Help me choose the right learning path to building my own Battery Management System

[evbkezzz]

Hey there!

I am from a completely non-technical background. I decided to build my own e-bike and this month has been a lot of learning... I learnt many new things calculating power requirements, mechanical calculations, battery pack sizing, motor controllers, etc.

I am now in the stage of selecting a Battery Management System for my build. This area interests me so much that I plan to build one myself from scratch.

My BMS should have the following features:
-Overcharge Protection
-Overdischarge Protection
-Overvoltage
-Undervoltage
-Thermal Runaway
-Cell Balancing
-Charging (implement a modified CC-CV algorithm based on a research paper)
-SOC
-SOH
- Secondary protector fault detection
-Total voltage, voltages of individual cells, minimum and maximum cell voltage
-Current in or out of the battery
-Maximum charge current as a charge current limit (CCL)
-Maximum discharge current as a discharge current limit (DCL)
-Energy [kWh] delivered since last charge or charge cycle
-Internal impedance/resistance of a cell (to determine open circuit voltage)
-Charge [Ah] delivered or stored
-Total energy delivered since first use
-Total operating time since first use
-Total number of cycles
-Average Temperature, Temperature of each cell (switching on air cooling when temperature exceeds a value)
-Communicate all data to be nicely visualised on a smartphone using bluetooth

I looked up on the internet and understood that a Fuel Gauge can monitor these things. I decided to go with TI BQ78350-R1, with a TI BQ76930 AFE. Is it a right choice? Are there any others that I should look into? Open for suggestions. My battery pack is a 6S3P pack.

I think, these require a MCU to work and I haven't decided one yet. Open for suggestions.

I looked up on the reference designs but I am not able to understand anything. It is all too much for me RN.

Should I use a single cell gauge or a multi-cell gauge? Are there any advantages of one over the other?

My questions is how do I start? What all things I should learn before I can design a BMS myself? I have completed All about circuits Vol I book and have now started reading The Art of Electronics.
I can put 6hr/day. How long would it take me to build circuits like that? What learning path should I follow?



Thanks a lot!

TL;DR: What should be the learning path for a beginner in electronics to be able to design Battery Management System from scratch?

 

[john61ct]

Well looking at the existing related Open Hardware / FOSS projects out there would certainly be a part of it, the goal being reverse-engineering their design process, figuring out why **those** components were selected.

Or a shortcut being to start with one and "fork" it to meet your needs.

Personally I would break down some of that list and modularize separate components, no need to have a single complex monolithic device.

ElectroDacus and foxBMS are two I've skimmed through, I'm sure there are many more.

Please keep posting back to this thread as your approach evolves and you discover good resources.

 

[jonyjoe303]

chargery bms8t(cost 100 for the 100 amp version) does almost everything including SOC, battery temp, balancing on your list except the bluetooth and will handle your 6s pack. I tried to build my own bms for my 4s solar system and got nowhere with it. Like some one mention, just use existing circuits and connect them together until you get something that works. For balancing I would just use active balancers and then concentrate on something else. Over/under voltage can be done with a 6 dollar overvoltage protection relay. I would also use audio alarms for over/under voltage. You can buy over temp circuits relays for less the 5 dollars.

But for the fuel gauge I recommend the tk15, they have different ones that can handle different amp ratings, the 50 amp version cost less then 25 dollars and can handle 8-80 volts. You program you battery amp capacity and then it counts amps in/out. Works with any battery li-ion,lifepo4,lead acid.
"DC8-80V 50A Battery Coulometer TK15 Professional Precision LiFePO Battery Tester"

 

[john61ct]

I am assuming the point is a fun entry into learning electronics.

If the goal is just to get BMS functionality, then yes, purchasing OTS components is infinitely more practical.

 

[evbkezzz]

Well looking at the existing related Open Hardware / FOSS projects out there would certainly be a part of it, the goal being reverse-engineering their design process, figuring out why **those** components were selected.

Or a shortcut being to start with one and "fork" it to meet your needs.

Personally I would break down some of that list and modularize separate components, no need to have a single complex monolithic device.

ElectroDacus and foxBMS are two I've skimmed through, I'm sure there are many more.

Please keep posting back to this thread as your approach evolves and you discover good resources.

Thanks, I was thinking the same. I looked up on the internet and just some idea about how the TI's ICs are connected in the board.
Sure, will keep my progress posted in this thread. I initially planned on modularizing too, but later dumped that idea as it will get complex. Making multiple boards communicate and things like that. But, let me know if I am wrong.

chargery bms8t(cost 100 for the 100 amp version) does almost everything including SOC, battery temp, balancing on your list except the bluetooth and will handle your 6s pack. I tried to build my own bms for my 4s solar system and got nowhere with it. Like some one mention, just use existing circuits and connect them together until you get something that works. For balancing I would just use active balancers and then concentrate on something else. Over/under voltage can be done with a 6 dollar overvoltage protection relay. I would also use audio alarms for over/under voltage. You can buy over temp circuits relays for less the 5 dollars.

But for the fuel gauge I recommend the tk15, they have different ones that can handle different amp ratings, the 50 amp version cost less then 25 dollars and can handle 8-80 volts. You program you battery amp capacity and then it counts amps in/out. Works with any battery li-ion,lifepo4,lead acid.
"DC8-80V 50A Battery Coulometer TK15 Professional Precision LiFePO Battery Tester"

Thank you the suggestion, but the whole point of the thread is to learn to do it myself, i am sure there are better OTS products if I am looking to purchase one.

I am assuming the point is a fun entry into learning electronics.

Yep!Correct!