# New BMS designed for DIY



## sholland (Jan 16, 2012)

Wow, read 162 times and no feedback? Is no one interested in this?


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## rtz (Jul 3, 2013)

Read page 6:

http://media3.ev-tv.me/cellcare.pdf 

No BMS needed or required.


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## Baratong (Nov 29, 2012)

The BMS is probably the most self-developed part of an EV's electronics. There are many examples of DIY BMS's in the build forums. I built one because I wanted more bells and whistles, and was not happy with the lack of safety features in most of the commonly sold commercial units available. ( http://www.diyelectriccar.com/forums/showpost.php?p=446241&postcount=21 )

There was one DIY builder here who used I/R for communications from the cell modules. The interesting part there was how well he had the comms working. 

Anyway, I wish you the best of luck with your BMS system.


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## sholland (Jan 16, 2012)

rtz said:


> Read page 6:
> 
> http://media3.ev-tv.me/cellcare.pdf
> 
> No BMS needed or required.


So, you're ignoring this paragraph?

"The basic rule is do NOT overcharge these cells and do NOT overdischarge them. Observing those two precepts will ensure many years of service. If you fail to observe this, even once, it will most likely result in cell destruction and loss, and it will absolutely lead to early capacity loss of your pack. But achieving this takes a bit of strategy."

You don't want to monitor any cells during use?


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## rtz (Jul 3, 2013)

When you buy your set of batteries; drain each cell down to a certain voltage so each one is the same. Assemble the pack. Charge the pack. Now never, ever discharge it past a certain point. Have your charger set so it doesn't overcharge the pack.

So much less expense and complexity not having a BMS installed all over the place.


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## dougingraham (Jul 26, 2011)

sholland said:


> You don't want to monitor any cells during use?


As a scientist and engineer I originally wanted to see the data. There seems to be a huge compulsion to want to know what is going on. It turns out that none of this helps you drive the car or protect your batteries. And after just a couple of weeks going without it I no longer wanted it. I don't even have a display that shows the volts or amps because it isn't necessary. About the only thing a BMS adds to a bottom balance strategy is the ability to tell you exactly which cell or cell interconnect is going bad. It doesn't stop it from going bad. At least this is the case with LiFe type cells. I am starting to think it is true with other types of lithium cells as well. The big problem with adding a BMS to the system is that you are adding a device with lots of points of failure (the BMS) to protect a device that really doesn't have any points of failure (the battery).

If you bottom balance you have overcome human nature when you run the pack dead. Human nature would tickle you with the idea that you can make it. Its just a couple tenths of a mile. With a bottom balance all cells drop out at the same time and I can tell you it feels like someone opened a switch. But no cells are damaged. If you top balance with a BMS you get an alarm when some cells go below some preset threshold and you have the choice to stop driving or continue on. Human nature will win out and the car will be driven and a cell will be ruined. The other side of the equation when you are charging is not an issue either. Your first charge after the bottom balance you find the cell that hits 3.5 volts first and set your charger to stop at the pack voltage where that happens. Or even a little less than that. This has worked fine for what is approaching 1000 charges for me. No cell drift in 3 years now. And if a cell started to drift then I would replace it as bad.

The BMS for a DIYer is an unnecessary expense. It is ultimately a source of problems. And for those who have added some sort of shunt balancing during the last phase of charging in the mistaken belief that these cells drift out of balance, you are not actually performing a balance. You are chasing the diffusion delay which can unbalance the pack as easily as balance it.


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## sholland (Jan 16, 2012)

rtz said:


> When you buy your set of batteries; drain each cell down to a certain voltage so each one is the same. Assemble the pack. Charge the pack. Now never, ever discharge it past a certain point. Have your charger set so it doesn't overcharge the pack.
> 
> So much less expense and complexity not having a BMS installed all over the place.


I understand all that, and it sounds simple, but what is monitoring your pack to to warn you when a cell is unexpectedly lower than all the others, and helping you to ensure no cell ever gets over discharged? Do you just get out the DMM and check every once in a while? I don't know about you, but most of my individual cells are assembled into a pack that is pretty much sealed and inaccessible without significant effort, just like any OEM pack. 

The balancing is almost a secondary function of a BMS, and I think people focus too much on that feature of a BMS... The primary requirement is to have monitoring for accurate state of charge calculation, and a redundant protection function which will automatically alert a higher authority when an individual cell is outside of prescribed limits (low or high thresholds). The protector function is implemented with individual comparators for each cell, and operates without an ADC sample command. 

At a very minimum, any battery pack should have a protector function... Even power tool packs have that. You are not even implementing the simplest feature of a power tool pack!!

No pack from any auto maker would or could be implemented that way.


