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[BrianTRice@gmail.com]

I've never seen it done, and yes, I've looked at several BMS's for several different systems. Cell equalization is done by the charger, after charging has reached "100%", by a string of resistors that trickle-charges cells that aren't quite yet up to terminal cell voltage. If someone shows me an actual schematic that does something else, I'll believe it, but until then I'm sure not going to take the word of some probably misinformed salesman who's talking up his product.

Doug, if you click through to the BMS Parts section of the wiki, the picture of the board shows 5 PL536 chips connecting to a total of 28 individual circuits leading to 28 pins under that white block. I have the board depicted sitting right next to me and will see about uploading more pictures just to get you to stop projecting.

It's a very observable set of connections.

If you're referring to me as a "probably misinformed salesman who's talking up his product", you're way out of your scope of expertise and should examine why you think I'm a salesman rather than an overcurious and now reasonably informed owner; what happened is that I broke that very BMS board with SCv1 by an accident of overloading the precharge circuit before I know you did.

Don't wave your professional experience around and try to insult my credibility. It was you who ignored my installation instructions and broke your own BMS in exactly the way I just described. So maybe I'm not a shill and maybe you need to take what people say seriously, if not naively.

[BrianTRice@gmail.com]

I also have photos of a 2013-2014 era BMS which make the connection more obvious. But I should visually scrub relevant serial numbers to be careful before I upload. At least I can say it's finally a good time to do that, if it means I can encourage people to take a set of information seriously and stick with discussing more interesting questions.

For example, I'll double check mrwilsn's claim from my charging logs and probably publish it as an inference that seems to have good evidence in its favor.

[Doug S]

Doug, if you click through to the BMS Parts section of the wiki, the picture of the board shows 5 PL536 chips connecting to a total of 28 individual circuits leading to 28 pins under that white block. I have the board depicted sitting right next to me and will see about uploading more pictures just to get you to stop projecting.

Very cool, I looked up the data sheet for that part. What do you think that chip does? I'm still essentially 100% convinced that cell balancing only occurs when the charger is attached.

If you're referring to me as a "probably misinformed salesman who's talking up his product"...

I was referring to DPsSRnSD's comment that "I've been told that the bike will balance the cells anytime the contactor is closed if the SOC is above about 50%." I assumed, perhaps incorrectly, that that came from someone with a vested interest in selling him a bike. If it came from you, I apologize. I still believe it's misinformed.

...you're way out of your scope of expertise...

Very possible. It's been known to happen, and not all that rarely.

Don't wave your professional experience around and try to insult my credibility.

I'm not taking this personally, and I hope you're not. You're much too valuable to this community for me (or anybody) to get riled up, and if it's seemed like I was attacking you personally, I apologize and hope you believe it wasn't intended that way. I have no interest in getting into a pissing contest with you or anybody, but I'm also not going to back down and say you're right when I'm pretty sure you're not.

It was you who ignored my installation instructions and broke your own BMS in exactly the way I just described. So maybe I'm not a shill and maybe you need to take what people say seriously, if not naively.

For the record, while I've tried to keep it off of this forum, the user's manual PDF you sent me showed the following (attached as a jpeg). I assumed that the SC1 would fall under condition 3; that it would have implemented the signaling to close the contactor. I was wrong about that, and we know the result. Again, I've been quiet about it, but why didn't the manual say in an active voice that the SC1 didn't have that signaling, and would require the bike to be keyed on or the onboard charger used to close the contactor before powering up the SC1? Seems like there's fault enough to go around about that incident.

Back to the cell balancing, it's fine if we agree to disagree. I'm still quite sure it doesn't happen except at the very end of CV mode charging. It really isn't all that big of a deal if you don't agree with me...nobody's going to destroy anything if they believe either of us.

[Doctorbass]

mrwilsn is right at every points.  Thanks btw for explaining that so well.

Doc

[BrianTRice@gmail.com]

Doug, if you click through to the BMS Parts section of the wiki, the picture of the board shows 5 PL536 chips connecting to a total of 28 individual circuits leading to 28 pins under that white block. I have the board depicted sitting right next to me and will see about uploading more pictures just to get you to stop projecting.

