ActiBMS - Discussion about the DIY active balancer BMS

I have just started collecting my 18650’s to build a powerwall, now coming for and RC background I understand the importance of keeping your cells balanced, and the diyBMS project really interests me. I also feel the value of being able to monitor your cells via web or mobile with some sort of alerting is awesome.

So can someone thier direct me to the details or explain here the features of this project
Things like what’s the balancing current, can this bms balance a bank where the cell packs have 80-100 18650’s in each cell pack, what is passive balance or active charge

I know that the emonpi can do this, but it would be good to be able to add a shunt and monitor the discharge and charge current of the bank, have the option to add multiple temp sensors to each cell pack especially if the packs contain a 100 individual cells you really what to measure groups of 20 batteries, also push alerts to something like push bullet which can alert you.to a temp problem or major voltage descrepancy.

I do understand there are limitations to the size of the code and things like that, but if you.look at the Batrium Watchmon you guys are so close to providing a very similar product at a fraction of the price

Keep up the good work this is awesome stuff

Hello @rolfbartels

The cell modules balance current is up to 850mA - although this drops if the modules exceed a temperature limit.

They have been used on large battery packs so 80-100 cells shouldn’t be a problem.

DIYBMS is a passive balance system - it “burns” energy to balance cells through heat and reduce the voltage on a cell. The BMS does top-balancing so balances whilst charging and tries to prevent cells going over a certain voltage.

Active balancers move energy from cell to cell to balance - this sounds ideal but is difficult to achieve in practise. Normally well designed battery cells which are well matched shouldn’t require balancing very often.

Thanks Stuart,

To clarify I am looking to build a 7s powerwall with 100 cells per 1S so 700 cells in total, can this be handled by the diyBMS ?

You will have to determine if the design is suitable for your needs as every DIY powerwall is different.

You could also split your power wall into 50 cell groups and have 7S50P x2 and then use 14 modules to provide more granular control/higher balancing.

Awesome, that would work,
Next question, you have a part list are there any services out there that offer assembly, I am in South Africa so would prefer to order the 14 modules, controller assembled, shipped to an office in the uk and then they come over every month or so would bring it onto me, I can solder find just SMD’s are not a simple.

But again I really like this project and feel it has and can have a major impact, Is there any plan to include a shunt ?

Thanks again

The main forum is over here…

https://community.openenergymonitor.org/t/diybms-v4

Plenty of people have used JLCPCB to assemble the boards - you just have to add the ATTINY and solder the sockets.

Thanks Stuart, I appreciate the help.
After some reading and more investigation I think I am either going to hold out for the v5 active balancing or, just buy an active $15 balance on aliexpress, I still will do the BMS but my just take a look at the code and disable it’s balancing options.

Again thanks for the help. I’ll be watching these threads keenly

I won’t be making an active balancer myself, this forum is a sub-project.

You won’t need to make any code changes to DIYBMS v4 to stop it balancing, just set the voltage to a high number and it won’t do anything except monitor and control relays etc.

I am interested to know if any further development has been made on this ?

The active balance isn’t my project so I’ve not been working on that.

Hi!

@stuart Thanks for initiating the diyBMS project back then, and for supporting it for so long!
@hitech95 Thank you for taking the next step and thinking about of active balancing.

I have some experience in electronics, but I am totally new to BMS, making lithium batteries and so on! However, I want to replace the two Pb engine starter batteries (12 V / 12 Ah each) on my ship with a lithium starter battery. Some of my requirements and constraints made it impossible to find a suitable solution so far. So, here I am, doing it myself :slight_smile:

As a start, I have two questions from the very top of my list:

  1. Would it be possible to use this v5 to manage LiFePO4 cells?
  2. Would it be possible to manage bigger cells (e.g. 38120) instead of 18650 cells with v5?

Thank you!

Cheers,
Willy

I’m not sure the v5 boards are progressing very much @hitech95 was working on it, I’m not directly involved in it.

Development is on hold, due to some issues with the welll know Virus.
I’ll come back on the development once, this emegency passes away.

Anyway, some progress on the code has been done. I’m unfortuantly having issues on finding a source for the active balancing chips.

With some research we could try to implement our own buck boost circuit!

Nicolò, what I like most about @stuart 's approach is using a multipurpose microcontroller instead of a specialized cell controller chip. This not only avoids “issues on finding a source for active balancing chips” but also allows for implementing features that chips made for mass markets normally don’t have (e.g. communication interface).

So, let’s do some research, yes! My present field of ‘research’ is to work through the diyBMS-passive material (v4 and earlier) to learn as much as possible about cell balancing in general. Since you are some steps ahead, you may think about other activities. Please share you ideas with us.

OT: My thoughts go out to you guys in Italy. You suffer so much from that micro monster! Keep on singing from your balconies. It’s so heart warming!

Hey @hitech95 greetings from fellow Altium user.
I was looking into the diyBMS Rev5. Awesome…
I use normally PSOC controllers in favour to Atmel Controllers. Why would take too long now.

I saw You had problems with the Memory stuff. This was one of my main reasons to switch to PSOC.
Also the PSOC has custom Logic and changeable pins. but more on that in a different text.

It might be that the PSOC4 could replace the ETA3000 and the Atmel chip. ( PSOC4 from Cypress, up to 256K memory, about 1.30$ at Mouser as 32K version)

The development software is also free to get.

I did a lot of projects with it. one version was with a custom HW designed SPI multiplexer inside the chip… Yes You can design also small custom circuits inside the chip.

I am looking to implement the active balancing into the PSOC as separate HW/SW combo. the dedicated ANALOG subsystem could handle also the measurement. I think we can do better than the 30mv stuff and You dont need the separate Serial com to the ETA3000…

It is still DIY but more advanced. Programming is different to Arduino IDE.
Dont get me wrong I use the Arduino IDE also for ESP32 and other stuff too.

It would be like the diyBMS_V5_Plus or similar.

One thing i want to know is the hookup of the BMSv5…
for instance if i have a 5S System…

Could You create a wiring diagram or pinpoint me to a ressource for it ?

I check with my friends in CN for a source for the ETA3000 chip. I think i can import and distribute the chip.

So enough for now.

Greetings to all the ppls out there… especially to You Nicoló (sorry didnt find the other accent ) and Stuart Pittaway for creating the v4 and other circuit parts

Glad people are interested in expanding other ideas.

Please do me a favour though, don’t use the diybms or v5 as part of the projects name, it will be confusing to end users.

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Okay i will look about naming.

@stuart Just found out that You are the father of the diyBMS plattform… Hats up… Awesome stuff…

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Hi @hitech95 I will keep and eye in your code as I am begining to do my own diybms but with promini boards and other components that I have in home. I not feel confident with smd soldering.
I understand that you code is compatible with ATMEGA168/328 an “similar” to diybmsv4 code, isn’t it?
Thanks

By the way,
This is NOT active balancer.