How much does electricity weigh in an electric vehicle? Can the weight of my EV change based on its charge level? #electricvehicles #electricityweight
Do the electrons going into an electric vehicle battery have mass? Is there a noticeable weight difference in a 100KW battery when fully charged versus empty? #EVbattery #energyweight
Understanding Electricity Weight in EVs
– Do electrons have mass?
– Impact of charging on battery weight
– How energy input affects vehicle mass
Effect of Charging on Vehicle Weight
1. Exploring the concept of energy and mass in EVs
2. Analyzing the weight difference between full and empty battery
3. Connecting electricity input to vehicle mass gain
Electricity or electric charge is essentially just a whole bunch of electrons. Electrons do have a mass but it’s so small that’s it’s pretty much negligible. At least in amounts of something like an EV battery.
So to answer your question, no it won’t weigh substantially different.
The answer is yes, your car battery will weigh more when fully charged. But that difference in mass is tiny. So tiny to be meaningless.
Electricity is an abstract concept; a series of linked phenomena, related to moving electrons around. Electricity doesn’t have mass, although some of the things that make electricity work (like electrons) do.
When you charge or discharge a battery you are moving electrons around (and depending on the kind of battery, doing a bunch of other stuff). But none of those ‘physical things’ are leaving the system or being added to it. No things being added or taken away, no change in mass, right?
However, when you charge the battery you are “storing” energy in it (how depends on the kind of battery). And mass is an expression of energy; the more energy something has, the more mass it has. That is mostly what the famous *E = mc^(2)* formula means.
A quick Google says EV car batteries store somewhere from 40-100kWh of energy.
If we plug that into our formula:
> m = E/c^(2)
we get 1.6-4μg. So around a millionth of a gram. Across the whole battery. Not much.
It doesn’t.
All the material is already inside your battery, what charging is doing is essentially rearranging the positively and negatively charged particles so that later they can be again “unleashed” on each other.
In other words, using your battery is not like draining a bucket – particles are not leaving it, so the weight doesn’t change, and conversely charging it does not “pour” the material in. They both just rearrange the material that’s already there.
Negligible but yess. based on https://physics.stackexchange.com/questions/34421/does-the-mass-of-a-battery-change-when-charged-discharged, your 100KW battery weighs 3.75×10^-8 kg less than when full.
Basically the weight of half an eyelash. (interestingly, about the same weight as the uncertainty in the kilogram before the watt balance redefinition)
Yes It does. Charged batteries have more electrons in them then discharged and electrons weigh something.
Plus there is the fundamental concept E=mc^2. A full battery has an amount of extra energy and thus an amount of extra mass.
A single electron volt weights 1.8 * 10^-36 Kg. There’s 2.25 * 10^25 in a kw.
Assuming the car battery is 100 KW/h (100KW is not a storage quantity), then you end up with 0.00405 milligrams. Which is probably the weight of a short enough human hair.
Yes
And so does your digital data….people put a blank kindle on a very precise scale; weighed it; then filled it with books and weighed it again and the device registered heavier
I didn’t realize that was what was happening. As in even though the car is plugged in, nothing is going into it. The material inside the battery is being re-ordered?
A lot of wrong answers here.
A lithium battery is made of 2 layers; when charged up one of those layers is “missing” a ton of electrons, and the other has a ton of “extra” ones. If electrons can move between the two layers, they’ll naturally do so, until they’ve pretty much equalized. You can visualize this a lot like water flowing from a higher up bucket to a lower one, until the water level is the same in both. We keep the layers mostly separate, and only allow those electrons to flow from A to B through some metal wires, and they do useful work while they’re moving. Think, a man-made channel between bodies of water, that we put a waterwheel in. When the electrons have equalized, there’s no more force to move them and the battery is dead.
Charging the battery involves pushing those electrons back into one layer, using energy to do so. Like pumping water back into the higher bucket. So, energy was used to move things, no matter was added to the system.
…That said, according to general (or special, idk) relativity, energy isn’t just able to turn into matter, energy itself has mass. The water raised up higher against gravity *literally* weighs a tiny, tiny amount more than it did before. A spring literally weighs a little more when it’s compressed. And the electrons in a battery have just a little more mass when they have that electromagnetic potential energy waiting to be spent. It’s just so little that the most accurate scales on Earth couldn’t measure the difference.
