Open source BMS for 48V to 400V lithium-ion battery pack

[flippy]

I would like to hear your solution to this problem. Clearly you did not understand the problem.

your solution is to start your own topic and flesh out your project there. your problems do not belong in this topic.

this bms is not even rated for 900V so you cant even use it for your intended purpose. its also a stupid idea to run at such a stupid voltage.

[Solarsail]

and please stop using 1980 tacky sales tactics.

Please stop being condescending. No need for that, in particular you have not understood the issue.

pretty sure you need to stay inside the box. you have no concept of the basics,

What basics is it that I don't have a concept of? That electric potential results in a current? Please explain.

let alone be in a position to ask for crazy features that dont make sense and are only to serve you personally and nobody else.

Who gave you the authority to tell members here what they can ask or not?

And what's wrong with asking features that may "serve me personally"? Are you saying that only features that serve collectively are allowed on this forum? And you decide what issues are collective or not? Are you trying to silence me? Do you also believe that speech should be censored for example in universities?

This whole forum is about individuals talking about their own issues, and asking for help. But you come along and dictate that only collective questions are allowed?

Do you have any idea how large packs are constructed? This is not a 500 Wh skateboard pack. This is a 40 kWh aircraft pack. A lot of people are running into these issues with large packs -- but quantity of people is not the point. You are confused.

without trying to sound rude: you are not being constructive, you are being ignorant.

You have not been able to explain why my ideas are bad or "ignorant" or not constructive. Additionally you are very rude and offensive and authoritarian.

you have no clue what you are even asking or even have the understanding why it would be a bad idea.

I explained in my previous post why you were so wrong with the "one charger" idea. You don't seem to understand the basics of serial circuits or how packs are charged.

So tell what other idea of mine is "bad".

[ENNOID]

Only if that were possible. I have 6 to 9 modules permanently cabled together in series. How do I charge the modules with a single charger? By running around every three hours and re-plugging the charger? Or are you suggesting a 900V charger which will not work as you are dealing with multiple BMS in series? I will have to build a power multiplexer with 6 to 9 contactors and a controller and an enclosure and communications. For overnight charging, I will have to charge each module at the rate of 30A to 45A which the BMS cannot handle. At the BMS limit of 20A, my charge time now doubles for the entire pack.

I don't understand :/ You should probably use a single BMS in a master slave configuration like all automotive manufacturer are doing. If 2 main contactors are too heavy for your design, you can design your own master board with 1200V fets. it will end up being lighter & cheaper with all the specs you need.

[JackFlorey]

Can someone explain Flippy's comment?

Sure.

1) Safety comes from a BMS being completely separate from the load and the charger. That results in redundancy - no one failure can cause damage to the cells.

2) The BMS is usually in intimate contact with the battery. This is already a bit of an issue with passive balancing loads (they get hot, and warm up the battery unevenly.) Add a charger and the problem gets a lot worse.

[flippy]

So tell what other idea of mine is "bad".

basically anything you are planning on doing. starting with using a 400V bms in a 900V system in a PLANE. are you nuts?

start your own topic and detail your setup. its very clear you need help with your setup. but stop polluting this thread. this is not the bms you are looking for.

i will not apologize for upsetting you for the simple fact that from the very first post in this topic you have shown that you have no clue what you are talking about and is planning on taking this into the air. you need to stop right here and now and start your own topic and ask for help before you kill yourself or someone else. you need a solid wakup call and get both feet on the ground and start with some basics. for example: you dont use 400V rated components in a 900V system. hell, if something happens and the insurance company finds out they will sue you into oblivion. (providing you survived)

[Solarsail]

basically anything you are planning on doing. starting with using a 400V bms in a 900V system in a PLANE. are you nuts?

start your own topic and detail your setup. its very clear you need help with your setup. but stop polluting this thread. this is not the bms you are looking for.

Ahhhh ... so you admit to how confused you are and don't even know the basics of serial / parallel circuits. I think you should get some help as stuff that me and Ennoid discuss is way above your head. You have no solutions, except to rudely tell people to shut up.

You don't even know what the voltage of the BMS is. 400V is wrong. Ennoid, can you explain to Flippy how flipped out he is with his ignorance? Trying to collectivize and dominate a discussion that he doesn't even understand.

