# I have 6 Tesla modules...how do I handle BMS?



## Hollie Maea (Dec 9, 2009)

stealthE said:


> I know there are some people that don't believe in BMS, and part of me believes that they are right. But with batteries costing as much as they do....I think...better safe than sorry.
> 
> So...I am told the Orion BMS is what I should be using. But when I look at the systems...they say: 1-16 cells or 16-180 cells. Well this has me confused, I mean... I have 2600 cells. Thing don't add up. Unless 6 modules = 6 cells?
> 
> What BMS should I be using?


For purposes of BMS, a "cell" is an entity that is connected in series. So don't worry about the parallel groups, each one is a functional "cell".

Edit: each "module" is six groups in series, so you have a total of 36 "cells" from a BMS standpoint.


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## stealthE (Jan 31, 2016)

So 6s72p means: 6 (series) groups of 72? I think that was the key I was missing. It is all coming together now.

Thanks so much.


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## Karter2 (Nov 17, 2011)

stealthE said:


> I know there are some people that don't believe in BMS, and part of me believes that they are right. But with batteries costing as much as they do....I think...better safe than sorry.
> 
> So...I am told the Orion BMS is what I should be using. But when I look at the systems...they say: 1-16 cells or 16-180 cells. Well this has me confused, I mean... I have 2600 cells. Thing don't add up. Unless 6 modules = 6 cells?
> 
> What BMS should I be using?


Yes,..better safe than sorry,
But not because of the cost of batteries, but your own safety !
Sorry but When folk ask basic questions like this, I worry if they realise the potential energy and dangers of the batteries they are handling ?
One wrong connection and a lot of sparks and heat will be released. 
Take care....think twice, recheck, before you make any connections.


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## dougingraham (Jul 26, 2011)

stealthE said:


> I know there are some people that don't believe in BMS, and part of me believes that they are right. But with batteries costing as much as they do....I think...better safe than sorry.
> 
> So...I am told the Orion BMS is what I should be using. But when I look at the systems...they say: 1-16 cells or 16-180 cells. Well this has me confused, I mean... I have 2600 cells. Thing don't add up. Unless 6 modules = 6 cells?
> 
> What BMS should I be using?


The Tesla modules are 6S74P for a total of 444 cells. The 85/90 kWh packs have 16 modules wired in series for a total of 96S74P. The 40/60/70 kWh packs have 14 modules for a total of 84S74P. I have never seen the module from a 60kWh pack so I don't know if they still have 74P but I suspect that all modules have exactly the same arrangement.

The 6S tells us that the peak voltage during charge and just off charge is 25.2 volts. The nominal voltage for a module is 22.2 volts and the pack is dead voltage is 15 volts. I have seen the full charge voltage while on the supercharger at 405 volts indicated by the car. This is 4.219 volts per cell. When I was at less than 10% SOC and just starting charging the voltage was 280 before the supercharger ramped the current up to 330 amps. The voltage rises rather quickly after that. But my near empty cell voltage would have been 2.92 volts per cell.

The best deal would be to use the Tesla BMS. After all it is already wired up. And maybe in a year or so someone will have it figured out.

Best Wishes with your project!


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## GoElectric (Nov 15, 2015)

Hi - since the question was asked, is there anyone out there who HAS hooked-up some Tesla modules? I have 10 of 'em. Will be meeting with an Electrical Engineer who has worked with EV research soon, and would like to be able to share as much information about BMS needs as I can. 

Will report back too!

Jim


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## stealthE (Jan 31, 2016)

I have 6 that I just unpacked. Looking at these things...I have no idea where to start. Lol. Given that the cells are so "one piece"...it is hard to imagine anything more than just hooking up two wires (+ -) and calling it a day. 

Please keep us informed with what you learn.


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## stealthE (Jan 31, 2016)

I am told the Orion bms is the one to use though.


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## GoElectric (Nov 15, 2015)

Hi. Good to find like-minded souls!

The more I have thought about it, the less BMS I think I will need. With 74p there is no point measuring internal resistance, I don't think. One cell would be undetectable?

I am actually thinking of joining the bottom-balancing camp. As I said, I will get back with the skinny from someone whose opinion matters more than mine.


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## electro wrks (Mar 5, 2012)

Could someone measure the size(length, width, and depth) of the modules for those of us interested in using them in conversions?


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## Hollie Maea (Dec 9, 2009)

Even Jack is suggesting BMS for non LiFePO4 chemistries these days...


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## Kevin Sharpe (Jul 4, 2011)

EVTV have made some progress decoding CAN messages from the Tesla BMS;

"It was determined that 6F2 is a matrix containing the voltages and temperatures for all 96 cells in the Tesla's battery pack, as well as 32 temperature readings (2 per module, 16 modules in the pack)"

For more details watch the following video starting from 1:31:15;

https://youtu.be/r2JOS-SlsZg


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## WolfTronix (Feb 8, 2016)

Hollie Maea said:


> Even Jack is suggesting BMS for non LiFePO4 chemistries these days...


The way I see it, you know that the BMS is important when the car manufacturers don’t take it out… 

Car manufacturers are all about cost reduction… Even at the expense of life…

Defective ignition switches, no problem, saves a few cents per car.
Defective air bags, no problem, saves a few dollars per car.
Not including a urea system to reduce emissions, no problem, saves hundreds of dollars per car.


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## GoElectric (Nov 15, 2015)

Approx 3 1/4 inches high 27 long and 11 1/2 wide.


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## GoElectric (Nov 15, 2015)

Since the topic is diverging, I'd like to know what peeps are paying for modules. I bought 10 at once and paid $US1000 for them. Won't be telling you where, but the supply is limited anyway, and I'll be looking for more.


