Inmotion V5F BMS charging behavior

[OzMek]

Hi, I'm new to this forum and would like share some information I found studying the V5F BMS.
On this BMS, charging control is achieved by 20 Ablic S8209AAF chips chained, one per cell.
Those chips include a balancing capability, but IT IS NOT IMPLEMENTED by inmotion : No balancing resistor, no transistor for driving it.
So the behavior is as follow : Once any of the cells reach 4,25v, charging is disabled.
Until this cell voltage drops below 4,1v (release voltage).

With aging, with the spread of internal resistances and charge/discharge cycles, the voltage of each cell will diverge and you'll get an imbalanced battery pack.

Edited July 8, 2023 by OzMek

[meepmeepmayer]

Great information! I put it into its own topic so people can find it more easily (via search). Thanks!

[v8nice]

3 hours ago, OzMek said:

Hi, I'm new to this forum and would like to bring some informations. I hope not to be off topic, as my informations are about the V5F BMS.
On this BMS, charging control is achieved by 20 Ablic S8029AAF chips chained, one per cell. Those chips allow for balancing, but IT IS NOT IMPLEMENTED by inmotion : No balancing resistor, no transistor for driving it.
So the behavior is as follow : Once any of the cells reach 4,25v, charging is disabled. Until this cell voltage drops below 4,1v (release voltage).

your study is interesting. You told me in private that you installed a balancing circuit, but I did not find it, could you post the Aliexpress link here? I balanced the v5f that I had bought with a battery that was malfunctioning,  at the end of the charge it discharged a little and the autonomy was bad. After manual balancing everything was working normally and now 300km after the problem returns so I think that the imbalance has returned... I think that a cell reaches 4.25v a little before  the others which cuts off the charge, then the battery drops back down to 82v. I tried to drive for 5 minutes and put the charger back on but it didn't change anything. I'll open when I have time and empty the cells that are too high but it's  not too funny to open every 300km... You have to dismantle everything on this wheel as well, unlike the v8/v8f.

[v8nice]

I search about  Ablic S8029AAF, i see nothing about this référence .

if you have pdf of the chip to see.

thanks 

[OzMek]

Hi there, happy to share my findings with you guys.

The Ablic datasheet can be found here https://www.ablic.com/en/doc/datasheet/battery_protection/S8209A_E.pdf
Look at page 4 the precise reference S8029AAF, the version defines the levels when it stops charging (Overcharge detection:4,25v), and when it authorize charging again (Overcharge release:4,10v).

Here you can see the daisy chain of the 20 cell monitoring circuits. The components below are the 470R and 0.1µF for the power supply and voltage measurement.
While making measurements, I unfortunately destroyed 2 of those chips. I was lucky enough to find on aliexpress a company offering a service to quote BOMs. They were able to sell me some spare ones, and I could replace the two I burnt. I can confirm the pcb tracks below the chips just link CTLD(n) to C0(n-1), without even the 1K resistor suggested in the datasheet!
The two transistors on the left are, from left to right, connected to C0 (charge control) and D0 (discharge control) as you'll find on the datasheet.

Question now, how to balance the cells ?

Edited July 7, 2023 by OzMek

[OzMek]

I found 2 options:
1st : designing a board with similar chips (Why not choose some other levels, for ex. for cell release), implementing the balancing, then produce board, solder components, etc.. Not a full BMS, just the charge control part to replace the S8209 chain. Realistic for me, but I quickly concluded this is an expensive task, from either time and money investment.

2nd : add an independent equalizer, but does that exists ? Answer is yes.
This is not advertising, just to show an example of such product https://fr.aliexpress.com/item/1005003751473612.html.
Choose the 20S of course.

Price : Ok
Board size : 20S:100*88*6.5mm. Fine, it will fit on the opposite side of the mainboard (Do not forget to seal this compartment, otherwise water could penetrate from the wheel arch).
Power consumption : fine also, according to ETA3000 datasheet, it's about 2µA in idle state
Cable length : Was delivered with 60cm long cables, it is .. just what you need. Do not shorten the cables, as it is better to keep their resistance equal. Otherwise voltage level measurement will be distorted.

