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KS16S, damaged battery

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Just thought a bit more about such a KS18L/XL pack balancing capabilities: With the normal Li Ion charging (from https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries):

new.jpg

and a charging current of 1.5A (stock charger from KS18XL?) one has during the CC phase of course the 1.5A charging current.

So once the first cells reach (abit above) 4.2V the balancing should/could start -> a 100 Ohm bleeding resistor is put in parallel to such a 2 cell pair. (roughly 35mOhm/2 as internal resistance)

With this and the formulas from the above post still 1,458A would flow through the already fully charged cell and just 42 mA going through the bleeding resistor. So more or less to be neglected... :( 

Once the CV charging cycle reaches the end about ~0.1-0.2 A and cells could/or are still balanced this current is more or less still just halfed by an 100 Ohm bleeding resistor.

So with just one dead cell pair (0V) out of the 20 pairs the remaining 19 are charged to 4.42V, once 2 pairs are dead the remaining 18 to 4.66V!

.... if not the second comperator seen on ecodrifts pictures performs overvoltage protection by turning of the mosfets in the charge path?

So this would lead to the insight that this BMS has no real effective balancing - with this (non amount) of current bypassing the cells through such bleeding resistors one does not need this balancing circuitry at all! ... or i am missing something ? ...

PS.: Just got the ideathat only overcharged cells (Voltage "really" above 4.2V get balanced - bypassed by the bleeding resistor)...

But also at a charging current of just 0.1A and a cell voltage of already 4.6V just half of the current gets bypassed... :(

Edit: PS: @1RadWerkstatt already stated that the ninebot one E+ balancing circuitry is absolutely not performing (he got many dead e+ battery packs for "repair") - could be the same here with the KS18XL? @US69 - you have some insight if i forgot something or this is the sad thruth?

edit: 

ps: that's not intended as ks bashing, it just occured to have some details and a "case" here. I'm very afraid that this shortcoming is spread throughout all the brands more or less... Just a consequence of passive balancing (with a bleeding resistor)?

 

Edited by Chriull

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I agree with your assumptions and concerns. Balancing will work as long, as the cells are of very similar parameters. But with cell degradation balancing will soon become ineffective :(

Edited by Seba

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@Chriull

I actually had a call with Chris and like to make some things more clear here, sorry for my poor english and my probably lack of technical knowledge and english terms...but here we go:

The KS BMS HAS control over the single (or dual) cells and actually stops single cells from overcharging at exactly 4,24 Volts.

The problem from the thread opener is actually that he charged his battery packs by circumventing the overcharge protection.

Seams he has gone over the “power outlet” cables(red and black)...instead of going over the “charge IN” (blue and red).

With doing it like this there is NO overcharge protection anymore (and so no correct balancing happens)...it can not be overcharge protected this way...imagine you make a hard brake on nearly full battery, then you would directly faceplant, if there would be a small overcharge.

But..if you use the “normal” charge port and charge cables there IS a overcharge protection, and yes, it is for single (dual) cells...

...and for these “bleeding” ....i am actually asking one more, but as Chris hardly stated the BMS to stop on single cells i doubt that this is a possibility.

 

Other things:

And yip, it was Chris who -at the time- revealed that the 9b eplus had no balancing at all on the board.....(and he also berated KS on a lot of things to make their products better). So Sorry..... Chris really would like to, but just hasnt the time to be more often here and answer all thise specific questions :-)

He is busy with his shop and likes to be more on the practical side of things... :-) 

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39 minutes ago, US69 said:

The KS BMS HAS control over the single (or dual) cells and actually stops single cells from overcharging at exactly 4,24 Volts.

That's a great relief to have this stated!

Quote

The problem from the thread opener is actually that he charged his battery packs by circumventing the overcharge protection.

 

44 minutes ago, US69 said:

Seams he has gone over the “power outlet” cables(red and black)...instead of going over the “charge IN” (blue and red).

An sound explanation - did not get this detail from this topic! "Crazy" to do so!

39 minutes ago, US69 said:

...and for these “bleeding” ....i am actually asking one more, but as Chris hardly stated the BMS to stop on single cells i doubt that this is a possibility.

As it seems it could balance maybe bit until the first cell reaches this 4.24V. So, as long as the cells are in a quite similar state they can be kept at mire or less similar voltages - once they differ too much the battery pack cannot be charged to 100% anymore, because the BMS shuts off the charging side. As we already got many reports of such cases (... if it was not a bad charger...)

Thanks for the clarifications!

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Yes, today Chris told me I was charging the batteries badly ('power outlet' instead 'charge in'). However, both batteries had two dead cells with 0V, which caused the rest to overload up to 4'4V.

I also loaded the new battery that he sold me in the same way without any problem, because all the cells are perfect.

Now I know the cells overload is my own fault but what is clear is both batteries already had 2 dead cells (0V), with only one year old.

Edited by Augus

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On 2/2/2019 at 11:57 AM, Seba said:

1) Don't charge battery immediately after ride.

2) Don't disconnect the charger just after the green LED turns on. 

1) Why not? (sorry i really have no clue and I often charge it as soon as i get up in the apartement - like a minute after turning off the wheel)
2) I normally disconnect before it turns green, to charge to around 90% (and have more charge cycles on the pack) but sometimes i forget it on green a few hours, so Im sure its charged full every now and then. 

Edited by Boogieman

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The batteries are at higher temperature after riding. It would be better to have the batteries cool off a bit before charging. Hard to say if it matters much.