And no, my aircraft is not 900V. It is about 300V. So wrong again. And why can't you use his BMS in a 900 V modularized pack?

So tell me and Ennoid why I can't use his very good BMS in my power pack. Why is Ennoid's BMS not useful for me? Is it the current capacity? The S number? Do you even know what the S number denotes? He has done a beautiful job and got things right. I am just explaining my large pack multi-module issues to him and making suggestions. This said, Flippy, none of these are your business anyways.

[Solarsail]

I would like to hear your solution to this problem. Clearly you did not understand the problem.

your solution is to start your own topic and flesh out your project there. your problems do not belong in this topic.

You still don't understand the issue of charging serial modules, do you? An enhanced BMS is the right solution to this problem.

this bms is not even rated for 900V so you cant even use it for your intended purpose. its also a stupid idea to run at such a stupid voltage.

I never said my pack is 900V. I said if you put 9 modules in series you get 900V. My pack is about 300V. It is most likely 2p4s or 3p3s. Each module being 100 to 120V. Clearly you have a comprehension issue.

[flippy]

basically anything you are planning on doing. starting with using a 400V bms in a 900V system in a PLANE. are you nuts?

start your own topic and detail your setup. its very clear you need help with your setup. but stop polluting this thread. this is not the bms you are looking for.

Ahhhh ... so you admit to how confused you are and don't even know the basics of serial / parallel circuits. I think you should get some help as stuff that me and Ennoid discuss is way above your head. You have no solutions, except to rudely tell people to shut up.

You don't even know what the voltage of the BMS is. 400V is wrong. Ennoid, can you explain to Flippy how flipped out he is with his ignorance? Trying to collectivize and dominate a discussion that he doesn't even understand.

And no, my aircraft is not 900V. It is about 300V. So wrong again. And why can't you use his BMS in a 900 V modularized pack?

So tell me and Ennoid why I can't use his very good BMS in my power pack. Why is Ennoid's BMS not useful for me? Is it the current capacity? The S number? Do you even know what the S number denotes? He has done a beautiful job and got things right. I am just explaining my large pack multi-module issues to him and making suggestions. This said, Flippy, none of these are your business anyways.

this is you right?

Only if that were possible. I have 6 to 9 modules permanently cabled together in series. How do I charge the modules with a single charger? By running around every three hours and re-plugging the charger? Or are you suggesting a 900V charger which will not work as you are dealing with multiple BMS in series? I will have to build a power multiplexer with 6 to 9 contactors and a controller and an enclosure and communications. For overnight charging, I will have to charge each module at the rate of 30A to 45A which the BMS cannot handle. At the BMS limit of 20A, my charge time now doubles for the entire pack.

I would like to hear your solution to this problem. Clearly you did not understand the problem.

that you dont understand why you cant use 400 parts in a 900v setup just shows you need to learn the basics first.

please dont trow around the word "ignorance". you have no idea what my background is or even by day job. your attempt to impress me with a 40kWh battery setup does not impress me in the slightest. i build larger batteries then that on a average tuesday. (wich is my job). your whole setup is flawed from the ground up because you dont understand the basics properly. i have no issue helping you (you clearly need it) but that belongs outside this thread. that is my whole problem with your polluting this topic. this bms is not for you without some serious modifications. such a large battery is not something you want to run on a bms (or a stack of them) with a balance current of <100mA. you need active balacing around 1~2A and manual backup overrides just to name 2 things if you want to put such a battery setup in a plane.

and before you start: i have worked on batteries for planes, and they have been flying for 3 years now. safely and without any incident. and they also run on 144V, much safer and a LOT simpler to charge and maintain. making 400V wiring safe in a plane is no joke.

lives depends on this stuff, you need to get it right and nothing you said so far gives anyone the idea you -actually- know what you are doing. and no, knowing how series and parralel works is NOT a flex.

[Solarsail]

Just go yourself and visit the E-skateboard forum & you will see all requests that I received from many user about the initial BMS size...it was considered as "huge" or would not fit in most builds even when only 6x14cm...so I decided to swith the SS design to dual sided components & ended up at 6x10cm & 6x6.5 for SS-LITE which is a good improvement IMO.

They even pushed me to go with USB C which I did. They had a point.

