ElectricMotorcycleForum.com
Makes And Models => Zero Motorcycles Forum | 2013+ => Topic started by: gt13013 on July 14, 2018, 11:35:18 PM
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Some references before beginning:
https://zeromanual.com/index.php/Cell_Balance
https://zeromanual.com/index.php/Unofficial_Service_Manual#Cell_Balancing
http://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing
My interrogation is: in which conditions is the self balancing starting?
At which SOC? When the bike is plugged or not?
We can read things that seem contradictory:
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".
In http://electricmotorcycleforum.com/boards/index.php?topic=7836.0 we can read: "There is a need to charge to 100% occasionally to let the balancing happen".
I have explored my BMS logs, and there are lines with the string "SOC adjusted for voltage". I grep'ed this string in the whole log and it gives the attached file.
Question?
Does the string "SOC adjusted for voltage" log the cell balancing?
If yes, it seems that it starts at 80% SOC (I have no line with less than 80% SOC. But that is not a proof...).
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Good question, good research.
Now hoping an insideman has the correct answer, we wait!
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I'm no "insider", but I am an EE with tons of experience with battery-powered systems, including electric vehicles.
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.
In http://electricmotorcycleforum.com/boards/index.php?topic=7836.0 we can read: "There is a need to charge to 100% occasionally to let the balancing happen".
That one I believe completely. The charger/BMS systems that I've seen trickle-charge each cell individually once the main charging current is turned off. It takes a while because the trickle-charging current is very low.
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Does it switch an 4,15V source to any of the cells in need, successively (positive balancing), or is there just a resistor switched across the "too high cells" to align them with the lower ones, while the main charger ups the whole string (negative balancing)?
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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.
Why not? The BMS could take energy in the cells with higher voltage in order to feed the cells with lower voltage. Why would it not be possible?
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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.
Why not? The BMS could take energy in the cells with higher voltage in order to feed the cells with lower voltage. Why would it not be possible?
I've been told that the bike will balance the cells anytime the contactor is closed if the SOC is above about 50%. I charge my bike to 80-90% and don't recharge it until it gets down to about 25-50%. My cell inbalance stays low, about 3-5mV, despite frequent fast accelerations on my commute. Maybe I'm just lucky or tempting fate.
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The bikes 'cell balancing' function doesn't take place until the very end of the charge cycle when current going to the battery pack is less than 4 amps. The Zero App will not show current when it goes below 4 amps so the only way to know that it is happening is if you either use a watt meter on the outlet the bike is plugged into or if you have a DVM connected to the battery (like I do) and can see that the contactor is still closed even though the app doesn't show the bike is charging.
As the battery discharges the cells slowly get out of balance as a function of the internal resistance of each individual cell. Cells with the highest internal resistance will discharge slower and cells with the lowest internal resistance will discharge faster. Cell imbalance will be the highest the lower the pack voltage gets.
Even if your pack is at 0% SOC this process reverses naturally the second you start charging the battery pack. The cells with the lowest internal resistance will charge faster and the cells with the highest internal resistance will charge slower. Since voltage of the cells with the highest internal resistance would be slightly higher at low SOC than the cells with the highest internal resistance the effect is that cell balance naturally starts to get smaller. This doesn't require any special function of the charger it just happens as a result of chemistry.
The cells Zero uses are so well matched that cell balance will typically be very low (less than 5 or 10mV) before the actual 'cell balancing' function takes place.
Anyone can test this just by using the Zero app. Ride your bike down to low SOC and use the app to check cell balance. At low SOC the pack cell balance can be anywhere from 50mV to 100mV or more. Connect your bike to the charger and within minutes you will see the cell balance start to drop. Check on the bike every hour and you will see that every time you check the cell balance will be smaller and smaller. By the time you get to 100% you should be less than 10mV (I frequently see 1-2mV cell balance on my bike).
In reality, it's not the charger that facilitates cell balancing the cells to be closer than what would happen naturally. The charger has two modes. Constant Current (CC) and Constant Voltage (CV). The value at which the charger goes into CV can be adjusted by the manufacturer. Once the battery pack is at 100% SOC the BMS actually facilitates cell balancing. The charge is still coming from the charger but the BMS allows individual cells to be balanced using the balance wires and bleed resistors. Thus it would be possible to balance the cells to the 1-2mV range at any SOC by using programming.
