Video on 80% charging, "Good or Bad?"

[RagingGrandpa]

Cells are a chemical sandwich that cannot be manufactured in an identical matter.
The same way that ice cream sandwiches cannot be manufactured with identical bubbles and overflow
Variation in capacity and resistance are normal, and our designs must tolerate it.
-- There are always (slightly) weak cells --

6 minutes ago, RockyTop said:

The weak cell is over drained and charged every cycle.

Not really.

As an example:
Assume one 'weak' cell in a series has 10% less stored energy than the rest.
Assume we begin with all cells 'balanced': every cell starts from 4.20 V.
During discharge, the EUC will bring the healthy cells down to 3.15V.
The 'weak' cell will become discharged to about 3.0V. It's lower than the others, but still a perfectly healthy and non-damaging voltage.
Then while recharging, the 'weak' cell will return to 4.2V almost perfectly. Resistive balancing will resolve any small offset.
--> This is the normal design approach that EUC's use to tolerate cell-to-cell variation.

And bear in mind, the thresholds for 'cell damage' are very far outside the normal voltage ranges seen in EUC applications. Things have to go very wrong to result in a fire. Cells do not suddenly explode at 4.3V

 

3 hours ago, Jason McNeil said:

The strongest correlation evidence of premature pack failure is:

1. the cell-brand, followed by
2. BMS fault & then
3. shock/trama events—where single cells break from the nickel strips in the series.

This seems quite plausible and applies to any large Li-Ion pack, EUC or otherwise.

#1 "cell defects" imply catastrophic developments of internal shorts, which become 'heaters' and cannot be stopped by BMS or fusing.
#2 "BMS faults" imply the normal design to tolerate cell-to-cell variation (discussed above) cannot function properly, and so cells exit their safe voltage ranges after many cycles of use.
(#3 "physical damage" hopefully requires no further explanation)
 

Love it when suppliers participate directly in community conversation, thx for posting @Jason McNeil

[RockyTop]

13 minutes ago, RagingGrandpa said:

The 'weak' cell will become discharged to about 3.0V. It's lower than the others, but still a perfectly healthy and non-damaging voltage.

So using one cell, the weakest cell more than the others, draining just a bit further is NOT going to weaken it even quicker than the good healthy cells? 

[RagingGrandpa]

51 minutes ago, RockyTop said:

using the weakest cell more than the others, draining it just a bit further, is going to weaken it even quicker than the good healthy cells

^ this, yes, but only slightly

It means: for every 100 full-cycles of the 'weak' cell, there are only 90 equivalent full-cycles of the strong cells. So the weak cell ages faster.

This is a small effect, because problems resulting from this usually don't matter until we're nearing 500 cycles. Since EUC's are not a high-cycle-count application, it's rare to find an example where this normal aging process makes a pack unusable. (500 cycles is 12,500 miles ridden for Tesla, and 33,000 miles ridden for Sherman!)

So when there's a failure, it's more likely that one of Jason's 1-2-3 is to blame

[Tawpie]

Would your 'weak' cell be in danger of getting pulled below the 2.5V damage threshold during large current draw events? Or do the individual cells have under voltage protection (in the olden days of primary lithium cells, each cell had over and under voltage protection and some had fused PTC—I don't know about individual LiIon cells).

[Planemo]

17 minutes ago, Tawpie said:

Or do the individual cells have under voltage protection

I don't believe any of our EUC's use packs with protected cells. Presumably the idea being that when used with a BMS, you shouldn't need them. Of course, the problem with this is that we are up to so many cells in our EUC's now, with silly amounts of them being paralleled, that each string monitored by the BMS has too many cells hanging off it for my liking.

[mrelwood]

Thank you Jason for taking part in the conversation! This backs up everything positive I said about eWheels even further.

13 hours ago, Jason McNeil said:

It's a good video, but the explanation of the causes of cell/pack failure is to simplisitc & far from complete.

I’m absolutely sure that it is. But it’s the first video talking about the issue. I definitely wish to see people more knowledgeable about the tech or even just the business side to also make videos on the subject.

13 hours ago, Jason McNeil said:

Over the past 5 years, we've sold many thousands of Wheels, of the couple hundreds of pack failures that we have dealt with

And herein lies the very reason we see so drastically different sides of any EUC issues.

