BMS "steam release" post

Hi,
This post is a bit "steamy", so I warn you beforehand. It's just that I feel kind of hopeless, so I thought to ask the community, and I am almost 100% sure that someone on ES had the same needs and found a solution.

I am still using my A123 20Ah prismatic cells without BMS for 4 years by now. They still have almost the same capacity since I bought them second hand.
These are precious cells and I want to protect them from going outside their voltage limits. In those 4 years I had them manually balanced like once per year.
Once in a while I try to find a BMS for them for the day the first cell will age faster than the others, and without immediate action it would cascade a catastrophe.
Unlike controllers, batteries, motors, BMS is a total *shit* (sorry for the expression) to browse for information.
It's a jungle of chinese makers with BMS's where most of them will do more damage to your battery rather than protect it, open source projects (but where can I actually BUY them??), and in addition the LiFe chemistry has a special 3.3V and their huge sustainable 100A discharge / 80A charge rate. The search was doomed. I just gave up.
And yes, I can buy miniBMS. It's just that my wallet is not that deep, considering I have 24S battery on bike, 25S on another, 8S on another project, and so on...

So I thought, let's compromise. Let's take Arduino which has 6-8 analog inputs, and add an input extension shield like this one so I can read all 24 cells into the same Arduino board:
http://www.dadaelectronics.eu/shop/arduino/analog-input-extension-shield-for-arduino-r-ka12-kit

This is the only product I found that can just "multiplex" analog inputs and come with the proper libraries without being complicated as hell, and the only store which sell it (all other places said it's discontinued) ask ridiculous amount to ship it over here. I would pay that "premium" shipping price, but if all shops have that shield discontinued, maybe it's for a reason.

Anyhow, with such shield, I can monitor all 24 cells, and show the information about the voltages on a screen of my choice at real time. This will not have an LVC or HVC, but it can visually alert me or "siren" me to warn me when I approach the limits.
Why not have LVC and HVC? I will need to find a proper power mosfets for the currents, and wire everything myself considering I am not very good with designing circuits that involve transistors.

Oh well, you can use a relay, right? Nope, at 100A and 80V DC, those would be super expensive and HUGE.
And so I thought, are there "electronic" relays where a mosfet is replacing the actual actuator and it's driven by a simple control circuit for those of us who don't have an academic electronic degree from university?

And then I had another idea: I already had my circuit breakers protecting me when one of my controllers became a FULL short-circuit in the middle of a ride. Household circuit breakers are small, reliable, and cheap.
It could have been easily converted into a relay (half one, at least), if there was one that had a coil that can receive external current on the magnetic element and trip the connection at will. That external current would be delivered to that circuit breaker from the arduino via a conventional relay.
I then thought of a Residual current breaker, and perhaps they can actually be that "one direction relay" I am looking for?

You say I didn't look enough for BMS's? Well, I did. I even got one which is supposed to be for LiFe. The bastard let the cells "fry" to 3.8V before it agrees to cut them off! (3.6V is the HVC)
This is why I don't trust those factory made BMS's. They have no faithful documentation, if at all, and they can't be trusted when you depend on them.
This is why I recommend everyone to buy E-bike gear ONLY at Grin. Too bad they don't sell BMS's, but maybe for a reason...
Only Grin has faithful documentation and a strong-back for their products.

That is all...
Sorry for the length, but I hope you understand me.
I will be happy if you can point me for a solution with either of the options.
For example, if you have LiFe battery, a BMS which works, obey the special LVC/HVC of LiFe, and is reliable - I will be happy to hear about it.

Thanks.

Yes, steamy topic indeed.

Personally, I think with a LFP bank looked after by a knowledgeable and diligent owner "no BMS" can be perfectly fine.

Really that term is just a nearly useless catch-all of functionalities, so best to break down specifically what you are afraid of, and how to achieve each bit of protection

safely and reliably

meaning when the protective gadget(s) fail (not if), their mode of doing so does not cause more problems than what it was trying to protect against.

Personally I think DIY efforts - as in custom programming a MCU - are more likely to be fraught than branded quality OTS units designed by professional engineers.

1. balancing automatically, usually at the top, end of charging stage

not a protective function, also often better implemented with other device types, including dedicated "non-protective BMSs"

voltage related protections

2. HVC - protection against overcharging

cell-level, if top-balancing means you don't trust your balancing

Pack-level only should protect against a charge source going rogue.

Actually controlling the charge source, based on cell-level is ideal but expensive.

3. LVC, only one required to actually be mounted on the bike while in use.

A CAv3 and/or many controllers should be primary on this function at the pack level, BMS there as a failsafe.

With a top-balanced pack, careful observation and calibration of the pack level cutoff can obviate the need for cell-level based protection, as long as you aren't trying to get every last Ah of range.