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## stealthE (Jan 31, 2016)

I paid $1000 per piece also.


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## GoElectric (Nov 15, 2015)

Good for you! 

And to all the battery geeks out there, I want to hear what you think about top-balancing 74P cells, or any group of cells in parallel. In one sentence, my question is if one cell has lower capacity, when charging the group, does the current just naturally shunt to the other cells until the cell with the highest capacity allows the voltage to rise?

And a more novice question: how much does it matter whether I charge the cells to 4.2V? I might add one more module, in which case the voltage will exceed the range of my controller. If I charge them all a little less, then not, and I think by far most of the capacity is below 4.0V.

Perhaps I should post this question on a separate thread.

Jim


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## AntronX (Feb 23, 2009)

I paid $1045 per module.


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## Hollie Maea (Dec 9, 2009)

GoElectric said:


> And a more novice question: how much does it matter whether I charge the cells to 4.2V? I might add one more module, in which case the voltage will exceed the range of my controller. If I charge them all a little less, then not, and I think by far most of the capacity is below 4.0V.


It's best not to charge all the way to 4.2. You'll lose some capacity if you charge to a lower level like 4.1V, but you will increase the life of the cells significantly.

Tesla doesn't charge to 4.2 unless you select "maximize range". And maybe not even then.


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## GoElectric (Nov 15, 2015)

Hi Hollie, thanks for that.

So, I had the Battery Engineer over here Sunday and he was a little fuzzier than I had hoped - kind of head in the clouds. He needs some time to get oriented, as he has been out of it for 3 years.

Really, there was no conclusion. Had another EE over yesterday too, and we talked about it for a long time. I should say I am an Electrical Engineer too. As I said before, I am wondering just what will happen with all those cells in parallel which cannot be addressed separately. When charging a bank of 74, it seems to me the cells with a lower capacity will naturally draw less current, so they will naturally balance themselves. _I am assuming internal resistance will at least fractionally increase with SOC, and therefore the other cells will draw more current._ Where can I find some information on this?? On discharge, it 'will' be the same? When charging cells in series, this cannot happen, so balancing is necessary to have the cells all at or near max SOC. Is this parallel design the genius of Tesla? Essentially, we are looking at passive charge shunting? Also, how is internal resistance related to charging current? This could also be important to maximize the shunting effect, but if the effect is the same (because I think internal resistance will change with charging current), one could just charge them all at high current. I think not - differences will be minimalized for lower charge currents. 

Meanwhile, BMS shunting between 74P blocks depends upon voltage - and with 74P, if there is one cell which is trying to creep up faster, won't it be held down by the other cells? I suppose there will be a Normal Distribution of internal resistances, but all of the blocks will have this. What balancing would be trying to do is compensate for a few cells which are significantly different in one block or another (IF they can be detected). 

Some experiments I can do below. Which would be the most useful? 

1) Measure internal resistance of cells at different SOC;
2) Compare the capacity of the blocks and see how different they are. Try at different charge currents. 
3) Charge a module (6 blocks) and compare their curves for different SOC;
4) Balance charge and just see if the capacity increases or not.

As mentioned previously, I am not a sceptic of bottom-balancing. I think the theory is sound but it would require occasional re-calibration, as capacities can change? The advocates point to simplicity and parasitic draw. In this case (Tesla modules) it may also be over-design. I would still want HVC and LVC monitoring, but balancing may not be effective, nor necessary.





Hollie Maea said:


> It's best not to charge all the way to 4.2. You'll lose some capacity if you charge to a lower level like 4.1V, but you will increase the life of the cells significantly.
> 
> Tesla doesn't charge to 4.2 unless you select "maximize range". And maybe not even then.


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## okashira (Mar 1, 2015)

GoElectric said:


> Hi Hollie, thanks for that.
> 
> So, I had the Battery Engineer over here Sunday and he was a little fuzzier than I had hoped - kind of head in the clouds. He needs some time to get oriented, as he has been out of it for 3 years.
> 
> ...


You are over-complicating it. Each 74p group is one cell.
230 amp hour.

Treat each one as 6s with 230 amp hour.

DCIR is about 0.0006 ohm per cell at 25°C

Orion BMS will work great for these.

We have ~6 left.

We can also sell converted modules that are 12s37p.


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## GoElectric (Nov 15, 2015)

Hi. That is not a very articulate answer, but perhaps I am. I know am loath to spend a ton of money on an Orion BMS for starters - perhaps you can spend a minute explaining how the Orion is better than a simple BMS. Great for data, yes. But how relevant will data like internal resistance be with 74P? False sense of security? I think I need some hard data RE the questions asked, as I don't want to waste my money. Meanwhile I sent the post my battery engineer to see if he can answer any of my questions now that he has had the time to get his head around it.


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## Ampster (Oct 6, 2012)

Can you find a simple BMS that will work with the voltages unique to the Tesla cells? 

Sent from my SM-N910T using Tapatalk


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## okashira (Mar 1, 2015)

GoElectric said:


> Hi. That is not a very articulate answer, but perhaps I am. I know am loath to spend a ton of money on an Orion BMS for starters - perhaps you can spend a minute explaining how the Orion is better than a simple BMS. Great for data, yes. But how relevant will data like internal resistance be with 74P? False sense of security? I think I need some hard data RE the questions asked, as I don't want to waste my money. Meanwhile I sent the post my battery engineer to see if he can answer any of my questions now that he has had the time to get his head around it.


I'll be blunt again, your battery engineer doesn't seem to know what the hell he is talking about.

What questions, the four questions?

