LiFeP04 Batteries for Solar & BMS

[tom rickard]

Just because you use shunts, doesn't mean you are "top balancing"

I use shunts to keep cell voltage the same when my solar controller is in the process of providing current for loads under a "fully charged" situation.

The "fully charged" voltage can be pre-set, and ISN'T at 3.65 or 100%SOC of the cells. It can be at any cell voltage you wish.

The shunts aren't expensive as Sunking has incorrectly stated, they cost me $13.50 AUD each.

If you don't use shunts, and just use a pack level voltage at which your system is designed to have zero net current, the cells will very slowly drift apart. Despite what Sunking says, this WILL result in one cell being lower than the others, and if you take the pack to it's original zero setpoint, one cell will reach the lower voltage knee first. If you are using pack voltage or capacity to reference your 0%SOC, you will run the risk of having no protection for that cell.

There are commercially available LFP solar controllers, GSL electronics make one that I have used.

If you don't ever bottom balance, it doesn't mean you aren't protected against over-discharge. The shunts I use monitor cell voltage, and will disconnect the pack from the load if any individual cell voltage falls below a pre-set value.

Of course this can be done with simple cell monitoring, but the extra cost of the shunts is negligible in the overall system cost. (the contactors required in either case are the most expensive components). The reason I use shunts is that it very quickly sets all cells at the charge controllers operating voltage, and in effect the batteries are inactive the majority of the time (ie. zero current)

I'm sorry Sunking, I missed the part about how you provide your inverter load from you solar panels while having zero current flow through your battery pack?

[karrak]

After further thought I would have to agree that you only have to bottom balance once to cover the issue of cells varying in capacity, but it comes at a cost, in that the voltages of the individual cells will vary when the cells are fully charged and this variation will get worse if the capacity of the cells diverge. Now if someone had put forward a good case that bottom balancing will not drift without trying to bully me into accepting this position I might have come to this position earlier.

I think that the bottom balance may drift if the cell current leakage is different between cells but will have to think further about this.

Does this mean I am going to change to bottom balancing for my solar power system, no for the following reasons.

1. Until someone convinces me otherwise I think that charging cells up to different voltages will put the weakest cells that are charged to a higher voltage under more stress so they will age quicker.

2. I would have to modify my charge controller to take input from my battery monitor to terminate the charging, for people with commercially made charge controllers this may not be an option.

3. One is relying on the BMS to end the charge cycle. If it fails and our battery has cells with differing capacity we could easily overcharge the weakest cells.

4. It is reasonably easy to top balance a 12 or 24 or 48 volt battery pack which are the common voltages used by people with solar power systems. I don't think this would be the case for EVs where the battery packs are more than 100 volts.

Simon

[Sunking]

Just because you use shunts, doesn't mean you are "top balancing"


I use shunts to keep cell voltage the same when my solar controller is in the process of providing current for loads under a "fully charged" situation.

Beg your pardon. but that is the main reason you use Vampire Boards for. They are the heart and should of every passive Top Balance system there is. They have no other purpose other than more expensive units will also have voltage and temp monitoring. But to get that means now means you need a BMS Programmable Controller. Those are not cheap.

The "fully charged" voltage can be pre-set, and ISN'T at 3.65 or 100%SOC of the cells. It can be at any cell voltage you wish.

The shunts aren't expensive as Sunking has incorrectly stated, they cost me $13.50 AUD each.

No $13 Vampire boards are programmable. 16 cells x $13 adds up real quick on a 48 volt battery. The ones that mount on the battery terminals I know of are pure shunts with indicator light to signal either on or off and completely passive and dumb. More expensive models add Cell Voltage and Temperature with Communications to a Central BMS Controller. To have programmable systems require a Central BMS

If you don't use shunts, and just use a pack level voltage at which your system is designed to have zero net current, the cells will very slowly drift apart. Despite what Sunking says, this WILL result in one cell being lower than the others, and if you take the pack to it's original zero setpoint, one cell will reach the lower voltage knee first. If you are using pack voltage or capacity to reference your 0%SOC, you will run the risk of having no protection for that cell.