Cell balancing only starts around 100% charge (above 4.2 V per cell) and it takes a long time (2.5 hours to balance 1% for my KS18XL). Ideally, charge to 100%, leave it to balance for 1-3 hours, go ride, store at 30%-80% charge. Bad to store at 100% charge (20% battery degradation in 1 year).

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3 hours ago, Tadas said:

Cell balancing only starts around 100% charge (above 4.2 V per cell)

Thats around ~~80% charge, once the cells reach the 4.2V at the change from constant curren to constant voltage charging.

Edit: but you are right that the wheel will report already 100% charge at this point. But if one let the cells settle they return to a lower voltage compared to a full charge cycle.

 

Edited by Chriull

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80% charge would only be 4.0 V per cell. Or no?

Balancing (for KS18XL passive bleed with small ~40 mA current, only 13 mA each cell) is only once the cell goes above 4.2 V.

Edited by Tadas

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6 minutes ago, Tadas said:

80% charge would only be 4.0 V per cell. Or no?

A voltage to charge status relation for li ion cells is only true after letting it rest for some time (some 15 min to an hour roughly).

So charging a cell with just the cc phase up to 4.2V and letting it settle them will lead to this ~4.0V or 80%.

Afaik this ~80% number after the CC phase depends on the current and is for ?1C charging?. The higher the current the lower the reachable capacity and vice versa.

If one charges the cell with cc and cv(4.0V) phase it will stay after settling at this 4.0V and 80%.

6 minutes ago, Tadas said:

Balancing (for KS18XL passive bleed with small ~40 mA current, only 13 mA each cell) is only once the cell goes above 4.2 V.

Yes. Afaik this is about the "usual" BMS implementation. This bleeding resistors are applied at ~4.2V and above.

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4 hours ago, Tadas said:

The batteries are at higher temperature after riding. It would be better to have the batteries cool off a bit before charging. Hard to say if it matters much.

In theory you are right, but the charging currents are so low wrt the size of the packs that I doubt it matters much.

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A friend of mine, have one of the two batteries of his KS16S with a pair of cells at 0V, so he only can charge until 63V aprox.

The strangest thing is that, as soon as the bad battery reaches 63V (may be a cell pair of its string goes to overvoltage) the two batteries stop to charge.

It is a smart feature, because the two batteries are in parallel, so the bad battery would receive charge anyway into the output side while the good battery keeps charging until 67.2V.

I do not know if the batteries talk each other to stop the charge, or to the motherboard to disconnect the charge port.

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On 2/1/2019 at 6:52 PM, US69 said:

What i would do:

Tell your experience to

1radwerkstatt.de

Write him a english eMail, tell your story, send the video, and ask him if he is able to repair the batterypacks...

He is the total expert, and perhaps he is anke just to change the defect cells. For sure he can check the BMS systems.

Dont worry...if he can repair it..it will be fair prices.

Thats all quite irritating..that both packs give up at the same time and both have a 2 pair cell defect or to high.

If anyone can help..its him...

is there someone like him in the US you know who can do this for fair prices. I have basically the same issue.  thinking about swapping one of my ks14s paralel packs  into the 18s if it fits

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On 2/2/2019 at 5:57 AM, Seba said:

Probability that your battery will fail is higher when always charging to 80 - 90 % than if always charging to 100 %. It's because balancing process occurs only when cells are fully charged. This is why you should also never disconnect your charger just after the green LED goes on / fan goes off. This LED usually doesn't mean that charging is finished. This LED usually turns on when charging current drops to about 0.25 A, but that may be long before the balancing process will even start. This is why it's good to have a current meter built into the charger (or use Charge Doctor to measure the charging current).

Fully charging is harmful only in elevated temperatures (well above 30 °C). Want to prolong your battery life? Use fast charging only when needed and slow charging when possible. Don't charge battery immediately after ride. Don't disconnect the charger just after the green LED turns on. Don't store fully loaded battery in temperatures above 30 °C. If using partial charging, use small charging current and charge the battery fully every fifth charging cycle.

this is the best advice in one post

the same thing happened to my battery because i kept only charging it to 80% thinking the smart charger was balancing it. Nowhere on ewheels website of the smart charger does it explain that you need to every once in a while get it to 100% and leave it.

i was very disappointed

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The first battery on my 16S developed dead cells at 4000km, the second pack at 8000km. Since I’m not at all alone with the issue, it seems like the BMS is indeed lacking in the balancing department, or the cells are just low quality.

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i wonder if we're better off at charging at 100% all the time or every other time. so there's less of a chance they won't get out of alignment

 

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On 8/2/2019 at 8:18 AM, Rotator said:

A friend of mine, have one of the two batteries of his KS16S with a pair of cells at 0V, so he only can charge until 63V aprox.

The strangest thing is that, as soon as the bad battery reaches 63V (may be a cell pair of its string goes to overvoltage) the two batteries stop to charge.

It is a smart feature, because the two batteries are in parallel, so the bad battery would receive charge anyway into the output side while the good battery keeps charging until 67.2V.

I do not know if the batteries talk each other to stop the charge, or to the motherboard to disconnect the charge port.

same thing happened to me on my 18S

took out the pack with the dead cells...

now with my remaining pack, now my charger shows full charge 67.2v instead of cutting off, but the app now shows my battery charging only til 64ish volts even when i set the dial to 100%

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39 minutes ago, someguy152 said:

now with my remaining pack, now my charger shows full charge 67.2v instead of cutting off, but the app now shows my battery charging only til 64ish volts even when i set the dial to 100%

Seems like the second pack has dead/bad cells by now, too.

The charger pushes them up to 67.2V, but they cannot "hold" the charge and the app shows afterwards less voltage....

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