But this is an area where an OTS cheap BMS might be useful. The ones with BT comms to Android, or their own display. . .

I would want an actual cutoff, not just alarms that require my noticing.

If you pay more for high ampacity, maybe upgrade the FETs to genuine / better quality, then no external relay needed.

I'd prefer a robust branded contactor myself, then no need to run the current through the BMS. Maybe 3x3" and $60, is that a lot afayc?

Fusing can then provide OCP.

Adjustable voltage setpoints are critical, the fixed setting ones are always wrong afaic.

Just for giggles, OCP is already mentioned, but over-temp and under-temp IMO **should** be included in "a BMS" claiming to be complete.

thunderstorm80 said:

So I thought, let's compromise. Let's take Arduino which has 6-8 analog inputs, and add an input extension shield like this one so I can read all 24 cells into the same Arduino board:
http://www.dadaelectronics.eu/shop/arduino/analog-input-extension-shield-for-arduino-r-ka12-kit

Click to expand...

Unfortunately the problem with this type of device (along with many ADCs) is that the inputs are often single ended (referenced to common ground), or even if they allow differential inputs, the input voltages are still constrained to within (or very close to) the power supply range (e.g. 0-5v). So the first cell is fine at ~3.3v, but every other cell in the series pack (6.6v, 9.9v, 13.2v, etc) is far above the allowable input range for each channel. Magic smoke will be released.

You could possibly use voltage dividers, but it adds complexity and reduces accuracy somewhat.

On a positive note, there are dedicated BMS ICs to fulfil the purpose you're after. Just as a random example, check out something like BQ77PL900. You could connect one (or more) to an Arduino via i2c.
http://www.ti.com/product/BQ77PL900
More work to develop a circuit around one than an off the shelf shield, but also much more capable of what you're after.

john61ct said:

3. LVC, only one required to actually be mounted on the bike while in use.

A CAv3 and/or many controllers should be primary on this function at the pack level, BMS there as a failsafe.

With a top-balanced pack, careful observation and calibration of the pack level cutoff can obviate the need for cell-level based protection, as long as you aren't trying to get every last Ah of range.

But this is an area where an OTS cheap BMS might be useful. The ones with BT comms to Android, or their own display. . .

I would want an actual cutoff, not just alarms that require my noticing.

If you pay more for high ampacity, maybe upgrade the FETs to genuine / better quality, then no external relay needed.

I'd prefer a robust branded contactor myself, then no need to run the current through the BMS. Maybe 3x3" and $60, is that a lot afayc?

Fusing can then provide OCP.

Adjustable voltage setpoints are critical, the fixed setting ones are always wrong afaic.

Click to expand...

Hi, I appreciate your answers, but they are the kind of answers I find on google and here on ES. This is why I wrote this post in the first place
I am looking for an ACTUAL solution... I already know the background of what kinds of BMS's are available and the concepts of over current, low voltage cutoff's pros and cons. No need to repeat them...
I want a kind of product which is actually SOLD somewhere on the planet, as part of an online store, and it can either be modular or I can choose the model I want for my needs. Just like you can do on Grin, or on em3ev stores. (and sadly em3ev doesn't ship to my country)
I saw you mentioned an actual product - OTS Smart Battery Pack Manager, and then I started googling it. I couldn't find one shop/store where I can actually see different models/how is it being sold (it's modular), and I am really TIRED from doing the full google searching and learning for every person that comes up with a certain BMS company they recommend. (and they don't write on the same forum message if they have experimented with it or not). If I wanted to do that for every BMS post on ES, I will need to retire from work.

serious_sam said:

thunderstorm80 said:

So I thought, let's compromise. Let's take Arduino which has 6-8 analog inputs, and add an input extension shield like this one so I can read all 24 cells into the same Arduino board:
http://www.dadaelectronics.eu/shop/arduino/analog-input-extension-shield-for-arduino-r-ka12-kit

Click to expand...

Unfortunately the problem with this type of device (along with many ADCs) is that the inputs are often single ended (referenced to common ground), or even if they allow differential inputs, the input voltages are still constrained to within (or very close to) the power supply range (e.g. 0-5v). So the first cell is fine at ~3.3v, but every other cell in the series pack (6.6v, 9.9v, 13.2v, etc) is far above the allowable input range for each channel. Magic smoke will be released.

You could possibly use voltage dividers, but it adds complexity and reduces accuracy somewhat.

On a positive note, there are dedicated BMS ICs to fulfil the purpose you're after. Just as a random example, check out something like BQ77PL900. You could connect one (or more) to an Arduino via i2c.
http://www.ti.com/product/BQ77PL900
More work to develop a circuit around one than an off the shelf shield, but also much more capable of what you're after.

Click to expand...

