Confusion between Amps and Watt

[K3nobi]

One night, I was about to go to sleep. Suddenly, it hits me. Why does phone batteries uses the unit milliamp-hour meanwhile laptop batteries uses the unit watt-hour. I then wasn't able to sleep that night, thinking why are there 2 units to measure battery capacity, along with some embarrassing stuff that I did a few months ago.

 

So the next day, I went ahead and watch a lot of videos explaining Watts, Amps and Voltage. Even though I get what voltage is supposed to do in an electric circuit, I still couldn't get what Watt and Amps is supposed to be. I mean like yeah there is video on Techquickie but even that is still giving me confusion. (Not to say that LMG make a bad explanation of it, it's just that I am a dumb F.)

 

Like is Amps supposed to mean the amount of electric that is stored meanwhile Watt is supposed to mean the rate the electric is flowing. 

 

(I know the story is a bit weird. I tried splicing two not-that-different stories [one story is about watt amps and voltage meanwhile the other story is about the battery capacity above] together and this spaghetti was made)

[The1Dickens]

4 minutes ago, Ionixt said:

One night, I was about to go to sleep. Suddenly, it hits me. Why does phone batteries uses the unit milliamp-hour meanwhile laptop batteries uses the unit watt-hour. I then wasn't able to sleep that night, thinking why are there 2 units to measure battery capacity, along with some embarrassing stuff that I did a few months ago.

 

So the next day, I went ahead and watch a lot of videos explaining Watts, Amps and Voltage. Even though I get what voltage is supposed to do in an electric circuit, I still couldn't get what Watt and Amps is supposed to be. I mean like yeah there is video on Techquickie but even that is still giving me confusion. (Not to say that LMG make a bad explanation of it, it's just that I am a dumb F.)

 

Like is Amps supposed to mean the amount of electric that is stored meanwhile Watt is supposed to mean the rate the electric is flowing. 

 

(I know the story is a bit weird. I tried splicing two not-that-different stories [one story is about watt amps and voltage meanwhile the other story is about the battery capacity above] together and this spaghetti was made)

Amps is the current, Watt is the work done. Amp * Volts = Watt

[manikyath]

watts = volts * amps

 

watts is a measure of amount of power (sort of like the amount of water moving)

volts is a measure for the "potential" (sort of like the width of whatever water is moving trough)

ampere is a measure of energy flow (sort of like the speed of water moving)

 

watts times hours = watthours, comparable to an amount of liters moved.

amps times hours = amphours, comparable to the amount of time a body of water (lets say a bucket) can sustain a certain flow speed.

 

for laptops watthours makes sense, because your laptop uses X number of watts, which makes for a direct calculation to amount of hours left. the battery controller and power circuitry in this case managing voltage differences for you.

 

for "bare batteries" (like when looking at the rating of AA batteries) amphours makes sense, because it is more relatable to current flow impacting battery life, and in a lot of battery-powered cases the voltage is actually of lesser concern.

 

as for why phone batteries list their capacity in amphours... i presume that goes back to the days of phone batteries literally being a pack of AA or AAA cells, and the circuitry not having voltage management anyways.

for modern phones watthours makes more sense, but there is also very little point in changing the standards, because at least everyone within a product category is sticking to the same standards, and all modern phones (i'm aware of) use a 3.7 volt lithium cell, so in a sense the voltage concern does not come into account when calculating capacity in watthours.

 

on the flip side of that story.. is those usb battery banks... for what i can only assume are marketing reasons, a lot of manufacturers decide to pretty much copy the amphour rating of the battery inside, to the outside of the enclusre, conveniently forgetting the battery is 3.7 volts, and the device output is 5 volts, making about a 25% difference in resulting amphour ratings.

the above being the reason why when you measure amphour ratings of battery banks on the 5 volt side, it is notably common to measure far less than the 'rated capacity', and why some manufacturers seem to have very disappointing amphour ratings compared to others for a similar size battery pack.

 

EDIT: should add, it is also very common for laptop batteries to range between 1 and 4 cells, meaning voltage ranging between 3.7 and 14.8 volts.

