Cell balancing on the Lynx

[txwheel]

I'm a bit confused about cell balancing on the Lynx.

The general consensus is that the Lynx's smart BMS begins balancing the cells only after some of the cells start exceeding 4.2V, with the cells above 4.2V sending their excess voltage to cells that are still below 4.2V, and the smart BMS steadily stepping down the amount of current it pulls from the charger as the cells get more balanced and approach the target voltage, until the current finally stops flowing altogether from the charger. However, I notice that if the charger is set to deliver 151.2V,  charging stops at 151.2V, but after the cells rest for a bit,  all the cells end up slightly below 4.2V, (see screenshot attached).  

This leaves me with a few questions: 

1) When doing a full charge to balance all of the cells, shouldn't the charger be set to deliver slightly more than 151.2V, such as 151.3V, to ensure the balancing process completes before any current from the charger stops? 

2) If using a smart charger with a custom cut-off based on current flow (such as the Roger SC charger), what is a good current level to set the shut-off to occur at?

3) I've seen suggestions to balance the cells every month or every five or so charge cycles.  However, what is the point of balancing the cells if their voltages aren't drifting apart beyond a minimal amount? I'm wondering if it's simply sufficient to keep an eye on the individual cells, and as long as they stay balanced within a certain range, we can avoid balancing and stick to shallow battery cycles (staying within 40-80% of full charge) to minimize battery stress, and only balance if/when we eventually see the voltage variance drifting outside that range?

4)At what "max diff" level can the cells be considered balanced, or is there another way to gauge if balancing is complete?

Edited June 7 by txwheel

[sffish]

I adjusted my stock charger (I don't remember the voltage it puts out) so that my individual cells never go above 4.2V at fully charged. They are all 4.19 or 4.18 at the end of charging. To me that seems like balancing.

[txwheel]

Thanks @sffish.   I wonder if there's any point to charging to 100% if the cells' voltages stay closely balanced.   Some folks recommend occasionally charging to full, but isn't there no reason to do that as long as the voltages don't drift apart much?

[sffish]

I suppose not if the batteries balance at a lower voltage. I just want to get my maximum range so I don't mind sacrificing some battery longevity for that. I just don't want to overcharge the batteries.

[peytole]

no need to charge above 151 volts.  Smart BMS balance cells continuously from rated voltage.  Always wanting to fully charge is not good.  Stopping at 150 is fine too.  I carried out around twenty charges between 125 and 145 volts and I did not notice any imbalance.  The BMS have a tolerance and do not cut off the charge at 4.2v, if the charger is incorrectly adjusted you will charge at 152 or more without cutoff.  So have the charger voltage checked and lowered to 151 volts maximum.

[Dubardo]

On the same subject, I have a imbalance of 0.06v in both pack, fresh off the charger.

Is this an issue and how to resolve it. Barely 500km on it.

 

[Skampster]

My cells are usually around 0.010v to 0.018 at any given time, fully charged or at 30%. If your cells are like this, they are as balanced as they can rationally be. If this is the case for anyone at any time, you don’t need to charge to 100%, but I still do so because you need power (headroom) and most definitely, range when it comes to the lynx. 
Also, the wheel itself by the time the battery is dying will be long dead before then, most likely. So charge up and enjoy, just don’t charge to 100% until your literally out the door with it. 

[Timwheel]

My left back shows 0.113v unbalance fresh off charge and blinks "BL" (I suppose battery left ?) on the screen. The wheel is brand new and has like 9km on it what should I do ? It seems concerning to me

[Rawnei]

People say the Lynx BMS will balance the cells above 80%, what balancing mechanisms does that I have no idea.

Personally I always charge to no more than 150V (charger adjusted + charge control in firmware) and cells stay balanced within 15mV.

[Skampster]

I often also find with my lynx that if my difference are slightly higher than usual at full charge, say a difference of 0.018v, by the time I come home after a ride, possibly down to 40%, the cells have a lower imbalance of say 0.013v, which is where they usually lie. The best I’ve seen is 0.010v

[Seba]

On 6/7/2024 at 12:11 AM, txwheel said:

The general consensus is that the Lynx's smart BMS begins balancing the cells only after some of the cells start exceeding 4.2V

No. Lynx BMS balance the cell groups when the charger is connected. What you're describing is typical for regular, "non-smart", top-balancing BMSes used in other wheels.

On 6/7/2024 at 12:11 AM, txwheel said:

with the cells above 4.2V sending their excess voltage to cells that are still below 4.2V

No. Lynx BMS is using passive balancing, just like all other BMSes used in wheels manufactured to date. Passive means that cell groups that has higher voltage than others are discharged on shunt resistors. Definitely there's no charge transfer. Where did you found this info??

On 6/7/2024 at 12:11 AM, txwheel said:

the smart BMS steadily stepping down the amount of current it pulls from the charger as the cells get more balanced and approach the target voltage, until the current finally stops flowing altogether from the charger

No. Current tapering is a combined effect of battery voltage, battery circuit resistance, charger output voltage and charger current limitation. BMS has no means to regulate charging current. It can only connect/disconnect charging circuit to/from the battery. It's mainly used as a overcharge protection but may also be used to terminate charging at SoC less than 100%. This feature is available in Lynx and Sherman L.

Just curious - where did you get all this information??

[Chriull]

On 6/7/2024 at 12:11 AM, txwheel said:

and the smart BMS steadily stepping down the amount of current it pulls from the charger as the cells get more balanced and approach the target voltage

 

2 hours ago, Seba said:

No. Current tapering is a combined effect of battery voltage, battery circuit resistance, charger output voltage and charger current limitation. BMS has no means to regulate charging current. It can only connect/disconnect charging circuit to/from the battery. It's mainly used as a overcharge protection but may also be used to terminate charging at SoC less than 100%. This feature is available in Lynx and Sherman L.