Hey!
Thanks for the very HELPFUL answer!
I didn't think about the common ground thing, and yes - I would have fried my Arduino (and perhaps short-circuited some battery cells).
So I guess the Arduino idea goes off the line, unless I am willing to install 24 of them and make them communicate with each other...
I don't think I will go the path of your second suggestion. It makes the electronics too complicated and I am afraid of doing too much of DIY in that field, since we talk about lithium battery cells which are hooked up...
I guess then my option is to just find a factory made BMS for LiFe chemistry, and find someone here on ES that can VOUCH for it.
Good luck?

Man, you sure come off as entitled with your complaints, are you trying to discouraging responses?

https://youtu.be/nUBtKNzoKZ4

If a post does not meet your exact requirements maybe just ignore it, may be useful to others in the community googling after.

By actually responding with your preferences may help narrow things down, trigger more recommendations.

OTS = Off the Shelf

Chargery and the Bluetooth ones are often used and well recommended

BT threads: https://www.google.com/search?q=site%3Aendless-sphere.com%2Fforums%2F+bms+bluetooth

Xiaoxiang type
Jiabaida Technology
Dongguan Jiabaida Electronic Technology Co., Ltd.
SZLLT

software
https://endless-sphere.com/forums/viewtopic.php?p=1515412#p1515412

Ali seller JBD Battery PCB Board Store
https://s.click.aliexpress.com/e/OstYsoYY
https://s.click.aliexpress.com/e/qUAMAkA8

john61ct said:

Man, you sure come off as entitled with your complaints, are you trying to discouraging responses?

Click to expand...

You kinda asked for it though. You could have just directly answered his question to start with (like you eventually did, thank you), rather than multiple posting about tangential/unrequested information.

john61ct said:

https://s.click.aliexpress.com/e/qUAMAkA8

Click to expand...

This type of bluetooth BMS that john61ct posted is common on this forum. Does the job and seems like there are relatively few issues people have had (especially when set up correctly). I have been running one for several months now successfully. I like that you can change parameters, and montior cell voltages and functions from a smart phone.

hv alarm
https://endless-sphere.com/forums/viewtopic.php?f=14&t=40628&start=25

serious_sam said:

john61ct said:

Man, you sure come off as entitled with your complaints, are you trying to discouraging responses?

Click to expand...

You kinda asked for it though. You could have just directly answered his question to start with (like you eventually did, thank you), rather than multiple posting about tangential/unrequested information.

john61ct said:

https://s.click.aliexpress.com/e/qUAMAkA8

Click to expand...

This type of bluetooth BMS that john61ct posted is common on this forum. Does the job and seems like there are relatively few issues people have had (especially when set up correctly). I have been running one for several months now successfully. I like that you can change parameters, and montior cell voltages and functions from a smart phone.

Click to expand...

That BMS is for standard Li-Ion, only up to 14S (although I could place two), and doesn't have the capability for the peak discharge/charge currents I have. My peak regen (if I am going downhill really fast) is in the order of ~3500W, which translates to 40A.

The bluetooth BMS has even an inferior current capabilities. It's still impressive, though.
That's why I consider just aiming for a monitoring (and alarm) solution rather than a fully fledged BMS.

Think the “Ant” 300A smart bms does what you want. You can set any voltage limits.
https://a.aliexpress.com/_BT3U6r
It’s also in the bluetooth bms thread. I’ve used one for a year, no issues. I like the possibility to read out individual cell voltages, screen is also a plus for me.

thunderstorm80 said:

That BMS is for standard Li-Ion, only up to 14S (although I could place two), and doesn't have the capability for the peak discharge/charge currents I have. My peak regen (if I am going downhill really fast) is in the order of ~3500W, which translates to 40A.

The bluetooth BMS has even an inferior current capabilities. It's still impressive, though.
That's why I consider just aiming for a monitoring (and alarm) solution rather than a fully fledged BMS.

Click to expand...

That generic bluetooth BMS comes in different flavours: Different cell count. Different chemistries. Different current limits.

You could do what I did and replace the mosfets with genuine quality parts and run a 50A unit at 150A comfortably.

larsb said:

Think the “Ant” 300A smart bms does what you want. You can set any voltage limits.
https://a.aliexpress.com/_BT3U6r
It’s also in the bluetooth bms thread. I’ve used one for a year, no issues. I like the possibility to read out individual cell voltages, screen is also a plus for me.

Click to expand...

Wow! That is perfect!
Thank you so much..
That's what I wanted - to hear from someone who already have the experience with a certain BMS that works.
Here's what I wanted to ask:

1. It looks like the charger and the controller go through the same negative terminal, right?
2. The BMS has the control of allowing/stopping the connection via the negative side, while the positive goes directly from the battery to the load (and charger) ?
3. I understand this BMS also perform cell balancing at the entire spectrum range and not just at the upper voltage cut ?

thunderstorm80 said:

still impressive, though.
That's why I consider just aiming for a monitoring (and alarm) solution rather than a fully fledged BMS.