Completely false. Capacity fades. That only possible changes what the weakest cell can be. With No Vampire boards or monitors, there is no way to drift from 0% SOC and AH level. That is the basic fundamental of series circuits.

There are commercially available LFP solar controllers, GSL electronics make one that I have used.

Never said there were not. I said a few for Marine applications and Toys. Those are toy sized. I took a look at GSL BMPPT which they say can be used with Lithium. But there is nothing special about it that makes it good or bad for lithium. It has no interface to communicate with a BMS. I can think of 3 other manufactures that can do the same thing.

If you don't ever bottom balance, it doesn't mean you aren't protected against over-discharge. The shunts I use monitor cell voltage, and will disconnect the pack from the load if any individual cell voltage falls below a pre-set value.

I agree with you there but you did not disclose that takes an extra expensive programmable Central BMS control unit on top of those 16 $14 Vampire Boards. If your Inverter cannot interface to the BMS, that program feature is useless. You would have to put some external LVD between the battery and Inverter like your GSL model has to do. Theyy worked around th eproblem which has already been discussed in great detail here.

Bottom Balance no external LVD, no BMS or anything is required. Just set your Inverter Low Voltage Cut Off to whatever you want, or leave it at default will work also at 11, 22, and 44 volts.

Of course this can be done with simple cell monitoring, but the extra cost of the shunts is negligible in the overall system cost. (the contactors required in either case are the most expensive components). The reason I use shunts is that it very quickly sets all cells at the charge controllers operating voltage, and in effect the batteries are inactive the majority of the time (ie. zero current)

Yep about $300 to $600 dollars for a 16 channel PLC, plus 16 x $13 Vampire boards. Should not cost you much more than $550 to $800 to add BMS with control. You still have to solve the interface for LVD and Controller. That cost extra

[Sunking]

After further thought I would have to agree that you only have to bottom balance once to cover the issue of cells varying in capacity, but it comes at a cost, in that the voltages of the individual cells will vary when the cells are fully charged and this variation will get worse if the capacity of the cells diverge.

Capacity will drift Simon, but that does not relate to voltage. The only thing that might change is which cell becomes the weakest. Loss of capacity cannot be fixed. Only replacement can fix that. There is no sacrifice.

Does this mean I am going to change to bottom balancing for my solar power system, no for the following reasons.

1. Until someone convinces me otherwise I think that charging cells up to different voltages will put the weakest cells that are charged to a higher voltage under more stress so they will age quicker.

2. I would have to modify my charge controller to take input from my battery monitor to terminate the charging, for people with commercially made charge controllers this may not be an option.

3. One is relying on the BMS to end the charge cycle. If it fails and our battery has cells with differing capacity we could easily overcharge the weakest cells.

4. It is reasonably easy to top balance a 12 or 24 or 48 volt battery pack which are the common voltages used by people with solar power systems. I don't think this would be the case for EVs where the battery packs are more than 100 volts.

Simon

1. Charging Voltage stress does not happen until you get to the top. The weakest cell is only taken to 90 to 95% capacity. So that reason is not valid.

2. Completely false assumption. No need to signal your controller to do anything. You set Bulk = Absorb = Float to make your controller behave as a CC/CV which is the correct algorithm to use on Lithium batteries. The voltage you set is lower than 100% SOC. It is set just high enough to get the weakest cell to 90 to 95% SOC. When the batteries equalize current stops flowing through the batteries and they stop charging. You panels and controllers are still active and supplying power to your load like an Inverter. You don't don't need to have anything turn off, just change your way of thinking. The only other requirement is to set you rInverter LVD to whatever you are comfortable with. You do not even need to do that as default is good enough because it is set and designed for Lead Acid Batteries. Default is 11, 22, and 44 volts respectively. You can even go a bit lower with LFP with no worries of 10, 20, and 40 if you want to go to the edge of 2.5 vpc. Or if you are like me, I were suspenders and a belt and set my LVD to 49.6 volts or 10% SOC 3.1 vpc.