Here is an except from your post;
*and with 74P, if there is one cell which is trying to creep up faster, won't it be held down by the other cells? I suppose there will be a Normal Distribution of internal resistances, but all of the blocks will have this. What balancing would be trying to do is compensate for a few cells which are significantly different in one block or another (IF they can be detected). *

I am sorry - but this is all nonsense. What relevance does internal resistance have here? NONE
"Once cell trying to creep up faster..."
I have no idea what you are trying to mean, but like I said, you are over-complicating it.

The 74 cells can be treated as a single cell. PERIOD. Forget that there are 74 cells.

Balancing is achieved by matching voltages. Charge to 4.1, 4.2, whatever. Make sure they are all at the same voltage at rest. Done.


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## okashira (Mar 1, 2015)

Ampster said:


> Can you find a simple BMS that will work with the voltages unique to the Tesla cells?
> 
> Sent from my SM-N910T using Tapatalk


The tesla cells don't have a special unique voltage. You can use any BMS designed for 2.5-4.2 volt cells.

Furthermore, if your goal is SoC calculation, the linear voltage of NCA (tesla cells) makes SoC calculation easy based on voltage.

Unfortunately, BMS options are limited unless you want to spend money.

1.) cheap chinese that sucks
2.) orion
3.) elithion
4.) a few other diy - like stuff that will require alot of research
5.) one of these two up and coming at E-S:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=78535
https://endless-sphere.com/forums/viewtopic.php?f=14&t=76011


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## Yabert (Feb 7, 2010)

okashira said:


> Unfortunately, BMS options are limited unless you want to spend money.


From what I know, simple mini BMS and Zeva bms can also do the job.


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## okashira (Mar 1, 2015)

Yabert said:


> From what I know, simple mini BMS and Zeva bms can also do the job.


Thank you for those. Had not heard of Zeva. Looks good.


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## GoElectric (Nov 15, 2015)

Hi - your reply still doesn't shed any light on the issue - I believe if a cell has a different capacity its voltage would creep up faster for the same amount of charge as one which has more capacity. But if in parallel with the same cell, the latter will draw more charge, thus they will naturally balance themselves out. I'm willing to be convinced I am wrong, but need some sort of an explanation.

Thanks to others for their input. I was thinking about a mini BMS, but it has limitations, and the terminals are all wrong for my application, so will investigate the options suggested.

I'm testing a single cell for changes in internal resistance.


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## Ampster (Oct 6, 2012)

You are correct. A single cell in a parallell group will always have the same voltage as other cells. I use the term brick to refer to the group of parallel cells in a Tesla module

Sent from my SM-N910T using Tapatalk


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## Moltenmetal (Mar 20, 2014)

Cells connected in parallel behave as a single cell of higher capacity. All cells of higher capacity already consist of multiple subcells in parallel, perhaps swimming in the same shared electrolyte. Individual subcell properties no longer matter unless one sub cell becomes defective and becomes a short circuit resulting in self discharge of the undamaged cells in parallel with it. The capacity of the new larger cell is a composite of the capacity of the individual cells. Take a 2P arrangement of a 100 Ah and a 200 Ah cell: the resulting capacity isn't 300 but it isn't less than 200 either- the 200 Ah cell will share charge with the lower capacity cell, keeping its terminal voltage from falling too low on discharge, and the same but inverse on charge. If the cells are close in capacity anyway, and Tesla certainly ensures that, the capacity is close enough to the average capacity X the number of cells in parallel not to matter.


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## Karter2 (Nov 17, 2011)

GoElectric said:


> I'm testing a single cell for changes in internal resistance.


 .?? Why, what are you going to do with the data ?
....you could save yourself the effort and learn much more about these cells, by following Okashira's (And others). threads over on ES.
There is IR testing, capacity testing, voltage stress testing, cycle life testing , charge rate effect, etc


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## okashira (Mar 1, 2015)

GoElectric said:


> Hi - your reply still doesn't shed any light on the issue - I believe if a cell has a different capacity its voltage would creep up faster for the same amount of charge as one which has more capacity. But if in parallel with the same cell, the latter will draw more charge, thus they will naturally balance themselves out. I'm willing to be convinced I am wrong, but need some sort of an explanation.
> 
> Thanks to others for their input. I was thinking about a mini BMS, but it has limitations, and the terminals are all wrong for my application, so will investigate the options suggested.
> 
> I'm testing a single cell for changes in internal resistance.


I think your problem comes from a fundamental misundersatnding of what being in parallel means.

All cells are in parallel are FORCED to be at athe same voltage.

Sure, if one cell has less capacity then another in the 74p group, it will take less current. But, it doesn't matter to you or any user of the battery.

Balancing is done by matching voltage. thus, all cells in a 74p group are always perfectly balanced with each other.

The only thing that needs balancing are the series cells, of which there are six in a Model S module. (or 12, if you modify it)


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## okashira (Mar 1, 2015)

stealthE said:


> I know there are some people that don't believe in BMS, and part of me believes that they are right. But with batteries costing as much as they do....I think...better safe than sorry.
> 
> So...I am told the Orion BMS is what I should be using. But when I look at the systems...they say: 1-16 cells or 16-180 cells. Well this has me confused, I mean... I have 2600 cells. Thing don't add up. Unless 6 modules = 6 cells?
> 
> What BMS should I be using?


I should answer this post directly.

Each module has 6 cells.
You have 36 cells if you run 6 modules in series.

You need a BMS for 36 cells.

The Zeva BMS should work good for your purpose


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## stealthE (Jan 31, 2016)

Thank you!