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## sholland (Jan 16, 2012)

dougingraham said:


> As a scientist and engineer I originally wanted to see the data. There seems to be a huge compulsion to want to know what is going on. It turns out that none of this helps you drive the car or protect your batteries. And after just a couple of weeks going without it I no longer wanted it. I don't even have a display that shows the volts or amps because it isn't necessary. About the only thing a BMS adds to a bottom balance strategy is the ability to tell you exactly which cell or cell interconnect is going bad. It doesn't stop it from going bad. At least this is the case with LiFe type cells. I am starting to think it is true with other types of lithium cells as well. The big problem with adding a BMS to the system is that you are adding a device with lots of points of failure (the BMS) to protect a device that really doesn't have any points of failure (the battery).
> 
> If you bottom balance you have overcome human nature when you run the pack dead. Human nature would tickle you with the idea that you can make it. Its just a couple tenths of a mile. With a bottom balance all cells drop out at the same time and I can tell you it feels like someone opened a switch. But no cells are damaged. If you top balance with a BMS you get an alarm when some cells go below some preset threshold and you have the choice to stop driving or continue on. Human nature will win out and the car will be driven and a cell will be ruined. The other side of the equation when you are charging is not an issue either. Your first charge after the bottom balance you find the cell that hits 3.5 volts first and set your charger to stop at the pack voltage where that happens. Or even a little less than that. This has worked fine for what is approaching 1000 charges for me. No cell drift in 3 years now. And if a cell started to drift then I would replace it as bad.
> 
> The BMS for a DIYer is an unnecessary expense. It is ultimately a source of problems. And for those who have added some sort of shunt balancing during the last phase of charging in the mistaken belief that these cells drift out of balance, you are not actually performing a balance. You are chasing the diffusion delay which can unbalance the pack as easily as balance it.


Doug, you can't tell me every cell in your pack is under the exact same influence as all others. Especially in conversions the pack is distributed all over the vehicle, and there will be at least some temperature delta across the cells. The car was simply not designed from the start to be a BEV.

What's the biggest factor affecting cell impedance? Temperature. The cells under the hood are likely getting cooler than those in the trunk, and in time, the charge on those cells will drift apart... at lower temperature they simply do not have the same current carrying capacity as the rest. Those cells at higher temperature can (due to higher I^2R heat dissipation) run the risk of thermal runaway. This will all be visible to the BMS before it goes too far.


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## Hollie Maea (Dec 9, 2009)

rtz said:


> Read page 6:
> 
> http://media3.ev-tv.me/cellcare.pdf
> 
> No BMS needed or required.


Well, I guess that settles it then, huh?


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## okashira (Mar 1, 2015)

sholland said:


> I have been a long-time lurker (and learner ) here on the forums, and have successfully converted my own car, a 1996 Honda Civic, which I have driven almost every day in my commute for the last 8 months and 8000 miles. It has been flawless, but it helped me to understand the BMS (or lack of) solutions that are available to the DIY community. You can see more information about my build here.
> 
> I have been working on a new BMS designed to target the DIY community.
> 
> ...


I'm interested. Post on endless-sphere. I think you'll see a better response.


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## dougingraham (Jul 26, 2011)

sholland said:


> Doug, you can't tell me every cell in your pack is under the exact same influence as all others. Especially in conversions the pack is distributed all over the vehicle, and there will be at least some temperature delta across the cells. The car was simply not designed from the start to be a BEV.
> 
> What's the biggest factor affecting cell impedance? Temperature. The cells under the hood are likely getting cooler than those in the trunk, and in time, the charge on those cells will drift apart... at lower temperature they simply do not have the same current carrying capacity as the rest. Those cells at higher temperature can (due to higher I^2R heat dissipation) run the risk of thermal runaway. This will all be visible to the BMS before it goes too far.


I have two battery boxes. One under the hood and one in the back. So yes I have a temperature differential. All cells are in series. All amps flow through all cells identically. Ions move from anode to cathode or cathode to anode. You cant have more or less ions moving around in the cells just because of a temperature difference. The only difference the temperature makes is the voltage. But the SOC remains in lockstep. Properly operating LiFePo4 cells don't drift. They don't self discharge either. Now I can't claim that the cells in the center of the pack don't get hotter and because of this that they don't age faster, they probably do. But so far I am not seeing anything significant. Early on I was looking at them every couple of weeks, then it became every month and then several months and only when it was nice out. Last time I checked it was last summer when I got back from EVCCon when I abused my pack with back to back 1000 amp blasts down the drag strip on a 90 degree day. I will probably check it again when the weather warms up in a couple of months. Or not, as so far I have seen no reason to do so.

Just make certain that your BMS doesn't place any kind of unbalancing load on the cells. Even a few microamps will unbalance the pack over the life of the pack. A few milliamps of imbalance will require some sort of active balancing. The other big thing is to make certain that however you attach your BMS to the cells that it does not affect the integrity of the cell interconnects. For example, a wire connected to a ring terminal under a terminal bolt is asking for that bolt to come lose. Solder the wire to the interconnect strap instead. And don't forget to include some form of current limiter. A fuse for every wire is ideal but you can probably get by with a resistor to limit the current.

It is your car and your investment in batteries and ultimately up to you as to how you want to manage them. I am just pointing out that there is another way that is working for a lot of people that has saved considerable time and money. These projects are big enough that anywhere you can save time helps you to complete them. And few are rich enough to ignore the additional cost of the BMS.


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## sholland (Jan 16, 2012)

All good points, and I 100% agree on your mounting advice. I do see screw mount connections quite often at OEMs though, so perhaps there is required types of screws/lock washers to make it work reliably. I haven't paid much attention to the exact part numbers used...


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## kennybobby (Aug 10, 2012)

Tesla uses the same TI chip for monitoring and protection plus implemented the cell balancing feature, but they are using a hot chemistry and have every cell touching a liquid heat exchanger tube, individual cell fuses, etc.
They use spot-welded wires for each of the 6 Cell collector plate voltage lines running to a BMU in each module, and then the modules are connected in series to make either the 60 or 85 kwh packs. The master BMS board has not been revealed anywhere that i have found.

Monitoring voltage and temperature is a noble task, balancing can be tricky. i believe that Tesla has resistor bleed balancing circuits both for balancing at the top and to bring the overall pack capacity down in the event of single cell failures to allow continued (safe) operation until the pack can be swapped out.