3. So WTF does that have to do with Bottom Balance. There is no BMS or Vampire boards to fail or waste money on. Bottom Balanced systems cells all have the same capacity. So I am clueless what your argument is with this one.

4. Again False. Mine is 48 volts. DIY EV's start at 36 volts up to 144 volts in 12 volt increments.

[karrak]

No that would be DIY EV owners. Well to start the thinking you do not operate a Lithium battery in a Solar system in the lower SOC range is delusional in of itself. With a Lithium system you do not normally size the batteries for 5 day autonomy like you would for Lead Acid. That line of thinking is just plain ole nucking futs. You size Lithium for 2 to 3 day autonomy, and unless you live in Utopia Green Land where the sun shines bright everyday all day, the rest of us in the real world have long cloudy spells and cloudy days. That means you spend a lot of time near the bottom before running the generator. That is just a fact of life. Deal with it.

What average SOC do you run your Solar system at? From my battery monitor my average battery SOC in ah is 103.997703 (71%SOC) for the period from when it was installed in November last year to now.

My battery capacity is around 3 times my daily use as you suggest, and I don't have a generator.

Cells do not stay Balanced if you Top Balance because you have parasitic loads. The Vampire Boards, Temperature and Battery monitors are attached to each cell and powered from each cell. No two draw the exact same amount of power, thus unequal load throwing them out of Balance. In Bottom Balanced system you have no Parasitic Loads. The exact same current flows through each cell every time in Series circuits.

If you just have balancing boards, unless they are balancing they should draw less than 100uA. Now 100uA for a year equates to 0.876Ah per year, for a 100ah cell this is way below the cell leakage, and of course our solar panels are charging the battery every day.

Now if we have fancy battery monitoring that could be powered from the whole pack as I do, we don't have any problem with with unequal load or even if they are powered by the individual cells the unequal load should certainly not be more than 100uA, and more likely less than 10uA so the same applies as with just balancing boards.

Expecting any battery to last 10 years is far fetched.

Yes, maybe with the way you treat LFP batteries it is far fetched. How about Tesla's 10 year warranty with 10 year extension, not sure what the fine print is here. I believe Bosch and Sony are talking about 10 years with their home LFP batteries.

You are taking things out of context and cherry picking. My guess is you have not read all replies and threads on the subject matter. I charge at C/2 constant Current with Commercial power. I or NO ONE EVER SAID you turn off the controller. First thing to know is there are NO SOLAR CHARGE CONTROLLERS made for Lithium batteries on the market with the exception of a Marine and toys with very limited power of 130 or so watts. A Solar Charge Controller made for Lithium would require to interface with a BMS. How do you do that since there are none available? Simple you don't. You have to deal with it and work around it and only if you know exactly what you are doing.

If you top balance most of the programmable Solar Controllers can be used with LFP batteries.

I thought you have been recommending to others that you don't need a BMS to charge an LFP battery, just set the charge controller to stop charging at the weakest cells fully charged voltage.

In a Top Balanced System you would set the voltage to 3.55 to 3.6 vpc or whatever your Vampire Board Trigger voltage is set to. The problem with that analogy is the Vampire boards can only shunt .5 to 1 amps, and there is no way to tell the Controller to limit current to Vampire Board limit. When the first Vampire Board turns on, it can only shunt a small amount of current.

Maybe you should follow your recommendation and reread the post that have been made before. This has already been covered in this thread. You only need to charge to 3.55-3.6 Volts/Cell once in a blue moon to re-balance the battery. The battery will only be slightly out of balance so the 0.5 to 1 amp is ample to balance the individual cells.