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## GoElectric (Nov 15, 2015)

Hi. MoltenMetal follows my thinking, even though it was probably not too articulate. His example is just what I was imagining on a smaller scale. Internal resistance is just an external way of describing the ability of a cell to accept charge more quickly than another cell. Anyways, thanks for that Mr MoltenMetal.

So. Now that at least one person understands me, let's take it up past the cell level to the block or brick level. Using a simple BMS to balance the voltage on the 36 bricks will just mean topping-up the cells with a higher capacity inside the bricks. But the ability to use that power is limited by the brick with the lowest capacity, so what is the point of forcing more charge in there? 

I would like to have something to monitor HVC, LVC, and temp, but beyond that, I just don't see the need to top-balance. I suppose you could say when the SOC goes down, it does not go down as FAR, which is good for them. What am I missing?


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## Moltenmetal (Mar 20, 2014)

GoElectric: I don't see the need to top balance either. In fact there are good (chemical) reasons NOT to top balance. I charge my pack until my lowest capacity cell reaches HVC, then I let the BMS stop charging and do not let it re-start. 

In my view there's no benefit to a low current soak/balance charge with shunt balancing- all it does is give you significant extra time at high voltage, causing electrolyte damage the whole time, in return for a insignificant increase in useable capacity from the pack. Mind you, that statement is based on the LiFePO4 chemistry and its voltage-capacity curve. Other chemistries may have curves which are flatter at the top, rendering that balance charge step more useful- I don't know the other chemistries well at all. But from what I do understand, I suspect that the mechanism for electrolyte damage should be related quite strongly to voltage somewhat irrespective of what you use as a cathode material. So it depends on what is most important to you: squeezing every little bit of capacity out of the cells when they're new, or keeping them around with acceptable capacity for as many charge/discharge cycles as possible. The latter is definitely my goal, since I blew my money on expensive prismatic LiFe cells before this DIY re-use of OEM packs became an option I was comfortable with.

I also don't think it's safe to charge a bottom-balanced pack without a cell-level HVC cut-out for the charger. Would I compromise to doing that HVC alarm trip on each group of six cells in series if they were six cells in a Tesla brick? Perhaps I would- the cells are likely to be very well matched and their environmental conditions cell to cell are going to be very similar. I wouldn't trust doing so with large prismatic cells though. Others don't bother and manage to just monitor total pack voltage during charging with occasional checking from cell to cell, and they seem to get away with it. Personally I don't think that's adequately safe for most users, given the catastrophic consequences of over-charging.

A LVC alarm is also a very good protection against ruining the lowest capacity cell by putting it into reversal.

And where you live, if you intend to drive in winter, you do need a) a means to heat the batteries and b) a means to avoid engaging the charger until the batteries are warm enough to accept charge. You likely don't need a high temperature cut-out for charging, but if you already have the temperature sensor it is likely an easy option. The only question is: would it be worth being stranded as a result of a prematurely terminated charge that didn't automatically re-start when the temperature fell again, or as a result of a defective temperature sensor? Maybe not very likely- maybe I'm just being paranoid- but unless you intend to charge at very high C rates I don't see the need for the high temperature cutout.

So we agree on the need for a BMS, and on the minimal functions required for it. The only question is: whose do you use?

You could use a dedicated CellLog8 for each group of six cells- that would be very cheap, but the devices are pretty flimsy and I don't know how much I'd be comfortable to rely on them to protect an expensive pack. The good thing is that if you used each one as a cheap alarm trip module on a single group of six cells, they would not be responsible for creating imbalance in the pack. 

You could use one of the more expensive BMS options, assuming it can handle the high voltages required to monitor groups of six cells. Or you could find a way to tap into each cell in series and implement a more ordinary cell-level BMS, assuming that the correct HVC and LVC trip voltages for the Tesla chemistry are set. 

It would be very helpful to me if you could post a pic of one of these modules, pointing out how the cells are arranged and whether or not cell-by-cell terminal access is available on them without too much of a Frankenstein job.


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## okashira (Mar 1, 2015)

I don't even know where to begin with you guys. What a bunch of nonsense.

Top balancing is ideal. This is because lithium ion cells degrade the fastest at higher SoC.

If you bottom balance - when you have the pack fully charged, some cells will degrade faster then the others because the "weaker" cells will be at a higher SoC (aka VOLTAGE)

This process will accelerate as the SoC gap widens because the weaker cells are degrading faster and faster as they will be at a higher and higher SoC when charged. 

Thus, bottom balancing is a great way to minimize the calendar life of your pack.

You guys have some serious research to do, which includes the basics on electrical and battery theory.

I won't reply here anymore. I replied to stealthE because he bought the modules from me and I don't want him misinformed.


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## GoElectric (Nov 15, 2015)

Hi MoltenMetal,

Just a quick reply to say "Thanks." I'm pretty-much on board with everything you said. 

There may still be others whose experience could add to this picture.

There are seven wires plus two thermistors coming out of each module, so yes, I can read individual 74P 'cells' easily. Will look into BMSs when I get some time this weekend, but all I really need is an alarm of some kind. I want something I can connect these wires too, not which attaches to a terminal - impossible maybe.

I was thinking about what you said about temperature, and I will likely have a PLC controller which will need low and high temperature limits and make sure the charger doesn't turn on until they are warm enough. Heating will be the issue, not cooling. Drawing power FROM the cells to run the circulating heater is okay though, as then they are warmed from the inside as well, and I will just be charging them up again anyway. I'm thinking about 1500W, and maybe 10 minutes. 

I'll just attach one cool pic - don't have anything which shows the wires, terminals, but here you can see the individual fuse wires and the common conductor for each 74P group. Actually there are 148 cells on each plate - 74 positives and 74 negatives. Let me know what else you want to see.

