Fast Charging - What is the secret?

[Hummina Shadeeba]

What temp you figure is too high for cells to get when charging and can you just look to the cell temp as a guide to what deterioration is happening?

What’s the best cell temp to start charging?

I imagine there’s a lot of trade offs and you could go all out with cooling jackets but with cells being cheap and time money...or worth more than money...I wonder about the above for a typical pack of maybe 50 30Q cells.

 

[Pedrodemio]

This would be figured out with the testing, from what I've been reading it depends, each cell is different and you absolutely can't use findings from one cell in another

It's not just temperature, but the big problem is lithium plating, I'm talking now without any good understanding of what is happening, but at the higher end of the voltage spectrum, if you push too much current, you can actually induce a negative voltage potential on the anode of them and that is what lead to plating and kills the cell in few cycles

Yeah, the cooling jacket would be just for test, for the actual pack something slimmer need to be designed

it really depends, for both of your use that a pack is made of 50 cells or less usually, it's not a big deal if they die after a year, but if we are talking bigger vehicles, for example, the motorcycle I would love to use this for, throwing in the garbage 800 to 1000 cells is a huge waste in all aspects

The 30Q is already a cell with bad cycle life, so it isn't even a candidate, but it can be charged fast and maybe last a year of almost daily use before going completely bad

 

[john61ct]

Both too-low and too-high temperatures are critical problems.

For too-low ambients, can instantly destroy the cells.

But it's not a single B&W pojnt, depends on the C-rate.

For longevity, the ideal is *no* detectable internal temp rise. Impractical in many use cases, so reducing lifespan is an accepted cost.

For higher charge rates, ambient pre-heating the cells reduces damage.

Again, no fixed temp points, varies by C-rate.

And for both sitting unused and while in use discharging, cooler the better for longevity.

Not simple straightforward issues!

 

[Pedrodemio]

Agree with everything, it's a matter of finding a optimum compromise

And the no temperature rise I disagree, if a hot battery has faster reactions, and the consequence is that it allows faster charging, maybe it's good that when charging, even at lower rates, making it hot improves cycle and calendar life

I've found this discussion, that even on low power DC charging they heat up the cells, while some people are saying it is bug, I think it's hard to believe something like this went unnoticed on such a critical system. They have a point that on really low power it seems pointless, but who knows

https://teslamotorsclub.com/tmc/threads/did-you-know-the-3-heats-the-battery-actively-constantly-while-dc-charging-at-any-speed-or-temp.175027/

 

[flippy]

Or narrow down to one cell and focus in what is the best we can get with it

this is why my go-to is the samsung 29E and the panasonic PF. they hold the balance between lifepspan, power and price.

 

[Hummina Shadeeba]

Everyone uses their vehicle differently and has a different battery but hoping someone has some advice:
I have a battery I mostly use maybe only 1/4 of its capacity before recharging and wondering what’s the best voltage to be using that 1/4 to have the most cycles. They’re 30Q cells. To keep it simple assume I’ll charge just before riding. It’s 4p and I charge at only like 6 amps. Charge to 3.8v A cell? 4v? Maybe should be mainly considering the voltage the pack will be resting for 23 hours a day after riding?

 

[john61ct]

And the no temperature rise I disagree, if a hot battery has faster reactions, and the consequence is that it allows faster charging, maybe it's good that when charging, even at lower rates, making it hot improves cycle and calendar life

Sorry if I wasn't clear.

Yes heating the battery reduces the damage (lowered life cycles off the back end) inherent in fast charging, especially in cool ambient temps critical to at least get them warm **from the outside** and **before** you start charging.

But if the goal is maximum longevity, the heat **internally generated** from fast charging is a cause & signal of that damage occuring, and that sort of "heating" should not be considered a way to accomplish the above goal.

 

[john61ct]

Really OT for the thread but here goes:

I have a battery I mostly use maybe only 1/4 of its capacity before recharging and wondering what’s the best voltage to be using that 1/4 to have the most cycles.

Center your utilization cycling around the midpoint, IOW, your usage cycle is from ~35% - 65%

Use a coulomb-counting SoC meter or proven test results published here, but really **resting** voltage should be your benchmark

Say 3.67Vpc at rest is your 50% point.

And your normal riding session uses 2.2Ah out of 9Ah pack capacity.

Discharge to 50% or lower for when you aren't just about to ride.

From there, add 1.1Ah when you want to ride.

When you return, no need to charge back up to 50%, next session add 2.2Ah.

Most people would not bother with great precision, getting it "about right" is good enough.

But definitely easier with an accurate SoC meter.

The principle of "for maximum longevity stay in the middle"

IOW avoiding the shoulders both top and bottom, hold for **every** LI battery & chemistry.

