Bad battery cell?

Hi, I'm Glenn and I live in The Netherlands. I really appreciate how much knowledge is being shared on this forum. I hope you can forgive me that I'm not able to write in Deutsch, but I have no where else to go as the English Twizy forum evowners was suddenly gone a few months ago. On the Dutch Renault forums the Twizy is not populair and once in the 6 months there is a post. So I'm reading this forum thanks to the power of google translate and it works pretty well.

Last year I purchased a 2012 Twizy with Rental battery, the milage is 27489 km at the moment. At moment of purchase the breaks where stuck and the Twizy was (permanently) tuned, so of course the range was pretty bad. I cleaned breaks and got an OVMS to bring the Twizy back to orginal state.

On the OVMS I noticed that cell 9 is always at a lower voltage than other cells, my concern is that this cell is draging down the entire performance on the battery pack. The range is max 50 km with carefull driving.
The SOH is 88%

Fully charged:


25%:


What I also noticed, other tuned Twizy's are beeping with the SERV light when you give full throttle. Mine doesn't do that when I load a tuning profile.

I already asked a Renault dealer to check the cells, but they don't seem to care as long the SOH is above the minimum.
Also the terms and conditions are changed since 1 January 2020 for rental batteries:
When the Twizy is older that 10 years, the battery will replaced when the SOH is under 60% instead of 75%.

Die schlechteste Zelle mit der geringsten Kapazität bestimmt die Leistungsfähigkeit der ganzen Batterie.
Die Zelle 9 scheint schlechter zu sein.
Versuche doch mal ob durch wiederholtes laden des Akkus die Zelle 9 auf das gleiche Spannungslevel wie die anderen
Zellen bei 100% kommt. Das könnte die Leistung des Akkus verbessern.

Wenn die Zelle 9 aber eine deutlich geringere Kapazität hat wird sie immer das ganze Bat-pack und die Reichweite begrenzen.
Der SOH wird von der Twizy Software berechnet. Die schlechte Zelle wird den SOH nach unten bringen.
88% ist ja auch nicht so gut. Leider kann ich Dir nicht sagen wie schlecht eine Zelle werden muss damit der SOH auf 60% sinkt. Ich kenne auch nicht die Formel wie der SOH berechnet wird.
Man müsste die Zelle 9 eigentlich austauschen. Das macht aber keine Renault Werkstatt.
Ich fürchte Du musst den Twizy fahren bis die 60% SOH erreicht sind.

it's a little bit strange that the cell has low voltage when the whole pack is charged. If the capacity is real low, the cell should be increase in voltage FASTER than the others.
My suggestion:
Keep the pack fully charged for a longer time. Thr BMS should discharge the other cells (very slow unfortunately) with the determination to reach all cells with the same voltage.
will be interesting whether this state will be reached. Just measure the voltages for to see a trend.
IF all cells are balanced to equal voltages discharge the pack. If the suspicious cell has really got a lower capacity, it will show again a lower voltage...

Ok, so how do I do that? Just keep the Twizy plugged in the socket?
Or should I unplug it and charge it again next day without driving?

Ich weiß leider nicht nach welchen Regeln das Twizy BMS seine Arbeit macht.
Ich würde einfach beides ausprobieren.

Stecker rein und 24h warten.
Oder
Laden , ein klein wenig fahren und wieder laden , ein klein wenig fahren und wieder fahren. Usw……

Mit dem OVMS zwischendurch immer wieder die Zellspannung anschauen. Dann müsste man schnell
sehen können ob sich die Zellspannung von Nr. 9 sich den anderen Werten angleicht.

Wenn die Zellspannung von Nr 9. bei 100% Ladung dauerhaft zu klein bleibt könnte auch ein
Defekt im BMS oder der Verkabelung dieser Zelle möglich sein.
Um so einen Fehler zu finden müsste man den Akku ausbauen und öffnen. Was man bei einem Mietakku aber nicht darf.
Eigentlich sind alle Fehlfunktionen in der Batterie ( bei einem Miet-Akku ) ein Problem von Renault.
Z.B. Defekte (verschmorte) Steckverbinder am Akku führten schon zu einem Akkutausch seitens R.
Man müsste Renault nur dazu bringen anzuerkennen das hier ein technisches Problem im Akku vorliegt.
Natürlich kann Renault per Can-Bus Diagnose auch die Zellspannugen anschauen.
Eventuell überzeugt das die Renault-Werkstatt das hier ein Defekt und kein Verschleiß vorliegt.