In a Bottom Balanced system you set the voltage well below 100% SOC in the range of 3.3 to 3.4 volts. The final voltage is a a bit of trial and error for the first few days. You settle when the weakest cell reaches 3.4 volts. All other cells will be just slightly lower in voltage. So in a 48 volt pack a Bottom Balanced set point voltage is something slightly less than 54.4 volts.

Sounds dangerous to me, lets just hope that that weak cell doesn't drift and we remember to keep an eye on it. Now on my system 3.375 volts/cell can take the cell SOC between 80% and the same SOC as if I charge to 3.45 volts/cell to a current of C/20 depending on the current coming from the solar panels. SK, you give a resting voltage of 100% = 3.450, not far away from your 3.4 volts?

A Top Balanced system would be 57.6 volts.

Wrong, could be exactly the same as the voltage you set your lower balanced system to.

At that point the Controller is Constant Voltage keeping the batteries charged up and supplying power to the load assuming the panels are able to meet the demand.

So you are talking about keeping the weak cell at 3.4 volts for a long period of time, isn't high cell voltage bad for LFP batteries. No wonder you give a lifespan of only 5 years.

Simon

[Willy T]

What average SOC do you run your Solar system at?

Simon

He doesn't have LFP batteries in a Solar System, he has a Golf Cart, charged on grid power.

It doesn't mean that his input is invalid though. Some works for me and some doesn't. At some point I'll try bottom balance, until then I'll keep on slogging along.

[catharsis]

There is a huge difference as you charts are showing you. In a Bottom Balanced system all batteries arrive at 0% capacity at the same time making it IMPOSSIBLE to over discharge any one cell. Look at the Lower Right Discharge Curves. That is what you are not catching or understanding.

The right answer is: There is NO difference of charge you can use. The weakest cell determines the charge of the battery whether the cells are top or bottom pre-balanced. But, if the cells are not pre-balanced, you can't get it all.

Perhaps you didn't notice the used cell voltage in my example was between 3.04 and 3.5 V. The TOP pre-balanced cells will reach their high charging voltage (3.5V) at the same time and the high voltage can be monitored and cut-off by the battery voltage. Discharging will require cell-level monitoring to cut-off and to prevent over discharging.

The BOTTOM pre-balanced cells will reach the low limit voltage at the same time. So this can be monitored as a pack (maybe just by noticing the lack of power). But, charging will call for cell monitoring to not overcharge the weakest cell. If you just use "safe" battery voltage the battery is never full (which can be good for the battery life but limits the amount of charge).

And above has nothing to do with balance boards, BMS or Golf cart.

ps. Actually, the top pre-balanced battery can hold slightly more energy in it because the average voltage is a bit higher.

[Sunking]

So you are talking about keeping the weak cell at 3.4 volts for a long period of time, isn't high cell voltage bad for LFP batteries. No wonder you give a lifespan of only 5 years.

You really do not understand any thing about LFP batteries. 3.4 volts at rest is 85 to 90% SOC. Stress only occurs at 100% SOC of 3.47 volts and up at rest.

[Sunking]

Yes, maybe with the way you treat LFP batteries it is far fetched. How about Tesla's 10 year warranty with 10 year extension, not sure what the fine print is here. I believe Bosch and Sony are talking about 10 years with their home LFP batteries.

You have no clue what you are talking about.

Tesla and Bosch do not use Chi-Com LFP batteries. No commercial manufacture uses Chi-Com cells. They do not use any form of Top Balance either. Tesla uses Panasonic LiCo cells in the Roadster all 6831 of them. They do not monitor any cell Voltages, they monitor 11 Sheets made from 9 bricks. Tesla battery is 11S 9B 69P. Similar design concept in the Nissan Leaf, Toyota Prius, and Chevy Volt, just fewer cells and modules to monitor. No commercial manufacture uses TOP BALANCE.

I understand why you are stuck on Top Balance. You are from Australia, you guys do not know any other way. Time to catch up to modern technology.