Guess what : you'll have to trust me as I didn't expect to post about this, and took no pictures.
Integration on the battery required nothing especially tricky, but yes, I have some knowledge in electronics, DIY and I'm a handy guy.

And let's now have several charge and discharge cycles to confirm the benefits. But on paper and according to the feedback of the users of this equalizer, it should just perform as expected.

Edited July 7, 2023 by OzMek
added pictures, in case AE link doesn't work in the future

[OzMek]

4 hours ago, v8nice said:

I search about  Ablic S8029AAF, i see nothing about this référence .

if you have pdf of the chip to see.

thanks 

Sorry, I mistyped the reference. This is now corrected.
By the way, thank you v8nice for motivating me posting my findings about V5F BMS. Have safe rides.

Edited July 7, 2023 by OzMek

[v8nice]

ok for the reference, it's S-8209AAF. So normally the balancing should start around 4.1v or around 82v, but you say that they haven't implemented the circuit that allows it... At least it's clear, if the  cells are not from the same batch or age differently the wheel becomes unusable. For the test it will be necessary to drive and load a lot. For my part, the manual balancing made the wheel work perfectly for 250 km I had to recharge 25 times, I  monitor at each charge, long, it blocked around 84.15v at the beginning then slightly less. then after 250km a charge reaches 84v and then the battery discharges up to 82v despite the charger connected to it. I still have an acceptable autonomy but I will  have to disassemble. I don't really understand the mechanism that makes the battery almost charged start discharging. And it was the same problem when I got the wheel, the imbalance was not huge and I had this behavior. Your balancer  additional should solve all the problems, on the other hand if it were possible to fix it on the battery it would be simpler and less dangerous, we will wait for your return and when you disassemble to check, take some pictures.

[OzMek]

I really can't understand Inmotion decision to not implement the balancing feature, as it costs only a few cents per cell. And the battery pack is sold several hundreds of usd, this would have been the best solution for 1 extra $. Probably a lack of space on the components side, and the will to not have components on both side of the BMS, that would have increased much the production costs.

I got an old V10 BMS, charging chips are different brand (Ricoh R5436T, model 502BA) and manage 5 cells each, but still no balancing.

Below is a picture of a recent V10 bms, it's different, only one chip to manage the 20 cells and a bunch of surrounding components (Left, circled). Did they finally implement balancing on the BMS, the easiest and best solution to keep your battery at its best condition ?

Btw, I'm interested If someone can tell me the reference of the big chip circled on the picture

Edited July 8, 2023 by OzMek

[OzMek]

Back to our V5F BMS, @V8nice, I found no room to install the external balancer on the battery. I would have preferred also.
I can just tell that the wires I received with the balancer are kind of silicon wire, that appears to be suited for long time use.
And integration is really clean once done (Wires runs below the BMS, i.e between the plastic structure of the pack and the BMS), pack is rewrapped in shrink tube, ...

My pack was having the same behavior that you describe. Even worse.
For english readers (Mise en charge : Voltage measured just before connecting charger. Then measurements after 30, 60 and 90 minutes). And a last one after 12hours unplugged. After one hour, one of the cells triggered the overvoltage protection (My meter is not calibrated, and is underevaluating voltages. I realized this aftewards). See last line about the pack voltage. Once charged, the full charge voltage was about 77v only.

Edited July 8, 2023 by OzMek

[OzMek]

I recommend you have a look here : https://evreporter.com/understanding-charge-discharge-curves-of-li-ion-cells/
Particularly for those curves.

My personal interpretation of those curves and the behavior of the pack is as follows:
The cells are imbalanced, and charged at constant current.
As soon as one of the cells reaches Vovervoltage, then S-8209 raise the signal to disconnects the charger.
And by the mean of some control logic, it switches off the FET (on the left in the picture below, the one that is "alone") which breaks the connection between the negative pole of the charger and the negative pole of the battery.

