Battery FAQ

[mrelwood]

@Chriull, the first post is so far the best single source for the current current (pun intended ) information and knowledge we have on EUC BMSs and batteries. Thank you so much for the great work!

[Chriull]

3 hours ago, bryon01 said:

I wanted to give proof that while correct that CV stage gets longer as you charge at higher currents,

I'd take this over to here, as "general battery" discussion to not get too off topic in the veteran sherman topic.

For "over there" your correction of the charge times should be "enough".

3 hours ago, bryon01 said:

it is completely incorrect to say this concept that this time extension somehow offsets the CC stage time of the charge.  Not correct at all.  As I have the exact cells, and the gear to record all this, I did it.  Note that unless charging the cells way outside their spec, then the area under the curve for any charge profile, will be equal.  The energy in is conserved, while voltage and amperage change.

I deducted my statements from https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries showing a charging graph as

and this table

Charge V/cell	Capacity at cut-off voltage*	Charge time	Capacity with full saturation
3.80 3.90 4.00 4.10 4.20	~40% ~60% ~70% ~80% ~85%	120 min 135 min 150 min 165 min 180 min	~65% ~75% ~80% ~90% 100%

 

3 hours ago, bryon01 said:

  Here is the data. 

As your data shows (and the graphs on lygtge-info.dk) the graphs/tables on batteryuniversity.com show just the principle of li ion charging but the exact values cannot be taken for modern li ion chemistries, especially for EUCs battery packs with ~0.2C charging!

Looking now (the first time) in detail on their charge graph for a 1C charging - they start at 1V cell voltage and charge from 2.5V to ~4.2V in ~0.5 hours...

I should learn to examine sources in more detail and question much more for plausibility...

With their data the CV phase would have had more impact on the charging time, as it would still charge the last 15% of capacity with decreasing current. Getting the idea from there, that the CV phase should take something about +2 hours!

As you showed in reality it's just about some 4-7% beeing left to be charged while the CV phase!

And the CV phase just takes about 30 min!

So this "change to reality" should also impact the thoughts about passive cell balancing used by the BMS. As it "has now much less time" and "much less capacity" to perform balancing it should be much more critical. It was always rumoured/thought to have very limited possibilities - such data really should not leave this passive balancing too much margin for operation... ;(

As some Gotway chargers were reported to show the green light (full charge) at ~700mA (~5% C for 4 3.5Ah nominal cells in parallel) this can then really be considered as fully charged! Letting the battery pack on the charger longer makes no real sense? And if one wants to enforce the passive balancing some repetitive minimal discharge and then recharge should be the only and best way?

And noone should spread the unfortionately common rumours anymore that full charging every 5th to 10th charge is enough for balancing?

3 hours ago, bryon01 said:

Keep in mind that my pack was 4S3P, but I listed the cell amperages in the figure.  I picked 3.15 cell voltage as the cutoff based on Marty's video.  For a Veteran in a 24S10P config, the 4 tests equate to:

1) 15A Discharge, 5A Charge: 6.2055 hours

2) 15A Discharge, 8A Charge: 4.0908 hours

3) 15A Discharge, 10A Charge: 3.2219 hours

4) 2kW Discharge, 16.5A Charge: 2.0947 hours (The rated charge current for the cell.  You wouldn't hurt the cells charging the Veteran at this rate, but could break the control board BMS, which could then hurt the cells...)

...

And the raw data if anyone wants it:

https://drive.google.com/file/d/1TqPUpp1FVeYyKEvDc_x38SGjohPJEFhx/view?usp=sharing

Thanks for the data!

So here a real world charging graph for the NCR18650GA for 0.8A (~0.2C) charging current:

And the usable/used capacity data for the NCR18650GA (min 3,3Ah, typical 3,45Ah, nominal 3,5mAh) downto 3.15V:

Charging
Current *)	Capacity
A	Ah
0,5	2,9865
0,8	3,0155
1	2,9501
1,65	2,9808
Discharging
Current *)	Used Capacity
A	Ah
1,5	2,9597	2,9482	2,9696
2,5	2,7613

*) per paralleled cell

[Pengloong]

@Chriull,  I wondered, in layman's term, can you please explain the advantages/disadvantages of using a 2.5 amp fast charger over the 1.5 amp normal charger please? Does the 2.5 amp fast charger have detrimental effect on the batteries if used overtime? Would you recommend using the faster charger? Any comment will also be much appreciated. Thanks.

[Chriull]

5 hours ago, Pengloong said:

@Chriull,  I wondered, in layman's term, can you please explain the advantages/disadvantages of using a 2.5 amp fast charger over the 1.5 amp normal charger please? Does the 2.5 amp fast charger have detrimental effect on the batteries if used overtime? Would you recommend using the faster charger? Any comment will also be much appreciated. Thanks.

