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The 80% charging "rule"


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20 hours ago, Rich Sam said:

Thanks @mrelwood, yeah that is how they sold me a fast charger! hehe.  But after some extended research into the topic I quickly learned about balancing and how it may not be the best choice to not charge to 100%.

Ultimately I'm not salty about the purchase of the charger as I still have a fast charger, and I can also take one to work and one at home.

I feel this info should be stickied somewhere in a maintenance section!

My wheels and scooter have e-wheels fast chargers. I could see how the 80% could be useful if a person was charging with intent to store them. I got mine so I could use the FAST section of it IF need be. I typically charge on a cooled battery and slowly. Im guilty of keeping my wheels fully charged so I can grab and go at any time. Hell, if i cant be bothered to grab safety gear, I sure as hell wont remember to charge BEFORE every ride. Oddly enough, the ewheels charger seems to taper off and stop BEFORE my wheels reach 100%. I asked about it, and was told it was safer to be just under max, than over. Be that as it may, I still use my factory chargers every 3-4 charges, and let them sit at green for hours to balance. Looking at the fast charger, it seems like it stops altogether, but the factory chargers trickle forever(dont quote me on that).  I did notice ONCE on the factory charger, my scooter had that wonderful smell of batteries cooking. 15 miles on the scooter even now. Meh, it still fully charges and who knows what damage may or may not have been done. I do know the e-wheels charger doesnt cook it tho. 

There's tons of threads on batteries. I simply charge mine full and monitor it while it charges. Light goes greeen and done. Every handfull of charges, let it stay green. I have better things to obsess over, and Im pretty sure if my batteries last even close to 1000 cycles, its a miracle. 1000 cycles = 30,000 miles on the 18L, 65,000 miles on the sherman and hell if I know on the mten. Something will be destroyed, the wheel will simply wear out, or a random cheap part will fail, LONG before I can be blamed that I shortened a battery's life. Charge it, ride it, set it free!!!

Edited by ShanesPlanet
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Short - by regularly charging battery to anything less than 100 % will greatly increase a risk of single cell failure. And single cell failure is something that will make your entire battery useless,

Balancing starts when the first cell reaches 4.2V. With a perfectly balanced pack that would be when the pack reaches full voltage and enters the CV phase. In practice a bit earlier. Balancing ne

No. You need to regularly charge to 100% for the cell balancing to happen. Otherwise the battery will die much faster because some cells are always more stressed than the others and fail first. S

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9 hours ago, Seba said:

It's very easy to replace fan to a silent one:

 

Fantastic thanks Seba!  Great find on that fan as well, I looked up similar fans in the 60x60x25 range and the specs are hard to beat on that one.

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Copied from other thread:

xiiijojjo: From 8000 km on the tesla v1 i got from 84v to 82.8v

I used a charge doctor from day 1 and would charge to 80% every day and only charged to 100% every 14 days or so. Rode it daily for a year and discharged it from 80% to 0% approximately twice a day. 

Now I have learned that all that is kind of futile unless you plan on your children inheriting it. 

Now I simply:

ride my rs, arrive at home, turn it off, connect it to charger seconds later, have to go for a ride next day, disconnect charger, rinse and repeat. 

No charge doctor, no 80%, no problem. 

 

Edited by xiiijojjo
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I'm away on holiday (24 days) and I left my wheel at 80% or so, I'll top it up to fully charged and balanced after I get home and before I go for a ride.

If you go for a ride and finish around zero then you should definitely give it an hour or more of charge ASAP.  Li-Ion cells don't like to sit at zero for any amount of time.  For multiple weeks of storage it would be a really good idea to not leave the battery under 20% or over 80%.  If I'm riding again within the next few days I'll just charge it fully.

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On 2/9/2021 at 9:47 AM, alcatraz said:

As your pack ages you might want to increase the time spent at 100% to give the balancing more time.

If only we could monitor individual voltages so we wouldn't have to rely on guesswork.

80% or 90% refers to the charge level. 90% of a 4.2v cell is usually around 4.1v. 80% is a bit extreme for euc use as the packs don't cost a fortune, but on cars 80% is likely very real.

Charging to 80-90% increases the amount of cycles drastically. If 100% offers 1000 cycles before the effective capacity declines to 80% of new, charging to 80/90% increases that tenfold.  The jump from 100 to 90 is big, the jump from 90 to 80 is smaller. I saw a paper on the subject. The numbers were like 1000 - 8000 - 20000 (cycles) or something of the sort.

Another interesting discovery was that even with 100% charging, after the cell being tested (NCR18650B) reached 80% of original capacity, it basically stopped deteriorating and stayed over 75% capacity for thousands of cycles. So they come to 80% rather quickly but after that they stay there for a loooong time. The deterioration tapers off and flattens out.

The problem is that the bms essentially kills the cells as the imbalances become too great to handle. It's not the fault of the cell. With stronger balancing your battery pack could outlive you and still have 75% of original capacity.