Good luck with the design, it you build them and they work and the price is right then there will be some folks that will want to try it out.


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## sholland (Jan 16, 2012)

Here is a 3D plot, and a photo of 2 in the enclosure base...


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## PThompson509 (Jul 9, 2009)

Hollie Maea said:


> Well, I guess that settles it then, huh?


Yeah, where's my popcorn anyways?


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## sholland (Jan 16, 2012)

The Kickstarter campaign has been launched!

It's taken far longer than expected to get through all the reviews at Kickstarter, but we feel taking the time to reach out to those interested and incorporate your feedback was well worth it. With your help (and some luck), this will be just the beginning!

Best Regards,
Stephen & Stephen

Please take a look at:
https://www.kickstarter.com/projects/1009074214/the-professional-grade-battery-management-system-b


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## bwjunkie (Jul 31, 2013)

Thanks sholland, for your idea and keeping the idea going. I am a believer in the DIYer BMS need. Maybe the other posts happened before the fire took place. The BMS is an important double check, in many scenarios, and considering we are talking about potentially burning your garage to the ground, I'd say it is a valid opinion to want one.
I frown on the added complexity of a BMS, and went without for 6 months, but I've got one now and am more than happy to have it.

Did you post about quiescent current or is that not a factor in your design?

josh


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## rpress (Dec 9, 2015)

It looks pretty close to what I need for my upcoming project. So did I get this right, the full MMB source code will be released if successful?

The BMSC isn't quite what I want, I'd like it to integrate the J1772 and CAN bus charger control as well. There won't be source code for this, correct?


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## Hollie Maea (Dec 9, 2009)

Well, in the time since you started this thread, Jack "No BMS needed or required" Rickard burned down his shop due to discharging and charging a pack without BMS...

Good luck on the kickstarter.


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## dcb (Dec 5, 2009)

but it is incredibly tasteless to use the abuse of a testing battery as an excuse to sell BMS's. They pushed an overdischarged pack back into service, anything that could have monitored just the pack voltage (without draining it itself) would have saved it.

In fact the monitoring equipment itself occasionally causes the overdischarge, ruining the pack.

Lets not be complete asshats and use EVTV's misfortune for personal agendas.


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## sholland (Jan 16, 2012)

rpress said:


> It looks pretty close to what I need for my upcoming project. So did I get this right, the full MMB source code will be released if successful?
> 
> The BMSC isn't quite what I want, I'd like it to integrate the J1772 and CAN bus charger control as well. There won't be source code for this, correct?


Yes, the source code for the MMB will be provided. I have some simple Arduino code I can also using the chipKIT Max32 which has built-in CAN support. 

Charger control, SoC and all the other higher level stuff is included with the BMSC, but source code will not be provided there. It would not be of much use anyway as you would need special tools and software to program the ECM anyway.


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## Hollie Maea (Dec 9, 2009)

dcb said:


> but it is incredibly tasteless to use the abuse of a testing battery as an excuse to sell BMS's. They pushed an overdischarged pack back into service, anything that could have monitored just the pack voltage (without draining it itself) would have saved it.
> 
> In fact the monitoring equipment itself occasionally causes the overdischarge, ruining the pack.
> 
> Lets not be complete asshats and use EVTV's misfortune for personal agendas.


You know what? Jack has spent the last five years calling anyone who uses BMS a moron and anyone who sells BMS a fraud. 

So no, I'm not going to go easy on him just because his anti BMS religion bit him in the ass.

There's no "misfortune" involved with what happened to him. He overdischarged the pack, and one or more cells went into reversal, because they weren't as balanced as he thought, and he had no way of knowing. Then he charged the pack up using false assumptions about how many good cells he had in series.

All of these issues are solved with BMS. Jack has been using his bully pulpit to convince everyone else not to use BMS. So no, I don't feel particularly sorry for him.

Edit: And no, I'm not trying to "sell BMS". I'm not the thread starter here. Not everyone is just trying to trick people into buying stuff. You've been watching too much EVTV.


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## dcb (Dec 5, 2009)

my point is that there are a lot of ways to manage a pack, and a lot of different situations, and budgets and etc. This wasn't a BMS failure per-se, it was a procedural issue, and there are plenty of "BMS"s that wouldn't have made a single difference.

"ooh fire" is just more politics/scare tactics. It had nothing to do with the bms, anymore than it had to do with a multimeter.


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## sholland (Jan 16, 2012)

If anyone is going to CES I will be in the TI booth showing an isolated active balancing BMS solution...


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## Moltenmetal (Mar 20, 2014)

Sorry, but watching that pompous ass burn down his shop was a serious schadenfreude moment for me. I have no skin in the game either- other than thinking that a BMS is minimal and essential safety equipment for any large Li ion battery pack. Doesn't mean you can't get away without dead cells or a fire for a long time before it happens unless you have a BMS- some people manage. But nobody is that vigilant forever.

In no way am I implying that active cell balancing doesn't come with its own problems, or that BMS aren't a potential failure mode in and of themselves, especially if they are the only protective tool used. But a properly designed system with BMS is very, very much safer and more worry free than one without.

I wish sholland well with his project, especially if he offers a means to shut off the shunt balancing and keep only the alarm trips that really matter.