There is absolutely no disadvantage for the 2.5A charger.

With about all wheels on the market thats no fast charger, but still a very slow charger!

[Pengloong]

@Chriull, thank you for your response, very much appreciated. I feel happier using the 2.5amp charger now. Thanks. 

[Tinkererboi]

@Chriull thank you for sharing your findings, I think battery knowledge is one of the most important things to learn as a rider of any PEV. 

One thing that has been bugging me recently - cells are generally advertised at 4.2v max but there is always some level of deviation in different cell models and brands. Do you happen to know the tolerances for the kingsong 16x? (Lg mj1 cells as far as I know) 

Have realized my charger outputs 84.2v. Was wondering if this can be considered to be out of acceptable tolerances. Am I stressing my batteries through overcharging?

[Chriull]

11 minutes ago, Tinkererboi said:

@Chriull thank you for sharing your findings, I think battery knowledge is one of the most important things to learn as a rider of any PEV. 

Thanks. But there still seems much to find, gather and this needs participation and more knowledable members.

I fully agree with you - as mistreated batteries or "ignored signs" could get extremely dangerous.

11 minutes ago, Tinkererboi said:

One thing that has been bugging me recently - cells are generally advertised at 4.2v max but there is always some level of deviation in different cell models and brands. Do you happen to know the tolerances for the kingsong 16x? (Lg mj1 cells as far as I know) 

Kingsing imho used lg mj1. No idea if they changed inbetween to the ncr18650ga, which is used for other wheels.

All of them have the recommended max of 4.2V. But it's always good to look at datasheets as reliable source.

11 minutes ago, Tinkererboi said:

Have realized my charger outputs 84.2v. Was wondering if this can be considered to be out of acceptable tolerances. Am I stressing my batteries through overcharging?

No. There is some (tenth of volts) voltage drop at the protection circuitry.

[joca]

Thanks for the excellent thread. Could I just ask a quick question about heat when charging?

I can't find a fireproof charging bag large enough for a wheel so I'm planning to wrap them up in fire blankets instead. As with charging bags, this will cause everything to get that bit hotter while charging. With such low C used for charging it's probably not much of a worry? Any concerns or better solutions (short of a metal cabinet or secure outside space)?

[Chriull]

45 minutes ago, joca said:

I can't find a fireproof charging bag large enough for a wheel so I'm planning to wrap them up in fire blankets instead. As with charging bags, this will cause everything to get that bit hotter while charging. With such low C used for charging it's probably not much of a worry? Any concerns or better solutions (short of a metal cabinet or secure outside space)?

Probably not. Most cells used in EUCs are specified in the datasheets just for temperatures up to 45°C. So with higher ambient temperatures imho that could already be reached without any additional "enclosing". Depending on the number of cells in the wheel, charge current per cell, air convection/fan airstream in the wheel...

I don't have any experience with fire blankets - if they could be of any help?

In one youtube video of @Kuji Rolls i've seen that he uses a metal box for charging - seems to be a nice solution for risk reduction and couod have enough airspace to keep temperature low? Maybe he want's to make once a vid about his charging safety measures - or already did this?

One other measure should be that one watches the final full charge voltage carefully! If it's getting lower over time, or drops the first hours/day after charging this could be a first sign of batteries getting misbalanced.

[Seba]

15 hours ago, Tinkererboi said:

One thing that has been bugging me recently - cells are generally advertised at 4.2v max but there is always some level of deviation in different cell models and brands. Do you happen to know the tolerances for the kingsong 16x? (Lg mj1 cells as far as I know) 

+-0.05 V per cell according to the datasheet (see 2.4 - https://www.nkon.nl/sk/k/Specification INR18650MJ1 22.08.2014.pdf). Typical King Song BMS circuitry will break charging path if any cell reaches 4.25 V.

[null]

My 18XL stock charger charges the wheel up to 84.5v (internal reading) and I dont have my multimeter here (other country)
It seems all measures a a bit off anyway, could it just be the wheels circuits or should I worry any more about it?
The charger could be cracked open but being plastic and compact I'd be glad to avoid..

Thanks for any input

edit: To format it more like FAQ material: is 84.5V internal reading on a KS wheel over voltage to be considered?

Edited July 28, 2020 by null

[Tryptych]

Most of this thread is over my head. However, someone once told me that only charging to 80% capacity increases the lifespan of EUC battery packs. This was the exact quote they used:

Quote

"Extend the Lifespan the Battery Pack by up to 2-3x:  if the battery pack is regularly charged to around 4.05v (or 80% nominal capacity) studies show that this will help to preserve the useful lifespan of a lithium-ion battery pack by up to 3x the standard cycle rating. A typical modern cell is rated to last ~70% of the original capacity after around 500-700 discharge/recharge cycles. With a partial charging, this can well exceed 2000 cycles!"