Tesla's for example allow you to set your max SOC value. If, for example, you set the max charge to 60% the charger will go into CV mode once the voltage rise value hits the 60% SOC value. As the 'resting' pack voltage hits the 60% SOC the cells can then be balanced at that voltage. Unfortunately, Zero does not support setting a max charge and will always attempt to charge to 100%. Changing this for a Zero would require new programming for the charger (to go into CV at a lower voltage) and the BMS (to facilitate balancing).
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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.
Why not? The BMS could take energy in the cells with higher voltage in order to feed the cells with lower voltage. Why would it not be possible?
I agree with gt13013 from my observations and many insiders confirming. The BMS definitely performs balancing of each set of cells in the same place in the series.
The "Battery Connections" label in the manual are a set of pins that connect to each layer of the series and are the means by which the BMS intentionally directs current to that layer of the series. The only question is what logic it applies to do this.
Ref. https://zeromanual.com/index.php/Unofficial_Service_Manual#BMS_Parts (https://zeromanual.com/index.php/Unofficial_Service_Manual#BMS_Parts)
The BMS has a function where it invokes the onboard charger to turn on periodically so it can get the power to perform the balancing, but any charger is just putting power into the battery's main DC power connections (bottom and top of the series, really).
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As the battery discharges the cells slowly get out of balance as a function of the internal resistance of each individual cell. Cells with the highest internal resistance will discharge slower and cells with the lowest internal resistance will discharge faster. Cell imbalance will be the highest the lower the pack voltage gets.
Even if your pack is at 0% SOC this process reverses naturally the second you start charging the battery pack. The cells with the lowest internal resistance will charge faster and the cells with the highest internal resistance will charge slower. Since voltage of the cells with the highest internal resistance would be slightly higher at low SOC than the cells with the highest internal resistance the effect is that cell balance naturally starts to get smaller. This doesn't require any special function of the charger it just happens as a result of chemistry.
I do not agree with that. You seem to consider that the cells are in parallel, but they are in series inside a pack, so it does not work this way.
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As the battery discharges the cells slowly get out of balance as a function of the internal resistance of each individual cell. Cells with the highest internal resistance will discharge slower and cells with the lowest internal resistance will discharge faster. Cell imbalance will be the highest the lower the pack voltage gets.
Even if your pack is at 0% SOC this process reverses naturally the second you start charging the battery pack. The cells with the lowest internal resistance will charge faster and the cells with the highest internal resistance will charge slower. Since voltage of the cells with the highest internal resistance would be slightly higher at low SOC than the cells with the highest internal resistance the effect is that cell balance naturally starts to get smaller. This doesn't require any special function of the charger it just happens as a result of chemistry.
I do not agree with that. You seem to consider that the cells are in parallel, but they are in series inside a pack, so it does not work this way.
Within a single brick, there is a single stack of cells that are in series.
In a long brick, there are two stacks of cells. Each stack is in series, but there are interconnects between each pair of cells at the same level of the stack.
In a monolith, there are interconnects between all available cells at the same level of the stack (IIRC for the long brick architecture it is different).
The BMS for a long brick or monolith or single power pack module has 28 pins for balancing - one for each layer of the stack, interconnected.
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Thanks Brian.
I was focused on my bike which has two 3.3kWh batteries, each of them with 28 cells in series.
But bigger batteries are more complex
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What I wrote is correct. I'm aware the bricks are 28S.
You don't have to believe me, as I said you can test for yourself using the app.
Sent from my SM-G950U using Tapatalk
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From my point of view, the cells with the higher internal resistance are the bad ones, so generally they have less capacity than those with small internal resistance. When you discharge a set of cells in series, since all the cells deliver the same Ah, those cells with high resistance will discharge faster than the other (and by the way they will heat more than the other).
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From my point of view, the cells with the higher internal resistance are the bad ones, so generally they have less capacity than those with small internal resistance. When you discharge a set of cells in series, since all the cells deliver the same Ah, those cells with high resistance will discharge faster than the other (and by the way they will heat more than the other).