The voltage vs SoC mapping, and thus the 50% midpoint will vary though.

The less capacity you use on average, the longer the lifespan.

Say one bike uses 80% on average, and the pack lasts 400 cycles (to 70% SoH EoL).

Everything else being equal, another bike averaging 25% might last 1400 cycles, **if** the above advice is followed, and of course assuming the other care factors are solid.

 

[Pedrodemio]

And the no temperature rise I disagree, if a hot battery has faster reactions, and the consequence is that it allows faster charging, maybe it's good that when charging, even at lower rates, making it hot improves cycle and calendar life

Sorry if I wasn't clear.

Yes heating the battery reduces the damage (lowered life cycles off the back end) inherent in fast charging, especially in cool ambient temps critical to at least get them warm **from the outside** and **before** you start charging.

But if the goal is maximum longevity, the heat **internally generated** from fast charging is a cause & signal of that damage occuring, and that sort of "heating" should not be considered a way to accomplish the above goal.

Oh yeah, I miss read it.

The heat generation from the cells is actually pretty big. on the 250 kW charging, each cells produces between 10 W and 15 W of heat loss, I guess since the time it stays at that high power level is short enough that the thermal inertia and the cooling does a good job of keeping it under control

 

[Firedog]

Tool batteries charge at successfully at very high rates. Makita 18V chargers charge at 9 amp maximum. Their secret is good engineering and design. The the batteries surface area/weight ratio is many time that of a ebike battery. The design is rugged from the sturdy weld grids and the close fitting, nearly unbreakable cases. The chargers has a fans and the case ducting to blow air around the cells. The charger monitors the battery's temp and voltage and adjust the charging current constantly.

I repair ebike batteries and am constantly appalled at the shoddy builds and what they cost. Thin nickel tabs, not stamped grids, loads of tape, foam and goop fill a oversized weak battery case. Then, of course, the bike's owner crams the battery and controller (and probably their jacket) in a black bag to hide the fact it's electric. Of course that's where it stays during charging. Any wonder so many fail?

 

[flippy]

Tool batteries charge at successfully at very high rates. Makita 18V chargers charge at 9 amp maximum. Their secret is good engineering and design.

no, they use low capacity high current cells with short cycle life. not high capacity cells with high cycle life like you see in automotive or laptop use.
if you would put the LG cells that dewalt uses for example in a tesla you could pull 5000hp from it, but your range would be sub 50 miles and the pack would be worn out in a year.

cycle life in stuff like tools and esigs is not important, high power delivery and charging is the only thing that matters for a user of said tool. for home gamers it does not matter because they will last all day or weeks with a single charge, a contractor will charge them several times a day and replace them every year if they make it that far. i earn quite a bit of money on the side recelling dewalt and matika batteries from local contractors.

 

[goatman]

Everyone uses their vehicle differently and has a different battery but hoping someone has some advice:
I have a battery I mostly use maybe only 1/4 of its capacity before recharging and wondering what’s the best voltage to be using that 1/4 to have the most cycles. They’re 30Q cells. To keep it simple assume I’ll charge just before riding. It’s 4p and I charge at only like 6 amps. Charge to 3.8v A cell? 4v? Maybe should be mainly considering the voltage the pack will be resting for 23 hours a day after riding?

im playing with a 40t right now and im finding the best charge temperatures between 82f and 73f

im still playing with charge amps and c/o amps and then when discharging how many mah can be supplied

im finding 3.75 amps w 0.10a c/o performs better in mah available and its the fastest charge time even faster than 5amp charge and better than 3amp 0.10a c/o charge.

okashira did a 700 cycle test with a 7amp discharge and 2.5 amp charge on the 30q its here on es under a 30Q thread title, here browse this

https://endless-sphere.com/forums/viewtopic.php?f=14&t=68556&start=50#p1056865

Re: Samsung 30Q INR18650-30Q 3000mah 15a cell
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Quote

by okashira » Jun 22 2015 10:23am
Ok, so it turns out that there is a little more to supercharging then originally thought.
The Model S cell was still taking a beating on the 7A run after adding in a drop to 2A at 3.0V.

So I set another one up and used a new slower charge routine to ensure it wasn't being charged to fast:

charge 0.3A for 1 minute
charge 1.8A until 3.77V with 0.8A cut
charge 0.8A until 4.15V with 0.12A cut
wait
Discharge 7A until 3.0V
Discharge 2A until 2.8V
wait
cycle

The Model S cell is doing MUCH better this time ... so.... I was charging it too fast (or the low current precharge helps)
It is certaintly the fast charge regimin that I was using in the prior post that was killing it, NOT the discharge rate.

I also reduced the charge rate of the 30Q at cycle 114, didn't seen to have much effect.