Can you guys confirm or dispute this claim for me (using layman terms)? From what I understand in this thread we should be doing the opposite: letting the EUC charge to 100% and then letting it sit further to "balance". Please confirm for me! Thanks!

Edited November 5, 2020 by Tryptych

[Planemo]

Its an excellent question, as you say the advice is at odds with each other.

Personally I feel the benefit of balance charging (full charging) far outweighs the benefits of 80% charging in our use case so thats what I do. Absolutely full charge every time.

However, I ensure the wheel is used as soon as possible afterwards, and never, ever left for more than 6 hours. This drastically reduces the amount of time for dendrites to form, which can indeed ruin batteries in very short order. I have had laptop batteries flake out after only a year by being constantly left on charge.

I use a plug in timer if I need to time the finish charging as close as possible to when I plan to use the wheel.

Other riders will have their own thoughts on charging, I am only providing mine

 

[Chriull]

On 7/28/2020 at 10:30 AM, null said:

edit: To format it more like FAQ material: is 84.5V internal reading on a KS wheel over voltage to be considered?

Can't be said - but most likely the internal voltage measuring is a bit off.

This 0.5V divided by 20 cells would still be within the specifications, too.

4 hours ago, Tryptych said:

Most of this thread is over my head. However, someone once told me that only charging to 80% capacity increases the lifespan of EUC battery packs. This was the exact quote they used:

The quote is 100% right in regard to one single cell, but contraproductive with our big battery packs.

The "high" number of serial cells (20 for 84V) need balancing or the majority of cell will spot the weakest and beat it to dead! (Li Ion cells are not very social...). Most/many reports of bad batteries are just with one dead cell (parallel group)!

Our BMS (GW, KS, most probably similar with the other brands) only balance once the cells reach about 4.2V (100%).

So for most of the cells in a battery pack 80% charging will increase the lifespan, but some cells (the outliers) will die much earlier and render the whole pack useless (and dangerous).

[mrelwood]

The reason for the bad 80% tip comes from the difference between charging a single battery cell, or a battery pack that has multiple cells in series.

80% charging does increase the lifetime of a single battery cell, and a single cell doesn’t need to be balanced at any point. A few cells in series, like in power tools, isn’t picky about balancing either. The 80% tip works for those batteries.

 The way the BMS in all EUC battery packs function is that it balances the cells closer to the same voltage only when charging to 100% (and leaving the charger connected).  And a large pack with many cells in series works as well as (or actually worse than) it’s weakest link: The charge is interrupted if the high cells go above 4.2V, but the wheel only monitors the total voltage while riding. If some cell groups have a lower state of charge, they will be burdened the most so they will dip below the average voltage, all the way down to harmful voltage levels.

The condition of the low cells goes down fast, and soon they reach 0V, only functioning as a burden to the rest of the cells, and the wheel no longer charges to 100%. We have many reports of these happening at just a few thousand miles in, worst being around 1500 miles.

 That makes balancing the pack 10 times more important than trying to increase the lifetime or the cells.

 And even if the pack didn’t require any balancing, the best math yet is from @Mike Sacristan: If the pack only has 80% of it’s capacity when charging to full for 15000 miles, what is the gain from 80% charging? You have only lost the top 20% by choice from day one.

[Chriull]

8 minutes ago, mrelwood said:

And even if the pack didn’t require any balancing, the best math yet is from @Mike Sacristan: If the pack only has 80% of it’s capacity when charging to full for 15000 miles, what is the gain from 80% charging? You have only lost the top 20% by choice from day one.

I can't follow this?

If charging to 80% increases the lifespan (full charge cycles) let's say by two one has lost this top 20% after 30000 miles. So 15000 miles won?!

From what i read recently (modern?) li ion cells degrade much faster once they reached this 80-70% max capacity. So they should be considered more like "end of life" than just 20% lost...

... But on the other side, i'll never reach 15000 miles with an EUC, not to think of 30000...

[mrelwood]

7 minutes ago, Chriull said:

I can't follow this?

If charging to 80% increases the lifespan (full charge cycles) let's say by two one has lost this top 20% after 30000 miles. So 15000 miles won?!

From what i read recently (modern?) li ion cells degrade much faster once they reached this 80-70% max capacity. So they should be considered more like "end of life" than just 20% lost...

... But on the other side, i'll never reach 15000 miles with an EUC, not to think of 30000...

