"Low current overcharge"
- Thread starter venquessa
- Start date
wattmatters
Solar Wizard
"A" and "B" grade are just sales/marketing terms with no technical consistency. It's a meaningless term. It's like a company putting "Pro" on the end of a model name to make it sound better.
When buying cells just look at their technical specifications to assess their suitability.
sunshine_eggo
Happy Breffast!
EXCEPT, EVE is specifically lasering a "B" over the QR code for non EV-grade cells. In that case, I would assign meaning to grade "B"
Of course, after the gray market distributor buffs it off and lasers a new on one, I guess it doesn't matter.
The easiest way i can explain it is the cell is fully charged when there is no more room for lithium ions in the anode lattice.
At that point if you continue charging you will be lithium plating the anode - causing irreversible capacity loss and seeding dendrite growth that will lead to premature failure.
You can argue about how severe or mild the capacity and lifespan loss will be - or you can simply avoid filling the lattice.
Plenty of people have successfully started dendrite growth by parallel top balancing at low current for long periods, and we are starting to see the effects of that trend.
With a mix of dubious quality cells, and modified ebike BMS’ that are not really suited to stationary applications there are a lot of system failures, so unfortunately the cause is often masked.
The beauty of the cheap crap available these days is that the majority of people are overjoyed to pay half price for something that has a third the lifespan.
Score one for the marketing team!
At that point if you continue charging you will be lithium plating the anode - causing irreversible capacity loss and seeding dendrite growth that will lead to premature failure.
You can argue about how severe or mild the capacity and lifespan loss will be - or you can simply avoid filling the lattice.
Plenty of people have successfully started dendrite growth by parallel top balancing at low current for long periods, and we are starting to see the effects of that trend.
With a mix of dubious quality cells, and modified ebike BMS’ that are not really suited to stationary applications there are a lot of system failures, so unfortunately the cause is often masked.
The beauty of the cheap crap available these days is that the majority of people are overjoyed to pay half price for something that has a third the lifespan.
Score one for the marketing team!
Here is a doc from 2012 I believe describing the issue of keeping a cell at high voltage for prolonged periods of time. Note that some of the terminology/etc. reflects the time this document was written:
TomC4306
Solar Obsessive
But the only way to "continue charging" is with a higher voltage.
Not sure I understand now this "low current overcharge" happens if your charger is set correctly.
sunshine_eggo
Happy Breffast!
Interesting that it identifies 3.60-3.65V as the safe charge voltage and ...
"the voltage level of the fully charged cell will be reduced to a safe voltage (usually 3.4V per cell) where the cell is neither charged nor discharged."
3.40V is the voltage of concern these days - this is where low current overcharge can occur according to the alarmists.
To me, that paper further supports that low current overcharge, at today's current practices - 3.55-3.65V charging and 3.4V float - is just not a real concern.
Also note that in that paper, the recommended charge voltages were "4.0V for Winston cells, 3.9 for CALB cells, 3.7 to 3.9 for many other brands of LiFePO4 cells)". We've come down from those as well in the mean time.
Last edited:
In the broader sense I agree. However. (There is always a however and a depends?).
The cell charging process itself is not 100% efficient. The losses go up with higher voltages. At a point a cell can reach an equilibrium with it's supplied voltage. Just as you suggest. The things is, the current is not zero. If the cell at 1 Amp has 1 Amp of losses at that voltage, then it will sit there "wasting" 1 Amp.
Such a hypothetical cell might equilibrium out at a slightly higher voltage if you apply 1.1 Amp and even higher with 2 Amps.
Ultimately, on reaching that equilibrium the remaining net current (quiescent) is being wasted. Along the way to becoming, in the process of becoming and after becoming raw heat, what damage does it do?
If you give a sleeping pill to a cat, you kill it. Give a sleeping pill to an elephant and it doesn't even notice. What works for one battery could be really bad for another.
Low current overcharge is when the anode is full, and while the voltage is still at 3.65V lithium ions are now being plated to the anode as they cannot intercalate.
As you say, it cannot happen if your charger is set correctly. Experience has shown that under 3.5V will be a low enough voltage to prevent it.
sunshine_eggo
Happy Breffast!
and the alarmists are saying 3.4V is too high...
3.375V and not a millivolt higher!
Hahahahaand the alarmists are saying 3.4V is too high...
I’ve got 12 year old cells that have “floated” at 3.4V their whole life.
I’ve seen the same cells destroyed in less than 2 years by floating at 3.65V (yes back in 2010 that was considered a good idea)
Maybe i’ll turn them down to 3.375V to give them a rest in their old age ?
You also have to keep in mind that there have been changes in the LiFePO4 chemistry over the past decade as our understanding of the chemistry grew. This is one of the reasons that older Winston cells could handle 4.2V, but do that with a recent EVE cell and it will bloat like a balloon. Some of the things that were true for those old cells doesn't apply anymore to new cells today.
Ampster
Renewable Energy Hobbyist
It is way more efficient than Pb chemistry. As mentioned earlier, with a correct setting when current tapers to a set current a charger should shut down and there will not be wasted power. I am not sure what that has to do with the topic of "low current overcharge"?
TomC4306
Solar Obsessive
Mine are in use. Charging and discharging everyday. Charged with 56 volts float at 54.2 volts. Divide those numbers by 16 and those are the cell voltages that all 32 of my cells exist at. Does that mean I don't give them an opportunity to low current overcharge?
Robbert
Solar Enthusiast
I am getting the impression that this low current overcharge actually is a non-issue, as long as we stick to the recommended charge profiles. Most of us even charge more conservatively.
Similar threads
