that I have a device that requires 1.5 volts to operate, but how does it even work at all? I know this sounds dumb, but I just can't get it, because the battery's voltage drops when it is used, so how can it still work when the voltage is lower?

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11 minutes ago, Godcer said:

This might be in the wrong subforum, but it was the closest I coul find. I don't know much about electronics, so this might be a really stupid question.

I know that batteries have a rated voltage, like regular AA batteries are rated at 1.5 volts and li-ion batteries are typically at 3.6-3.7 volts. The battery's voltage drops during use, and a dead AA battery is around 1.2 volts. Let's say that I have a device that requires 1.5 volts to operate, but how does it even work at all? I know this sounds dumb, but I just can't get it, because the battery's voltage drops when it is used, so how can it still work when the voltage is lower?

Most battery powered devices can accept a certain amount of voltage drop before cutting out or giving a low battery warning. There are certain devices that require a regulated supply so it will constantly give a specified voltage using circuity and also monitor the battery where it will cut off the again provide a low battery warning. 

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Part of it is also the current the battery can supply. As you pull more current from a battery, the voltage drops lower. I think a AA can take like half an amp before the voltage drops too low. This video talks a little more about voltage sag along with blowing shit up :)

 


ASU

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Most devices which are are using AA cells drop out between 0.8-1v per cell.

 

There should be a eevblog YT video about this.

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Posted · Best Answer
14 hours ago, Godcer said:

This might be in the wrong subforum, but it was the closest I coul find. I don't know much about electronics, so this might be a really stupid question.

I know that batteries have a rated voltage, like regular AA batteries are rated at 1.5 volts and li-ion batteries are typically at 3.6-3.7 volts. The battery's voltage drops during use, and a dead AA battery is around 1.2 volts. Let's say that I have a device that requires 1.5 volts to operate, but how does it even work at all? I know this sounds dumb, but I just can't get it, because the battery's voltage drops when it is used, so how can it still work when the voltage is lower?

When a circuit is designed. the designer of that circuit is aware of these things and other things you're not even aware of.

 

Here's for example some things you might be interested about, and what designers usually keep track of when designing something

 

The voltage of a battery will vary depending on the battery's chemistry.

A regular alkaline battery you find in stores will have around 1.65v when fully charged and as you take energy out of it, you'll find the battery will still give a reasonable amount of energy up to as low as around 1.3v

However, a rechargeable alkaline battery because the chemicals inside are different, they'll have a peak voltage when fully charged at around 1.35v but as soon as you start taking energy from them, the voltage will quickly lower to around 1.25v and the battery will still give reasonable amount of energy down to as little as 1..1.1v

Also, more recently, companies have started to manufacture non-rechargeable batteries using Lithium, and you can easily find in stores lithoum AA batteries which will have a "fully charged voltage" hovering at around 1.8v and they'll slowly discharge down to maybe around 1v

 

A website tested a bunch of these AA batteries - and I'm proud to say I actually sent a bunch of batteries to the person that owns the website - and you can see how three different chemistries behave when something uses them (in this case, think as if the batteries are in a flashlight or something that uses a small constant amount of energy) :

 

Website : http://batteryshowdown.com/results-lo.html

Image :

 

curve-200ma-135.png

 

So designers are aware that the maximum voltage of the batteries may vary a lot but they mostly care about the lower threshold, where the batteries may no longer be able to output the minimum amount of energy the circuit requires. So for example, a designer may check the battery from time to time and, if the battery voltage goes below let's say 1.1v, the circuit may turn itself off on purpose even through there may still be some amount of "juice" in the batteries. They do this simply because below that threshold, the circuit may behave erratically and that's something that may make the product look bad.

Designers also have to keep in mind the temperature range where the product would be used. Most batteries are sensitive to cold, and the voltage of such batteries will be lower when batteries are cold and the energy will have a harder time coming out of batteries - think for example a person using a walkman or a cd player in the winter in an outside pocket of the jacket - the batteries' voltage may prematurely go below the minimum voltage and you may think the batteries are low, but as you go inside the house and the batteries warm up, they'll start working again.

 

The maximum voltage is not that critical, though there are electronic components like transistors or mosfets that are sensitive and can be damaged by big voltages.

 

In general, because of different techniques and manufacturing processes, in products using low voltages, the point where there's a risk of damaging integrated chips or components is generally at around 5.5v..6v

A smaller percentage of integrated circuits and components are more sensitive and can tolerate only about 3.3v to 3.6v

 

Some products aren't that sensitive to voltage, think for example clocks, or remote controls..

If a product requires a minimum voltage or a maximum voltage lower than what is provided by batteries, the product may have a circuit which converts that voltage into the desired voltage. You can have either a buck (step-down) regulator, which takes for example 2 x 1.5v down to let's say 2.5v , or you may have a boost (step-up) circuit which takes voltage from a couple of AA batteries and makes sure the voltage is raised to 3.6v or 5v or whatever is required by some components inside the product.

 

A minimum voltage is usually required by microcontrollers (tiny processors in products). Some microcontrollers can function with very low voltage up to certain speeds, for example let's say 1 Mhz with as little as 1v, but if you want more processing speed like 4 Mhz you may need at least 1.2v and if you need 8 Mhz you may need at least 1.8v and if you need 16 Mhz you may need 2.5v

So you could probably make a simple remote control or a clock using a microcontroller running at 1 Mhz but if you need something more complex that does a lot of calculations, you may want to add a step-up circuit to raise the voltage to the minimum the processor requires to function at 8 Mhz or 16 Mhz

 

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16 hours ago, W-L said:

Most battery powered devices can accept a certain amount of voltage drop before cutting out or giving a low battery warning. There are certain devices that require a regulated supply so it will constantly give a specified voltage using circuity and also monitor the battery where it will cut off the again provide a low battery warning. 

I think you just described every smoke detector/alarm I've ever owned.

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7 hours ago, PineyCreek said:

I think you just described every smoke detector/alarm I've ever owned.

*3am seems like a good time to start* xD 

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