None of the cells is charged at its 100% capacity (not even the one that triggered the disconnection), and this deprives all cells of the stabilization phase -> the voltage of each cell will drop a little, this is the normal behavior for a cell partially charged (also for a charged one, but less)

Imagine now the situation when the pack is balanced correctly, each cell having a very similar behavior.
The voltage delivered by the charger is 84v (Approx. I have 3 chargers, measured with an accurate meter, they deliver between 83.4v and 83.8v. You have a potentiometer inside the charger that you can use to tune the output voltage, but I didn't found it necessary).
Then the cells will charge to 4.1, 4.15, 4.20 ... Hey, wait : 4.15x20 = 83v, 4.20x20 = 84v -> in between those two values, you reach stabilization phase at constant voltage, over-voltage has not been triggered, and the batteries will get fully charged ! (Note: The charger's voltage can't be exceeded, the pack will stabilize at this voltage. When equilibrium is reached, and all cells fully charged at their max capacity, charge current will be 0 or really small)
Led on charger is usually green at that time (as soon as the charge current drops below 400mA), when the last segment of battery display on the wheel is blinking.

This is how the balancing feature of the Ablic would help if implemented (But IT ISN'T by Inmotion) : for any cell passing 4,1v, a small resistor should be connected in parallel of the cell, slowing down its charging speed compared to the others, allowing the different cells to reach the same voltage. You should have a look at the following application note : https://www.ablic.com/en/doc/datasheet/battery_protection/S8209A_AN_E.pdf. Especially p10-11, that focuses on the balancing.

In case anyone of you have better experience, i'll be glad to read your comments and advice.

Edited July 8, 2023 by OzMek

[OzMek]

By the way, I'm interested if someone could give me a V5F BMS (Out of order, even burnt, otherwise keep it for your own use :-) )
I would like to reverse engineer it further to try to learn more about the communication between the BMS and the mainboard, also how the safeties work.
(Yes, it has no balancing, but several conditions to authorise charging, to authorise battery output on the power port, and has a controlled fuse on the charger input that blows in case of incoherence between charging control and real charging. I learnt it when I tried to force charging and charging wasn't working anymore... )

Inmotion, if you read this post, please have a look at this gem for your next BMS: https://www.qorvo.com/products/p/PAC22140.

Edited September 2, 2023 by OzMek

[v8nice]

to your degree of involvement, maybe you will have more information on the Russian telegram channel inmotion, https://t.me/euc_inmotion I don't have much time to read everything but your research is very good, concerning the v10f may be the news but it will surprise me, even the v8f released mid 2020 has no balancing. Nothing to do, today I bought 2 broken wheels, an inmotion v11 which seems to have a battery problem and a v10 which seems to have a motor problem, every 2 s lights up, when I have time I have what to take care of!

[OzMek]

I know about this telegram channel, I spent some time digging into it, but too much talking in Russian that I can't understand.
V10 is not small, and V11, humm, looks good and is really huge ! I don't have any experience with their BMS.
To restore your packs, in case you're not already equipped, I can advice you build a microwave oven spot welder. That works great.

Edited July 8, 2023 by OzMek

[goos3man]

Might explain why my v5f doesn’t like charging over 80v now… bought a new charger and yet it’s still charging full to roughly 80%. Got it at a steal but can’t complain now 

[Funky]

1 hour ago, goos3man said:

Might explain why my v5f doesn’t like charging over 80v now… bought a new charger and yet it’s still charging full to roughly 80%. Got it at a steal but can’t complain now 

4.2V - is one cell. So it's also a possibility of one cell group being dead.. Be careful, you may have a crash or even worse a bonfire one evening, if battery is "damaged".

Edited July 26, 2023 by Funky

[Illifant]

On 7/8/2023 at 12:44 PM, OzMek said:

and has a controlled fuse on the charger input

Is this fuse permanently blown or can be reset (and how)?

I have an V5F battery that I opened to check, and it stopped charging, but all cells are at 3.97-3.98V except for one with 3.92V

[OzMek]

I re-openend the wheel and took some photos, to show how I Installed the balancer onto the free space available.
A hidden detail at the center of the cover : I reduced the well deepness by cutting it, shortening it and gluing it back in place.

I also glued some pads (hard plastic) to screw the balancer into.

Edited September 2, 2023 by OzMek

[OzMek]

Wires may look not well organised, but it is important to keep their original length (therefore their electrical resistance) to ensure voltage measurements have the same offset when balancing currents are flowing. wires are 60cm long.

Edited September 3, 2023 by OzMek

[OzMek]

You may then ask "So what, did it provide any benefit to your battery ?".

