Noob question, what does diyBMS cover and what not?

I have been looking at the youtube videos and reading some forum posts the past few evenings about diyBMS but so far I have not found documentation about what a diyBMS exactly does and what it does not do to see if it would be useful for my needs.

Did I miss some general overview documentation somewhere ? Please RTFM me :slight_smile:
If I click on docs on this forum there is rather disappointingly nothing about diyBMS.
If I go to there are a lot of videos about specific details or incremental changes, but no high lever overview.
Are there other sources ? (sadly, off grid garage has not yet covered diybms :slight_smile: )

Anyway, so far I think the idea is the following, do correct me if I am wrong! :
A minimum setup is composed of a controller board and either a monitor board per battery cell or a 16s monitor board.
The monitors gather the cell voltages.
The controller board gathers and displays info from the monitor(s), and has rules you can program to switch 2 relays and to talk to an inverter (not sure if also to eg an mppt charge controller ??, it almost has to to prevent overcharging )

Optional modules at the moment are a current shunt and a passive balancer board, and a temperature sensor module.

There are however no protection mechanisms in this BMS.

There are no mosfets that will prevent charging and discharging under certain conditions.
There is no current limiter.

The only way this BMS can protect against overcharging or charging < 0 degrees is if it can talk to your charge controller.
And against draining your batteries if all your loads are behind an inverter the BMS can talk to, not if you have loads directly connected to the battery.

To conclude;
I was looking for a BMS for an offgrid campervan setup but from what I now understand this BMS is not intended for such a use case, at least till there is a mosfet module the controller can talk to.

If I am wrong and there are already solutions for that I would love to hear it, I would really like an open source BMs.

And if it can somehow talk to a Victron mppt charge controller with I would also like to hear how.

Welcome, Bram, to the OEM forum.

I can answer only one of your questions:

This is because diyBMS isn’t an OEM project. It’s actually @stuart’s project and OEM only provides the forum for discussion.

Hopefully, having made a “@mention” of his name, he should get a reminder to look at your post and respond.

Thanks for the clarification Robert.
Since diyBMS is a kind of an open hardware/source energy monitor, and the github page refers to this site, at first sight it looked liked it could belong to something called openenergymonitor.
So I was confused when I started reading the (very nice btw :slight_smile: ) emontx4 documentation but could not find how diyBMS fitted into the picture.

I can understand that - and of course, it doesn’t, at least directly. If you’ve put together your own battery and inverter/charger, then of course emonCMS would be able to tie everything – emonPi2 measuring grid & PV inputs and EV & house consumption - together.

Hi @BramEPC thanks for the interest in DIYBMS, as Robert mentioned this isn’t an official openenergymonitor project, but I was given permission to create a section/topic on their forum for chat/assistance etc.

Do you have any specific questions about the project? Most of the background is on the YouTube videos/channel that I run.

Hi @stuart , my main questions would be if this bms is able to be a replacement for eg a jk bms.
I think it is not, since it is missing all of the protection functionalities at this moment and seems intended for monitoring only ?
With protection functionalities I mean things like stop charging when a cell reaches a voltage limit, or when the cell temperatures get too high or too low, …

Those features are there, but they are not the same as the JK BMS which uses MOSFET’s to control the charge/dischage.

DIYBMS is a modular system, similar to how Batrium system works. It has a range of voltage, temperature and current sensors to allow it to trigger various rules - those rules can be tied to a physical relay on the controller to fire a trip shunt device for example - killing the power.

The BMS is also capable of instructing Victron and Pylontech compatible devices on the charging cycle, with the concept that the physical relay triggers would only get fired in emergency situations. Normally, charge and discharge is controlled by the software.

Ok that is what I suspected.

And via which route it is able to talk to an mppt controller with a interface ? I assume you need eg a pi with venos os then as an intermediary (I don’t run that so not really familiar with this kind of setup or what it is capable of).

But the mosfet setup like jk bms and others are doing seems still more flexible. Imagine for example the low temp situation, with diyBMS the only option is to tell the charge controller to not charge, but maybe there are other actors in the system that are able to accept a current (like a lead acid starter battery, heating pads for the batteries, heating element for warm water) (this is the case in my setup), so for those it is interesting to just keep generating a current from the solar panels.

The current limiter in the latest jk invertor bms is also pretty nice.

Anyway I understand those things are outside of the scope of what you are trying to do here.
And I can always try adding them myself, but I am more of an embedded sw guy than an electronics guy so for now I am going to leave designing pcb’s on my todo list for when i have a loooot of free time,

Thanks for the clarifications , and for the interesting project of course !