[Sunking]

The right answer is: There is NO difference of charge you can use. The weakest cell determines the charge of the battery whether the cells are top or bottom pre-balanced. But, if the cells are not pre-balanced, you can't get it all.

I agree. When you receive your cells from the distributor, they are sent at Storage Voltage of 40 to 60%. When they arrive you have to pick one method or the other and balance the cells before assembly. Bottom Balance is precision, Top Balance is only a 100% SOC Voltage Reference Point and does not indicate any capacity. Bottom Balance is both a 0% SOC reference and also a capacity reference point

Perhaps you didn't notice the used cell voltage in my example was between 3.04 and 3.5 V. The TOP pre-balanced cells will reach their high charging voltage (3.5V) at the same time and the high voltage can be monitored and cut-off by the battery voltage. Discharging will require cell-level monitoring to cut-off and to prevent over discharging.

Perhaps I am missing something because that would be impossible. A LFP cell resting at 3.04 volts is essentially 0% SOC, and 3.5 is just a bit over 100% SOC

The BOTTOM pre-balanced cells will reach the low limit voltage at the same time. So this can be monitored as a pack (maybe just by noticing the lack of power).

Absolutely correct. There is no requirement need for any cell level voltage monitoring. However you do not have to really even to monitor the pack voltage for it to work. The danger is cell reversal, which requires cells in a series string to have capacity left in them to drive the depleted cell(s) into reversal. If all cells are depleted and you apply a load, the voltage collapses and no current flows. No current flow, no damage.

By the addition of say your Inverter default Low Voltage Disconnect either programmable or not, gives you two fail safe modes. Default voltages are 11, 22, and 44 volts which is above 2.5 vpc limit of a LFP cell. 2.5 vpc is what all the manufactures specify low limit to CYA, but all LFP being the same chemistry is really 2 volts. So lots of room to spare if the Inverter should fail.

If you have an Inverter with Programmable LVD, you can set the voltage to trip off at 10% SOC or 3.1 vpc which equates to set points of 12.4, 24.8, and 49.6 volts. Due to Ri of the batteries and voltage drop under load 12, 24, and 48 volts is a really good LVD set point. Lead acid batteries are spent at 12, 24, and 48 volts under load.

But, charging will call for cell monitoring to not overcharge the weakest cell. If you just use "safe" battery voltage the battery is never full (which can be good for the battery life but limits the amount of charge).

No Sir, cell voltage level monitoring is NOT REQUIRED. Initial charge, you set the charger voltage to 3.3 to 3.4 vpc. Example 52.8 to 54.4 volts on a 16S battery. You monitor cell voltages during the first charge. Once the batteries begin to reach the charger voltage, current will start to taper down and you find the cell with the highest voltage and make note of it. Allow the charge to complete, terminate the charge (disconnect), and allow the pack to rest for a few hours. After resting measure the weakest cell voltage. You are looking for about 3.4 volts at rest. If it is to high, lower charger voltage for next round. That is how it is dome on an EV.

Solar is pretty much the same method, except you want the Float voltage to be 3.4 volts after charge while holding voltage in Float during the day. Once you find the correct charger voltage set point, you are done. No cell level monitoring or control is needed. Not to say you cannot do that if you wish. but it is added expense.

If you do have cell monitoring, how the heck are you going to tell your Solar Charge Controller to switch to Float and lower the voltage? You cannot because they are not designed to charge lithium batteries and communicate with a BMS. You have to work around it.

Stop and think about something for a minute. You can go out and buy yourself a 12, 24, or 48 volt LiFePO4 battery for your car/truck starting battery, RV house battery, golf cart battery, Wheel Chair or whatever gizmo you got. They are drop in replacements. Nothing external needed. None have any BMS. Some have a built-in electronic LVD inside so you cannot over discharge them and they call that a BMS in Marketing terms as a sales point, but LVD is not really a BMS. So how can they do that and give 2 to 5 year warranties?