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## sholland (Jan 16, 2012)

Moltenmetal said:


> Sorry, but watching that pompous ass burn down his shop was a serious schadenfreude moment for me. I have no skin in the game either- other than thinking that a BMS is minimal and essential safety equipment for any large Li ion battery pack. Doesn't mean you can't get away without dead cells or a fire for a long time before it happens unless you have a BMS- some people manage. But nobody is that vigilant forever.
> 
> In no way am I implying that active cell balancing doesn't come with its own problems, or that BMS aren't a potential failure mode in and of themselves, especially if they are the only protective tool used. But a properly designed system with BMS is very, very much safer and more worry free than one without.
> 
> I wish sholland well with his project, especially if he offers a means to shut off the shunt balancing and keep only the alarm trips that really matter.


The shunt balancing current on the MBB is very low (~90mA @ 4.2V), and only enabled when requested by the host. There is no automatic algorithm included. However, the source code for the board will be provided so you could add that yourself if so desired. 

The primary focus of the project is to provide a reliable monitor (ADC sampling) and protector (redundant OV, UV comparator based monitoring) functions with robust CAN communication at a reasonable price.

I only mentioned active cell balancing as I design BMS systems for all kinds of applications... all with very different requirements. The one I will be showing at CES is an example of a BMS that has the power to also be the 12V DC-DC as well.


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## dcb (Dec 5, 2009)

fyi, active balancing is probably way over the top on an ev, considering they don't seem to go out of balance on their own (though some "bms" circuits cause an imbalance).

I mean that if one of your cells is that short on capacity, just replace it. if you have one cell that is much higher in capacity, it won't make much difference in range anyway. If half your cells are low capacity, you will need a ridiculous amount of transfer current capability.

I was a little surprised to see it mentioned on the "professional" kickstarter, it is kind-of a newbie feature, like when you first start looking into bms design.

couple Q's:
How much current does it draw, and does this unit draw the same current regardless if it is connected to 3 or 6 cells? Does it draw equally from each cell within a module? I didn't see an answer to the "quiescent current" yet.

What is the resolution at 14 bits? It doesn't jibe with the 1mv statement. What is the min/max cell voltage.

Is there any way to precisely capture all cell voltages at the same time along with the current (for more accurate IR measurements)? (looking at the bq76pl536a datasheet, I'm guessing not)

What is the module behavior when cell voltage is already low, and the module is offline and is the only remaining load? (i.e. the rest of the system is off to conserve power, perhaps because the pack voltage is so low after running various microcontrollers and gadgets for a couple weeks/months while waiting on your new shaft coupler, so the dc converter is offline as well)

what is the module behavior if an open bar occurs exposing cell leads to reversed pack voltage?

edit: do you have any field data, i.e. how much these sort of things actually do active balancing after initial balance (and was it done in error due to temporary temperature differences?)


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## sholland (Jan 16, 2012)

I think some clarification is needed. 

The Kickstarter board does not implement active cell balancing. I only mentioned this as it is another project I am also working on and demonstrating at CES if someone happens to be there and wants to chat. We can separate the discussion of the features and merits of an active cell balancing solution to a separate thread, or PM me if you want more information.

Current consumption... I have tested the power consumption, and with the bq76PL536A attached to cells and in sleep mode and the MCU shutdown, standby current is ~18uA. With the MCU powered up and the bq76PL536A in sleep mode, the consumption from the cells is ~149uA. Consumption is the same if it is 3 or 6 cells.

Regarding your questions about resolution and accuracy... You can see the specs for the bq76PL536A-Q1 at http://www.ti.com/product/bq76pl536a-q1. It samples with a resolution of ~305uV and is accurate to ~1mV in the typical operating range.

Of course all cells can be sampled at the same time. A broadcast CAN request to the entire stack will start all boards converting at virtually the same time. Immediately following that the host can request the pack voltage and current from the IVT-MOD sensor we include in our system bundles. A stretch goal for the project is to design our own add-on pack voltage and current sensor in the same form factor as the MBB.

An open bus bar between modules or an open bus bar with just a single unstacked MBB is no issue, but an open bus bar between channels on the same MBB in a stack would be destructive, as the open would have the potential of reverse full pack voltage. This issue is the same in any OEM pack in vehicles today. Other systems would likely also be damaged in that failure mode. 

As I mentioned, all functions are enabled by the host, so no locally self-enabled balancing unless you modify the provided source code to do so.

I work for a major semi designing and supporting BMS ICs specifically for EV/PHEV applications, and this project is an implementation of what we would advise our customers designing their own BMS. The Kickstarter is meant to be a way to share a robust, professionaly designed BMS solution at a reasonable price.

I don't understand how you can say active cell balancing is a "newbie" feature. It is a complex circuit and not something a "newbie" could implement.


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## dcb (Dec 5, 2009)

According to the datasheet, the conversion times are a function of the number of cells being read, therefore the readings are NOT simultaneous, nor could they possibly be synchronized to a current reading. It isn't a big deal, just wondering what you mean by "professional".

reporting the micro-controller current demonstrates a lack of understanding of my question. You have module level dc converters drawing from another dc-dc converter drawing from the pack. The 1st conversion is out of your control, but the second one isn't. You should have quantified the power requirements of all the hardware under various conditions, that would be professional, right? Every lead on the thing is a sink or a source to some degree, please expand on that in detail. I can't write a professional front end for it with appropriate safeguards without knowing what it is. Clearly you have arbitrated safety to the open source community.


I mean it is a "newbie feature" in that everyone starts there, wanting to incorporate it, then eventually realizes when they look at the bigger picture that it is a waste of time/money/etc.