I think that is exactly what has happened to one or more of the cells in my old 2014 S with PT, that have caused the charger to cut off at 92%. But if you leave it plugged in for about a week, it will eventually increase the charge to 98% on the display. I don't think the lack of charging to 100% has anything to do with a charger malfunction, just a cell or two suffering from old age tricking the charger to cut off charging before the rest of the cells are fully charged. ???
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You're making this too complicated. In any battery pack, some cells will have slightly lower or slightly higher capacity than the average, just because of manufacturing variations. That doesn't make any of them "good" cells or "bad" cells. Similarly, some will have slightly higher or slightly lower internal resistance, not necessarily the same cells that have higher or lower capacity. Some people are good at cooking AND poker, some not as good at either, right?
Again, equalizing cells in parallel is easy -- in fact, it would be hard to avoid it. Connect cells together in parallel and by definition, they're going to have the same cell voltage. That doesn't mean they're holding the same amount of amp-hours, due to the manufacturing variations, but at least the cell voltages are identical, and they will be all through any charging or discharging cycles.
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.
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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.
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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.
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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.
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mrwilsn is right at every points. Thanks btw for explaining that so well.
Doc
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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.
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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%.
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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.
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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.
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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 ;)
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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.
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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.
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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.
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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!
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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? ;)
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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.
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I kind of like watching the Kill-A-Watt meter when my Zero is charging. With my old 2014 S, I would see it bulk charge most of the time, but every 10% or so when charging the power draw would drop from about 12 amps to 4 amps for a while and then ramp up to bulk charging again. I assumed that it was taking time off from bulk charging to balance the cells. Interestingly, I haven't noticed that happening with my 2018 S. It seems to bulk charge until the SOC display reads 100% and then the power draw drops to 4 amps for a few minutes, before dropping to 4 watts until I pull the plug. ???
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OK. I would have a lot to tell, and I would do it if this forum was in French. But I am not fluent enough in English to tell what I'd like to... And it would probably be misinterpreted.
My initial questions were:
1) Is the cell balancing occurring only during the charge of the battery, or is the BMS able to do it when the bike is resting?
2) In the case where the BMS is able to do it when the bike is resting, of course it will use a little bit of energy. So the BMS probably does it only if the SOC is above some value.
3) To try to clarify that, I was wondering if the balancing activity is reported in the logs. But it does not appear clearly in my logs.
4) The string "SOC adjusted for voltage" in the logs seems to be related with some activity of the BMS, probably updating the SOC from different algorithms, and I was wondering if it was balancing the cells at the same time
So, it seems that the way the BMS acts to balance the cells will keep some mysteries (for me at least).
Anyway, probably it does not matter a lot, since I tried to never full charge since many cycles (stopping the charge between 75 and 85% SOC), and the cell balance keeps fine at any time (4 mV).
I will now focus on building my fast charger, as stated elsewhere in this forum, and forget about self balancing that seems to work magically for me ;)
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I can't answer any of your questions definitively, only speculatively, and am tired of this thread.
I will suggest that (without commenting on your charger implementation one way or the other) it will be better if your charger's tapering strategy allows the BMS enough time at a low charge rate to balance cells.
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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? ;)
I'm with Brian, I'm tired of this thread too, but I will make one last comment regarding this point. When I overstated my case before by saying that it wasn't possible to balance a series string, then retracted the statement, this sort of "flying capacitor" technique was exactly what I was thinking about. It is possible to transfer charge, a little bit at a time, from one cell to another by connecting a capacitor to the higher-charged cell, then connecting it to the lower-charged cell. MOSFET switches are used to do the switching. This technique is used a lot at low power levels when, say, you need just a small amount of current at a negative voltage when all you have available is a positive power supply.
But if you run the numbers, using any reasonable amount of capacitance and switching rates, the charge transfer is exceedingly slow, and really not worth doing with 25 amp-hour cells.
It is POSSIBLE that the part Brian identified (the PL536) uses this technique, but that's not how i read the data sheet.
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About 9 people reacted on this thread, so it's an interesting subject.
Thx all.