 The battery warranty is generally 6 months (haven’t checked yours). If a pack fails to charge above 70% after 9 or 12 months, what does the owner do? Based on what I’ve read and what I’d do myself, contacting the seller at that point is already way down the list. More attractive wheels come available every year, and I’ve seen many owners write that they’ll rather just ride a few months with the failed battery and then buy a new wheel, than to ship the wheel back to the seller and not ride at all for a few weeks. Once the new wheel arrives, the one with the failed pack is simply tossed, or fraudulently or unknowingly sold 2nd hand.

 Therefore it stands to reason that the battery issues you have dealt with are mainly actual manufacturing faults, and the ones we read about here at the forum (or face locally) are drastically different. Neither of which presents the correct ratio of issues. Many times I’ve even tried to convince a rider to even utilize the warranty in the first place when their wheels were having clear manufacturing issues.

13 hours ago, Jason McNeil said:

In response to Mrelwood's concerns last year, I had instructed our charger supplier to implement a CV phase into the partial charging modes to potentially minimize cell drift, & a Wh counter into the LCD output for Customers to be able to monitor the pack health/capacity.  

I am stoked to hear this! Unfortunately it might not do much to help the cause, since it won’t engage the balancing function of the BMS. But at least it could help the user to monitor the capacity.

13 hours ago, Jason McNeil said:

I agree that this topic needs further research to try to address the questions of:
1) What is the degree of cell imbalance if the charge cycle is terminated during the CC/CV transition?

Tests like this might require a budget and a sample size that is simply not possible for EUCs for several years. And btw, charging to 80% still leaves a good chunk of the CC phase to go before reaching the CC/CV transition.

13 hours ago, Jason McNeil said:

2) Does tapering down the current in partial 80/90% modes reduce drift? In theory it should, but it ought to be demonstrated

I agree, it should be demonstrated. Since the charging current is the same for all cell groups, I’m not sure why there would be a meaningful difference in charging the low and high voltage groups. I recall seeing charts of the charging process to show a perfectly linear increase in battery voltage during the whole CC phase.

13 hours ago, Jason McNeil said:

3) Collect pack samples from both a control group (100%) & frequent partial charge usage to see if there's any descernible longevity effects, measure the IR of each cell

The thing is, the cells themselves only get damaged if the imbalance is drastic. Case #1: A variance of 0.5-1V that should still be able to be salvaged by either pumping the BMS feature (100%-90%-100% looping) or manually charging the individual low groups. Case #2: The cell groups are already down to 0V like they were on my 16S, way beyond saving.

If the pack is only charged to 80%, the user has absolutely no way of knowing whether or not they’re having either of the above two cases. In the test you suggest, the case #1 probably wouldn’t show any actual cell aging or damage, although the pack is well on its way to the case #2, fast.

13 hours ago, Jason McNeil said:

4) Future BMSs ought to have an interface to view individual cells & cell-groups

This would be a HUGE jump forward! Experienced users would easily be able to keep their packs in good health for the lifetime of their EUCs.

13 hours ago, Jason McNeil said:

5) Evaluation of active-balancing so that cells remain balanced over the whole charge cycle

And THIS would completely obliviate the battery related issues we have seen time and time again, even for the ones who don’t know what to do with the cell group monitoring in the step 4)! This would be a PERFECT solution. Even if only on Begodes bought from eWheels at first, it would surely drive all manufacturers to catch up with the progress.

13 hours ago, Jason McNeil said:

In the larger context of targets for mfgrs to improve, battery issues consistute a minor rounding error to controller & motors issues.  

I do agree that especially during the past year, burnt controllers have kind of made a comeback. I definitely agree that they should be improved first, as they are an imminent safety issue to the rider. But as I pointed out above, eWheels’ rounding error is a much much larger issue in the whole community.

 

5 hours ago, Planemo said:

I don't believe any of our EUC's use packs with protected cells. Presumably the idea being that when used with a BMS, you shouldn't need them.

I think a bigger factor might be that the transient current peaks are probably too high for the protection to handle.

[Dogmaticjoe]

so if I charge my wheel (the KS18XL) to 100% with my stock charger how long after it hits 100% should I leave it plugged in to let it balance?

