Accumulator/battery and weight (charged vs depleted) - Page 1
Forum section: electronics / general

author: evava
author_rank: Regular Contributor
timestamp: October 24, 2019, 11:31:27 am
content: I wonder if here on the forum is some physicist, who can calculate weight of the battery/accumulator which is depleted vs fully charged.Is it significant amount of weight, or not any at all?Energy delivered to the battery/accumulator should appear somewhere?E=mc2

author: amyk
author_rank: Super Contributor
timestamp: October 24, 2019, 12:01:55 pm
content: Not significant but the energy does contribute a really really tiny amount of mass.

author: evava
author_rank: Regular Contributor
timestamp: October 24, 2019, 12:05:13 pm
content: How much tiny?Tesla car battery 80kWh, how much it weights fully charged vs depleted?

author: Gyro
author_rank: Super Contributor
timestamp: October 24, 2019, 03:50:13 pm
content: Far too small to measure.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 24, 2019, 04:27:45 pm
content: The formula is already give: a rough calculation in the head give something around 1 ng for the large battery.

author: IanB
author_rank: Super Contributor
timestamp: October 24, 2019, 04:57:43 pm
content: Quote from: evava on October 24, 2019, 12:05:13 pmYes, it's an interesting question. But you already posted the answer: E = mc²E = 80 kWh = 3e+8 Jc = 3e+8 m/sm = E / c² = 3e+8 / (3e+8)² = 3e-9 kg = 3 µgThat's more than I might have thought, actually.

author: bdunham7
author_rank: Super Contributor
timestamp: October 24, 2019, 05:48:56 pm
content: Quote from: blueskull on October 24, 2019, 05:03:55 pmActually that is exactly how it works. Although the binding energies and enthalpy change in chemical reactions or ion intercalation are much less than in a typical nuclear fission or fusion, the idea is the same--energy is released or absorbed depending on the relative energies of the before and after states and the mass of the system changes in proportion to that energy change.

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2019, 06:11:30 pm
content: Quote from: evava on October 24, 2019, 11:31:27 amJust a little FYI, since you made a point of adding the term “accumulator”: in English, that word does not mean “rechargeable battery”. (It does, in quite archaic usage, refer to lead acid rechargeable batteries, but only lead acid, and again, it’s obsolete English.) I know that many European languages use “accumulator” to mean any rechargeable battery, but English does not.

author: mzzj
author_rank: Super Contributor
timestamp: October 24, 2019, 06:41:56 pm
content: Quote from: IanB on October 24, 2019, 04:57:43 pm540kg battery and 3ug. That is almost measurable, ie Mettler HK1000MC mass comparator has 1kg capacity and 0.1ug resolution.Scaled to tesla battery size that would be 54ug resolution

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 24, 2019, 07:48:09 pm
content: Looking at energy densities taking only that delta into account shows how much room is left for improvement in battery solutions

author: thm_w
author_rank: Super Contributor
timestamp: October 24, 2019, 10:49:08 pm
content: https://physics.stackexchange.com/questions/34421/does-the-mass-of-a-battery-change-when-charged-dischargedhttps://www.physicsforums.com/threads/weight-difference-between-a-charge-and-discharged-battery.703057/page-2https://www.reddit.com/r/askscience/comments/1hj8k7/do_discharged_batteries_weigh_less_than_fully/The answers here are assuming a perfectly sealed ideal battery but that is usually not the case. From the third link it looks like you have to go deeper, and consider the chemical effects as well, some will lose some will gain.

author: evava
author_rank: Regular Contributor
timestamp: October 25, 2019, 11:41:09 am
content: Thank you all for answers!Interesting subject.