Have you ever thought about that or questioned yourself?

What do the manufactures know that you do not? No commercial EV manufacture uses Top Balance. No Laptop manufacture uses Top Balance. So why do you use Top Balance? It is a fair question. Could it be you do not know any other way? That it is just the way we always have been told and always done it that way?

So how do manufactures get around it with packaged 12, 24, and 48 volt batteries? Real simple they buy hundreds of LFP cells, match the capacities. Bottom Balance the cells, put them in a box with a +/- post for you to connect to, charge them up to storage voltage, and sell them to you.

So when you get your 12 volt 200 AH Lithium RV House Battery the instructions tell you in great big print to limit Charge Voltage to no higher than 14.2 volts, and never discharge them below 10 volts. Do that and your new LFP batteries will give you years of reliable service. No expensive monitoring or BMS needed.

Now if you want to use Top Balance BMS. You go right ahead and do it. In fact you should because that is all you know how to do.

[Willy T]

If you do have cell monitoring, how the heck are you going to tell your Solar Charge Controller to switch to Float and lower the voltage? You cannot because they are not designed to charge lithium batteries and communicate with a BMS. You have to work around it.

You set the Float voltage, Float time and the silent period takes over ( charger shuts off ) and set the re-float voltage. This is a feature on every Outback product made for the last 10 years, of course you already knew that.

[Sunking]

You set the Float voltage, Float time and the silent period takes over ( charger shuts off ) and set the re-float voltage. This is a feature on every Outback product made for the last 10 years, of course you already knew that.

Yes I do know, but the point is Controllers for lithium batteries have no set points or algorithms. They are pure FLOAT CV controllers with no interface. Your Outback is optimized for Lead Acid using a 3-stage algorithm which is useless for solar. But that is another subject.

Go look at the Genasun MPPT Lithium Charge Controller Specification page. It can only handle up to 120 to 160 watts depending on which Lithium Chemistry you are operating. There is nothing for you to set or adjust. No BMS. Just Panel Input and Battery Output. You tell them what battery configuration you are using, and they program the firmware. The algorithm is FLOAT only.

Lipo 3S = 12.5 volts
LiFePO4 3S = 14.2 Volts
LiPo 4S = 16.7 volts

They are made to use on 12 volt lithium batteries you can buy from any Marine or RV Lithium battery manufacture. They are sealed battlers with no access to the individual cells or a BMS inside. At most a LVD relay to prevent accidental over discharge.

Willy honestly what is what is so hard for you to understand? No BMS is required if you follow a couple of simple rules.

That same Genasun MPPT charge controller is the exact same one they use for Pb batteries. What is different? The charging algorithm. The Pb version uses 3-stage algorithm (Bulk - Absorb-Float with temp compensation). Look at the specs Willy and see for yourself.

Note where some of your confusion may stem from is natural. There is no definition for BMS. When the term is used for with Lithium Batteries can mean two different methods.

1. Passive. Which is Top Balance using Vampire Boards attached to each cell. They are dumb boards with only two states of on or off. They turn on when the battery voltage reaches 3.55 to 3.6 volts and shunt or bleed a small amount of current around the battery when charging. They turn off when the battery voltage has bleed down to 3.5 volts or 100% SOC. Some models will add voltage and temperature monitor capabilities and interconnect with a small Ribbon Cable connected in series to communicate with a monitor controller. Each of those Vampire boards have a dip switch you set to tell it which number cell it is. Otherwise it is just a dumb passive board. Those use the cell power to communicate and are a parasitic load.

2. Active. This type really opens up a can of worms. They can be used to Top Balance, Middle Balance, and Bottom Balanced. Commercial EV manufactures use Active BMS in the Middle Balance topology. They do not monitor at the cell level as that would be way to complex basket of eggs. They monitor modules or a group of parallel and series cells. Tesla calls them Sheets. A "sheet" consist of 9 Bricks in series. Tesla only monitors and charges the battery at the Sheet level. not cell level. But it is not Top Balance, it is Middle Active Balance. That means they take power for a Stronger Sheet and transfers it to a weaker sheet if needed. Sorry to go off on that but the point is no manufactured system uses Top Balance.