[Chriull]

1 hour ago, Dogmaticjoe said:

so if I charge my wheel (the KS18XL) to 100% with my stock charger how long after it hits 100% should I leave it plugged in to let it balance?

TLDR: once the charger shows the green light.

If the KS18XL is (still?) using the NCR18650GA panasonic recommends:

"(5) Termination of Charging
The system will determine that the battery is full by detecting the charge current.
Stop charging once the current has reached 0.1 It to 0.07 It. Note that there will be some degree of
variation for each individual battery.
(6) Charge Timer
A total charge timer and a charge completion timer should be included"

in https://industrial.panasonic.com/cdbs/www-data/pdf/ACA4000/ACA4000PE4.pdf

For this specific cell they use/recommend for a full charge in their cell datasheet in one diagram 67mA as charge current threshold, 100mA in another.

With the KS18XL having 6 cells in parallel this translates to 6 x 67...100mA~400...600mA.

It's not secure how the charge current threshold of the individual chargers to show the green light are adjusted, but normally, from what us reported here this green led has chances to show at some a bit lower current thresholds.

The effects of charging downto 600, 400 or even 250mA should imho be minimal, but it is interesting and notable that panasonic in their dazasheet charges downto 67mA for the "performance graph", but only downto 100mA for their "cycle life graph"!

[Chriull]

1 hour ago, div said:

(The selection point on the graph is when the charger goes green, at 67,43V, it stabilises at 67,59V)

Seems your green light really comes a bit early.

For comparison the charge graphs (with EUC Worlds "estimated" charge current via the HS110 plug) are from my KS16S https://forum.electricunicycle.org/topic/18317-battery-faq/?do=findComment&comment=307641 . Our batteries very likely have some different "internal state" by now, but in my graphs this last ~0,15 happen from ~0,5..0,7A on...

... and sounds plausible. Perfect internal 16s4p resistance (48mOhm per cell) would be about 0.2 Ohm. 0.7A * 0.2Ohm = 0.14V

[Chriull]

17 hours ago, RagingGrandpa said:

Not really.

As an example:
Assume one 'weak' cell in a series has 10% less stored energy than the rest.
Assume we begin with all cells 'balanced': every cell starts from 4.20 V.
During discharge, the EUC will bring the healthy cells down to 3.15V.
The 'weak' cell will become discharged to about 3.0V. It's lower than the others, but still a perfectly healthy and non-damaging voltage.

Li Ion Cells drop voltage very fast in the last state of charge.

The Discharge rate characteristics of NCR18650GA show for 2A discharge current:

~3000mAh used until 3.15V

So such a cell with 10% less capacity should be at a voltage were a "normal 100%" cell used up ~3000mAh/0,9~3333mAh which would be 2,5V or even below - it's more or less the end of the graph...

I know numbers like this 10% are just some assumptions but the nonlinearity in cell discharge characteristics could be a degradation reason for a battery pack.

17 hours ago, RagingGrandpa said:

Then while recharging, the 'weak' cell will return to 4.2V almost perfectly. Resistive balancing will resolve any small offset.

Could be that this, in combination with 80% charging is the reson for imbalanced packs.

Burdening a wheel till empty - the one weak cell gets a little bit degraded and just reaches a little bit less voltage as the others. Since no balancing happens to remove this small offset it will get even lower in voltage the next time the pack is emptied, degraded bit more, offset gets a bit higher and is not balanced again.

Sounds like a positive feedback loop... ;(

So with if one does not use his whole battery capacity for ones rides it's better to recharge before every ride than empty the battery fully and then recharge...

[mrelwood]

2 hours ago, Chriull said:

If the KS18XL is (still?) using the NCR18650GA panasonic recommends:

Panasonic doesn’t have recommendations for large packs in series with a passive top balancing systems though… I think that balancing even just a bit longer easily overrides the microscopic difference that the charging current cutoff can ever bring.

 

[Unventor]

I haven't been bothered with cell degradation due to I bought so many new wheels because the development went so fast. 

So far I have yet to see a problem. Well my V11 had a BMS state failure on one battery pack but beside that neither of my wheels showed any signs of degradation. 

Now going forward I suspect the upgrade cycle at least in my part will be much slower. I have the speed and in general the range I need. And the comfort of the V11 suspension too. 