Jim


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## Ampster (Oct 6, 2012)

okashira said:


> ......
> Top balancing is ideal. This is because lithium ion cells degrade the fastest at higher SoC.
> 
> If you bottom balance - when you have the pack fully charged, some cells will degrade faster then the others because the "weaker" cells will be at a higher SoC (aka VOLTAGE)
> ...


That is one of the clearest statements I have seen about the risks associated with various charging, discharging and balancing strategies. It is not surprising that at some point this thread would evolve into the classic top vs bottom balancing discussion. To avoid those risks a BMS could cutoff charging when one cell reaches a predetermined point. To me the advantage of the more expensive programable BMSs is that you can do that without engaging the shunt resistors. This is what I understand Tesla does, and we are talking about Tesla modules here. Again, it is my understanding that no balancing or equalizing takes place unless a Tesla is charged above 90%. Above 90% the Tesla BMS begins shunting the high voltage cells and that is consistent with what Okashira is saying. 


Sent from my SM-N910T using Tapatalk


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## onegreenev (May 18, 2012)

okashira said:


> I don't even know where to begin with you guys. What a bunch of nonsense.
> 
> Top balancing is ideal. This is because lithium ion cells degrade the fastest at higher SoC.
> 
> ...


I disagree, When you are talking hundredths of a volt differences at the end of charge and that you never charge to the top anyway and after a short rest the cells will all fall into the same voltage and all will have equal SOC put into them. Having the cells equal at the bottom will prevent a catastrophic death of any single cell that happens to reach that bottom while all the others are still pumping full current into the cell. If you do bottom balance and you do happen to find that you have a cell that is way too high in the terminal voltage as to damage the cell then that cell needs to be culled from the pack. The surface charge from charging is not counted in the final fully charged voltage at least with the LiFePO4 cells. 

For those that actually overcharge their cells every time and you happen to bottom balance then, yes, I can see that you could over time ruin a battery prematurely with this method. 

When you first bottom balance you do need to check the end voltages so you know if you do happen to have cells that are of differing capacities. I have found that if you bottom balance correctly you will find very little difference in the end f charge voltages and the minor differences will dissipate after sitting because of the surface charge dissipating away. 

My old pack of hi-power cells were charged to 3.65 volts nominal for the pack. At the end of the charge I never had a cell go over 3.75 volts and after an hour all the cells were in the 3.33 to 3.32 volt range. 

Remember that when you charge you are actually putting in a higher voltage than you want so you can actually fill the battery. Once you stop that extra pressure so to speak goes away and it all settles down nicely. 

Another to consider. How often is our pack actually sitting at FULL. Once you charge your pack and you turn on your car and head down the street it is no longer FULL. The purpose of bottom balancing is to protect your cells in case you happen to over discharge the pack. That is all. Top balancing does what? Lets you have a balanced top end for the brief moment of driving out of your driveway then it does not matter. But if you top balance and you risk loosing cells in the event that you take your car beyond the point of empty. Down at the bottom of the charge things happen fast. 

At the top during charging at very low currents things happen rather slowly. If you have a system in place to prevent you from overcharging the bottom balanced pack you will have no trouble. My BMS is already in place. My controller and my charger and that I have all things set so even those that may be a hundredth of a volt higher it won't go into a zone where it could kill the cell or cells. 

But if you insist on the BMS it is up to you.


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## Moltenmetal (Mar 20, 2014)

> I don't even know where to begin with you guys. What a bunch of nonsense.
> 
> Top balancing is ideal. This is because lithium ion cells degrade the fastest at higher SoC.


 If you shunt charge to top balance, you HOLD all but the highest capacity cells at an artificially high voltage for a period longer than necessary, hence hastening the demise of all those cells.

Instead, I did a crude top balance once. Thereafter I simply terminated charge when my lowest capacity cell reached HVC. That's been my strategy ever since. Regrettably I cannot turn off the shunt charging feature of my miniBMS, so they do shunt charge a bit- but not for long. My charge now terminates just as the charger hits its CC/CV tapering charge setpoint, and the shunt charging doesn't go on for very long.

Cells degrade fastest at highest SOC, but they degrade even faster when they are being held at an artificially higher voltage at the end of charge. Time at high voltage, especially at high temperature, is what is doing electrolyte damage to the cells. Spending unnecessary hours near 100% SOC is bad, but spending unnecessary hours at 100% SOC voltage PLUS the charger-driven overvoltage is worse still.

Yes, my lowest capacity cell will be the first to fail, because it spends the longest time at the highest voltage- but it's the penguin at the edge of the icefloe, protecting the rest of my pack. Given the equipment I have, this is the best strategy I can find to keep my pack alive for the longest period.



> ]If you bottom balance - when you have the pack fully charged, some cells will degrade faster then the others because the "weaker" cells will be at a higher SoC (aka VOLTAGE)
> 
> This process will accelerate as the SoC gap widens because the weaker cells are degrading faster and faster as they will be at a higher and higher SoC when charged.
> 
> Thus, bottom balancing is a great way to minimize the calendar life of your pack.


 Bottom balancing is a strategy to protect your pack against over-discharge leading to cell reversal. Since for longevity you should be avoiding going below 70% DOD (30% SOC) ever, it's not a strategy I use. I rely on my Ah meter and I don't challenge the bottom of my pack, ever. I have a LVC alarm, but I've never heard it, and I'm going to keep it that way.



> You guys have some serious research to do, which includes the basics on electrical and battery theory.
> 
> I won't reply here anymore. I replied to stealthE because he bought the modules from me and I don't want him misinformed.