[straight_stewie]

Coloumb = 6.25x10¹⁸ electron charges

Ampere = 1 Coloumb / 1 Second

Ampere-hour = (1 Coloumb / 1 Second) * 36,000 Seconds = 3,600 Coloumbs / 1 Hour = 2.25x10²² electron charges / 1 hour

 

Given the above, the Ampere-Hour is a unit of electricity flow over time.

 

Watts are significantly harder to show in this way, at least relative to electrical terms, because the definition of Watt relies on the definition of Joule which relies on the definition of Volt which in turn relies on the definition of Joule, creating a recursive definition.

So, without showing the derivation for Watt-Hours (bummer), a Watt-Hour is a unit of power over time.

 

Power is a commonly misunderstood thing, I'll leave it up to you to look up the actual definition of power in physics terms.

[manikyath]

2 minutes ago, straight_stewie said:

Coloumb = 6.25x10¹⁸ electron charges

Ampere = 1 Coloumb / 1 Second

Ampere-hour = (1 Coloumb / 1 Second) * 36,000 Seconds = 3,600 Coloumbs / 1 Hour = 2.25x10²² electron charges / 1 hour

 

Given the above, the Ampere-Hour is a unit of electricity flow over time.

 

Watts are significantly harder to show in this way, at least relative to electrical terms, because the definition of Watt relies on the definition of Joule which relies on the definition of Volt which in turn relies on the definition of Joule, creating a recursive definition.

So, without showing the derivation for Watt-Hours (bummer), a Watt-Hour is a unit of power over time.

 

Power is a commonly misunderstood thing, I'll leave it up to you to look up the actual definition of power in physics terms.

i appreciate the extremely scientific explanation.. but you may have just confused OP even more

[JovanD]

Watts are like horsepower for electricity, you measure horsepowerr with Torque * RPM and you measure watts with Voltage * Amps, simple as that

[straight_stewie]

11 minutes ago, manikyath said:

i appreciate the extremely scientific explanation.. but you may have just confused OP even more

Better to spend a few minutes explaining what power and flow are in plain English than a few days explaining how it's possible that a Joule is Volt * Coloumb while a Volt is Joule / Coloumb.

[K3nobi]

5 hours ago, manikyath said:

but you may have just confused OP even more 

You're god damn right

[Unimportant]

6 hours ago, Ionixt said:

One night, I was about to go to sleep. Suddenly, it hits me. Why does phone batteries uses the unit milliamp-hour meanwhile laptop batteries uses the unit watt-hour. I then wasn't able to sleep that night, thinking why are there 2 units to measure battery capacity, along with some embarrassing stuff that I did a few months ago.

 

So the next day, I went ahead and watch a lot of videos explaining Watts, Amps and Voltage. Even though I get what voltage is supposed to do in an electric circuit, I still couldn't get what Watt and Amps is supposed to be. I mean like yeah there is video on Techquickie but even that is still giving me confusion. (Not to say that LMG make a bad explanation of it, it's just that I am a dumb F.)

 

Like is Amps supposed to mean the amount of electric that is stored meanwhile Watt is supposed to mean the rate the electric is flowing. 

 

(I know the story is a bit weird. I tried splicing two not-that-different stories [one story is about watt amps and voltage meanwhile the other story is about the battery capacity above] together and this spaghetti was made)

In simple terms, mAh is the amount of current, in milliamps, the battery can supply for an hour. So a 1500mAh battery would be able to supply 1.5A for an hour, or 3A for half an hour, etc... (In reality it's not as linear as that, but let's keep it simple). It's an absolute number for a certain battery, regardless of battery voltage.

 

Wh is the amount of energy the battery can supply for an hour. The battery voltage affects this. A 5V, 1500mAh battery would equate to 7500mWh or 7.5Wh. A 10V, 1500mAh battery would be 15000mWh or 15Wh, etc...

 

Phone batteries all tend to be single-cell li-ion these days, which are all 3.7V. Given that the voltage is always the same, I guess they just chose to go with the mAh rating.

However, laptop batteries are available in different voltages. The voltage can be whatever the manufacturer chose to go with for that particular laptop. Some are 11.1V, others are 14.8V and so on. In this case it makes more sense to go with the Wh rating.