Not even your lithium power tools use Top Balance. There is no need to and only increases the risk of damage by using top balance. Not to mention getting deeper into your pockets.

Top Balance comes from RC Hobby and DIY/Custom EV markets. In those markets the users use a wide mix of off the shelf parts and pieces that follow no industry standard. There is no way a BMS manufacture can make a product to fit every possible configuration a user can come up with. So they created a niche product to get into the consumers pockets. That is the purpose of any business. BMS is the Spandex Pants of the Lithium battery world where one size fits all and ugly as sin. If you do not have the knowledge to work with Lithium batteries, you use a Top Balanced BMS and take your chances. Otherwise it is not needed. That is the secret.

Four years ago, I was pro BMS. Then I got educated. End of story.

Now it is your turn. What are you going to do? Stick with status quo, or break free? Either wayy makes me no difference, what ever floats your boat.

[karrak]

I think that the bottom balance may drift if the cell current leakage is different between cells but will have to think further about this.

Here is a quick thought experiment
What if we have two identical cells connected in series with a capacity of say 100Ah, one has a cell leakage of 5% per year, the other 2.5% per year. We charge them both to 100%SOC, We then leave them for one year. At the end of the year one has 97.5Ah of charge stored, the other has 95.0Ah of charge stored. If we try to draw 97.5Ah from this battery one cell will be at -2.5Ah. Are they still balanced at the bottom end?

Simon

[solar pete]

[ BMS is the Spandex Pants of the Lithium battery world where one size fits all and ugly as sin. If you do not have the knowledge to work with Lithium batteries, you use a Top Balanced BMS and take your chances. Otherwise it is not needed. That is the secret.

Four years ago, I was pro BMS. Then I got educated. End of story.

Now it is your turn. What are you going to do? Stick with status quo, or break free? Either wayy makes me no difference, what ever floats your boat.[/QUOTE]

Hehehehe,

My brothers hybrid system is nearly ready to finish, there was some debate as to the type and brand of batteries and inverters and CC and BMS or, to BMS or not to BMS that is the question.....Going to get some photos and spec's together and when that is done we are starting a new Solar Hybrid section...

[karrak]

Tesla and Bosch do not use Chi-Com LFP batteries. No commercial manufacture uses Chi-Com cells. They do not use any form of Top Balance either. Tesla uses Panasonic LiCo cells in the Roadster all 6831 of them. They do not monitor any cell Voltages, they monitor 11 Sheets made from 9 bricks. Tesla battery is 11S 9B 69P. Similar design concept in the Nissan Leaf, Toyota Prius, and Chevy Volt, just fewer cells and modules to monitor. No commercial manufacture uses TOP BALANCE.

http://www.teslamotorsclub.com/showthread.php/34934-Pics-Info-Inside-the-battery-pack?p=737775&viewfull=1#post737775

The BMS Service Screen has 96 voltage measurements (one for each brick) and highlights the high bricks and low bricks. On the Roadster the high bricks are bled off during balancing - the Model S probably does the same, the pack architecture is very similar between the two (Roadster having 99 bricks of 69 cells).

For those interested around page 30 of this thread we get pictures of the balancing circuitry (the dreaded Vampire circuitry) and monitoring boards that Tesla call BMB boards that are connected via CAN bus to the overall BMS controller, and some more technical descriptions of it. Now maybe I am missing something and have made a horrible mistake as I have only skimmed the thread and only got to page 38 but it looks to me like top balancing using resistors to bleed off power.

Actually I wasn't talking about EVs. I was talking about home power systems Bosch, Sony and Tesla are making.

Simon