That is not to say something better might make me want a new wheel. But having 2x V11 with winter/all season tire on I think they will outlast me for some time. And I can choose to use one for spare parts if any problems occur in one of them. But I am fairly sure most do not have a wheel similar just for backup. I chose this as I know how hard spare parts can be to come by these times. And I predict it will take a year maybe more before this get stabil. 

So far I charge as long my wheel get below 70% in battery. And I use EUC.WORLD to monitor the charging though a TP-link HS110 smart plug. 

It might degrade the battery over tid. On the other hand I am more worried of cells getting out of balance.

I am not a battery or charging expert at all. What I am doing could be all wrong. 

What I do think is very very interesting is the @Jason McNeil joined in. I think he will hold more data in view perspective what causes problems. But like @mrelwood said one thing is warranty resolved issues another is what happens outside warranty. That leaves a blank data sheet in most cases compared to what I know from my line of work.

As battery pack gets larger the impact of degradation might show more as it is less prone for people to buy a new wheel if the old one is sufficient if in working order.  Also charge cycles might show different because of different charging behaviours.

[RockyTop]

 I have watched @mrelwood rack up excessive miles on many new wheels in just a year or two. ( 16s > MSX > v11 ) The DarknessBot tends to set him near the top of the mileage list. So I am going to trust his observations. 
 

As a hobby rider, weekend explorer, I will never put the miles on a wheel like the commuters. I have always assumed that my batteries are going to age out before they wear out. 
 

I thought that max battery preservation included a cycle of  4:1  Four times at 80% then a full charge. Is this not true? 

[mrelwood]

9 minutes ago, RockyTop said:

The DarknessBot tends to set him near the top of the mileage list.

Stalker. 

9 minutes ago, RockyTop said:

I thought that max battery preservation included a cycle of  4:1  Four times at 80% then a full charge. Is this not true? 

Could be. Or it could be 8:1. Or 1:1. Varies by battery manufacturer, cell matching, and usage. Until we get individual cell group voltage monitoring, we have no way of knowing which is the correct ratio for your specific battery.

 What we do know is that even with a 1:1 ratio you won’t lose any range until something like 20000km (1800Wh). We also know that if you don’t balance as often as your battery secretly requires, your range and power will plummet, and the battery becomes a fire hazard.

So, anything other than 1:1 means huge risk with zero gain.

[RockyTop]

1 hour ago, mrelwood said:

Stalker. 

I like your voice.   

Hey it's not me. Blame Darknessbot. You are a Darknessbot celebrity.

RockyTop 136 miles this week. rank 995. So who is in the top 10?  mr.elwood. 

[mrelwood]

1 hour ago, RockyTop said:

I like your voice.  
 

Someone said that I sound like Arnold Schwarzenegger!  (But thanks! I made it myself!)

 

1 hour ago, RockyTop said:

You are a Darknessbot celebrity.

RockyTop 136 miles this week. rank 995. So who is in the top 10?  mr.elwood. 

It’s actually interesting, since I haven’t used DarknessBot for a year or two. I have connected it a few times though, so maybe it catches up for the long term charts. But It has been maybe a month since I last connected with it.

[EUC Endurist]

On 9/29/2021 at 10:06 PM, Chriull said:

Splitted these posts over to here - unfortionately it is sorted in by date...

If cells are fully outbalanced they'll stay at exactly one 24th of the charger voltage (in case of a 100.8V wheel).

If everything is adjusted perfectly this would be 4.2V per cell, just before bleeding resistors are "applied".

So they'll trickle charge forever and build up some platings/dendrits over time.

As nothing is 100% perfect the charge voltage will be at bit above or below this threshold. If all resistors are applied trickle charging current will be a bit lower for the cells as some current is bypassed.

As all resistor voltage threshold are not 100% equal there also could be the case that some resistors are applied and some not. This could lead to some very slight balance by different trickle charge currents. But should not really change too much...

thanks really much. so ill opt for 1-2hours green led and then cut the charger. you helped me many times chriull

[MetricUSA]

They suggest a large final charge...

 

https://www.autoevolution.com/news/li-ion-batteries-in-electric-vehicles-will-last-a-lot-longer-thanks-to-a-neat-trick-178697.html

[mrelwood]

4 hours ago, MetricUSA said:

They suggest a large final charge...