Very cool, I looked up the data sheet for that part. What do you think that chip does? I'm still essentially 100% convinced that cell balancing only occurs when the charger is attached.

I'm unsure whether that is true or not (although it's at least the primary case it's intended for and functions in an obvious way), and separately whether that's enforced by the hardware design or is decided wholly in firmware.

PL536 basically encapsulates the functionality you describe, right on the BMS board. There are schematics online to go through the circuits; it's not sophisticated, just designed for just this application.

If you're referring to me as a "probably misinformed salesman who's talking up his product"...

I was referring to DPsSRnSD's comment that "I've been told that the bike will balance the cells anytime the contactor is closed if the SOC is above about 50%." I assumed, perhaps incorrectly, that that came from someone with a vested interest in selling him a bike. If it came from you, I apologize. I still believe it's misinformed.

I'm not taking this personally, and I hope you're not. You're much too valuable to this community for me (or anybody) to get riled up, and if it's seemed like I was attacking you personally, I apologize and hope you believe it wasn't intended that way. I have no interest in getting into a pissing contest with you or anybody, but I'm also not going to back down and say you're right when I'm pretty sure you're not.

Okay, that's fair and I misunderstood where that comment was aimed. Thanks.

It was you who ignored my installation instructions and broke your own BMS in exactly the way I just described. So maybe I'm not a shill and maybe you need to take what people say seriously, if not naively.

For the record, while I've tried to keep it off of this forum, the user's manual PDF you sent me showed the following (attached as a jpeg). I assumed that the SC1 would fall under condition 3; that it would have implemented the signaling to close the contactor. I was wrong about that, and we know the result. Again, I've been quiet about it, but why didn't the manual say in an active voice that the SC1 didn't have that signaling, and would require the bike to be keyed on or the onboard charger used to close the contactor before powering up the SC1? Seems like there's fault enough to go around about that incident.

Back to the cell balancing, it's fine if we agree to disagree. I'm still quite sure it doesn't happen except at the very end of CV mode charging. It really isn't all that big of a deal if you don't agree with me...nobody's going to destroy anything if they believe either of us.

Regarding SCv1, the PDF was hosted publicly on EMotorWerks' website until recently when they withdrew the product. Of course I still have copies and the source text, but it doesn't have much value except as a tiny piece of history.

I documented what I was told and framed it as evenly as I could manage. I was under NDA on that project and don't feel free to discuss what might have been withheld or why, but I guess I can say that there was a balancing act about what to describe as a detail versus what to warn around broadly to avoid damage.

Again, my effort on the wiki grew out of being dissatisfied with the SCv1 documentation project, since there was no documentation of the bike itself I could reference. Some of the form of SCv1 was dictated by not having a reference to cite.

[DPsSRnSD]

If you're referring to me as a "probably misinformed salesman who's talking up his product"...

I was referring to DPsSRnSD's comment that "I've been told that the bike will balance the cells anytime the contactor is closed if the SOC is above about 50%." I assumed, perhaps incorrectly, that that came from someone with a vested interest in selling him a bike. If it came from you, I apologize. I still believe it's misinformed.

Funny, but no, I have not had a conversation with a salesperson about cell balancing, the state of the contactor, and the dependence of cell balancing on SOC. This "misinformed" information came from Terry and, in whole or part, from Brandon as part of a fractured discussion mostly on Facebook that included reassuring me that I don't have to worry about cell balancing not occurring until 100% SOC. And, in fact, my cell balance doesn't waver much from 3-5% before and after charging to > 80%. If the inbalance I experience was much worse, I'd do things differently. But it isn't so I don't. So I'm going to continue to ride the bike hard, fast charge, and mostly keep the SOC between 30 and 90%.

[Doug S]

PL536 basically encapsulates the functionality you describe, right on the BMS board. There are schematics online to go through the circuits; it's not sophisticated, just designed for just this application.

Agreed. It just reduces the parts count and assembly problems.