 I'm an amateur, like most people here. I've read a bit about this. I'm a chemical engineer, but not an electrochem specialist. I don't claim to know everything. But I try not to be an @ss about what I do know, either, though I guess I fail in that regard when people start pitching HHO or overunity scams etc. I remind you that this is a DIY website. If you can't be patient with people bouncing ideas off one another in an effort to build their collective knowledge, then perhaps this isn't the right place for you.


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## Moltenmetal (Mar 20, 2014)

GoElectric: it sounds like you have seven wires, i.e. the + and - of the 6S module and a wire to each of the five series junctions between paralleled cells. If so, you can implement cell-level BMS of whatever kind has the right LVC and HVC trip values set for the Tesla chemistry. And if those were my batteries, that's what I'd do.

You don't need anything as complex as a PLC to prevent charging when the batteries are cold, or to control external battery heaters, but whatever is easiest for you. Whatever you use, will merely need to open an isolated relay contact in series with whatever circuitry controls your charger.


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## Karter2 (Nov 17, 2011)

> ...If you shunt charge to top balance, you HOLD all but the highest capacity cells at an artificially high voltage for a period longer than necessary, hence hastening the demise of all those cells.


Any sensible person considering how to manage these packs should take a lead from the original pack designers.
They are not amatuers, they didnt just randomly pick any cell to use, or any BMS to protect them with , and im sure they did not randomly decide how to manage the balance protocols.
They have probably the best EV focussed battery brains in the game currently and a pretty successful record with many thousands of packs out in the wild with a 8 year warranty and no significant history of problems or failure.
If you chose to ignor that experience or feel you can do better, then fine, but do not expect wholehearted support for your train of thought.


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## okashira (Mar 1, 2015)

Moltenmetal said:


> If you shunt charge to top balance, you HOLD all but the highest capacity cells at an artificially high voltage for a period longer than necessary, hence hastening the demise of all those cells.
> 
> Instead, I did a crude top balance once. Thereafter I simply terminated charge when my lowest capacity cell reached HVC. That's been my strategy ever since. Regrettably I cannot turn off the shunt charging feature of my miniBMS, so they do shunt charge a bit- but not for long. My charge now terminates just as the charger hits its CC/CV tapering charge setpoint, and the shunt charging doesn't go on for very long.
> 
> ...



I get the feeling that many of your problems stem from using low quality cells in the first place.

Use high quality cells, Like A123, Panasonic, Samsung, LG, and your experiences will change.

If you're using bottom balancing to prevent cell reversal, then there is something seriously wrong with your pack/design to begin with.
I know the tesla modules, even at 50,000 miles will be within 0.005V at 5% SoC with top balancing above 4.1V.
Stop using crap cells like "Thundersky," "GBS," "CALB" and stick with real quality cells.


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## Ampster (Oct 6, 2012)

Karter2 said:


> Any sensible person considering how to manage these packs should take a lead from the original pack designers.
> .......................
> If you chose to ignor that experience or feel you can do better, then fine, but do not expect wholehearted support for your train of thought.


Not only do they have tens of thousands of packs out there, they collect lots of data about how those packs perform. That data is transmitted back to them from the cars. 


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## Moltenmetal (Mar 20, 2014)

I don't disagree with any of that. You're using an OEM's parts, and they have a great reputation for knowing how to keep them alive long term. Taking the lead from the OEM's strategy is a good idea.

Regrettably, the OEM's BMS etc. are not so easy to use on part of a pack which has been amputated from their vehicle.

I don't bottom balance. I don't top balance. I merely selected cells with close to the same capacities at the start, stop charging when any one gets to HVC, and use my Ah meter to avoid challenging the bottom of the pack. It's a strategy that works for me as a DIY. It requires a perfunctory BMS but doesn't require a fancy charger. Is it the optimum strategy for part of an OEM pack installed in a DIY converted vehicle? Dunno- what are we comparing it against?

Perhaps you can enlighten us as to what BMS strategy Tesla uses. If each module comes with seven wires, are they monitoring voltage on each cell? (By cell, I mean each group of cells in parallel, which is effectively one larger cell as we've discussed). Or are those wires used for some other purpose? Or have they been added by someone else? Do they shunt balance during charging? Is that balancing done cell by cell, or is it done on each 6S module?

Top balancing is primarily a strategy to squeeze every little bit of charge into the cells that you possibly can. You can do that to any limit of SOC you want- 99%, 90%, 80% etc. merely by selecting the voltage (though the voltage vs SOC curve for some chemistries is very, very flat making the accurate selection of a SOC lower than 90% pretty difficult). By so doing you might be able to reduce the amount of electrolyte damage being done. I understand that some of the OEMs are using that strategy, staying away from the very top of SOC. But it's also clear that the lower voltage you take the cells to during charge, the less electrolyte damage that happens. There is only so much antioxidant added to the electrolyte "soup"- when it's spent, it's spent, and capacity loss after that is inevitable. If merely storing cells at a high SOC is doing a meaningful amount of damage, you can bet that the damage occurring during an extended period of shunt balance charging is doing far more damage than that- 0.2 of a volt is a huge amount in terms of the rates of those electrochemical reactions.


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## onegreenev (May 18, 2012)

okashira said:


> If you're using bottom balancing to prevent cell reversal, then there is something seriously wrong with your pack/design to begin with.


First we need to be clear, most all DIY vehicle builds are done on a budget. We are not Tesla, Nissan or Chevy. We do not have the abilities to build to that level and most of the DIY battery management systems available to the average DIY conversions are rather crappy and not so well made. One however is reasonable and that is the Orion. 