So, do you have DIY usage data? Most of the failures I've seen were exactly unattended small loads, while it was waiting for some longer term external event to happen (i.e. parts), fwiw. Which is why I want to ensure this doesn't exacerbate the problem, esp since people are praising it as a solution to that problem for no apparent reason.


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## sholland (Jan 16, 2012)

dcb said:


> According to the datasheet, the conversion times are a function of the number of cells being read, therefore the readings are NOT simultaneous, nor could they possibly be synchronized to a current reading. It isn't a big deal, just wondering what you mean by "professional".
> 
> reporting the micro-controller current demonstrates a lack of understanding of my question. You have module level dc converters drawing from another dc-dc converter drawing from the pack. The 1st conversion is out of your control, but the second one isn't. You should have quantified the power requirements of all the hardware under various conditions, that would be professional, right? Every lead on the thing is a sink or a source to some degree, please expand on that in detail. I can't write a professional front end for it with appropriate safeguards without knowing what it is. Clearly you have arbitrated safety to the open source community.
> 
> ...


Did I offend you somehow with my calling this a professional solution? I only state it as such, as the basic building blocks of this system are based on systems that my partner and I have designed and supported for years at actual automotive OEM and pack integrator customers. Apparently only you can have some expertise in BMS design considered "professional"?

The total conversion time for the PL536A sampling 6 channels is 42us, and all MBBs will get the command with a couple of us of each other. This is actually one of the fastest BMS IC solutions out there... I said virtually identical, and this is what it is. The lowest I have ever had a customer ask for all samples including pack voltage and current measurements is within ~2ms. So ~2ms is perfectly acceptable for any OEM (ie. "professional") system, and with the MBB we can sample everything well within that window.

The current consumed on the 5V input to the board when enabled is ~100mA, though is one of the areas we are currently optimizing and should see that reduced. 

There will be user's guides and manuals available for it in due time. Some of the documentation is already available on request for those that are serious.

BTW, there a many customers that require active cell balancing for their particular applications. Different horses for different courses... Many are in production and you may not even know they were there...


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## eldis (Sep 3, 2013)

Damn, why does BMS systems always cause so many emotions?

What sholland did here, is that he went through all the trouble and pain to develop and offer a BMS of his own design, for very reasonable money. He is not getting rich on this, he is not hiding any facts, and even offers some of his code for people to use and modify.

Now, is his system professional? Let's try to tick some boxes:
Does it use modular approach, instead of horrible noisy single unit solution? - YES
Is the communication interface isolated to keep good separation between HV and LV? - YES
Is he using automotive certified components, with external temperature range? - YES
Is the measurement system based on professional analog front end? - YES
Is the balancing centrally managed? - YES
Is the communication interface designed to operate in high EMI present in EVs? - YES

Is it using off-the-shelf arduinos? - NO
Is it bodged together using chinese voltmeters? - NO

I challenge people having "professional" after market BMS systems to open them, post high res photo, and then we can talk component quality. If I find a single commercial temperature grade chip in it, it is not professional at all. Even without looking on anything else in the system.



dcb said:


> You claimed to have gotten community feedback, there is zero evidence of that. Even now you resist feedback.


He did get a feedback, I was among the people he contacted and asked for review of his solution, and I surely provided one. I know that I was not the only one, as other reviews were already present there.

I have pretty much all OEM battery monitor systems from production cars on my table. I did teardowns and reverse engineering on most of them. This includes the Tesla BMS (which is by the way operating on exactly the same principle). If there is an interest on the forum, we can go through all of them and look how BMS's are done when people are serious.

Sholland, please don't judge this forum based on strong and unjustified hate of one individual, I'm delighted to have a TI application engineer here with us on the forum. At CERN we cooperate with many silicon manufacturers and their product engineers on making our accelerator systems as safe and robust as possible.

Even though I don't know if this system doesn't have any flaws, it sure is not in the approach taken.

So, if you are ready to present real arguments about his design, let's discuss it like professionals, and keep our emotions where they belong.


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## GerhardRP (Nov 17, 2009)

I have deleted some unfriendly and useless posts. Please stick to the topic. TheOP wants to discuss a BMS design, not argue about the advisability of using a BMS>
GerhardRp


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## dcb (Dec 5, 2009)

eldis said:


> Is it bodged together using chinese voltmeters? - NO


Edit, this was being referenced before the deletions

Just to clarify, I have no particular attachment to such devices, nor do I put much faith in the word "professional", except that it is about making money, and DIY is not.

If you can afford better meters, go for it, make it as "professional" as you like. But lets continue the comparison off of real world points, and not merely subjective "ivory tower" ones, because if it works it works.

Cost: less than the minimum donation to the kickstarter, which only gets you a "feel good".
ease of installation: 3 wires, perfect for testing/development, good enough for lots of other cases.
phantom loads/unbalanced loads: none/none vs untested/dont care.
comes with display: yes vs depends, looks like extra.
skills required: able to connect 3 wires and be able to drive a car without running it to empty vs untold wires and peripherals and protocols, or donation levels. 
features: pack/half pack voltage and balance on demand, completely disconnected the rest of the time for maximum battery isolation/protection, longest shelf life. No special steps added for storage.

professional: who cares? this is diy.


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## eldis (Sep 3, 2013)

dcb said:


> Just to clarify, I have no particular attachment to such devices, nor do I put much faith in the word "professional", except that it is about making money, and DIY is not.
> 
> If you can afford better meters, go for it, make it as "professional" as you like. But lets continue the comparison off of real world points, and not merely subjective "ivory tower" ones, because if it works it works.
> 
> ...