The design for SS & SS-LITE 15S & 18 are completed & in production. The 24S version is 90% completed (second iteration), I'm now just trying to fit the whole thing on 6x10cm and testing should start in a month or so...

Well, I am strictly speaking of your 24S model. It has a much wider market than skateboards. The skateboard market will be dominated by the Chinese in due course if not already. Of course there will always be a small DIY contingent like fish in a fishbowl. But the multi-module and EV market is exploding and you have a good solution. Lots of used Tesla and Leaf packs on the market looking for a competent BMS. But these are all above 100V and multi-module. And volume is not an issue. Only in aircraft weight becomes an issue.

[Solarsail]

Can someone explain Flippy's comment?

Sure.

1) Safety comes from a BMS being completely separate from the load and the charger. That results in redundancy - no one failure can cause damage to the cells.

2) The BMS is usually in intimate contact with the battery. This is already a bit of an issue with passive balancing loads (they get hot, and warm up the battery unevenly.) Add a charger and the problem gets a lot worse.

This is Flippy's comment. Is that what he said?

do a number 2 before taking off to compensate.

or just wait until he releases his 18S and 20S models.

1) Again, I am not suggesting the power supply to be on board. I am just suggesting the CCCV function be on board!

I can see that a 5A CCCV function on board may pose a fire risk to the BMS and the cells. But is it more than the BMS itself that manages 150A during discharge and 20A during charging? Probably the li-ion cells are the largest risk factor in a module, and not the electronics. Again, a CCCV function is not the same as a power supply. The power supply remains external to the module. CCCV is the minimum circuitry needed to regulate an incoming 60V or 100V 5A current to perform the CCCV function.

Ennoid - is the CCCV function already built into the BMS? If so, then this idea is already implemented.

If this function is not already in the BMS, how difficult would it be to add a 5A switching MOSFET to regulate the current for CCCV? The PWM is already there with the STM32. The bank voltage sensor is already there. The current sensor is already here. All you need are a few capacitors, diodes, an inductor and a MOSFET. And a bit of code. It should generate no heat.

The problem of heat and weight I think arises for isolation (from other modules) and step-up (if any). Isolation being mandatory. Power is 300W or less (5A x 60V). Any ideas here? A 90% efficient circuit will generate 30W heat. Not a deal breaker for a module that weighs 20 kg and is in a 35 cm x 22 cm x 15 cm metal enclosure.

2) A non-isolating switch mode charger (i.e. CCCV function) does not generate heat.

Besides, charging for aircraft happens only when it is on the ground.

[Solarsail]

I don't understand :/ You should probably use a single BMS in a master slave configuration like all automotive manufacturer are doing. If 2 main contactors are too heavy for your design, you can design your own master board with 1200V fets. it will end up being lighter & cheaper with all the specs you need.

If I read this correctly, you are suggesting a single BMS for the whole pack of 6 to 9 modules? With 1200V fets multiplexing the balance lines from each module and the power lines? That does not sound practical.

If you are suggesting one contactor and one BMS per module, then I would like to avoid the contactor. There will have to be 9 contactors, one per module (not including the standard two contactors)

BTW, I am assuming your BMS are isolated (i.e. the I2C is isolated). If not, how do you suggest serial modules be connected to the I2C bus?

Please solve me this problem: Let's say I have two 14S modules in series. Does each module have its own SS-15 BMS? How would you simultaneously charge the modules with a single 40A 60V charger? Can this method be extended to 8 modules 2p4s?

[JackFlorey]

1) Again, I am not suggesting the power supply to be on board. I am just suggesting the CCCV function be on board!

That is the power supply. You could say it's just a low overhead switcher to minimize power dissipation - but if it regulates voltage and current it's a switchmode power supply.

I can see that a 5A CCCV function on board may pose a fire risk to the BMS and the cells. But is it more than the BMS itself that manages 150A during discharge and 20A during charging?

It's not a fire risk, it's a thermal risk.

As I am sure you know, cells charge, discharge and equalize differently when they are hot vs when they are cold. When they are hot they age faster. Their ESR is lower, so they appear to be lower voltage during charge and higher voltage during discharge. Which means that they will be balanced incorrectly during some phase of the charging.