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Speaking of cell balancing, I used these cheap little BMS devices on top of the Hi Power batteries of my Electric Motorsport GPR-S when its BMS system failed. They seemed to work OK, but of course they didn't prevent those Chinese batteries from puffing up and dying one at a time. :( The Hi Power batteries just didn't seem up to the task of supplying power to my huge D&D Sepex motor.
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Found this thread - hoping to find an answer to a different, but related question: Since Zero changed their recommendations on charging ("leave it plugged in all the time" vs. "charge only to 80%"), and if the active cell balancing occurs at 100% charge, then How Often Should We Charge to 100%?
On my antique Vectrix (12 yrs old!) the cell balancing occurs after 100% charge and the BMS firmware automatically pushes the cells to continue charging/balancing by shunting the excess voltage from one (full) cell to another (less charged) cell - but it was programmed to do this every 10 charges.
I swapped out the original NiMH batteries for LiFePo cells (from 30AH to 50AH - same pack voltage), using a BMS 'kit' that included the shunts that are attached directly across the terminals of the batteries. These shunts close the circuit after reaching 3.65V so the voltage can flow across the terminals and to the other cells, until they all reach the maximum 3.65V to achieve balancing.
So no 'passive' balancing. This arrangement has kept my old Vectrix alive and well for a long time (although it is showing some signs of degradation now).
Does charging to 100% every 10 charges sound about right?
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FWIW, my SR/F gets to 100 % then charges for an additional half hour or so. The current drops steadily and slowly, fairly linearly, from 5800 down to 0 watts before shutting down. That’s cell balancing, no?
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FWIW, my SR/F gets to 100 % then charges for an additional half hour or so. The current drops steadily and slowly, fairly linearly, from 5800 down to 0 watts before shutting down. That’s cell balancing, no?
No, this has nothing to do with the cell balancing. The slow decay of the current is typically the characteristic of a constant voltage charging, which is a common way to end the charge.
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Cell balancing by Zero's BMS occurs in a certain charging regime of low current, where the BMS directs that current to a layer of the cell stack.
This often happens during the taper noted above as constant voltage charging, but can also happen on demand where the BMS wakes from long-term plugged-in storage.
There are enough notes in this thread to understand more if required, or the unofficial manual has a tiny article on the topic which I'll probably revise shortly to be clearer:
https://zeromanual.com/wiki/BMS/Cell_Balancing
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Thanks for enlightening me.
There are tons of posts on this forum about occasionally recharging to 100%+ to rebalance the cells. IIUC, this thread tells me that those posts are erroneous. If that's correct, you will find many confused fellow forumites.
So is there any reason to wait that last half hour after SOC has reached 100% while the charging power slowly tapers? Is there is no gain whatsoever beyond a couple of inches of range?
Thanks
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Thanks for enlightening me.
There are tons of posts on this forum about occasionally recharging to 100%+ to rebalance the cells. IIUC, this thread tells me that those posts are erroneous. If that's correct, you will find many confused fellow forumites.
So is there any reason to wait that last half hour after SOC has reached 100% while the charging power slowly tapers? Is there is no gain whatsoever beyond a couple of inches of range?
Thanks
In the case of my 2018 S there is no charge tapering. It charges at 1350 watts until it turns off suddenly after hitting 100% SOC. My old 2014 S did taper the charger power, but that is not the case with my new model. ???
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According to Zero, load-balancing doesn't need to be done more than once in ten charges or once a month or so. So very infrequently!
As long as the on-board sensors are happy, it's not going to show much tapering or balancing at the box. I'm not seeing any tapering, either. (maybe that's part of the newest firmware? I have no idea what they can modify.)
-Crissa
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There are tons of posts on this forum about occasionally recharging to 100%+ to rebalance the cells. IIUC, this thread tells me that those posts are erroneous. If that's correct, you will find many confused fellow forumites.
So is there any reason to wait that last half hour after SOC has reached 100% while the charging power slowly tapers? Is there is no gain whatsoever beyond a couple of inches of range?
In my opinion, both are correct. Occasional cell balancing is a good idea, but charging up to 100% every single time does reduce the life of the battery.
The real questions are, "HOW BENEFICIAL is periodic cell balancing?" and "HOW MUCH reduction in battery life will you see if you charge to 100% every time?". I don't think the answers to either of these questions is at all clear. I don't even think Zero has a very good handle on them -- if they did, they'd give us better guidance.