I didn't get the reference (why did you decide to comment on one particular point?) Then I went through the posts and found that there was a reference to your BMS built using something like that. There is nothing wrong with a solution "that does the job". The important is always to clarify what the job is. I see a clear shift in this forum towards something I would call professional builds (I agree that professional can mean different things for different people). For me that is that people use high power AC motors, complex electronics to make the instrumentation clusters work, nice and clean wiring, OEM chargers, CAN bus control and so on. 

Now if someone wants to build a car with forklift motor and lead batteries in the trunk, I'm not going to criticize that, as long as the person understands what he's building, and what he expects from it, nothing wrong with that. There are many people who would never even put a BMS in a car (one less actually, as was mentioned few posts ago). For me a BMS system is as important as a good charger or inverter. A good BMS will not burn your car down, it will even prevent you from doing that. A sufficient BMS works like a temperature gauge in an old car. If you pay attention, your engine will not explode. Then there are BMS that will eventually melt your batteries, no matter what you do.


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## dcb (Dec 5, 2009)

I wouldn't call it a bms (what does that mean anyway?), just a two level on demand voltmeter.

Nor do I hate, I just don't sugar coat.


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## AntronX (Feb 23, 2009)

sholland said:


> Full SoC and contactor control, via integration of a system/pack controller, would come at a higher cost for those interested


Very nice OEM quality system you made. But I think its too expensive for DIY crowd. Make complete turnkey system for 36 cells with tiny 4" LCD touchscreen (Tesla Roadster like) and basic usable GUI included for about $1000. Basically, if I am going to spend money on BMS system, it has to be drop in ready no extra programming required. You are competing with miniBMS that can be had for <$800 ready to go. Factory electric cars are getting so cheap that converting your own car to EV make less and less sense from financial point of view.

Edit: Also, why are you placing each BQ76PL536A on it's own board with own micro controller, dc-dc, isolation ic? The datasheet says you can daisy chain up to 32 of them for 192 cells without galvanic isolation and control the whole string with one MCU. While that sounds impractical, why not place at least 3 of them on the same board with one host MCU? This would save 2/3 of the cost of supporting components and allow one board to run 18 cells.


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## sholland (Jan 16, 2012)

AntronX said:


> Very nice OEM quality system you made. But I think its too expensive for DIY crowd. Make complete turnkey system for 36 cells with tiny 4" LCD touchscreen (Tesla Roadster like) and basic usable GUI included for about $1000. Basically, if I am going to spend money on BMS system, it has to be drop in ready no extra programming required. You are competing with miniBMS that can be had for <$800 ready to go. Factory electric cars are getting so cheap that converting your own car to EV make less and less sense from financial point of view.
> 
> Edit: Also, why are you placing each BQ76PL536A on it's own board with own micro controller, dc-dc, isolation ic? The datasheet says you can daisy chain up to 32 of them for 192 cells without galvanic isolation and control the whole string with one MCU. While that sounds impractical, why not place at least 3 of them on the same board with one host MCU? This would save 2/3 of the cost of supporting components and allow one board to run 18 cells.


These are all good points and we did consider these options. Most of the features in this particular BMS design came from my own experience converting my own car. This pointed out some key differences from a typical OEM BMS implementation.

While the bq76PL536A does have a stacking interface, it is really only possible to implement it if the stacked ICs are all very close to each other, e.g. the pack is constructed all together in a single enclosure and very close together. Most packs in EV conversions cannot be designed this way as the car was really designed for an ICE first, then we are trying to make batteries fit, instead of any OEM EV which has a chassis designed specifically to accommodate batteries. As a result there can be long stretches of inter-IC communication in an environment not designed to accommodate a relatively sensitive communication signal. For this CAN was needed, which then adds a MCU per stacked element.

The choice of 6 channels only was just as a small building block to accommodate all the various series cell combinations. Most EV conversions are simply try to fit as many series cells in as many books and crannies as possible.

Another concern was to offer a sealed enclosure. Many EV conversion packs are not enclosed and exposed to the environment. We tried to find a good off the shelf solution, and none are really perfect, however the closest we came is with one from a company called New Age (the S-373717). While the lid does not have the openings for our headers, one of our stretch goals is to either have New Age designed a lid specifically for 2 of our boards side--by-side or 3d print one. The reason for the right-angle CAN connectors is to either fit 2 MMV boards nbext to each other, or some other accessory board yet to be designed.

I was also planning to create another board that would sit beside these to do pack voltage and current sensing, or maybe also a CAN to WiFi bridge board. A major cost in the full system is the IVT-MOD pack voltage and current sensor. If we could replace that with our own small board that would be great.

Another stretch goal is to increase the number of channels. Going to 12 or 16 channels right away might have priced out many smaller or odd series cell count packs. There are several options to implement a higher cell count, with multiple 6 channel devices or a larger cell count such as the recently released bq76PL455A-Q1 16 channel device. Some of the newer ICs are in high demand so lead times simply ruled them out.

The miniBMS are cheaper (for now) but really are very expensive for the features that are provided. The Orion BMS is really a more valid comparison, but is even more expensive than our solution. The Orion also requires all cell sense connections to come back to a central box which is virtually impossible in most EV conversions.

At the lowest level of jst purchasing the MBBs only, we are close to the target price you mention. With enough quantity ordering (the bulk of the cost due to assembly) we can reach some lower price points that comment close. We have also tried to stick with the lowest cost assembly options we could find while keeping the work being done in the USA. We could definitely cut the cost in half by going to China, but that doesn't create jobs here. 