Remember the measurements I shown above in a table (July 8), one cell is highlighted in green, corresponding at the cell N°16.
(The calibration was due since decades on the meter I used in july. I checked it against a voltage reference this week, it is under evaluating the voltages by a few %)
Even if I fully charged each element individually before I plugged the balancer for the first time, this cell keeps having a slightly higher voltage than the others.
In other words, it is responsible for cutting the charge of the whole pack when it reaches 4,25V (Ablic over voltage threshold)

So I decided to monitor a full charge :
emptying the battery by driving until I receive the low battery warning, and pedals tilting (Strong tilting, you don't have much time to get off the wheel!).
Plugging in the charger.
After approx 1 hour, one led lighted up on the balancer. No real surprise, it is related to C16
Balancer started its work to reduce the C16 voltage, because it was higher than C17 by more than 0,1v. (4,15 vs 4,05 at that time).
Note: I expected an inductive balancer doesn't heat too much while balancing, but I was afraid it heats and to see my unicycle shell melt. 
While balancing the 2 cells, the balancer kept almost cold, this is a really good point !

At the end, the full charge voltage reached 83,2v before charger cut-off.
This means (roughly) the pack has 19 elements around 4,15, and one at 4,25 (I sampled some voltages, this is confirmed by my measurements).

My conclusions :
Yes, adding this balancer is beneficial
Before installing the balancer, the charging indicator on the wheel was never stopping blinking. Even after hours plugged in, the last segment was always blinking. Now it stops blinking, and the app shows battery at 100% (83,2V, measured 83,35V with a new and accurate meter).

Balancer helps maximizing the battery charge, but doesn't bring back your pack to its original status (anyway, the measured capacity (~3,0Ah) dropped to 60/65% of a new one (4,Ah))
Balancer works better if you charge a fully discharged battery, otherwise the 0,1v difference between 2 cells might not be reached (Imagine a worse case where all cells are at 4,05V, C15 is at 4,15V and C16 is 4,25V, your pack ends up at 81,3v)

This doesn't perform as good as a BMS having built-in balancing feature, but is better than no balancer at all
So I consider this a good 'aftermarket' upgrade to compensate the unbelievable lack of balancing on Inmotion BMS

Edited September 2, 2023 by OzMek

[alcatraz]

On 8/3/2023 at 6:30 PM, Illifant said:

Is this fuse permanently blown or can be reset (and how)?

I have an V5F battery that I opened to check, and it stopped charging, but all cells are at 3.97-3.98V except for one with 3.92V

If you fast charge it you can hit the overcharge protection earlier.

[alcatraz]

FYI these ETA3000 balancers exist in smaller packages. The nice thing about them is that they're high current and they don't get warm (supposedly).

Then there are the slightly larger ones with bluetooth and an app. Those balance to an accuracy of 0.001v, and not 0.03v like ETA3000. 0.03v is between two adjacent groups. It can compound to a larger difference between several groups.

Edited September 4, 2023 by alcatraz

[OzMek]

You're right, and 0,03v is not so small and I would of course prefer 0,01v or less. The accuracy you're mentionning is amazing. Could you share a link to such product ?

One advantage of the ETA3000 boards is their very low standby current. The more precise balancers I've seen so far were capacitor balancers. Better accuracy, but standby current too high for this kind of use on standalone batteries (I guess they're more suited for solar stations).

Edited September 7, 2023 by OzMek

[alcatraz]

Yep, I'm pretty sure it's capacitor balancing.

There are tons of settings you can change. One of them could have something to do with standby power draw. 

极空 Jikong balancers are viewed as some of the best within China. https://www.jkbms.com/

They come in 16s, 20s, 24s and 32s I believe. You can program them for different chemistries etc. And there are different versions with different output currents and balancing currents. Since for euc we don't want output management you can go for the smallest 24S 40A bms and that comes with 0.4A balancing. It's about 240CNY ~ 40usd perhaps? If you pick a 100A bms you get 1A balancing.

You can set it to stop charging at 80-90% and balance at 50% etc. Almost whatever you want really.

It's the kind of balancer that allows you to use really garbage lithium cells and be able to ride.

[alcatraz]

As you can see in the picture it also comes with temperature sensors. However with an unmanaged output it's necessary to use some sort of alarm system to notify the rider.