I’m pretty aware that this is a “dumb” question, but my basic understanding of electricity can’t figure it out. I know the basic concept of resistance, currency and voltage, but I can’t comprehend how it takes so long to store charge in a battery
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Well, you can make a very high speed flow of water in a straw. Realistically speaking, no matter how fast you make the water flow in a straw, it will take some time to fill a large tank.
The speed of electricity is not the issue, the question is how fast can a battery or capacity store ENERGY.
Chemical batteries can only accept a certain amount of charge per second (chemical reactions are not very fast in a battery). Therefore it is not relevant how fast electricity “moves” but how much charge can be accepted.
While electricity travels fast, batteries have to undergo a chemical reaction to regain their charge which takes time.
Capacitors should charge quickly, usually in devices, there is some resistance to prevent capacitors from charging ir discharging too quickly due to safety reasons.
Electricity “spreads” fast, and individual electrons *can* be fast.
But to fill a capacitor you need a lot of electrons, and the more there are already the harder it gets to add more. And batteries are also limited by the reaction speed of the chemicals inside.
So as an example if you connect a capacitor through a long wire to a 5V source. The 5V will reach the input of the capacitor at the speed of light, but that’s just “electrical pressure”, no electrons moving yet. This pressure then starts moving electrons through the wire depending on it’s resistance. A voltage accelerates an electron until it hits an atom in the wire and is slowed down again, so they mostly just bounce around with a general trend to move forward.
The classic analogy is a waterhose. If it’s already filled with water opening the tap will (almost) instantly push some water out of the front. But only because that happens fast doesn’t mean you can fill an olympic pool in a second. Equally you can make the individual water particles very fast by using a thin hose, but that doesn’t help you filling the pool either, it gets faster but there is less of it.
When you push on one end of a stick, that push is carried to the far end of the stick almost instantly. The stick itself has barely moved.
Electricity moves like the force on the stick. In fact, it moves way faster. The actual electrons move very slowly.
Capacitors charge almost instantly. If not for some other component limiting them, they *would* charge instantly.
Batteries are limited by the chemicals in them. These chemicals rearrange themselves to store the charge, and if you force this too fast the battery just destroys itself. This is not a limitation with electricity, but with battery chemistry.
This is not literally how it works obv but just as an analogy, think of electricity running through a wire as a hose. A battery is a water tank in the air. Takes a bit for the hose to fill up the bucket and depends also on the velocity/thickness of the hose (volt/amperage). The speed of the water (volt) times the width of the hose (amp) gives the total water moved (wattage). Bigger bucket (battery) takes longer to fill and more water (wattage) is faster to fill.
Once the water is suspended, you can poke a hole in the tank and the stored “potential energy” is released. Of course this is a chemical process and electricity is a field and all that but just as a way to conceptualize.
To charge a battery, you create a voltage difference between its two ends. The creation of that difference is the super-fast part.
But once you’ve got that difference in place, that’s when the work of charging the battery begins. In the case of a lithium ion battery, you’re actually moving lithium ions from one end of the battery to the other, through some gooey stuff in between. That’s the slow part. It’s like if you put a turtle in a corridor and opened a gate at the far end with turtle food. It only takes a moment to open the gate, but that doesn’t put the turtle at the food immediately.
I don’t want to over-use the turtle analogy, so we’ll go back to lithium ions. The battery manufacturer wants to pack a lot of battery life in there which means they pack a lot of ions in there. Which means it takes time to move them all.
Cause charges pushing through isolated gapds can’t just hop to the other side, it is probabilistic, the more “tension” the easiest.
Also, chemical batteries like car batteries relies on redox processes that takes time to oxidate different metals, electricity is fast, but ions in an electrolytic solution arent.
There’s something called a RC time constant. R is resistance, C is capacitance. The time is what you get when you multiply them, and is how long it takes to charge(most of the way, the rate of charge slows down the more full it gets, because the difference in voltage gets smaller) Even capacitors have some series resistance and inductance in the leads of the component, so there’s always some amount of time it takes to charge. For small ceramic capacitors it can be pretty quick though.
When you’re charging a battery, you could put current in faster, but it would change what you’re doing chemically inside the battery. It takes time for the needed chemicals to get to where the desired reaction takes place, and if you push it too hard instead of the chemical reaction you want you might get something completely different, like decomposing the electrolyte, or you might overheat the cell to the point it self discharges and catches on fire.
Thanks you all for all the replys!! I am reading them all and, besides my initial curiosity, it is more interesting that I expected!!
Fwiw. At this point, we are being bottlenecked by the chargers in most cases.
Yes, batteries have a max charge rate to manage the heat.
But right now, many batteries *could* be charged faster if they had the juice. But the DC inverters, cables, and charging connectors become a weak point in the chain. There are some physical constraints on how thick it can be and remain flexible, and how big the charging port is in the car.
Keeping in mind, most charging is done at home with relatively low amps. So do we care to spend and sacrifice for peak charging speed we may never use.
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