So if you put a warm power supply on one side of the pack, then half the cells will be warm and half the cells will be cool. They will age differently, be balanced differently and share current differently. Compare that to fast charge (all the cells are warm) or very fast discharge (all the cells are hot.)

Again, a CCCV function is not the same as a power supply.

Yes, it is. It's a switchmode DC-DC power supply with voltage and current regulation. It's basically the back half of a standard 120VAC PFC charger; an input cap, a switching FET, an inductor, a diode and an output cap. The FET has ohmic and switching losses. The inductor has magnetic and ohmic losses. The caps have ESR losses. The diode has forward voltage losses. If it's an active diode, then it has the same switching losses that the primary switch has.

2) A non-isolating switch mode charger (i.e. CCCV function) does not generate heat.

You have a 100% efficient DC-DC? You're a shoe-in for a Nobel prize, then, since that's never been accomplished before.

[Solarsail]

2) A non-isolating switch mode charger (i.e. CCCV function) does not generate heat.

You have a 100% efficient DC-DC? You're a shoe-in for a Nobel prize, then, since that's never been accomplished before.

Don't have to be insulting or pedantic, if you have a point. Are you trying to make up for Flippy's gaffs?

"Does not generate heat" is not the same as 0%. Any reading of the 2nd law will tell you that 0% is impossible. What I said obviously means that relative to the object at hand, the heat is negligible.

Tell me, how much will the temperature of a 20 kg metal box of volume 12 liters rise due to a 5A switching mosfet, where the 60V DC supplied power is rectified, DC-DC converted and conditioned OUTSIDE the box? Numbers please. Have you built such a circuit? I have.

The CCCV function has conceptually nothing to do with a DC-DC switching power supply. It is an entirely different function that only applies to a li-ion pack. A li-ion charger has three parts -- AC power rectification, conversion and conditioning, DC to DC stepdown conversion and isolation, and CCCV function. You have a benchtop power supply in mind that is CV, and also has a current limiter knob to drop the voltage. Off-the-shelf power supplies generally do not have current regulation that can be controlled. Just think about this: Why would I want to bring AC line power and a 7 kW power supply into each of my nine modules?

Take any standard cheap 24V switching power supply. It does not allow for current regulation and current limitation except for short and exceptional conditions. It consists of AC to DC rectification and filtration, then a switching DC to DC step-down converter/isolater both of which generate heat. There is no CCCV function. The supplied voltage will stay approximately constant 24V and the current will vary according to ohm's law (unless the rating is exceeded). So it has a CV function but not a CC function or the ability to drop the voltage. In addition, the CV function lacks tolerance and may not be suitable for a li-ion pack in CV mode even if your cells add up exactly to 24V at 100% SoC.

In order to charge a li-ion pack, you need a CC function (and better CV regulation) which will drop the supply voltage depending on the SoC, and keep the current constant. A switching mode DC to DC step-down regulator with a low Rds at 5A and associated circuitry generates negligible heat. A IRFZ44 at 100% duty cycle will generate .0175 * 25 = 0.43 W of thermal energy. The rest of the circuit even less. Please let me know when you have calculated the temperature rise.

Cheap off the shelf power supplies are not suitable for charging li-ion packs without a CCCV function. In fact they are unable to drop the voltage.

How do you suggest simultaneously charging 18 modules each 14s11p, with the modules hard wired as 3p6s, and with no internal contactors, with just one charger? There is no common mode. Even if all 18 were in parallel, you still could not do that without each module having its own CCCV regulator. Are you suggesting we carry 18 power supplies around? Maybe you know how Tesla does this, and I am all ears. I would like to avoid timesharing the single charger and multiplexing the power.

[john61ct]

its a bms, not a charger. a charger has no business even being near the bms

I am amazed, 100% agree with this.

Now programmable CAN signalling, e.g. to control TC / Elcon chargers, that would be great.

Emus, Orion, Elithion, EPS and ZEVA all do so.

[john61ct]

.

Of course it is the OP's thread to dictate what topic diversions are acceptable

but afaic you have gone way over the usual forum netiquette line for derailing and thus devaluing a very productive and focused thread.

OK to ask for features, of course, briefly politely and succinctly.

When the project owner declines, back off, and if you want to continue that conversation, create your own thread and come back to post a link for those that might be interested.

And maybe another one asking for design assistance with your very interesting project.