 

https://www.autoevolution.com/news/li-ion-batteries-in-electric-vehicles-will-last-a-lot-longer-thanks-to-a-neat-trick-178697.html

They actually talk about a quick large discharge current at the end of the charge.

[RagingGrandpa]

5 hours ago, MetricUSA said:

https://www.autoevolution.com/news/li-ion-batteries-in-electric-vehicles-will-last-a-lot-longer-thanks-to-a-neat-trick-178697.html

The method for reactivating the lithium anode involves providing a big surge in discharging current at the end of a charge cycle. This moves the isolated lithium ions toward the anode. The higher the discharging current, the faster they move and the more efficient the process is. The results of the study have been validated with multiple test batteries and through computer simulations.

The study showed the lithium ions in a real battery could be recovered by simply changing the charging protocol. This should be enough to extend a battery’s life by as much as 30%. Recycling the lost lithium ions also lowers the risk of the battery catching on fire. This could be a real boon for second-life batteries used in residential energy storage systems.

 

An interesting concept... but we'd need more specific information to apply this to EUC batteries safely, in order to give time for balancing to complete. An important step in balancing is the 'rest' time after the charger is disconnected, where the bleed resistors finish lowering the high-voltage cells.

On 3/22/2021 at 10:38 AM, RagingGrandpa said:

so:

• undervoltage cells benefit from leaving the charger connected longer (extend CV phase)
• overvoltage cells benefit from letting the pack rest after disconnecting the charger

https://forum.electricunicycle.org/topic/22109-passive-balancing-a-simulation/?do=findComment&comment=360341

[mrelwood]

4 minutes ago, RagingGrandpa said:

An interesting concept... but we'd need more specific information to apply this to EUC batteries safely,

Since the aim of the concept is to prolong battery lifetime, there are no reasons to apply it to EUCs any more than there are for 80% charging. We simply don’t use the batteries long enough for any prolonging to matter.

[Tawpie]

It's important that in the full writeup, they started with an island of isolated lithium in the battery and that the big discharge moved the lithium island 'nanometer by nanometer' by (presumably) redepositing lithium on the end closest to the anode. It's an interesting theoretical exercise but also not ready for prime time.

Edited January 11, 2022 by Tawpie
clarify by using the same terms as their paper

[lagger]

I have looked the video and have some points. Layman can damage their cells this way but I will try to explain why its not utterly bad idea and when you can benefit from it.

Most of the Li-ion cell datasheet cycles values are around 500 cycles to achieve 80 % State of Health (SoH). 1 cycle means an energy discharged that equals to rated energy so 10 times discharge of 10% SoC equals to 1 cycle. The aging of the cell is non-linear but until 80 % it goes pretty much linear. Around 80% it starts to go down the hill. Also the internal resistance wont be good so you might be closer to cutoffs and wont get the torque you need with battery of low SoH.

Other thing is that for example my V10 does only 30 km on 1 charge. I have already 5500 km on that wheel so thats roughly 200 cycles and I am not really a daily commuter. I know people that have 15000 km on a single wheel.
But yeah If you have a wheel that has a big reserve in power and range maybe losing some SoH wont make you concerned and wont affect your commuting but on the other hand you could also very easily keeping your battery happy (when you know how to). I am riding like 90 % of the V10 capabilities so I am limited by its performance at the moment.

In your graph you say that the companies give some reserve for the cells so you are not discharging the cells from 100 %-0 % but rather 100 %-20 %. Thats not such in many cases.

Typical Li-Ions have characteristic like this (its example):
102 %  4.25 V (not best for longetivity)
100 %  4.2 V
5 %      3.0 V-3.3 V (this is always tricky part)
0 %      2 V

Now think about the imbalance between cells in battery pack and the fact that most of the EUCs let you go to something like 3.1-3.3 V. Its like 95 % of available energy in the cell and the imbalance might make that you completely discharge some of the cells -> permanently damaging them -> damaging them even more in next cycles (positive feedback loop). So yeah I agree with you in video but the case studies are inconclusive because it wasnt mentioned how deeply they were discharging how they behaved to the battery. Of course not balancing at all is a battery kill in long run and also some thermal runaway probability is increased. Some packs are better some worse, some might be nicely balanced and will take longer for the deviation to be problem.

