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Many batteries these days are rated in Ah, so that's something.
One reason is because most power supplies are voltage supplies and not current supplies. Though they do report the max current they can supply. Also voltage is in those cases (arguably) more important. The wrong voltage and it probably won't work at all or even breaks. Whereas to little current, it probably still does something, though at reduced power or it cuts off at some point.
Ah, or mAh might be a little confusing though - two different batteries can have the same Ah rating but wildly different capacities.
I always convert everything to watt-hours by multiplying ampere-hours by voltage.
It is confusing, but it is what they do. I'm not sure why they do it. Probably marketing reasons, seeing as a lot of people think bigger number == bigger better. Of course if you know the nominal voltage of the battery pack it's not a big issue. But yeah Wh or Joule would be better.
Popularity, tradition, laziness :)
The danger of electricity is the first thing about it that you learn as a little child. And later you learn: the more voltage, the more danger. Even such people who never learn anything else about electricity know that all their life. Now the voltage has an unbeatable popularity.
Power sources with a fixed voltage were invented before such ones with a fixed amperage. Therefore the voltage was used as "the" number to tell the size of it. People like to be lazy, they like to have one single number to tell the size of things. Accordingly, for the devices that use electricity the traditon was established to say only the voltage (often it must fit to the fixed voltage of the source) and then be satisfied.
While constant current sources exist, they're very uncommon. A battery's voltage is constant (or at least we consider it so), but the current it needs to supply is dependent on the load. In general, we consider current to be a result of voltage, to the extent that some teachers prefer that Ohm's Law be written as I = V/R (rather than V=IR) to show this relationship more clearly (where I is current, V is voltage and R is resistance).
For an example of where constant current sources are used -- and IMO, deeply necessary -- we can look to the humble LED driver circuit. LEDs are fickle devices, on account of their very sharp voltage-current curve, which also changes with operating temperature and is not always consistent from the factory. As a practical matter, the current through an LED is what predominantly controls the brightness, so constant current sources will provide very steady illumination. If instead an LED were driven with a constant voltage source, it would need to be exceedingly stable, since even a few tens of millivolts off can destroy some LEDs through over-current and/or over-heating.
For cheap appliances, some designs will use a simple resistor circuit to set the LED current, and this may be acceptable provided that the current is nowhere near overdriving the LED. Thing of small indicator LEDs that aren't that bright anyway. Whereas for expensive industrial LED projectors, it would be foolish to not have an appropriately designed current source, among other protective features.
Amperage is only relevant for a short moment, just before you go through the pearly gates.
So I’ll ~~see~~ be a bright light before? 💡
Because in most relevant scenarios amperage is essentially just a function of voltage and resistance/impedance
In a nutshell, voltage incompatibility is generally more damaging than current mismatch, typically in a frightening or energetic manner. Many Americans tourists find this out when they bring their 120v AC hairdryers to an overseas hotel with 230v AC power. If there is only room for one number to be emblazoned on an outlet or plug, it should be the rated voltage, first and foremost.
For current protection, we've had thermal fuses since the 1890s, and thermo-magnetic circuit breakers since the 1940s. There are even more fancy transistor-based current protections available for industrial equipment that can shut off extremely fast. In a sense, protection against over-current has basically been solved, in the scenarios where there's enough of a risk of humans or property.
Whereas voltage mix-ups still happen, although consumer electronics are now moving to automatic voltage detection (eg an 18v electric drill battery charger refuses to charge a 12v battery) and through actively negotiated power parameters (eg USB PD). And even without human error, under- and over voltage transients still happen in residential and commercial environments, leading to either instant damage or long-term product degradation (eg domestic refrigerator motor drive circuits).
It should be noted that a current starvation scenario, such as when an ebike is current-limited per regulations, does not generally cause a spike in voltage. Whereas in a voltage starvation situation, resistive loads will indeed try to draw more current in order to compensate. Hence why current protection is almost always built-in and not left to chance.
Amps are the variable part of the equation...
There are other parts of the equation, every one being constant would make every electrical component binary. Either full power or no power.
That's why we really only see variable amperage on battery charges to force a slower charge rate for the health of the batter. On something like a radio, you could think of the volume knob as amperage control. The more power, the louder the sound comes out of the speaker.
A steady amperage current would "lock" the volume at one setting forever.
Oh right yea that makes sense, thanks!
It's been a minute since I learned electrical stuff, so I might be off on details.
Like maybe a pretty steady amperage from the cord and it's regulated inside thru resistance or something more complicated?
But that's the general gist of why not all parts of the equation can be static.
The advertised Wattage is also "max" it can use/produce.
Like a 850watt power supply can handle an 850 power watt draw, but if all the computer is doing is playing YouTube, it's going to draw a lot less amps, and produce a lot less watts as a result. If it needs more watts, it "pull" more amps to make them
Steam turbines are actually self regulating because of this. The more power being used, the more amps are automatically produced. Once you spin it up it manages its own speed.
Steam turbines are actually self regulating because of this. The more power being used, the more amps are automatically produced. Once you spin it up it manages its own speed.
This is sort of true, within a narrow operating window and an idealized environment, but also pretty simplified. That sort of application of Ohm's law only works according to the naive interpretation when you're talking about ideal DC devices. In reality, inductance and capacitance become significant and muddy the waters a lot when you start getting into real power grids with huge inductive loads like motors and transformers all over them, and steam turbines trip and/or bypass all the time to avoid overload or overspeed.
Interestingly, in your example you put car battery. However CCA, or cold cranking amps is like the only thing interesting about the battery, other than physical size.
Amps are used when deciding the wiring. So that afterwords you know if your plug matches, it works in that outlet.
I don't have an answer but this video explains a lot of this stuff in a really good way:
Also:
220v: 4.5A
110v: 9A
Everyone is aware of amps when their breakers trip.
If you know the voltage of an outlet you know the amps of a 1000w microwave.