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Help me choose the right learning path to building my own Battery Management System
#1
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?
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#2
Have you read this thread?
https://secondlifestorage.com/t-TI-BQ769...ect-thread

Also there is Stuart Pittaways bms
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#3
First of all the list you set our for bms is not for befinner but advanced users. Secondly a bms does not itself regulate charging but it can send Commando or in some way controll the Charger

IF you want to do above and have a Good product you need many months, most likely 8-12. Just the prefase collecting information is 2weeks minimum.

IF you just want to throw something together perhaps 2months.
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#4
(07-20-2019, 11:34 PM)Korishan Wrote: Have you read this thread?
https://secondlifestorage.com/t-TI-BQ769...ect-thread

Also there is Stuart Pittaways bms

Thanks! Yeah, I did. I looked at both of them but the circuits are over my head.

(07-21-2019, 10:37 AM)daromer Wrote: First of all the list you set our for bms is not for befinner but advanced users. Secondly a bms does not itself regulate charging but it can send Commando or in some way controll the Charger
Thanks. Yeah, sending commands to the charger is what I meant, commanding the charger based on a modified CC-CV algo
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#5
(07-22-2019, 04:37 AM)evbkz Wrote:
(07-20-2019, 11:34 PM)Korishan Wrote: Have you read this thread?
https://secondlifestorage.com/t-TI-BQ769...ect-thread

Also there is Stuart Pittaways bms

Thanks! Yeah, I did. I looked at both of them but the circuits are over my head.

(07-21-2019, 10:37 AM)daromer Wrote: First of all the list you set our for bms is not for befinner but advanced users.

I agree with daromer. If these are over your head and you don't understand them, then the project of building your own is beyond your technical capabilities. Take the time to review and read a lot of information about these devices and how the different parts work together before attempting building your own. You will save yourself a lot of headaches, and wasted time and destroyed devices, in the end.
Adam Welch has used, built and explained Stuarts' bms so you could check out his youtube channel to get some more details about it.

I was in process of building my own bms as well based off the BQ769x0 series. I stopped because I still needed to learn a little more about electronics before I continued. I'll be re-attempting it later this year.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#6
(07-22-2019, 12:41 PM)Korishan Wrote:
(07-22-2019, 04:37 AM)evbkz Wrote:
(07-20-2019, 11:34 PM)Korishan Wrote: Have you read this thread?
https://secondlifestorage.com/t-TI-BQ769...ect-thread

Also there is Stuart Pittaways bms

Thanks! Yeah, I did. I looked at both of them but the circuits are over my head.

(07-21-2019, 10:37 AM)daromer Wrote: First of all the list you set our for bms is not for befinner but advanced users.

I agree with daromer. If these are over your head and you don't understand them, then the project of building your own is beyond your technical capabilities. Take the time to review and read a lot of information about these devices and how the different parts work together before attempting building your own. You will save yourself a lot of headaches, and wasted time and destroyed devices, in the end.
Adam Welch has used, built and explained Stuarts' bms so you could check out his youtube channel to get some more details about it.

I was in process of building my own bms as well based off the BQ769x0 series. I stopped because I still needed to learn a little more about electronics before I continued. I'll be re-attempting it later this year.

Thank You! Yep, I know I need to learn a lot, i'm confused about where to start and what to learn. That's why I wanted to know a good learning path. Cool, I will check out his channel.
Would be great if you share how you did/plan to do it! Thanks!

I started reading TI's datasheets and I am trying to implement the basic schematics from their reference design. I plan to split this project into different milestones and achieve one by one. That will make the progress easier and organised. Hope I get a lot of help from you guys.
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#7
(07-24-2019, 04:38 AM)evbkz Wrote: Thank You! Yep, I know I need to learn a lot, i'm confused about where to start and what to learn. That's why I wanted to know a good learning path. Cool, I will check out his channel.
Would be great if you share how you did/plan to do it! Thanks!

I started reading TI's datasheets and I am trying to implement the basic schematics from their reference design. I plan to split this project into different milestones and achieve one by one. That will make the progress easier and organised. Hope I get a lot of help from you guys.