Hello Dutch Twizy, I had something similar with my electric scooter .., I drove the battery completely empty and then put it on the charger for a day. It is admittedly not a twizy but it might be worth a try. Do you have it in writing by the way? in a car of 10 years the battery is up to 60%?

You could still try a battery reset.
- Drive the twizy on the lowest possible power. on one or at max two bars, till its empty.
- When empty disconnect the 12 V battery for a while.
- Connect it back and load the twizy to full.
- If needed rinse and repeat.

Hello Glenn!
I suppose nobody here knows how the BMS of the Twizy works exactly.
I would plug the Twizy in untill 100% is reached and then pull the plug. after some hours or a day plug in again for half an hour and so on.
Read out the cell-voltages once a day and look out for a trend

Hi.

Think about buying the Battery... Renault will not do anything until the Battery breaks completly down or the SOH drops below 60%...
Imho the Pack's around 300€, maybe below, so the financial risk ist small... and once ya own it, there is no reason not to open it for further checking.

I kept the Twizy on the charger for 3 days with some unplugging. But I don't see any difference at all.

I also ran the Twizy completely empty until I had to push it to the charger, but the voltage deviation stays there.


During charging the difference gets only worse. But this cell seems to be the slowest during charging, not the fastest.


Currently I have send a request to RCI to purchase the battery. Maybe I just gonna replace the cells myself, the CATL battery looks as a good replacement.
The Twizy is no fun with a bad range, this needs to be fixed.

When I experimented with old 18650-cells from used laptop-batteries I encountered cells which did not reach more than 4.0 or 4.1 volts during charging. Those cells only got warm…. A reason to discard them. Maybe cell 9 has a similar defect. Last try would be openenig the battery and charging cell 9 with a 4.2 volt dc-source while controlling the cell Temperature…. In a bomb-Proof bunker or similar….
If you really remove the cells from your battery keep them for a replacement! I‘m sure there will be a market for replacement - cells….

Henk68 schrieb: Hello Dutch Twizy, I had something similar with my electric scooter .., I drove the battery completely empty and then put it on the charger for a day. It is admittedly not a twizy but it might be worth a try. Do you have it in writing by the way? in a car of 10 years the battery is up to 60%?

Sorry missed this earlier. If you transfer a battery rental Twizy contract to a different person since 1 january 2020 the contract will change to 60% SOH before replacement for 10 year old Twizy's.
Contract is in dutch:

OLD:


NEW:

Pfälzer68 schrieb: Hi.

Think about buying the Battery... Renault will not do anything until the Battery breaks completly down or the SOH drops below 60%...
Imho the Pack's around 300€, maybe below, so the financial risk ist small... and once ya own it, there is no reason not to open it for further checking.

I requested a purchase, you are right. They are just asking 363 euro for the battery purchase.
With the SOH at 88%, it can still take years before Renault will fix the battery. And with this bad range it is no fun to drive and I won't use the Twizy much at all.

363 euro is already cheaper than an empty batterybox without connectors and electronics. However, the orginal BMS is most likely not usable.

I am also from the Netherlands (the Hague region) but it is nice to write in English, then the translation also goes well to German.
Thank you for your answer, by the way, I see that if your twizy is built after 1-10-20, the battery will only be repaired or replaced below 70%.

If you start the big adventure „building my own battery“ I‘m convinced using the original bms is much easier than adapting another one….
If you use lion-cells with an maximum voltage of 4.2 volts per cell there’s no reason to switch to another bms. Guys from this Forum had disconnected the original bms from the cell-pack and reconnected it without problems. The biggest challenge is to fit new cell in a mechanical proper way into the battery-housing…

udo229 schrieb: I‘m convinced using the original bms is much easier than adapting another one….

Darüber kann man auch anderer Meinung sein.
Er wäre der Erste, der das macht.
Ich bezweifle nicht, dass es funktionieren kann.
Und möglicherweise ist es auch wirklich nicht ganz so schwer.
Aber als Pionier wird er vermutlich kräftig Lehrgeld zahlen und doch noch manche Klippe umschiffen müssen.
Vom edriver-BMS ist bewiesen, dass und wie es funktioniert.
Und auch sauber dokumentiert.
Und es gibt Forums-Know-How.

Ich habe nur Bruchteile seiner Posts gelesen.
Aber wenn er fachfremd ist und bislang keine Erfahrungen mit Basteleien an solchen Akkus hat, dann würde ich nicht dazu ermuntern wollen.

Warum gibst du nicht den Pionier?