Okay, that's fair and I misunderstood where that comment was aimed. Thanks.

You're welcome and not a problem; misunderstandings happen.

Regarding SCv1, the PDF was hosted publicly on EMotorWerks' website until recently when they withdrew the product. Of course I still have copies and the source text, but it doesn't have much value except as a tiny piece of history.

I documented what I was told and framed it as evenly as I could manage. I was under NDA on that project and don't feel free to discuss what might have been withheld or why, but I guess I can say that there was a balancing act about what to describe as a detail versus what to warn around broadly to avoid damage.

Again, my effort on the wiki grew out of being dissatisfied with the SCv1 documentation project, since there was no documentation of the bike itself I could reference. Some of the form of SCv1 was dictated by not having a reference to cite.

I think we can all agree it was a total fustercluck, pretty much self-imposed by certain parties. Enough said.

[Doug S]

Funny, but no, I have not had a conversation with a salesperson about cell balancing, the state of the contactor, and the dependence of cell balancing on SOC. This "misinformed" information came from Terry and, in whole or part, from Brandon as part of a fractured discussion mostly on Facebook that included reassuring me that I don't have to worry about cell balancing not occurring until 100% SOC. And, in fact, my cell balance doesn't waver much from 3-5% before and after charging to > 80%. If the inbalance I experience was much worse, I'd do things differently. But it isn't so I don't. So I'm going to continue to ride the bike hard, fast charge, and mostly keep the SOC between 30 and 90%.

I have nothing but respect for Brandon and Terry, and I think they're both aware of that, but I do think they're wrong if they say that the cells are balanced at any time other than the very last part of CV charging.

I DO agree that it's probably not anything you should worry about unless it shows itself to be a problem. We're only talking about tiny capacity differences due to manufacturing spread, and as MrWilson pointed out, they tend to stay equal rather than wander apart. For all we know, the factory may even test their capacity and group them together in bins so the spread is even tighter. That being said, they might drift apart as they age and I'd make sure to check it once in a while.

[dennis-NL]

wow, heated discussions, but all wanting just the info too be legid.
Tho still no 100% agreement there is now a lot of usefull info and maybe time (real world testing) will tell the thale.
Good work guys, keep eachother sharp and focused but don't forget the fun bike it's all about 

[mrwilsn]

I will further explain cell balancing as follows and hopefully this will clear up what I described earlier...

There are TWO types of cell balancing.  For the sake of discussion I will call them (1) Passive Cell Balancing, and (2) Active Cell Balancing.

Passive Cell Balancing = Cell balancing that takes place naturally as I described previously.  This type of cell balancing is completely foreign to most self proclaimed "experts" on lithium batteries since their experience comes from the hobby world (i.e. radio controlled cars, trucks, planes, drones etc.).  The cells used by the hobby world are generally of a much lower quality than what is used in our bikes.  The cells in our bikes have a VERY tight spec tolerance on both capacity and internal resistance.  This is done by screening the cells and only using those that meet these very tight specs.  It is because of these very tight tolerances that this passive cell balancing actually works.  You can NOT rely on passive cell balancing for cells that are not matched (i.e. capacity and internal resistance).

Active Cell Balancing = Cell balancing that requires the BMS to actively manage the balancing of the cells while the charger is in CV mode and current is below 4 amps in order to get the balance to within a very tight margin (less than 5mV as I stated previously).  Doug and others are correct that this only takes place at the very end of the CV charge cycle.  As I stated previously, on our bikes it takes place when the current to the pack is less than 4 amps.  When most people talk about cell balancing this is what they are talking about.  For the charger, all that is required is for the CV voltage to be correctly set such that current is low enough when the pack nears 100% SOC.  If the CV voltage is set too high then the charger current will be too high when pack voltage reaches 100% SOC and the BMS will cut off charging without any active cell balancing.  If the CV voltage is set too low then active cell balancing never takes place because pack voltage doesn't get high enough to trigger the BMS to start active cell balancing.

