How in the world are you attaching alligator clips to 18650s?
The clips are connected to magnets on the ends? It looks like he has them between the cells and might just have added two more.
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The clips are connected to magnets on the ends? It looks like he has them between the cells and might just have added two more.
Exactly, bought a 100-pack of ∅8×1.5mm neodymium magnets 2½ years ago and soon they became one of my most used tools LoL. Super practical.
Magnet to alligator clip contact resistance may be a little bit high, thus if I charge at higher currents I usually set some double folded aluminium foil or copper sheet under the magnet where I can properly make the alligator clips bite.
Cheers
A few questions in this regard:
Leakage current rate of the cell… could you explain a little more?
I mean, I do often leave cells charged up to just ≈3.93-3.95V to maximize their life span cos I do not plan on using them short-term. At times I've left cells stored a little below that voltage, and after weeks of storage I've barely noticed self discharge in them, and when say barely I literally mean gnat's ar$€ league.
Do you believe cell leakage current is a function of cell voltage? I mean, is leakage current noticeably higher at close to maximum cell voltage?
And well, don't worry about no cut-off in my supply. I am the cut-off LoL.
Cheers my dears
A few questions in this regard:
Leakage current rate of the cell… could you explain a little more?
I mean, I do often leave cells charged up to just ≈3.93-3.95V to maximize their life span cos I do not plan on using them short-term. At times I've left cells stored a little below that voltage, and after weeks of storage I've barely noticed self discharge in them, and when say barely I literally mean gnat's ar$€ league.
Do you believe cell leakage current is a function of cell voltage? I mean, is leakage current noticeably higher at close to maximum cell voltage?
And well, don't worry about no cut-off in my supply. I am the cut-off LoL.
Cheers my dears
The electrolyte is not a perfect insulator so there is some electron flow from the anode to cathode all the time, effectively causing a tiny continuous discharge. Some chemical reactions also effectively cause a loss of charge. There can also be crystal dendrites from anode to cathode, causing internal current flow in older cells.
It could be just a few micro amps up to hundreds of micro amps depending on the chemistry and capacity of the cell. For our round cells it’s very low but it’s the current that causes a cell to fully discharge in a few years (maybe shorter, depends on the cell)
Because the resistance of the electrolyte is basic ohmic resistance, not electrochemically related, the leakage current rate is dependent on the cell voltage. The higher the voltage, the higher the leakage current rate.
The self-discharge rate is often quoted at around 1% per month for lithium-ion, after the faster initial voltage drop. Cell condition and temperature affect the self-discharge rate too.
Keysight has some great documentation about testing. Here’s one that covers self-discharge: http://literature.cdn.keysight.com/litweb/pdf/5992-2517EN.pdf
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Not that I've even hazard a pretend at understanding this conversation, I will say that @Mooch it's good to see you here on ECF. With your amount of busy schedule, we are HONORED. <wub>
By the way, a couple weeks ago I asked HKJ to make a brief test with one of his li-ion cells to make sure cell internal resistance (dV/I) is equivalent between charge and discharge, he came up with this graph:
Pretty symmetrical, about the same resistance.
Cheers
Pretty symmetrical, about the same resistance.
Cheers
By the way, a couple weeks ago I asked HKJ to make a brief test with one of his li-ion cells to make sure cell internal resistance (dV/I) is equivalent between charge and discharge, he came up with this graph:
Pretty symmetrical, about the same resistance.
Cheers
Excellent! Nice to see.
If the temperature is about the same for both charge and discharge the DC IR should be about the same as it’s related to state-of-charge and temperature. The ions pass through the same stuff going either way.
Hmm...I’m wondering though if measuring AC IR during charge/discharge would reveal the different reactions going on or if it’s just still a “snapshot” of the temperature and state-of-charge at that point?
At 3.93-3.95V seems a little high for that. The article linked below indicates below 55% SoC for NCA, below 60% SoC for NMC, and below 70% SoC for LFP is likely to yield improved calendar life if you don't plan on using the cells short-term.A few questions in this regard:
Leakage current rate of the cell… could you explain a little more?
I mean, I do often leave cells charged up to just ≈3.93-3.95V to maximize their life span cos I do not plan on using them short-term. At times I've left cells stored a little below that voltage, and after weeks of storage I've barely noticed self discharge in them, and when say barely I literally mean gnat's ar$€ league.
Do you believe cell leakage current is a function of cell voltage? I mean, is leakage current noticeably higher at close to maximum cell voltage?
And well, don't worry about no cut-off in my supply. I am the cut-off LoL.
Cheers my dears
Calendar Aging of Lithium-Ion Batteries
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