NineBot Z10 BMS does not balance. Any solutions?

[alcatraz]

You seem quite enthusiastic about working on the wheel. That's why I suggested the simplest solution of manual periodic balancing. You just need to install balancing wires for it to be convenient without taking much apart. The only problem is you have to keep the wheel. It's too risky to give away.

[Boris Lämpel]

I rode without a working BMS communication for around 1 year. I really cannot advice You replacing the ninebot BMS as long as it tells the firmware everything is ok. You can install the firmware "no BMS" (somewhat like that ist was called) by MRN67. I had it in my ninebot, after the communication between BMS and mainboard did not work anymore. As soon the firmware detects any BMS issue it will make a complete tiltback, so that You can´t ride anymore. With the firmware You can ride again. But with every harder acceleration (and therefore voltage drop) You will get limited because the wheel thinks the battery is empty. Because of the small battery this even happens at full charge. That´s really anoying.

I can´t remember anymore: Do you have 2 BMS wire connections (for both batteries)? Then maybe You can flash it to the Z6 firmware (where the wheel has only 1 battery). But with the missing BMS connection You won´t have joy to ride anymore...

[matthijs]

On 5/8/2024 at 3:46 AM, alcatraz said:

Yes but the broken bms will still possibly handle something depending on how that bms is designed.

I didnt understand the difference between a BMS and balancing board, hence my somewhat bad assumptions. However, with the assumption the BMS is okay and still does all the protection (which I somewhat assume, regarding that the statistics of the BMS still read fine), an added 2x 7s balancing board would take care of the balancing. As this option is cheap and allows me to drive with more "peace-of-mind" Ill give this a shot, because as
 

On 5/8/2024 at 11:24 AM, Boris Lämpel said:

As soon the firmware detects any BMS issue it will make a complete tiltback, so that You can´t ride anymore.

said, having the BMS disabled is kind-of a no-go with the Z10 sadly. If the added balancing board doesn't fit my needs ill consider switching it over to the working BMS, But I hope this will be the end of it and I can start riding again. 

I thank you for your advice. Ill give an update once it all has come together!

[alcatraz]

Cool.

Just one last heads up. The balancing boards can fail so it would be smart to add external balancing wires that cou can probe. Be careful how you install the wires so they don't short out or wear the isolation.

These balancing boards do not balance completely, just crudely. So you can expect a 100% charge to yield cells above 4.20v. 4.25v is a safe max voltage. You should figure out how long it takes for the pack to reach 4.25v on ANY cell. When you first install the balancing boards it will look good but over time it'll deviate. Why? Because balancing stops at 0.03v between two cell groups. Not at 0.001v as what we're used to think a balancer does.

Your bms screenshots earliet in the thread indicate to me that cell group 14 will exceed 4.25v first.

Groups 8-14 will all be at a higher voltage than 1-7 because you're using two bms in series, and 8-14 generally have higher avg voltage (lower capacity/more wear).

When you learn which group is your weak group (like group 14) you just measure that one after a 100% charge. If it's over 4.25v then even with the balancing boards, you need to manually balance. This is the problem with 100% charging. 

On my broken V8 I still have overcharge protection. You do not seem to have it since we saw a group at 4.27v earlier. This is a concern.

Monitor after every charge, if ok then every few charges etc. These balancing boards work the best if you don't charge to 100%. If you charge to like 90% you don't have to worry so much. Having an imbalance isn't dangerous while riding unless you're outside the range of 4.2-3.3v. 

[matthijs]

On 5/10/2024 at 2:53 AM, alcatraz said:

Just one last heads up.

Hey! I just received the 2 balancing boards, so I will go ahead with the procedure. Thank you for your comments, ill keep them into account. I will keep the Battery attached to the internal Z10 BMS, which is a smart BMS and allows me to keep an eye on the internal voltages after charging even after the balancing board is added. I will alter the output voltage of my charger to prevent any over-charging. The impact on the range will be minimal, but the impact on safety even larger. Thank you for your great advice and help! I will report back once the boards are installed and I have initial results gathered.

[alcatraz]

Good luck. 

Keep an eye on cell group 14 while/after charging.

[matthijs]

Happy to confirm that the procedure was successful! Added both balancing boards to the pack. It was somewhat of a struggle as even the original intended placement didn't fit the boards. However, I found 2 other spots which luckily could house the boards, although 1 needed to have its connector be removed. Check it out! (somehow didn't think to make a picture of the finished result.... oh well) 

Also, it seems like the balancing board is charging til a difference of 3mV (0.003), which was a nice surprise. Indeed, as the difference from cell 14 to 1 aggregate, a pattern can be seen where cell 14 is almost the fullest, and the cell1 is emptiest. still, much better than the results before the balancing board was added.  However, this difference can also be seen at BMS#2, so that shouldn't pose a problem? 

[alcatraz]

Interesting.

Whats the link to that board?

Are those voltages before/after?

[matthijs]

This is the link to the board; https://nl.aliexpress.com/item/1005006040281226.html?spm=a2g0o.order_list.order_list_main.15.644379d2vaCKRy&gatewayAdapt=glo2nld

And the voltages are before and after charging. Ive ridden ~2km as a test, and the voltages are even closer now, pretty cool!

[alcatraz]

The small/affordable boards that I've seen have exclusively used the ETA3000 balancing circuit/chip. That's the one that balances to 0.03v.