So with that, many of us who do convert must resort to other means to protect our investments in our cells. I do drive a Leaf and I am on my Second Leaf. I found that the other OEM battery packs are not all as well as you might think in quality vs the CALB and ThunderSky type Prismatic cells. 

Yes, you can set your vehicle up with an Orion BMS and even turn off the active top balancing and not top or bottom balance and rely upon the BMS to protect you from over discharge and over charge. Bottom balancing is just another safety just in case you happen to drive your vehicle beyond the safe limits. It will protect your pack. 

My setup has all safety components in the pack to prevent me from destroying my cells but I would need to know that my cells were all equal. If I had purchased all my cells from one batch and at one time I would have felt fine not bottom balancing or top balancing because I could set my controller to keep me off the bottom and my charger is plenty good to keep my off the top as well. 

But for me, both my lithium packs were purchased used and from two different sources. So with that I needed to be sure all my cells were matched and I chose to do so at the bottom because bottom balancing is easier than top balancing. So now I have to check my pack when I charge it so I can watch to see if they are in the same zone. If I find I have a cell that has a voltage too high I will replace it. 

People who end up with badly unbalanced packs are and have been due to things connected to the pack that drain the pack and many have actually had BMS systems that were connected to different cells in different bundles and the BMS systems drained cells while sitting and caused imbalances enough to cause issues. 

Its not that we don't have a BMS system of sorts but we surly don't have usable Nissan or Volt or Tesla BMS systems to integrate into our DIY builds. 

As for the companies having well designed packs and BMS systems, Well yes. They also have billions of dollars to invest. We, thousands. Big difference. 

PS. CALB cells are actually quite good. 

I have Nissan Modules going into my VW Bus build and those are being bottom balanced too. Just to be sure. I have no BMS except for what my controller can do. I may actually buy an Orion BMS for the Bus. For my Bug, no need. 

Pete


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## okashira (Mar 1, 2015)

............


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## onegreenev (May 18, 2012)

> There is like some disease that's infected this forum, and I think it started with all the crappy cells like CALB, Thundersky, etc.
> This lead to other symptoms, like "cell reversal," "Bottom Balancing," "Anti-BMS Syndrome" and all this other crazy stuff that's borderline pseudoscience.


Well I think you are not following the point here. It is a progression. We had lead, then NiMH, LiFePO4 and now an assortment of others and some are somewhat available. Actually your time frame of the Leaf Modules is wrong. 2013 is when the brought in the Lizard Leaf Modules to combat the heat issue experienced. But as for degradation of the cells, Im still seeing a degradation of capacity pretty equal to my 2011 cells at this point. I expect to loose my first bar by the end of summer which will coincide with the mileage similar to my 2011 Leaf. I drive a very strict route to work and back and my capacity is noticeably falling even after just 12,000 miles. I don't expect to have any better. So to say CALB are crap is pretty bold. 

The bottom balancing is a proven way to protect your cells if you happen to drive too low. It is not used by everyone and usually those that have had cells go into reversal was not due to bottom balancing. It was because of the cell reversal problem and the pack being imbalanced badly at the extreme ends of the charge and discharge that caused the issue. Bottom balancing eliminated that issue for those cells that were far enough out of whack but if you don't go to the extremes you won't have the issue either and that is what the BIG OEM's do. Keep the cells from being used in those extreme ends. We have learned and grown to know this just as the OEM folks. Many have taken our knowledge and taken it to the OEM. Our work is not unheard nor unseen. OEM BMS systems usually don't have active balancing either. They just monitor and keep the pack from either extreme. Simple and easy. 

My negative talk of the Nissan Leaf Modules is only because of the capacity but nothing else. My use of them will be just fine. As for balance, you know that the Nissan Modules are 2s and 2P per module. So all my testing has shown the they hold balance just as well as my CALBS. I have no need to bottom balance the each half of a module. Only the whole module. More information will come and yes we can still use the No BMS and depend upon our controller (which is a very smart one) and charger (which is also smart) to keep me from either extreme and the bottom balance is just a safety from over discharging a pack and preventing any cell from going into reversal. I will be installing a battery bridge device to keep track of the pack from going out of balance. If I have a problem with a cell (can happen to any pack OEM or DIY) and it can warn of a loss of cell or cells on one bank of the battery to warn of impending problem and a need to fix it. 

I and many have extensive experience witch these Lithium cells both CALB, and others. I know of others that are still running their LiFePO4 cells of different manufactures and still driving long distances. Capacity is pretty good. 

A123 pouch cells are good but require extensive fabrication to build a stable and safe pack. 

Bottom balancing. 

What is your beef with bottom balancing and why do you think its a bad thing? Have you extensive knowledge of bottom balancing and that its a bad thing or are you listening to others or are you a producer of a BMS that is just bashing this? We have had our bouts of these sorts trying to get people on board with BMS systems. 

I personally have an issue with OEM BMS systems that went bad and ruined cells within a pack, actually multiple packs and caused many cell reversal issues due to causing many cells to go imbalanced and the BMS was unable to diagnose its own problems to prevent problems. 

What system monitors the BMS? The BMS system was an active balancing style BMS system to keep the cells top balanced. Well, NO. It ruined hundreds of cells and it was not just one vehicle. It was many vehicles where this happened. 


You do know when people can get access to these used packs from old OEM electric or from wrecked EV's we will snag them up. But while this is a good source we are still unable to purchase packs from OEM for our own DIY builds. That will never happen at least for now. For those that are able the new cells are better. They are OEM builds. We would expect better. They are like I said from companies that have spent billions not thousands to make them the way they do. 

I don't knock the DIY and the early lithium and the LiFePO4 chemistry. Sure its not the newest but it is actually a pretty stable chemistry, which is good for the DIY guys. 