Click to expand...

Hence the importance of clarifying discussions on precisely what protections, at which "level" are given what priority.

I have never yet seen "a BMS" that ticks all my boxes, even those costing thousands.

And I don't (yet) trust from-scratch DIY solutions.

So in that middle ground, we target each bit of functionality and seek known-good

as possible, if not reliable at least with do-no-harm failure modes

OTS components for each.

For a pack costing thousands, I would also want multiple independent levels of protection, being a belt & suspenders kinda guy.

IMO this is a great reference design by German engineer/researchers, from the institute that developed the MP3 standard a few years back,

pretty well documented, interesting to read through, even if not implementing

https://foxbms.org/

That BMS looks interesting. I have a 24s pack with 1,480 cycles 6.5 year's 24,000 miles no BMS just have 4-. 6s sense wire. Bulk charge as two 12s. And only balance only once a year or so

999zip999 said:

That BMS looks interesting. I have a 24s pack with 1,480 cycles 6.5 year's 24,000 miles no BMS just have 4-. 6s sense wire. Bulk charge as two 12s. And only balance only once a year or so

Click to expand...

You talk about the ANT BMS right?
Yes, definitely.
It seems like THE solution for A123 guys like us.
And it can handle charge currents of 50A which also give some head room.
I am just wondering if it's not too good to be true?
I mean, the unit is smart, cheap, but it doesn't look physically large enough to have the components needed to handle such gigantic currents, and the leading "-" wires seem a bit thin.
Or am I wrong?

Yes, you are wrong :wink:

I’ve run mine at 350-400A (though only for short periods of time)

larsb said:

Yes, you are wrong :wink:

I’ve run mine at 350-400A (though only for short periods of time)

Click to expand...

Could I ask you few questions about the device that will probably be relevant to others? (like 999zip999)
1. I understand you use the 300A model? I think the 100A model would be enough for me, if it can handle short current burst in the order of 100-110A?
2. Were you able to find out if there are weight/size differences between the 100A and the 300A model (For example)?
From the pictures the only difference is the guage of the leading wires, while the device has the same size. (which is very strange...)
3. There is an ACTUAL (working) app that let you setup everything in English and not just on paper?

FYI and yes not from my own anecdote , but reading over thousands of posts in many dozens of forums, most reco the JBD/LLT BMSs over the ANT

LLT Power, SHEN ZHEN LI LU TONG ELECTONIC TECHNOLOGY

https://www.lithiumbatterypcb.com/product-instructionev-battery-pcb-boardev-battery-pcb-board/ev-battery-pcb-board/smart-bms-of-power-battery

john61ct said:

FYI and yes not from my own anecdote , but reading over thousands of posts in many dozens of forums, most reco the JBD/LLT BMSs over the ANT

LLT Power, SHEN ZHEN LI LU TONG ELECTONIC TECHNOLOGY

https://www.lithiumbatterypcb.com/product-instructionev-battery-pcb-boardev-battery-pcb-board/ev-battery-pcb-board/smart-bms-of-power-battery

Click to expand...

Now that's an interesting debate - whether the ANT is better or LLT.
The LLT one you just showed, can work with up to 30S while the ANT work with up to 24S, so the LLT can be usable for a 25S battery I have on a second e-bike.
LLT also give more specifications, including dimensions, peak currents (vs continuous), while for the ANT I had to google almost everything.
BUT, on the LLT they say the HVC for LiFe is 3.75V and the recovery is 3.6V, while a cell shouldn't be charged more than 3.6V!
They say it's adjustable on the app, but I wonder why they aim by default to cut-off LiFe at 3.75V and standard Li-Ion at 4.25V instead of 4.2V

john61ct said:

FYI and yes not from my own anecdote , but reading over thousands of posts in many dozens of forums, most reco the JBD/LLT BMSs over the ANT

LLT Power, SHEN ZHEN LI LU TONG ELECTONIC TECHNOLOGY

https://www.lithiumbatterypcb.com/product-instructionev-battery-pcb-boardev-battery-pcb-board/ev-battery-pcb-board/smart-bms-of-power-battery

Click to expand...

Could very well be the case. I am only a single user and quality can’t be judged from this.

For me so long as it's adjustable who cares about the defaults.

Winston used to reco going that high for his LFPs.

Also how many in series is just a model detail, they all have dozens to choose from.

The critical factor for me will always be consistency in build quality, longevity & reliability.

Suspicious at such low pricing by default, but I guess can keep spares on hand, never put too much trust in one gadget.