Being an EE who's worked with batteries a lot, my gut sense is that neither of these considerations are hugely important. I don't think performance will degrade much if you never cell balance. I do believe you can prolong the battery's life by "short charging", but in order to achieve any real gains, you really have to limit the parameters. Toyota uses 40% minimum charge on their Prius battery, and 60% maximum. That's one thing on a hybrid vehicle, but you'd only have 20% range if you limited yourself like that on an EV.
My 2014 SR has no means to limit the charge except for unplugging it; if it did, I'd probably use it and limit the charge to 80% or so, and maybe every couple of weeks perform a cell balance. But it doesn't, so I just plug it in every day when I get home from work, and it does a full charge and full balance every night. I've got 50,000 miles on my bike with no sign whatsoever of capacity reduction.
If you feel strongly about babying your battery, go for it. If you're lazy like I am, just plug it in and forget about it. If your bike supports early charge termination, use it and feel good about it. In any case, I just don't think it's worth worrying too much about.
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Doug, looks like I'll never catch up to your mileage, unless you get a new bike.
I've started using my quiq charger in the mornings so when I hit 100% SOC it's only there for a short time.
I do have a working theory that "using" these bikes helps keep the battery in better health than sitting. The guys on here with the really high mileage bikes seem to have the fewest issues.
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@NEW2elec That's my experience with pretty much all rechargables. Use it or lose it.
-Crissa
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I know a lot less than other posters on this thread, but I do see 100% incompatible responses that have have not been sorted out.
Cell balancing seems to be a good thing. Lots of explanations why and some explanations about how when are on this thread.
But I don't understand the where or when details.
Specifically: If cell balancing on the latest gen Zeros is not occurring during that long slow taper then when.? If no then the when?
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If there's no cell balancing being needed, it's not going to do it. Also, power meters may or may not catch the extra extra blips of power used for balancing. It's not going to be a high level of power needed.
Zero's own instructions say that it's not needed all the time, either.
I don't see anyone saying anything incompatible, either.
-Crissa
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I do have a working theory that "using" these bikes helps keep the battery in better health than sitting.
Unfortunately that will be me. I'll be a fair weather rider in Northern Ohio. I wish there was a way to exercise the battery on the occasional snow or rainy day in the garage without the obvious dangerous method of running the throttle while it's on a stand.
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I know a lot less than other posters on this thread, but I do see 100% incompatible responses that have have not been sorted out.
Cell balancing seems to be a good thing. Lots of explanations why and some explanations about how are on this thread.
But I don't understand the where or when details.
Specifically: If cell balancing on the latest gen Zeros is not occurring during that long slow taper then when.? If no then the when?
It is possible that the newer Zero models do not taper the charge to balance the cells every time the battery pack is being recharged by the onboard charger. Perhaps it is only done after a certain number of recharges have occurred? Recharging at maximum charger power right to 100% SOC and then shutting down will cut the overall time to recharge, which is a good thing for the owner. In any case, my cell balancing remains between 2 and 3 mV, so balancing seems to be OK. :)
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I can't speak definitively for the Zeros, but for maximum charging speed, a "constant current/constant voltage" (CC-CV) scheme is usually used, which looks like this:
1) If the battery is highly depleted (below say 20%), a fairly low constant current is applied to the battery until it exceeds the threshold -- maybe 1/5th of the highest charging current or so. Batteries are fairly delicate when at low SoC and can't handle high charging currents.
2) Full charging current is now applied. Typically no more than 1C, but some batteries can tolerate more (especially if they're well cooled). This is the "bulk charging" phase and it's where you want to operate if you're trying to charge fast on a road trip. For obvious reasons it's also referred to as the "constant current" (CC) phase. Voltage slowly rises as the battery charges.
3) When a certain voltage threshold is reached (116V for the battery in my SR), the charger holds that voltage. The current will then ramp down as the battery approaches "full charge". This is (obviously) called the "constant voltage" (CV) phase.
4) When current drops dramatically, any individual cells that aren't yet at their "full charge" voltage are given a tiny current individually until they do achieve that voltage. This is what's referred to as "cell balancing". It's usually a very, very small current, a couple of orders of magnitude smaller than the charging current. Charge current is usually reported as 0 during cell balancing.