I'll post my experience with the Leaf Cells in by BUS but as I said. The new Leaf Modules are a little better but there is still a long way to go. 

Can you show me your BUILD? What are you using in your build? Battery Choice and BMS choice. Since you have a good handle on this please share.


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## Ampster (Oct 6, 2012)

Which point? The point of the original post was finding the right BMS for Tesla modules. How much experience do you have with Tesla cells? As you have said, even Jack Rickard admits a BMS should be used with these cells. It is not about being on a budget, even Tesla has a budget. It is about risk management and choosing which method to use to protect an investment in batteries. 

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## Moltenmetal (Mar 20, 2014)

I agree with that completely Ampster. Now back to the OP- GoElectric was give only two choices- Orion BMS and one other I'm not familiar with. MiniBMS us still nit available with celltop boards set for voltages suitable for Tesla cell chemistry unless I'm mistaken. Presume both the other options would be used on each big cell. With Orion you can decide whether or not to turn on the shunt resistors during charging. Orion gives you reliability and options and data collection, but a fairly steep price. A cheap and dirty option wild be to go with CellLog8s, which are flimsy and can cause imbalance over time- workable, cheap but probably inadequate. Any others GoElectric should consider?


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## GoElectric (Nov 15, 2015)

Hi. I recall reading something about a bridging device - can someone post a link?

Someone mentioned Tesla only charges to max capacity for extreme range mode, or something like that. With these cells, I expect capacity to be pretty evenly matched, so although not ideal for every charge, it would be good to be able to do this when needed. Would I have to go to an Orion for this? 

(I still haven't looked at the zena(?) BMS as suggested, but will. Busy!)

Jim


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## Ampster (Oct 6, 2012)

I have a little experience with an Orion for a stationary pack. If I remember correctly I have a switch that controls whether the balancing comes on or not. I don't have an easy way to to change the voltage that I charge to but it can be done and I can go into the settings of the Orion and adjust those balancing settings. I currently am using a JDL programable switch to turn off my charger.

I did start a project using the Thunderstruck charger which might be able to do what you want. Their charger and the control unit that runs it off Canbus can have several switch inputs. I was going to set it up for a 85-90% charge normally that would be below the voltage the BMS would start equalizing. Another selection was going to be at a higher voltage, but with a current taper. That would coordinate with the BMS equalizing point and the equalizing (or balancing) would be done at low current flow. I still may implement that strategy for my stationary pack but I have to focus on selling my VW conversion because I need room in my garage for a Tesla that is arriving sooner than expected.

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## onegreenev (May 18, 2012)

Ampster said:


> Which point? The point of the original post was finding the right BMS for Tesla modules. How much experience do you have with Tesla cells? As you have said, even Jack Rickard admits a BMS should be used with these cells. It is not about being on a budget, even Tesla has a budget. It is about risk management and choosing which method to use to protect an investment in batteries.
> 
> Sent from my SM-N910T using Tapatalk


How much experience do any of us have with Tesla Cells in a DIY build? I know a few so far that are having total success with them and they don't use a BMS. How much experience did any of us have when the LiFePO4 cells came to be available. Not many and it was by trial and error and charge discharge testing showed where we need to stay away from on either end of the cells. We can use the same principles and so far testing has shown that we can. So, bottom balancing does work with these other chemistries of lithium.


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## onegreenev (May 18, 2012)

GoElectric said:


> Hi. I recall reading something about a bridging device - can someone post a link?
> 
> Someone mentioned Tesla only charges to max capacity for extreme range mode, or something like that. With these cells, I expect capacity to be pretty evenly matched, so although not ideal for every charge, it would be good to be able to do this when needed. Would I have to go to an Orion for this?
> 
> ...



http://www.evdl.org/pages/battbridge.html

https://www.youtube.com/watch?v=a-Ke_k0Dcoo


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## Ampster (Oct 6, 2012)

As the video mentions it is also known as a Lee Hart bridge. I use this on my stationary pack as an early warning that my pack is out of balance. It was quicker than figuring out how to use one of the alarms on my Orion and I could put the LEDS where I could see them as i go up the stairs from my garage. Some day i will tackle the Orion alarms.

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## GoElectric (Nov 15, 2015)

Hi. That bridge seems like a good idea - make the light go off on the dash.

As I think I mentioned, I`m looking at a PLC controller, which I might be able to use for controlling battery temp, HVC and LVC. Could perform the bridging function too. I looked again at the miniBMS for pricing, and for 36 cells it is still going to cost about $500, so a PLC is even cheaper.

Gotta go.


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## Moltenmetal (Mar 20, 2014)

Be very careful with the specs for your PLC: you need true differential inputs with quite a bit of isolation for use on a BMS.

I have separate Lee Hart bridges for the front and rear packs in my car, with six LEDs right on the dash. It's a quick and dirty indication of pack balance, which comes at the very minor cost of a continuous drain on the pack of a watt or so. The resistors have been selected so that the drain on the front and rear packs is nearly equal so it doesn't cause imbalance. You could eliminate that parasitic load during storage with a relay to shut off the LEDs when the ignition is off, but I didn't bother. My DC/DC stays on full time too, to keep the auxiliary battery charged while the car is in storage, and that consumes a lot more power from the pack than my miniBMS boards and Lee Hart bridge does. But it saves having a battery maintainer on the 12V aux battery all winter.


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## GoElectric (Nov 15, 2015)

Thanks. I have two guys coming over today to discuss and get things moving.


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## okashira (Mar 1, 2015)

Jim, since we sold the modules to you as well, I really want to see you do it right.
I can get you a proper 36S BMS for a good price. Email me or Eric


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