We are also providing the source code so you can modify the MBB to do whatever you want... A degree of freedom no one else is offering.

To summarize, there are compromises in this design that will not make it a perfect fit for every application, but it can support almost all EV conversion applications with these compromises. Making it more cost effective for particular applications may rule it out for others... I hope that makes sense...


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## jddcircuit (Mar 18, 2010)

sholland said:


> If anyone is going to CES I will be in the TI booth showing an isolated active balancing BMS solution...


Thanks
I will come by and check it out

Jeff


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## dimitri (May 16, 2008)

sholland said:


> I don't consider the miniBMS as a very robust solution. I have seen many examples of damaged packs and even fires caused by those boards.


Hi Steve, you just couldn't keep it civil and factual, it's a pity, I had such respect for your work, even considered joining your Kickstarter to support a fellow EV enthusiast. They don't teach you at TI to respect competition?

miniBMS is my registered trademark and what you did there was slander, which I take very seriously. I strongly recommend public apology, retraction of your slander and learn how to respect people even if you don't agree with them. Don't stoop to the level of your critics, you just became one of them yourself. Congratulations on becoming less human.

You would think that fires and damage caused by my boards would be first reported to me or at least on this forum, and yet I don't know of any. They must be reporting directly to you, right?

Indeed there are damaged boards and cells, but in every case its caused by improper installation, not following instructions, and general lack of understanding of batteries and electrical circuits. 

miniBMS is the simplest design for a good reason, to allow average DIY EV builder to protect their pack with minimal set of skills needed. And even then I see people do things that make hair stand on the back of my head. And here you are with a DIY system which requires advanced skills and you can't even defend it without slander of others. Just wait till you sell some of your boards and support calls start to come in, that's the real test of your work.

Over the past 2 years I designed a BMS using TI AFE chips, which has very similar specs as yours, but tailored to specific OEM partner I work with. Having experience supporting miniBMS in DIY EV market I would never consider offering my advanced BMS in the same market, it would be a support nightmare from hell.

Good luck with your campaign, Steve. I really mean it.


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## sholland (Jan 16, 2012)

dimitri said:


> Hi Steve, you just couldn't keep it civil and factual, it's a pity, I had such respect for your work, even considered joining your Kickstarter to support a fellow EV enthusiast. They don't teach you at TI to respect competition?
> 
> miniBMS is my registered trademark and what you did there was slander, which I take very seriously. I strongly recommend public apology, retraction of your slander and learn how to respect people even if you don't agree with them. Don't stoop to the level of your critics, you just became one of them yourself. Congratulations on becoming less human.
> 
> ...


My apologies Dimitri. The miniBMS is a good solution for some and I should not have repeated reports I have been told or contributed to spreading that kind of information. 

I am also a customer of yours... I love your EV Display 

I have to admit I am new to this product promotion side of things, and frankly I'd rather just stick to the engineering I know...


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## sholland (Jan 16, 2012)

I am honestly just trying to help contribute to the community... I am not trying to cause a fight or harm to other products, just to clarify that there is a niche that is not currently served that our product can try to serve.


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## dimitri (May 16, 2008)

sholland said:


> I am honestly just trying to help contribute to the community... I am not trying to cause a fight or harm to other products, just to clarify that there is a niche that is not currently served that our product can try to serve.


Your system is on par with Tesla's BMS and you should be very proud. As Tesla's battery modules become more available on DIY market your BMS could be a direct fit if you also offer compatible wiring harness or detailed instructions how to connect your MBB to Tesla's module.

Just realize that you can't please everyone and don't have to respond to every ignorant comment and don't have to defend your prices. Those who expect Chinese price on US made product are not your audience, just ignore them. Only engage in respectful and technical discussions. Most people here who understand your work are readers, not posters. If you read the forum long enough you know who the trolls are, just ignore them.

just my 2 cents worth


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## sholland (Jan 16, 2012)

dimitri said:


> Your system is on par with Tesla's BMS and you should be very proud. As Tesla's battery modules become more available on DIY market your BMS could be a direct fit if you also offer compatible wiring harness or detailed instructions how to connect your MBB to Tesla's module.


That sentiment has been exactly the feedback we have received from beta sites. When looking for a solution that could serve a small volume EV production or commercial test pack, the current list of commercially available solutions we're not considered appropriate for one reason or another, and the solutions that were acceptable all required significant NRE or were too expensive. The other alternative was to hire staff and design their own, but that is even more expensive and has risks of its own. Our offering served their needs perfectly, even with the compromises we thought necessary to try to make it more useful and accessible for the DIY community.

In fact, one of our beta customers is doing exactly that... Our MBB has replaced the Tesla BMS on a used Model S pack they purchased. A custom mount adapter and harness adapters could be made (the customer 3d printed these on their own) but I think that market is rather small...

I am hoping this can expand to multiple versions: higher channel count, versions with active balancing, pack voltage and current sense, communications bridges or other accessory boards.


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## dcb (Dec 5, 2009)

couple more q's.

It looks like the BQ76PL536A has a lot of comm support built in, and every board has a c2000 ($10) ti specific processor on it in addition. 

Is the c2000 really necessary?

Can't it be something less obtuse and costly, and less obviously self-serving, like ARM, if it really is needed? It isn't a terribly encouraging choice for "volunteer" support, esp DIY. Not that it is impossible, but every project has some random cpu and toolchain, not really that helpful in the diy space.


