Rowenta/Tefal battery

[David3g]

Hello. It would be a Rowenta battery. does anyone know how to reset the bms? the cell was replaced and the panel was deaf. rowenta x force machine. 7 cells

 

[D.A.(Tony)Stewart]

report your cell voltages. If too far out BMS will shutoff

 

[David3g]

report your cell voltages. If too far out BMS will shutoff

Neu cells. All 7s is 4.13v

 

[stenzer]

4.13 V for all 7 cells in series, or have you opened the pack and this is the mean value of an individual cell? Is the nominal pack voltage 25.2 V?

How does the pack behave/indicate (LEDs) when connected to the charger? Have you measured the output voltage of the charger? Have you checked if the charger itself has a loose contact?

 

[D.A.(Tony)Stewart]

Power cycling the charger ought to reset any BMS state to normal.

 

[David3g]

4.13 V for all 7 cells in series, or have you opened the pack and this is the mean value of an individual cell? Is the nominal pack voltage 25.2 V?

How does the pack behave/indicate (LEDs) when connected to the charger? Have you measured the output voltage of the charger? Have you checked if the charger itself has a loose contact?

cells tested separately. the factory value is 2000mAh, the cell in it has a capacity of 1930mAh. Charger is good. We also use this for other accumulators. This is an upgraded pack that does not last as much as the factory one that is a few years old. Bms, doesn't the processor need to be reset somehow?

 

[David3g]

Power cycling the charger ought to reset any BMS state to normal.

Yes. reset, the question is how is it possible?

 

[stenzer]

This measn you have opened the pack, replaced the cells and kept the old/original BMS?

This is an upgraded pack that does not last as much as the factory one that is a few years old.

So you are able to use the pack with the new cells? As far as I understood your explanation, the pack is locked.

 

[David3g]

This measn you have opened the pack, replaced the cells and kept the old/original BMS?


So you are able to use the pack with the new cells? As far as I understood your explanation, the pack is locked.

yes, there are new cells in it. but it doesn't perform as it should. there is not so much operating time. as with the old cells

 

[stenzer]

Have the cells been charged by an external charger, or by the BMS? I would expect you have to discharge the cells, and charge them by the BMS so it can determine its capacity and SoC (state of charge).

Are the cells "trustworthy" by means the provide the rated mAh? Do you have the possebility to check this by an external device/charger? I assume as you mentioned 1930 mAh for the new cells.

there is not so much operating time. as with the old cells

What's the rating of the old cells and how long do they provide energy, comparde to the new ones?

 

[David3g]

Have the cells been charged by an external charger, or by the BMS? I would expect you have to discharge the cells, and charge them by the BMS so it can determine its capacity and SoC (state of charge).

Are the cells "trustworthy" by means the provide the rated mAh? Do you have the possebility to check this by an external device/charger? I assume as you mentioned 1930 mAh for the new cells.


What's the rating of the old cells and how long do they provide energy, comparde to the new ones?

the new battery is factory set for about 30 minutes of vacuuming. this pack with new cells, which have been tested with a tester, stops after 10 minutes of vacuuming. The new factory pack is 2000mAh.

 

[stenzer]

Ok, to summerize it

• The pack is not locked
• the original pack (with original cells) is powering the vaccum cleaner for 30 minutes
• by replacing the cells, and still using the original BMS, the vaccum cleaner is powered for 10 minutes
• the orignal cells are rathed with 2000 mAh
• the new cells are also rated with 2000 mAh, and have been tested by an external device/charger, which leads to 1930 mAh

Please correct me if this summery is wrong.

Has your external charger the possibility to discharge the cells as well? I would recommend to discharge the cells, and install them into the pack. The BMS should take care of the charging, so it has knowledge about the pack capacity. As the voltage of a cell is rather flat when already charged to ~75% it's hard to judge for the BMS how much energy is already in the cell. If the BMS relies on coloumb counting, I would expect charging "empty" cells monitored by the BMS will help to increase the operating time. Maybe it even has the information stored, the original cells are empty (would depend on their SoC when removing them). Have a look here to see how the CC-CV charging approach works [1].