I'm certain that Terry and Brandon are very familiar with both passive and active cell balancing and they also know that active cell balancing only takes place at the end of the charge cycle.  I feel confident in saying that when they said " don't have to worry about cell balancing not occurring until 100% SOC." what they meant is that due to passive cell balancing the cells will be within "acceptable" balance without charging all the way to 100% and allowing active cell balancing to take place and not that active cell balancing starts at 50% SOC.

mrwilsn is right at every points.  Thanks btw for explaining that so well.

Doc

Thanks Doc, it's my pleasure.

[BrianTRice@gmail.com]

wow, heated discussions, but all wanting just the info too be legid.
Tho still no 100% agreement there is now a lot of usefull info and maybe time (real world testing) will tell the thale.
Good work guys, keep eachother sharp and focused but don't forget the fun bike it's all about 

I don't think you appreciate how difficult this is. Zero forbids its engineers from commenting on these issues, so we never get any formal confirmation and have to sort these things out in a very difficult way by discussion and independent testing.

This has been a very hard process, and it's not fun trying to build and maintain knowledge, while also ensuring that any bullshit gets labeled as such so people don't repeat bad information.

[mrwilsn]

Before anyone takes offense I should probably also clarify that when I referred to "self proclaimed experts" I was not talking about anyone that has commented on this thread.

[DPsSRnSD]

Before anyone takes offense I should probably also clarify that when I referred to "self proclaimed experts" I was not talking about anyone that has commented on this thread.

HA!

[gt13013]

In https://www.facebook.com/groups/zmcowners/permalink/1623588564377012/ we can read: "The battery will auto self balance at any SOC above 50%, even if not plugged in".

I don't believe that. I don't even see how it would be possible for a series string of battery cells to be balanced by the BMS Parallel cells, yes, but not series cells. Only the charger can do that.

Series connections are much harder to equalize. They're not hard-wired together to share cell voltage. Now, I did speak too strongly earlier when I said it's not possible to equalize a series-connected string of cells without using a charger -- anything's possible with clever circuit design, if you want to do it bad enough. But any solution would be complicated, clumsy, would itself consume power, and just not be worth implementing.

I've never seen it done, and yes, I've looked at several BMS's for several different systems. Cell equalization is done by the charger, after charging has reached "100%", by a string of resistors that trickle-charges cells that aren't quite yet up to terminal cell voltage. If someone shows me an actual schematic that does something else, I'll believe it, but until then I'm sure not going to take the word of some probably misinformed salesman who's talking up his product.

You can read at "Active balancing" here:
https://www.mpoweruk.com/balancing.htm

Here is an example:
http://www.evassemble.com/index.php?main_page=product_info&cPath=6&products_id=44
This BMS features: "Advanced capacitor balancing technique which is working at charging, discharging and static state all the time. It balances cells by transfering energy from higher cell to lower cell (by nominal 100mA). Save energy and reduce heat emission in balance process (compare with resistor bleeding bms)."
Here is its connection diagram:
http://www.evassemble.com/pdf/BMS/Capacitor-16S-BMS%20instructions%20of%20connection.pdf

But I never used these devices. Perhaps they do not work? 

[BrianTRice@gmail.com]

You can read at "Active balancing" here:
https://www.mpoweruk.com/balancing.htm

Here is an example:
http://www.evassemble.com/index.php?main_page=product_info&cPath=6&products_id=44
This BMS features: "Advanced capacitor balancing technique which is working at charging, discharging and static state all the time. It balances cells by transfering energy from higher cell to lower cell (by nominal 100mA). Save energy and reduce heat emission in balance process (compare with resistor bleeding bms)."
Here is its connection diagram:
http://www.evassemble.com/pdf/BMS/Capacitor-16S-BMS%20instructions%20of%20connection.pdf

But I never used these devices. Perhaps they do not work? 

Don't joke like that - those devices are operating on much smaller batteries and may not be safely rated or even scaleable to an EV battery.

You think you've figured out something clever but you may just be insulting your audience. Try to ask questions like this honestly and make it clear you want to learn instead of implying that the audience are idiots.