I did a LOT of reading, watching many hours of youtube vids, and asking questions. Also, I worked off anothers design to understand how it worked. The TI datasheet shows a basic schematic of the components needed to make it function. That is what i used to start learning how it all worked.

A brief list of YT Channels I'm subscribed to that have helped a lot:
  • Adam Welch
  • AddOhms
  • Andreas Spiess
  • bigclivedotcom
  • DIY Tech & Repairs
  • Electronoobs
  • GreatScott!
  • How To Mechatronics
  • ItKindaWorks
  • Julian Ilett
  • Marco Reps
  • Mega Mechatronics
  • SDG Electronics
And I'm sure I may have missed somebody, but that'll get ya started.
evbkz likes this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
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#8
(07-24-2019, 12:04 PM)Korishan Wrote:
(07-24-2019, 04:38 AM)evbkz Wrote: Thank You! Yep, I know I need to learn a lot, i'm confused about where to start and what to learn. That's why I wanted to know a good learning path. Cool, I will check out his channel.
Would be great if you share how you did/plan to do it! Thanks!

I started reading TI's datasheets and I am trying to implement the basic schematics from their reference design. I plan to split this project into different milestones and achieve one by one. That will make the progress easier and organised. Hope I get a lot of help from you guys.

I did a LOT of reading, watching many hours of youtube vids, and asking questions. Also, I worked off anothers design to understand how it worked. The TI datasheet shows a basic schematic of the components needed to make it function. That is what i used to start learning how it all worked.

A brief list of YT Channels I'm subscribed to that have helped a lot:
  • Adam Welch
  • AddOhms
  • Andreas Spiess
  • bigclivedotcom
  • DIY Tech & Repairs
  • Electronoobs
  • GreatScott!
  • How To Mechatronics
  • ItKindaWorks
  • Julian Ilett
  • Marco Reps
  • Mega Mechatronics
  • SDG Electronics
And I'm sure I may have missed somebody, but that'll get ya started.

Thanks a lot Smile
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#9
Hey there, I was wondering... Why do you want to do the BMS yourself? It's easily the most difficult and complicated part of an ebike. Also, there are hundreds of commercial options that are available for pretty cheap. I don't know how much you value your time, but as they said, designing a BMS will cost you thousands of $$ in man hours, not even including the materials cost for what you are trying to do.
The reason some people on this forum are trying to design their own is because they are cheap - they don't want to spend $700 on a battrium system. That's because the Battrium system is really the only option available for a powerwall user. However, for ebikes and scooters, there are at least a hundred different companies that make BMS systems for them already.

Honestly the price that battrium is asking for their system is worth it. They don't really have any competition, the market is really small, and they spent a huge amount of time and money designing and refining their system.

For ebike / scooter bms - all these companies are competing so many solutions are available for under $100

There are several open source designs already for the exact use case you have described. IF you look at the TI chip thread linked above, you'll see that they were insufficient for our home use, so we looked at designing our own.
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#10
(07-30-2019, 02:10 AM)Mikethezipper Wrote: Hey there, I was wondering... Why do you want to do the BMS yourself? It's easily the most difficult and complicated part of an ebike. Also, there are hundreds of commercial options that are available for pretty cheap. I don't know how much you value your time, but as they said, designing a BMS will cost you thousands of $$ in man hours, not even including the materials cost for what you are trying to do.
The reason some people on this forum are trying to design their own is because they are cheap - they don't want to spend $700 on a battrium system. That's because the Battrium system is really the only option available for a powerwall user. However, for ebikes and scooters, there are at least a hundred different companies that make BMS systems for them already.

Honestly the price that battrium is asking for their system is worth it. They don't really have any competition, the market is really small, and they spent a huge amount of time and money designing and refining their system.

For ebike / scooter bms - all these companies are competing so many solutions are available for under $100

There are several open source designs already for the exact use case you have described. IF you look at the TI chip thread linked above, you'll see that they were insufficient for our home use, so we looked at designing our own.
Hey there! I want to do it myself because I want to learn how to do it. I have lot of free time so I wouldn't mind spending more time on this.

Thanks
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