4.2V was picked as the best longevity/performance mark of the battery by manufacturers, the cells can be charged beyond that but the life decreases more rapidly the higher the voltage.

Charging one cell to 80% vs 100% will double the life of the cell.
Discharging one cell to 20% vs 0% will double the life of the cell.

Balance chargers start balancing at a set voltage which used to be 4.2V, however 4.1V is becoming common to extend cell life.

You cannot balance cells by decreasing the charge voltage to the Battery Management System, the BMS must be set to balance at a lower voltage.

No EUC that I know of uses Smart Balancing. [some] Ninebot/Segway hoverboards do, but I don't know about their wheels.

Edited by WI_Hedgehog
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7 hours ago, WI_Hedgehog said:

4.2V was picked as the best longevity/performance mark of the battery by manufacturers, the cells can be charged beyond that but the life decreases more rapidly the higher the voltage.

Charging one cell to 80% vs 100% will double the life of the cell.
Discharging one cell to 20% vs 0% will double the life of the cell.

Balance chargers start balancing at a set voltage which used to be 4.2V, however 4.1V is becoming common to extend cell life.

You cannot balance cells by decreasing the charge voltage to the Battery Management System, the BMS must be set to balance at a lower voltage.

No EUC that I know of uses Smart Balancing. [some] Ninebot/Segway hoverboards do, but I don't know about their wheels.

Actually 90% or 4.1v increases life by ~8 times. (If by life you accept the measure "amount of cycles until 80% of original capacity remains"). At 80% it's ~20 times.

After the "life" is up you can still charge for tens of thousands of cycles. But by then you will have overwhelmed any balancing circuit as the cells are aging at different rates. The study was done on individual cells, and no packs or bms's connected.

As soon as you make a pack you introduce complexity and the cell lifespan takes a huge hit.

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old school timer.... done and done. excellent and elegant solution! Have it turn on a radio too, so your wheel gets in the zone before its time to shred!

Edited by ShanesPlanet
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I have a couple of those but they don’t have RGB LEDs, no speaker (and no 3.5 mm headphone jack even), no Bluetooth, no app, and I can’t get them to connect to the internet. They’re at best 2 star doorstops because they’re very light and the prongs scratch the floor. Utterly useless.

Edited by Tawpie
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@Tawpie, bring it current, man! (said like Biden)

117266387_WiFirecvr.png.1bb5f3882b32666a2035e5d3aa260be4.png

(loooong-range audio receiver)

The funny thing is old amplifiers are really "smooth" (good quality), it's the speakers that are the weak link--replace the speakers and the sound is often (but not always) phenomenal.

-----

There are digital timers with battery backup for the same price...so weekend vs. weekday programs, etc. can be done. I have a fancy one (that costs more) and supports multiple daily (instead of weekly) programs, and it hasn't glitched once. But for ease-of-use, old-school works and you don't have to worry if it's set in the correct mode (Auto vs. Manual vs. Override...)

 

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If I didn’t have a day job I’d fool around and find a way to listen for the KS “done balancing” beeps and use IFTTT to unplug the charger. Nah. I’d ride more.

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I was thinking a loop antenna to catch the electrical noise generated by the beeper (likely driven by a square wave), current amp to threshold detector to an rPi, rPi to the inter webs. Why make it simple when overkill is available? Of course a thunderstorm could shut down my charger so there's that too. :laughbounce2:

Edited by Tawpie
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It is much more important to not let the wheel sit at 100% for a long time than it is to avoid charging to 100%.  Charging it 100% is bad because it ages the electrolyte inside the battery faster, so of you dont let it sit at 100% very little harm will be done.

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7 hours ago, WI_Hedgehog said:

How do YOU get the most out of your EUC cells? In general:

  • Let the cells cool to just over room temperature before charging.
  • Charge the packs just before use, minimizing chemical stress on the cells caused by being charged.
  • Fully charge the packs before every use so the balance circuitry keeps weaker cells from being overstressed.
  • Don't fast-charge the packs, the cells are packed closely together inside a plastic housing that acts as a heat insulator.

 

I distinctly recall reading a statement by some battery expert (either Elon Musk himself or one of his top battery science guys) one or two years ago that claimed the key to li-ion battery longevity was what they called "differential charging" meaning the battery should be kept relatively cool during discharging (room temps) but should be relatively hot during recharging (like 40°C).

 

it is not for nothing that Tesla cars have a feature that lets you prepare the battery specifically for being charged by their "Supercharger" - by preheating it.

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Tesla uses a proprietary battery chemistry that is optimized for use in their vehicles and is otherwise not available outside that narrow usage, so relating Tesla batteries to EUC batteries is generic in the sense that these are different types of lithium batteries, so there are similarities but things are different.

Tesla batteries are pre-heated to reduce thermal shock to the battery which would otherwise be caused by charging it extremely quickly, as in going beyond "fast charging" to "super charging." Pre-heating the battery using energy stored in the battery is essentially saving "ramp-up time" at a supercharger.