Technically yes, but practically no. Imagine a child’s playground slide and a ball next to it on the ground. This is the “uncharged” state of the EV battery. Now move the ball to the top of the slide. This is the “charged” state. There is clearly more potential energy in the system, but the overall mass is the same. This is not a perfect analogy because stored potential energy of an object due to gravity is not the same as chemical potential in a battery, but hopefully it ELI5s how something with more energy doesn’t need to substantially change the weight.
Energy and mass are equivalent, so your electric car if charged with 100kWh weighs 100kWh/c^2, or about 4 micrograms, or about 1/10th the weight of an eyelash.
A charged battery “weighs” more, yes, because it holds potential energy, and the mass-energy equivalence tells us that mass has energy and energy has apparent mass. The relationship between the two is given by E = mc^2
The battery in the electric car doesn’t store electricity. It uses electricity to drive a chemical reaction in a battery. That chemical reaction is reversed to power the car.
There are not weight changes you could measure on a scale that is capable of weighing something as heavy as a car. There are weight changes, but they are much to small to measure directly.
We can use E = mc^2 to determine how much additional mass an object will have if its energy increases.
In the case of a battery, when it discharges it is said to convert chemical potential energy to electrical energy through the chemical reactions in the galvanic cell. This causes the mass to decrease (the products weigh less than the reactants; the balance is converted into energy). When a battery is being charged, the cell becomes electrolytic and electrical energy is converted to chemical potential, reforming the original reactants – therefore the mass increases.
For a 100kWh capacity battery, we can convert this to the SI unit (joules). 1kWh = 3.6 megajoules so 100kWh would be 260MJ (3.6×10^8 J).
According to E = mc^2, 1kg of mass would be converted into 9×10^16J of energy, so your 100kWh battery would see its mass increase by (3.6×10^8)/(9×10^16) kg, or about 4 microgrammes
Does a ball weigh more when you carry it to the top of a hill? There’s a slight change in weight with batteries but it’s basically the same concept.
ELI5: the weight difference seems to be minuscule. Why do dead AA batteries weigh noticeably less in hand?
Although electrons have a (small) mass, you aren’t really adding them when charging. It’s more like you’ve got a bucket of water and charging is like pumping it into a higher reservoir for later use in your hydro damn.
The mass you are moving is minuscule. A 400V 81 kWh Tesla has 7.29^5 coulombs of electrons stored. That’s a total of 4.15^(-6) kilograms or 0.00415 grams.
Edit to add: Unless you have a nuclear reactor, E=mc^2 is irrelevant. You aren’t converting a fundamental particle to energy.
My calculation: a 400V 81kWh Tesla has 2.92^8 joules of energy stored. That converts to 7.29^5 coulombs as E=qV. plug the mass of an electron in and you get the overall mass.
Yes, by impossible sounding numbers of newly stored electrons…which have a negligable mass, so it’s definately someones fat ass fucking with the suspension. Don’t fall for their bullshit OP…..the fat asses did it.
When you go up a hill, you can fall back down very quickly. This is due to stored energy. There are different types of energy, a battery has chemical potential energy. When you go up a hill you don’t weigh more even though you have more stored energy, and it is similar for a battery charged with chemical energy.
You’re 5, do you know about wind-up toys? How about wind-up watches? It takes some effort to wind them up so they’ll work. We don’t really put anything IN them, but it takes energy to crank ’em up so they have power again. That’s kind of what’s happening when we say we “put energy into” an electric vehicle. We’re not really adding anything to them, we’re using energy to crank that car back up into a powered state, so it can go-go-go until it’s all unwound, and then we have to use more energy to wind it back up. Now go to bed.
Ok, so i can tell which of my AA batteries are good by dropping them about an inch onto the flat end. The bad ones “bounce”. I figger its due to density, and it seems like i could just weigh them.
thoughts?
Answer: Technically yes, but on a scale several times smaller than the accuracy of any scale that could weigh your battery. It isn’t even close to the weight difference from heating your interior.
If you want to verify: the difference in weight follow very similar laws of physics as when you hold a a loose rubber band vs one you are pulling on.