We are all very lucky, creating new threads is Free!

[Solarsail]

its a bms, not a charger. a charger has no business even being near the bms

I am amazed, 100% agree with this.

Now programmable CAN signalling, e.g. to control TC / Elcon chargers, that would be great.

Emus, Orion, Elithion, EPS and ZEVA all do so.

Where have I asked Ennoid to put the power supply on his BMS board. Please supply link.

All I asked is to put the CCCV circuit consisting of a few capacitor and one inductor and one fet (the very last block of a charger) on the board and there is a very good reason for that if you are dealing with multiple modules and you wish to charge them simultaneously -- which is what EVs do.

[Solarsail]

Of course it is the OP's thread to dictate what topic diversions are acceptable

Have you even read the thread? It is not Ennoid complaining. It is Flippy dictating what I can post and turning insulting and ad hom.

I have no issues with Ennoid -- he has a great product and I plan to be one of his customers.

but afaic you have gone way over the usual forum netiquette line for derailing and thus devaluing a very productive and focused thread.

I see serial insults by Flippy is not derailing the discussion. But THREE SHORT CONSTRUCTIVE suggestions of mine, a future customer of Ennoid is somehow derailing the discussion? You haven't even read the thread. You sure are hasty to reach some (absurd) conclusions. Just like the previous guy who claimed I am asking Ennoid to put a 7 kW power supply charger in each and every of his boards. Please next time understand the discourse before adding fuel to the fire.

OK to ask for features, of course, briefly politely and succinctly.

Show me where I have been impolite in succinctly asking for three features.

Are you another one of those who condescendingly feels they own the place and pulls ersatz rules out of the thin air? Ennoid has never complained about my suggestions. Doesn't Ennoid have the right to disagree with my suggestions? Don't I have the right to know why? And yes, I will ask Ennoid for changes on his thread, and it's none your business, is it? If Ennoid wishes that I stop asking questions, he can communicate that to me, and I will stop asking.

When the project owner declines,

Ennoid answered my question. Ennoid said that 6x15 is not a good idea and I asked why. Do you already know why a 6 x 15 board is unsuitable? Well, I don't. Don't you want to know why a 6 x 15 BMS board is unsuitable? If you have no interest in this technology and Ennoid's product, why are you even here? I am not going to start a new thread asking Ennoid why his board can't be 6 x 15. How silly would that be?

And maybe another one asking for design assistance with your very interesting project.

I will be happy to discuss my unique project with Ennoid and with people who don't make fake accusations without knowing the context. But I will not be posting about my project anymore on ES, given the kind of people that police the corridors, and condescendingly harass members.

We are all very lucky, creating new threads is Free!

Yeah, I will make another thread just to ask Ennoid why 6x15 is unsuitable? Like hundreds of people reading the new thread are going to instantly know the context? Have some respect for their time. Stop being nutty like that other guy. And stop dictating the terms of use. Don't like to read my stuff, don't read it.

Let me ask Ennoid. Do you want me to stop asking questions, or do you want me to ask questions about your board on another thread?

[flippy]

Have you even read the thread? It is not Ennoid complaining. It is Flippy dictating what I can post and turning insulting and ad hom.

i am not dictating anything, i am asking clearly to start your own thread for your project. this is basic netiquette. what you are doing is topic hijacking.

I have no issues with Ennoid -- he has a great product and I plan to be one of his customers.

you should not, this bms is not right for your application without serious modifications.

Just like the previous guy who claimed I am asking Ennoid to put a 7 kW power supply charger in each and every of his boards. Show me where I have been impolite in succinctly asking for three features.

this you?

Is there any way to add an isolated CCCV charger on board? A longer board such as 6 x 15 is just fine.
Even a 5 A or 10 A charger on an HD board would be highly desirable. 5 A charging will take 10 hours for a 10p 21700. Which is great for overnight charging.

If Ennoid wishes that I stop asking questions, he can communicate that to me, and I will stop asking.

he did, quite clearly.

Ennoid answered my question. Ennoid said that 6x15 is not a good idea and I asked why.

he answerd that in the same post so there is no reason to keep asking.