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## rpress (Dec 9, 2015)

@dcb Are you actually interested in buying the product? For some reason you just feel the need to pick it apart. I wonder what aggravates you so much about this.

I see no problem using the C2000, in fact I use them at my day job. The TMS320F28030 is < $4 in 1k quantity.


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## dcb (Dec 5, 2009)

Are you a shill? You just joined the forum, how many open source projects are you working on? It just seems a little smelly if he uses eldis, the one person he knows who is using ti to represent the whole "community".


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## eldis (Sep 3, 2013)

dcb said:


> Are you a shill? You just joined the forum, how many open source projects are you working on? It just seems a little smelly if he uses eldis, the one person he knows who is using ti to represent the whole "community".


Sorry, what? I'm getting a bit lost in this..
dcb, you got me there. Guilty as charged, I indeed use TI. In fact here is a bit more extended list of manufacturers of microcontrollers and programmable logic that I also regularly use:
Xilinx, Atmel, Analog Devices, Renesas, Microchip, Maxim, ST, Freescale, Lattice.. From the top of my head. Maybe there are others, I'll come back to you on that.


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## rpress (Dec 9, 2015)

dcb said:


> Are you a shill? You just joined the forum, how many open source projects are you working on?


Wow, you found me out. You're quite the clever one.

My point is that if you don't like it, just leave it alone. You don't need to be so toxic about everything.


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## dcb (Dec 5, 2009)

eldis said:


> Sorry, what?


Apparently you represent CERN, not the "diy community" as well.

And none of this has ANYTHING TO DO WITH MY ORIGINAL QUESTION ladies.


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## eldis (Sep 3, 2013)

dcb said:


> Apparently you represent CERN, not the "diy community" as well.
> 
> And none of this has ANYTHING TO DO WITH MY ORIGINAL QUESTION ladies.


I don't represent anything and anyone. I can't as a matter of fact. My opinions are my own. Sorry to ruin your day.
Maybe if you posed your questions without attacking other users, didn't wrap them in hate and ignorance, people would be more keen on answering them.

I agree that C2000 might be unnecessarily powerful for this use, and it could be done with a cheaper microcontroller. Most likely you could shave off at least a dollar or two on each board. For me the most annoying thing with using C2000 is the 16bit char. That architecture just won't do 8b. This can be a pain in the ass if you have to port legacy code that uses structures that are converted into data streams (as it will address them as 2B instead with 1B). A trap for the young players. Tesla is using 8051 clone on their slaves to control this BQ chip, but they don't use CAN between units.

I've seen people using arduinos for things like egg timer, where a 555 for a fraction of the cost would do the same thing. This is not a big overkill, so no need to make a drama out of it. Please, make yourself a tea or coffee, stretch your legs or whatever works for you before you answer. I'm not interested in continuing this debate and making this thread a mess.


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## sholland (Jan 16, 2012)

Ultimately, the choice of C2000 was simply that my partner and I know those devices, the programming environment and have coded for them in the past. I have used STM32, Stellaris (before and after TI bought them) and many others, but these are just the devices with CAN that are still around. If I really wanted to shave every little bit of cost, I could move to a dsPIC, STM8 or perhaps ATMEGA but I am not immediately familiar with those. There a bunch of other choices that aren't as easy to get through the normal distribution channels, but again, we'd be throwing away a lot of work and trust in that work that we already have.

The code we have based the MBB on has been running in customer test packs for years so there is a lot of testing we would lose if we ported it to another device...


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## dcb (Dec 5, 2009)

Thanks, I understand, just too many platforms from a not-for-profit position to be wild about it, if not downright grumpy. stm32 would have been nice though  Arduino would be the floodgates to hell.

I assume the c2000 is mostly for the module addressing and can<->spi message converting?

How is addressing handled? Are they pre-programmed, or some sort of uid scheme, or manual addressing? Mainly, can you discover the nodes automatically and how many cells are connected (and which cells are on which node?), or do you have to do some mapping at setup? 

Do you have a brief module command set cheat sheet? Or is the default firmware a work in progress?

Thanks Again.


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## sholland (Jan 16, 2012)

Yes, the C2000 is currently just used for CAN to SPI and 2 ADC channels. It is quite powerful, so users could write their own local algorithms or additional commands. 

Our current plan is have the MBB boards pre-programmed with a serial number at production and a unique CAN ID. The user will need to add them one at a time, sending a broadcast request for any register (usually the status information) to see the assigned ID. Forever after, that ID will be how that board is addressed.

We could add the ability to write the values over CAN to change them.

This is one area where there may be further development. 

The configuration tool can be any CAN tool. I personally use CAN hacker http://www.mictronics.de/projects/usb-can-bus/ with a VScom USB serial adapter http://www.vscom.de/usb-to-can.htm, which supports virtual comm ports. Maybe even a terminal would work, but CAN hacker is free... There are many other solutions. We have a manual for the CAN commands used to control the MBB which is attached. The CAN protocol is based on SAE J1939 with extended frame IDs (29-bit addressing), and the boards will ship with 250Kbps data rate, but 500K is also supported. I have attached a dbc file that has all the currently supported CAN commands.

Another possibility is to add programming over CAN, but this may require special licenses and maybe some higher level PC software with the correct features to support it.

There are a few things we'd still like to optimize in the software, namely getting the power consumption down and maybe adding some additional commands.

I hope this helps. Please ask any questions you might have.


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