 

 

How much the capacity has been decreased at any point from either behavior is of course anyone’s guess. AFAIR, the charts at Batteryuniversity suggested something like 80% of capacity left after 300 full cycles with normal charging, and 600 cycles with 80% charging. Depending on the wheel, it takes 15000-30000 km to reach 300 full li-ion charge cycles.

Storing the cells at 100% is of course a different matter, and that will do a lot of harm already in a few months. Which is why only charging before the ride (including a few hours for balancing) is a great idea.

I used charger doctor with the 16S, and charged only to 80-90% if possible, and balance charged every 10th charge. Result: one cell group dead after 4000km, second around 8000km. All of this within one year of daily riding, except a few months of winter storage at 40% charge.

I charged the MSX to 100% every time, and usually left the charger on for several hours. Result: 14000km in two years and I still can’t determine if there is any decrease in the range.

 But either way, unless you store the wheel at 100% for moths, cell aging takes a huge amount of miles to happen. So there is no need to try to prevent aging unless you plan on riding the wheel way beyond ~15000 where 80% charging (might) go even with 100% charging.

[Rawnei]

1 hour ago, Chriull said:

I can't follow this?

If charging to 80% increases the lifespan (full charge cycles) let's say by two one has lost this top 20% after 30000 miles. So 15000 miles won?!

From what i read recently (modern?) li ion cells degrade much faster once they reached this 80-70% max capacity. So they should be considered more like "end of life" than just 20% lost...

... But on the other side, i'll never reach 15000 miles with an EUC, not to think of 30000...

Keep it simple, charge to 100% and let the BMS do the balancing (this is important for multiple reasons), enjoy your wheel and don't overthink it.

Only time you should purposely not charge to 100% is if you are not going to ride for a long while.

[Mike Sacristan]

1 hour ago, mrelwood said:

 

 

How much the capacity has been decreased at any point from either behavior is of course anyone’s guess. AFAIR, the charts at Batteryuniversity suggested something like 80% of capacity left after 300 full cycles with normal charging, and 600 cycles with 80% charging. Depending on the wheel, it takes 15000-30000 km to reach 300 full li-ion charge cycles.

Exactly. 80%. It is one of the most quoted articles on the internet lol. Annoying and it has become broscience now.

1 hour ago, mrelwood said:

Storing the cells at 100% is of course a different matter, and that will do a lot of harm already in a few months. Which is why only charging before the ride (including a few hours for balancing) is a great idea.

Exactly... at 100% charge I would start getting stressed after a week haha.

1 hour ago, mrelwood said:

I used charger doctor with the 16S, and charged only to 80-90% if possible, and balance charged every 10th charge. Result: one cell group dead after 4000km, second around 8000km. All of this within one year of daily riding, except a few months of winter storage at 40% charge.

I charged the MSX to 100% every time, and usually left the charger on for several hours. Result: 14000km in two years and I still can’t determine if there is any decrease in the range.

Same. I hit 14000km yesterday. Hard to say if I have any loss in range. Also there are very few people who will ever ride their wheels that much. The point being that the batteries outlast the wheel.

1 hour ago, mrelwood said:

 But either way, unless you store the wheel at 100% for moths, cell aging takes a huge amount of miles to happen. So there is no need to try to prevent aging unless you plan on riding the wheel way beyond ~15000 where 80% charging (might) go even with 100% charging.

Agree. My MSX still feels 100% solid. I put 6500km on my Nikola since late June. And now my MSX is my wheel for playing around.
I charge my MSX with my 5A charger. I charge it to full. The charger turns off when the battery is charged.

If I were to charge to 80% I would get 40km instead of 50km every single ride.

If I were to charge to 100% I would get 50km 300 times leaving me at 15000km.
And then after that get 40km for every subsequent ride.

MrElwood it looks like you and me will be testing this with our high mileage MSX:es haha. 

[mrelwood]

13 hours ago, Mike Sacristan said:

MrElwood it looks like you and me will be testing this with our high mileage MSX:es haha. 

Unfortunately (out fortunately) my MSX testing days are over. There are no other EUCs than the V11 in my little world anymore! I’m now at 2300km with the V11, so I will be getting a decent amount of mileage with it as well. Charging to 100% (+0,5-4h) every time.

[Mike Sacristan]

1 hour ago, mrelwood said:

Unfortunately (out fortunately) my MSX testing days are over. There are no other EUCs than the V11 in my little world anymore! I’m now at 2300km with the V11, so I will be getting a decent amount of mileage with it as well. Charging to 100% (+0,5-4h) every time.

Great to hear that you are so happy with the V11. I am hoping to get the chance to try one soon.