What you've found is way way better 0.003v. This is the stuff that people with broken bms need. I'd love to find out what the circuit name is.

Also, if they're also equipped with a bluetooth module it would be a complete package.

I see there's an on/off switch too so you don't have to balance 24/7 like when riding.

[alcatraz]

If you get the chance please read the print on those chips.

[matthijs]

12 hours ago, alcatraz said:

If you get the chance please read the print on those chips.

WELL, As can be seen in the picture below something still isn't right, so I might just have to open the pack up again...  Cell 1 of BMS 1 seems to be getting no charge or is discharging too quickly. Weird, as the rest of the pack seems super okay with the added balancing board...

 

 

[alcatraz]

The board can be switched off by adding a switch conmected to two pads. 

Maybe if it wasn't on all the time that cell group wouldn't drop.

Also, maybe you forgot to connect B- (B0) to the board. To balance B1 you need B0 which is usually the same terminal as the high power output negative. 

A 14S battery requires 15 wires. N+1

[matthijs]

18 hours ago, alcatraz said:

maybe you forgot to connect B- (B0) to the board. To balance B1 you need B0 which is usually the same terminal as the high power output negative. 

A 14S battery requires 15 wires. N+1

CHecked the board again but there's no button sadly. Also, all the wires are connected and read okay. I remember though,  that during soldering I accidentally touched 2 balance leads together, as the connector was removed for space. This was during one of the first leads (b-), which might have affected the weird cell in the sc. After this happened I took extra measures to prevent this for the other leads, but it might've been to late already. Anyway, I ordered a new balance board. Ill be more careful with this install, so lets see if the issue is resolved then. 

[alcatraz]

Interesting.

The on/off switch has to be sourced and soldered to the pads on the board (next to the headers).

Open circuit must mean "on" and if you close it it means "off". This is my guess.

[alcatraz]

On second thought, your board looks different from the board in the aliexpress link. The linked board has those on/off pads.

[matthijs]

On 5/24/2024 at 1:49 PM, alcatraz said:

On second thought, your board looks different from the board in the aliexpress link. The linked board has those on/off pads.

Welp, This comment aged pretty ironically. I started smelling a faint trace of burned electronics today in my room. Checked the battery but couldn't identify it as the culprit. Started to smell more later this evening, checked again, and felt heat coming from one of the BMSs. The plastic and glue were soft and whilst I was getting it out of the pack another trace burned. The whole board was hot and this was the end result. 

Weirdly enough this isn't the board that was connected to cell 14 (the one with the low voltage) but the one attached to cells 8-14. I count myself lucky for not burning the house down lol. The cells in the pack are still charged so no other damage has been done so far, but damn. 

 

[alcatraz]

Hmm. Weren't groups 8-14 balanced? 

Turning it off could help. 

In your pic the one from last circuit burned, maybe the circuit that balances between cell 13. 9 and 12 look odd too.

What about the 1-7 balancer? Good as new?

Edited May 28 by alcatraz

[alcatraz]

Maybe double check that the balance wires for groups 9,12,13 are ok. Maybe one one got shorted out and/or detached from the pack.

[matthijs]

On 5/28/2024 at 2:28 AM, alcatraz said:

Maybe double check that the balance wires for groups 9,12,13 are ok. Maybe one one got shorted out and/or detached from the pack.

Thanks for the suggestions. I Checked all the connections, But they all seemed fine. Balance board 1-7 is fine (except cell 1 which had a delta of ~0.22V). The weird thing is that the pack was sitting unused for a couple of days already before this happened. Could there be some feedback loop between the BMS still charging and then the Balance board also charging? Might consider running the leads from BMS#2 down to BAttery#1 again now...

 

[alcatraz]

Hmm. Probably the circuit for group 1 is malfunctioning. It'd be nice to exclude the balancer drawing power from group 1 by turning it off.

Maybe it overheated. It could be so easy as to cool the chips with an alloy heat spreader.

Also riding the wheel while balancing is a problem because as you pull current the weaker cells voltage sag more than the good cells and so in that moment the balancer starts to balance back and forth possibly at full current and heat output.

Pity you don't have that on/off switch that's in the alixpress pictures.

Yeah connecting the packs together could be a good trick. But for the same reason above the cables need to be able to withstand a few amps like 3A continuously minimum. Like 20awg in case there are inter-pack currents going on while accelerating/braking. 

Edited June 6 by alcatraz

[matthijs]

On 6/6/2024 at 4:02 AM, alcatraz said:

Hmm. Probably the circuit for group 1 is malfunctioning.

This aged well. Decided to change the leads and see how I would continue the process. Seems like the Balance board completely discharged group 1, which is now at 0.8v. The pack is done for, which I am sad about. I guess Ill rebuild it over the summer, or see if I can sell it to someone who wants to use the parts, or build a fast-ass trike out of it, idk yet. But yea, its the end of a story. Rebuilding seems like a cool but time-consuming project. Quess that ill do it over the summer. Use some high-discharge batteries to push the topspeed, idk. 

Anyway, thank you for your help. It was a pleasure conversing and trying to find a solution. Ill guess you'll see me around the forum when I start with the rebuild.

[alcatraz]

Sorry.

If you can swap those 2-4 cells out with similar ones it's still rescuable.