I will be happy to discuss my unique project with Ennoid and with people who don't make fake accusations without knowing the context. But I will not be posting about my project anymore on ES, given the kind of people that police the corridors, and condescendingly harass members.

you should consider your own behaviour first. people with a LOT more knowledge and skill then you have already seen that you have no clue about what you are really doing or even understand the basics like how charging works but you somehow are some self proclaimed auhority while making no sense. you actually believe that a CC/CV circuit is separate from "the power supply" and state that with certainty. at that point you need a rude shock to wake you up before you litteraly kill yourself or worse: kill someone else. so not being nice is exactly the goal. you need help, a lot of help. the amount of mistakes you have already posted is greatly concerning for someone that plans to take to the sky. i dont want to see you crashing into someones house and killing an entire familly because of your misplaced confidence.

your current level of confidence does not match your knowledge or skill, this is a highly dangerous issue considering what you are planning on doing.

honest answer please: are you really a pilot? i and i dont mean gliders, i mean a acutal single/dual engine licence pilot. i am willing to bet you are not.

And stop dictating the terms of use. Don't like to read my stuff, don't read it.

we are not dictating, we are pointing out how forum netiquette works. you are sitting in the wrong room and are asking you to walk over to another room just for your project.

Let me ask Ennoid. Do you want me to stop asking questions, or do you want me to ask questions about your board on another thread?

this board is not suitable for your application in the first place so its not productive to pollute the topic even more then you already have. if you want to have a discussion on what is the right bms for you then you need to make a new topic and we are all happy to help, because you might not want to concede this: you REALLY need help. and i suggest you take it before you kill yourself or someone else if you actually start building or even flying this project.

please believe me that i am not trying to be a dick. but you do need to take a step back and get some help (from us) before you can move foward. simply because you might litteraly kill yourself if you dont.

[ENNOID]

"solarsail"

Stop this! For the second time...
Go to another thread. Your requests are simply out of scope.
This SS BMS is definitely not aimed for your project. Get a look at master/slave BMS topology with single charger instead. Sorry, but you are alone here...

The newly created compact SS versions are open source BMS with FET switches oriented toward LEV like e-bikes. This has been made clear since the beginning. Those BMS are not intended to be used above 100V with 150V absolute max for the 24S version. The target is compactness & small size while using best components/characteristics possible. This is quite the opposite of most other BMS on the market. Nobody with sufficient knowledge will try to use this BMS outside of this defined limits unless for doing some experiments.. Safety is also becoming a concern when going above 100V. Be careful with your project.

Thank you

[flippy]

back to the topic:

i have not decoded the schematic for it (sorry, kind of lazy) but is the usb port isolated (enough) from preventing a ground loop if you were to charge the battery and having it connected to the usb port? not saying its a must have in the slightest but there is probably someone that is going to use a cheap non-isolated recitfier/charger/computer with the expected "energetic" results.

prehaps a warning in the manual would be helpful to prevent some unnessary warranty claims....

a small SMD fuse on the usb ground plane might be something to add just to protect the cpu.

[ENNOID]

There are some TVS on the USB & serial to usb adapter. Never heard of any problem related to USB failure. There is no direct link between main power path & plane gnd on the SS version. Schematics are not released for SS boards.

But I agree with you there is always a risk. I paid attention to prevent this for the CAN bus by going isolated. CAN is the way to go if doing permanent monitoring while the BMS is in heavy use. An other option will be bluetooth comm.

I can imagine a situation where a user could use a common host computer connected over USB simultaneously to both ESC & BMS for monitoring while in heavy use. This could potentially create a damaging ground loop because the ESC, host & BMS might not be on the same GND reference. The host computer would then probably be the first affected. A properly rated fuse would save the host at least. I will take some time to investigate a bit into this.

[flippy]

one thing is always true when designing anything: when you make something idiot-proof the universe creates a better idiot.

just think of all those poor scopes that were blown up thanks to the user making a ground loop....

[ENNOID]

Thank you Flippy.

This is the kind of request that are useful & will be implemented. This will serve everyone using the product.

[Solarsail]

Ennoid -- I found a method to serial string the BMS and charge all modules with a single charger simultaneously. No contactors, relays, or isolation needed. No timesharing required.

[ENNOID]

No, you haven't discovered anything... It is obvious to use one single charger...this is how everyone does...

Start your own thread please and stop polluting this one.