Supercharging decreases the lifespan of the battery vs. slower charging methods, and is used when the vehicle needs to be back on the road quickly like during a trip where the battery doesn't have enough charge to make it to the destination. Tesla counters this by liquid cooling the battery and using very smart chargers, computer algorithms, detailed battery history, and smart batteries so that supercharging has reduced/minimal impact on battery life. BUT, they neglect they're using the battery to heat the battery, therefore decreasing lifespan. They're also charging hotter, decreasing the lifespan. It's "justified" by getting the consumer on the road faster.

The laws of physics and chemistry aren't being skirted by Tesla technology, the damage is being minimized. There's also creative marketing going on, like EUC manufacturer battery life ratings of 100 miles--IF you ride at 12 MPH, AND the battery is new, AND that's "maximum range," NOT "expected range." Unless you're 5'3" and rice-grain skinny, you're not going that far.

815500491_DCFC.png.9320fc3679666fe92274f202c0d47116.png

Edited by WI_Hedgehog
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@mrelwood said (a bunch of stuff)

If you show me a cell that in real-world conditions lasts 500 x20 = 10,000 full charge cycles (or "tens of thousands of cycles" -@alcatraz) I'll wet your flowers for a week. The chemistry doesn't exist for consumer cells to charge 3000mAh into a 3000mAh cell 10,000 or more times.

Tesla automotive cells have the most advanced consumer chemistry known, and they hope they'll last 6,000 charges. The "million-mile battery" is a long way from the current 60,000 to 80,000 mile life expectancy, and like most of Musk's claims that's probably "highly optimistic."

We're not going to see Tesla-level chemistry in a consumer-grade EUC, so (12,500 miles / 50 miles/charge= ) 250 full charges seems correct (it's also what has been reported in other threads and matches heavy-current draw application usage lifespan expectations).

s-l1600.jpg.87d8a41a12b7ac5bced2745d40fdf410.jpg

 

Edited by WI_Hedgehog
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Age, temperature, high drain might degrade the cells, but the amount of cycles themselves probably don't degrade as much as most people think they do.

I couldn't find the graph but it was a battery tested in a lab with capacity on one axis and amount of cycles on the other. It quickly dropped from 100% to 85% and then slowly from 85 to 78, and then it looked basically flat from there on. and they did nearly 3000 cycles I believe. Most of the change occurred within the first few hubdred cycles. Of course there is still degradation but it's very slow for that cell that was tested. I read this stuff years ago so I'm trying to remember from memory. Sanyo/Panasonic was the cycle king at least.

This could be an interesting read:

https://blog.evandmore.com/lets-talk-about-the-panasonic-ncr18650b/

Edited by alcatraz
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It’s a funny task, testing the number of cycles. In a prior life we were validating new cell phone battery designs and one of the tests was cycle count to degrade to 80% rated capacity. We set up a Cadex tester to charge and discharge the cells like a consumer would (as I remember we discharged to 10% over 16 hours then charged to full, but we didn’t hold at full while you were sleeping, we just started the discharge immediately). Because a cycle took nearly a full day, by the time we hit the 300 cycle mark the batteries were obsoleted. The spec was 500 cycles. We probably should have done a mental time estimate before starting the test.

An actual test to 3000 cycles at real world rates, not accelerated, would be a very boring thing indeed. 1C is rarely real world.

Edited by Tawpie
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On 2/16/2021 at 3:21 AM, WI_Hedgehog said:

Fully charge the packs before every use so the balance circuitry keeps weaker cells from being overstressed.

It seemed to have been common wisdom in this forum (maybe up until a few months ago) that we can balance the cells only every 5th-or-so cycle without doing any harm. What is the evidence that lead to a change of this common wisdom?

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23 minutes ago, Mono said:

It seemed to have been common wisdom in this forum (maybe up until a few months ago) that we can balance the cells only every 5th-or-so cycle without doing any harm. What is the evidence that lead to a change of this common wisdom?

I believe it's from an increase in reports of dead packs, as well as a few battery fires.

As we just dont know the state of the battery the safest bet is to charge to 100% and accept the wear.

I still do "limited" charging but balance more often than before, maybe every 1-2 full cycle..

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18 hours ago, mrelwood said:

Charging the 18XL at 0.5C requires a charge current of about 18A.

Correction:

ACtC-3cnWIY0l_3t0tjJwoNxIP9VfOsIfpLbHCxUrtY_olbZ-zyZX8I9tQihTot7pZX2uD3pQVybLhu2mxbVcjUWdnu_Z3RfJJiPCgGid28eGbcxAoLh5RL2HIu1eflcrmPpG1lAn9WCIxLa7QaKTVS7qfnU9Q=w363-h382-no?authuser=0

But I agree with your conclusion: recharging a 1554wh pack with a 10A 84V charger is fine (assuming that the rest of the system components, such as cables and connectors, are sized for it).

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