[1] https://www.digikey.at/en/maker/tutorials/2021/charging-lithium-ion-and-lipo-batteries-the-right-way

BR

 

[David3g]

Ok, to summerize it

• The pack is not locked
• the original pack (with original cells) is powering the vaccum cleaner for 30 minutes
• by replacing the cells, and still using the original BMS, the vaccum cleaner is powered for 10 minutes
• the orignal cells are rathed with 2000 mAh
• the new cells are also rated with 2000 mAh, and have been tested by an external device/charger, which leads to 1930 mAh

Please correct me if this summery is wrong.

Has your external charger the possibility to discharge the cells as well? I would recommend to discharge the cells, and install them into the pack. The BMS should take care of the charging, so it has knowledge about the pack capacity. As the voltage of a cell is rather flat when already charged to ~75% it's hard to judge for the BMS how much energy is already in the cell. If the BMS relies on coloumb counting, I would expect charging "empty" cells monitored by the BMS will help to increase the operating time. Maybe it even has the information stored, the original cells are empty (would depend on their SoC when removing them). Have a look here to see how the CC-CV charging approach works [1].

[1] https://www.digikey.at/en/maker/tutorials/2021/charging-lithium-ion-and-lipo-batteries-the-right-way

BR

everything you wrote is correct. if I understand what you are saying. probably the eprom of the bms can't extract the real capacity of the cells, so it breaks it down ahead of time?

 

[stenzer]

Depending on the charging algorithm, the BMS might only ess/know-about the energy/charge you have put into the pack by trying to charge almost full cells. So the BMS only allows you to consume the energy you have provided during charging. But of course this is only an assumption, as no one knows how the algorithm for this pack looks in detail. Most easiest way would be to allow a charging to ~4.2V (by the CC-CV method), and allow a dischgarging to e.g. 3.2 V ~ 3.5 V, indicating an empty pack. But for sure, it is not that easy as the BMS will include SoC and SoH (state of charge and health) information as well.

 

[David3g]

Depending on the charging algorithm, the BMS might only ess/know-about the energy/charge you have put into the pack by trying to charge almost full cells. So the BMS only allows you to consume the energy you have provided during charging. But of course this is only an assumption, as no one knows how the algorithm for this pack looks in detail. Most easiest way would be to allow a charging to ~4.2V (by the CC-CV method), and allow a dischgarging to e.g. 3.2 V ~ 3.5 V, indicating an empty pack. But for sure, it is not that easy as the BMS will include SoC and SoH (state of charge and health) information as well.

that's right. I should probably reset the soc data. I just don't know how to solve it

 

[stenzer]

As mentioned, if possible discharge the cells by an external charger. Install them into the pack, and give it a try by charging via the BMS of the vacuum cleaner battery pack.

 

[D.A.(Tony)Stewart]

Passive BMS are limited to the CC rating in bypassing current of the weakest cell when it reaches 4.2.

Unless your vacuum motor current has somehow increased x3 to reduce useful time from 30 to 10 minutes, there must be an error in the capacity of the weakest cell for Ah rating. This imbalance can only be measured under load during or shortly after by the difference in cell voltages. If possible, solder magnet wire or similar wire for convenient cell voltage testing to outside terminal or connector. They should be matched within <<2% of mean voltages if new.

 

[Easy peasy]

Your cheap new cells are not the same quality as the old ones.

 

[David3g]

Your cheap new cells are not the same quality as the old ones.

Who said it was cheap? By the way, the cell is the same as the one used in the factory, only much younger.

--- Updated Feb 10, 2024 ---

As mentioned, if possible discharge the cells by an external charger. Install them into the pack, and give it a try by charging via the BMS of the vacuum cleaner battery pack.

I drained the cells to 2.97v. I put it back in its place and charged it with its own charger via its bms. The test will be today. 4.15v charging stopped.

 

[Easy peasy]

The only way to really test a cell, is a full discharge, 1930mAhr = 950mA for 2 hours - it's a fair bet your " same as the factory " cells won't do this

( whatever PoC you are testing your cells on to get the 1930mAHr result - it is most likely not doing a full discharge - we have seen some Chinese sourced " testers" that are wildly optimistic, i.e just plain wrong )

which is why you are seeing poor performance. Oh - were the cells cheap ?