So cell balancing doesn't even start until "charging current" registers as 0. That's why you may not want to do it all the time -- you have to get to 100% charge before it even starts, and it is true that constantly 100% charging your battery isn't ideal for battery life.
That's why I presented it as a compromise between periodic cell balancing and 100% charging in my post above.
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I don't know whether Zero does it but it's possible to balance cells without them being connected to a charger. Some battery packs have built in balancing boards (or it could be a separate component on the bike I suppose) that shuttle charge from the higher voltage cells to the lower ones and keeps doing so until they're all close. Doing so would mean the SOC of the whole pack would drop a little, more so if the cells are really out of balance.
Reading through the 2019 manual last night and the charging recommendation notice on the Zero site (for 2013 and newer I think) Zero says it's okay to leave the bike plugged in at 100% but recommends that it is unplugged to extend battery life. If it is left plugged in it will discharge to 90% and then charge back to 100% and continue this cycle until unplugged, I suppose in an effort to not leave it at 100% but also give you a higher chance that it's close to that when you do unplug it (so you're not left at 90% if you forget to unplug it). I don't know what the time frame is for this 90-100% cycle, whether it's hours or days or even less. I imagine that leaving the bike still plugged in for an hour or two is probably fine and they're more worried about people leaving them plugged in for days at a time ready for riding at the weekend.
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On the subject of balancing, I have a question. If a cell or section of cells is a dead short inside the battery pack, will that show up as a serious imbalance on the app?
The reason I am asking is because the way my Zero DS behaves. Half the range it should have and charges twice as fast as it should, just as if my 6.5KWH battery pack was only 3.2 KWH. As if half the cells are shorted out or whatever.
But the Zero app shows my battery imbalance as only a couple of MVs.
IAC, I may soon be looking for a warranty replacement. IIRC, the battery is warranted for five years.
-Don- Reno, NV
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On the subject of balancing, I have a question. If a cell or section of cells is a dead short inside the battery pack, will that show up as a serious imbalance on the app?
The reason I am asking is because the way my Zero DS behaves. Half the range it should have and charges twice as fast as it should, just as if my 6.5KWH battery pack was only 3.2 KWH. As if half the cells are shorted out or whatever.
But the Zero app shows my battery imbalance as only a couple of MVs.
IAC, I may soon be looking for a warranty replacement. IIRC, the battery is warranted for five years.
-Don- Reno, NV
That is what happened with my 2010 Electric Motorsport GPR-S when its batteries started going south after 1000 miles. But then you can hardly compare a GPR-S with any Zero. ;)
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A dead short in the pack in a cell or series of cells would be highly detectable; both the pack voltage would be noticeably capped by the amount of voltage decrease from that layer of cells (~3V), and there would be a massive, shutdown-inducing cell imbalance.
I believe that the cells inside a Zero pack are also separately fused.
Basically, stop speculating like this and extract your BMS logs and read them, instead.
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Basically, stop speculating like this and extract your BMS logs and read them, instead.
Will do, but what will I be looking for? I had no idea such info. would be in there.
-Don- Reno, NV
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Basically, stop speculating like this and extract your BMS logs and read them, instead.
Will do, but what will I be looking for? I had no idea such info. would be in there.
I don't know, but for each BMS, 28 cell voltages will be listed out explicitly in a single log status event, and over time you'll see what voltage range that covers.
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Or, if you suspect your battery is really down to half capacity, just freakin' take it to the shop. You're asking opinions of people on this forum, from people who are generally well-informed but not knowledgeable of the details of the Zero construction. Those that ARE knowledgeable of those details work for Zero and aren't allowed to reveal that sort of information here. You're really not going to find your answers here.
Take it in and quit wasting bandwidth.
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Or, if you suspect your battery is really down to half capacity, just freakin' take it to the shop.
I will when I can, but I am 100 miles away from the bike right now and it will be a few weeks before I can take it anywhere.
IMO, some of the people here often know more than some of the people in the shops that service Zeros. It's sometimes best for me to know what could be happening before I bring the bike in.
-Don- Reno, NV