I get that, for a house/solar battery, it sort of makes sense as your typical energy usage would be measured in kWh on your bills. For the smaller devices, though, the chargers are usually rated in watts (especially if it’s USB-C), so why are the batteries specified in amp hours by the manufacturers?
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mAh as a unit for capacity is just a scam, because you don’t know the voltage and therefore not the batterie’s real capacity. But 3000 mAh sounds much better than 9 Wh. That’s why.
The correct SI unit for charge is Coulomb (1 C = 1 As), but for some reason nobody uses it.
The correct SI unit for charge is Coulomb (1 C = 1 As), but for some reason nobody uses it.
The correct SI unit for charge is Coulomb (1 C = 1 As), but for some reason nobody uses it.
Ah is the capacity of a battery, Wh is also the capacity of a battery. Both are giving you an estimate of how big the capacity is of a battery.
A battery with 10 Ah, running with 24 V will have a capacity of 240 Wh.
A battery with 240 Wh running with 24V will have a capacity of 10 Ah.
The 10 Ah will be able to give you 10 A for an hour, or 1 A per hour for 10 hours.
The 240Wh will be able to give you 240W for 1 hour or 24W for 10 hours.
How long your battery hold depends on the voltage and the item you are using the electricity for (how many watt it draws).
Ah is the capacity of a battery, Wh is also the capacity of a battery. Both are giving you an estimate of how big the capacity is of a battery.
A battery with 10 Ah, running with 24 V will have a capacity of 240 Wh.
A battery with 240 Wh running with 24V will have a capacity of 10 Ah.
The 10 Ah will be able to give you 10 A for an hour, or 1 A per hour for 10 hours.
The 240Wh will be able to give you 240W for 1 hour or 24W for 10 hours.
How long your battery hold depends on the voltage and the item you are using the electricity for (how many watt it draws).
Ah is the capacity of a battery, Wh is also the capacity of a battery. Both are giving you an estimate of how big the capacity is of a battery.
A battery with 10 Ah, running with 24 V will have a capacity of 240 Wh.
A battery with 240 Wh running with 24V will have a capacity of 10 Ah.
The 10 Ah will be able to give you 10 A for an hour, or 1 A per hour for 10 hours.
The 240Wh will be able to give you 240W for 1 hour or 24W for 10 hours.
How long your battery hold depends on the voltage and the item you are using the electricity for (how many watt it draws).
Amp-hours is a measure of charge, Watt-hours is measure of energy.
It’s really easy to measure how much power a device is draining in a house (a 100W bulb is drawing 100W of power, so in 1 hour it uses 100Wh of energy) we don’t care about what voltage or current its drawing, just the power. The electric company also isn’t charging use based on how much charge we use, but rather how much energy we use.
A battery can only hold so much charge, and once it’s spent, it’s gone. We could have gotten any amount of energy out if that because energy losses can vary a lot, and the current you draw from the battery can vary a lot, so it’s easier to express how much the battery holds in Ah rather than Wh.
If you want to convert between the two, V * Ah = Wh but this won’t account for energy losses.
Amp-hours is a measure of charge, Watt-hours is measure of energy.
It’s really easy to measure how much power a device is draining in a house (a 100W bulb is drawing 100W of power, so in 1 hour it uses 100Wh of energy) we don’t care about what voltage or current its drawing, just the power. The electric company also isn’t charging use based on how much charge we use, but rather how much energy we use.
A battery can only hold so much charge, and once it’s spent, it’s gone. We could have gotten any amount of energy out if that because energy losses can vary a lot, and the current you draw from the battery can vary a lot, so it’s easier to express how much the battery holds in Ah rather than Wh.
If you want to convert between the two, V * Ah = Wh but this won’t account for energy losses.
The main reason is that small batteries cannot give out amperes worth of current. The flow is generally in 10s of milliamps (the draw the device will need). Bigger batteries, like a car battery, have to give out a few Amps at max need (to start the car is about the biggest current draw). So, the capacity of the battery is discussed at the scale it is used for. It “could” be discussed using decimals instead (0.001 Amp versus 1 milliamp) but we tend to want numbers bigger than 1 rather than decimals. Just easier for average person to imagine 1000 of something than it is to imagine 0.001 of something, or the reverse, 10 of something is easier to deal with than 1,000,000.
This is the same idea behind someone saying “x million gallons is equal to 1000 olympic swimming pools” (whatever the conversion would be, I don’t want to look it up) when talking about the water flowing over a waterfall, as an example.
We “could” give the 3200 mAh battery as 0.0032 kAh, or 3.2 Ah, but people like 3200 better than 0.0032 when doing calcs in their heads. The device draws 30 mAmps per hour and has a 3200 mAh capacity, so we can get about 100 hours of use from it. Way better than doing “the thing has a draw of 0.03 amps and has a 3.2 Ah capacity so I can get about 100 hours of use from it”.
With chargers, you may have noticed that the time to recharge a battery is way less than the time of use that same battery generally gives. This is because the charger gives way more current than the battery is required to give when in use. So, it is “appropriate” (useful) to talk about a 3 amp charger, which would need a couple-few hours to charge that same 3200 mAh battery (because it does not give 3 amps the entire time of charging, just when it can give the max-the battery will not take 3 amps the entire length of the charge, usually). They “could” call it a 3000 mAmp charger. But why, when 3 amps does the same?
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