Just curious - where did you get all this information??

That current is reduced by the bms during the constant voltage stage is some "quite old" rumour often repeated. Most probably initiated by some youtube influencer?

[Dubardo]

Figured out the Balancing is when my charger fan is running intermittently 1 second, i saw the power lowering but still charging. I thought it was a bug. I also ride after the full charge imbalance and it fell back to .0018A on my next ride.

[Skampster]

Yes I’ve noticed that the Lynx is good at balancing while riding. 

[Patrick Robert]

On 9/9/2024 at 6:20 AM, Rawnei said:

Personally I always charge to no more than 150V (charger adjusted + charge control in firmware) and cells stay balanced within 15mV.

OMG, just tried that for the experience on both my Lynx and Sherman L. 

I was having issues with the balancing phase, especially on the Lynx (now well over 10k km). Final voltage after balancing was inching its way down, 0.1V at a time. 10k / 40 km a ride, then balancing, means about 250 cycles. Was wondering about those 50Ss (my 50E Sherman S was still charging to 101.2V after 23k).

Another thing I was noticing was that the cell imbalance was actually *increasing* to 0.016 in the balancing phase, up from 0.008 or so otherwise. 

So yeah, it appears that the SmartBMS balances all the time. So better to cut out the balancing phase altogether. 

1-2h charging for the L instead of 4-5h. Less on the Lynx. And hopefully longer battery life. 

Game changer.

Edited October 4 by Patrick Robert

[Rawnei]

5 hours ago, Patrick Robert said:

OMG, just tried that for the experience on both my Lynx and Sherman L. 

I was having issues with the balancing phase, especially on the Lynx (now well over 10k km). Final voltage after balancing was inching its way down, 0.1V at a time. 10k / 40 km a ride, then balancing, means about 250 cycles. Was wondering about those 50Ss (my 50E Sherman S was still charging to 101.2V after 23k).

Another thing I was noticing was that the cell imbalance was actually *increasing* to 0.016 in the balancing phase, up from 0.008 or so otherwise. 

So yeah, it appears that the SmartBMS balances all the time. So better to cut out the balancing phase altogether. 

1-2h charging for the L instead of 4-5h. Less on the Lynx. And hopefully longer battery life. 

Game changer.

I still let mine balance, I just changed the max voltage to 150V and that's it, still perfectly balanced after nearly 6000km.

[Skampster]

5 hours ago, Patrick Robert said:

to 0.016

That being said, that number is still way in the acceptable range. But yes, no need to fully charge if they are balanced. I’ve noticed on the L that my left side battery goes up to 0.065v at full charge but when riding both packs are around 0.016v. So it seems to be happier just shy of full charge. 

[Skampster]

Can someone explain to me as to why there’s the number 36 (36 what exactly) in the battery voltage screen on the lynx and its the same 36 on the larger L. 

[Rawnei]

12 minutes ago, Skampster said:

Can someone explain to me as to why there’s the number 36 (36 what exactly) in the battery voltage screen on the lynx and its the same 36 on the larger L. 

36 cells in serial gives you 151.2V (151.2 / 4.2), so each pack has 36 cells, Lynx has 4 packs in parallel 36S4P and L has 6 packs in parallel 36S6P.

18 minutes ago, Skampster said:

That being said, that number is still way in the acceptable range. But yes, no need to fully charge if they are balanced. I’ve noticed on the L that my left side battery goes up to 0.065v at full charge but when riding both packs are around 0.016v. So it seems to be happier just shy of full charge. 

While it's charging the numbers will fluctuate.

[Skampster]

3 minutes ago, Rawnei said:

36 cells in serial gives you 151.2V (151.2 / 4.2), so each pack has 36 cells, Lynx has 4 packs in parallel 36S4P and L has 6 packs in parallel 

This doesn’t make sense, what you look like you are saying is that both the lynx and L have 36 cells per side? Correct?

[Rawnei]

Just now, Skampster said:

This doesn’t make sense, what you look like you are saying is that both the lynx and L have 36 cells per side? Correct?

No, 36 cells per pack, Lynx has 4 packs, L has 6 packs.

[techyiam]

10 minutes ago, Skampster said:

That being said, that number is still way in the acceptable range. But yes, no need to fully charge if they are balanced. I’ve noticed on the L that my left side battery goes up to 0.065v at full charge but when riding both packs are around 0.016v. So it seems to be happier just shy of full charge. 

I would consider an imbalance of 16 mV between the highest cell group voltage and the lowest cell group voltage in a battery pack good.

16 minutes ago, Skampster said:

I’ve noticed on the L that my left side battery goes up to 0.065v at full charge but when riding both packs are around 0.016v.

I don't own a Leaper Kim wheel with a smart BMS.

I have experience with only the smart BMS"s in the S22 and the S16 Pro.

I am not sure, but for Kingsong, I noticed cell balancing occurs after a cell group exceeds 4.2 V. So I suspect it only does top balancing. 

However, I find it odd that one of your battery packs cell group imbalance goes up to 65 mV at full charge. 

I think 65 mV is on the high side.

For my packs, once the imbalances are brought down, it stays low for some time.

 

[Skampster]

Ahh, so the voltage screen is not showing every single cell then?

[Rawnei]

1 minute ago, techyiam said:

I think 65 mV is on the high side.

 

See my comment above, if charger is still plugged in this value can fluctuate while it's trickle charging which seems more likely if the actual difference is 16mV.

[Rawnei]

1 minute ago, Skampster said:

Ahh, so the voltage screen is not showing every single cell then?

The cells are grouped together, you see left and ride side.