Another thing is how to determine something like 80-90 % charge. When fast charging this might be little bit problematic. When charging normally its easier but still you need to be sure that your EUC reports realistic SoC values. If you are charging an EUC and the SoC over time between (20-90 %) doesnt look close to linear either the charging is "interesting" or the mapping of SoC to voltage is way off. But in general if you charge to 80-90 % its not that big of a deal but charging only to 70 % because of bad SoC indication would cost you some useful energy.

Regarding the tips in the end, I add some more that are missing and extremely important:
One of the biggest thing is not to deep discharge the battery if not necessary (going bellow 30 %) https://www.cedgreentech.com/article/how-does-depth-discharge-factor-grid-connected-battery-systems. Charge it back to some reasonable value if possible. Lets say if I am commuting I know that the wheel would make the ride to work and back on 1 Charge but in the long term I would unnecessary deep discharge (stress) the battery and lose SoH.
Also you shouldnt charge the battery when its too hot just after some heavy dynamic ride. Its best to wait an hour. They dont like high temperatures overall for longetivity so keep them cool if possible and dont let them burn when sun is shining.
You can normally charge the lithium cells above 5 Celsius but never bellow freezing. Normally people wont have their EUC in these freezing conditions. When coming back from a ride when freezing that doesnt mean the battery is also freezing.

So to wrap it up.

It can certainly help but wont do for many and maybe not significantly enough. If you know what you are doing and think that you can benefit from than you can do it.
But you need to have in memory that you should NOT deep discharge the cells because they might not be perfectly balanced and it also doesnt help them in long run. Also let the BMS balance the cells after some cycles by charging to 100 % and letting it there for few hours. How many cycles is a tricky question. Some low quality packs might need to be balanced every 3-5 times. Some might be well OK for 10 times. It also depends how deep you discharge your battery. When discharging only upper 50 % you can go with imbalanced cells little longer. I am doing it like 5-10 cycles on my pack and the battery life is still good after 200 cycles.

[mrelwood]

1 hour ago, lagger said:

I have looked the video and have some points.

Thank you, both for watching the video as well as for your comments.

I haven’t been able to confirm how the charge cycles should be calculated when stopping at 3-3.3V, so you could be right in that riding the battery all the way to empty is actually 95% of a full cycle, and not 80% like I suggested. Although, this doesn’t change how people should approach 80% charging.

If all goes well, your V10 will be past 14000km once you have reached 500 full charge cycles. I think that’s an incredibly respectable amount, and still have 80% of the SoH left!

 Worth reminding that my 840Wh 16S had it’s first battery failure at 4000km because I often charged only to 80% and only balanced the battery every 10th charge.

 And someone had a battery failure on their 1556Wh 18XL at 2000km because of only charging to 80%.

 

I’ve heard a few people mention the damage that batteries can get from being discharged to 3.15V, but I haven’t yet read anything that would’ve convinced me that I should take it into account when using my wheel.

And more importantly, I have deep discharged both my previous MSX (14000km) as well as my current V11 (6300km) numerous times, many times far enough for it to completely prevent me from riding any longer. Despite of this, the range figures I get haven’t decreased enough for me to notice.

 So, I understand the theory behind the warning, but unlike with 80% charging, I have yet to see anything that would suggest “deep discharging” to actually be harmful for an EUC.

[lagger]

As I mentioned due to covid and current EUC situation I am riding my V10 on its peak performance so I am really trying to keep it happy especially if it doesnt cost me anything and know what I am doing. I understand the argument. For someone the benefit is not significant or its better not to do it if unsure. There are many users with different needs. Wouldnt say its generally bad.

Regarding deep discharge I posted link in that comment. There is also physics / chemics behind that.

Many people do deep discharge and its one of the worsts things to do and easiest to avoid together with unnecessary exposing the battery to high temperatures.

Another thing is as you mentioned with balancing. Going to 0% SOC (realistically the cells will be around 5%-10%) on a wheel mean that slight imbalance will degrade the already weak cells so thats another reason why not to go that deep with a (multicell) batterypack.

Anyway, even  iPhone will give you notification when your battery is at 20 % so you dont deep discharge. It is really a fact that you can read a lot about.