Build your own BMS

[rgleason]

Bms code resource

https://blog.ja-ke.tech/2020/02/07/l...-protocol.html

[rgleason]

Some good resources from Stuart about his DIYbms with good videos.

https://github.com/stuartpittaway/diyBMSv4

Good videos and discussion.
https://community.openenergymonitor....s-v4/11292/139

Hand assembly parts
https://github.com/stuartpittaway/di...semblyParts.md

This site was suggested for the PCB prototyping using Stuart's files
https://jlcpcb.com/RSZ

Watching some of the videos in the openenergy forum, where you can see the skill involved in soldering, I seriously doubt I could do it properly, but this is very interesting.

[rgleason]

Originally Posted by s/v Jedi

Here’s another picture from the prototyping: it has 4 INA219 modules and 3 different types of temperature sensors. This was a working BMS on a breadboard after I added control of a Blue System RBS. I used overkill, too large mosfets for that so will downscale it probably to a transistor. I’m trying to make it work with 3.3V vcc this time so we can use newer Arduinos with wifi and Bluetooth.

For temperature I have changed my mind and am now using the OneWire sensors because of their easy of use. You can buy waterproof models and slap them on and it’s done.

This certainly is an appealing approach. The cost of the REC BMS and all the Victron equipment is quite significant, $4200 with the REC BMS or TAOS BMS plus monitering being between $800-$1000.

I like the idea of using smaller LFP batteries for testing. Is your breadboard setup documented anywhere with the code and wiring? Also since I have the early prototype Wakespeed board (called smart alternator regulator) I think I could use that to charge the final set of batteries). Obviously I would have to create the BMS control for that too.

Since ABYC recommends not paralleling LFP and FLA, it appears that the X2 BMS despite it's simplicity, and the advantage that there is no boat "blackout", would not be an approach that I should take, however I have written them to see what their response is.

As you may recall, we repurposed a 3-way switch to provide a quick way of switching over to FLA to power the lights and nav equipment in the event there is a BMS shutdown, see Small Boat BMS/LFP with backup. So the X2 BMS diagram has some appeal to me for its simplicity, and the "no blackout" feature.

Should I even consider making a similar DIY Arduino BMS (using your suggestion) that uses the X2 BMS diagram and just ignores ABYC?
X2 BMS Comparisons

[s/v Jedi]

Originally Posted by rgleason

This certainly is an appealing approach. The cost of the REC BMS and all the Victron equipment is quite significant, $4200 with the REC BMS or TAOS BMS plus monitering being between $800-$1000.

I like the idea of using smaller LFP batteries for testing. Is your breadboard setup documented anywhere with the code and wiring? Also since I have the early prototype Wakespeed board (called smart alternator regulator) I think I could use that to charge the final set of batteries). Obviously I would have to create the BMS control for that too.

Since ABYC recommends not paralleling LFP and FLA, it appears that the X2 BMS despite it's simplicity, and the advantage that there is no boat "blackout", would not be an approach that I should take, however I have written them to see what their response is.

As you may recall, we repurposed a 3-way switch to provide a quick way of switching over to FLA to power the lights and nav equipment in the event there is a BMS shutdown, see Small Boat BMS/LFP with backup. So the X2 BMS diagram has some appeal to me for its simplicity, and the "no blackout" feature.

Should I even consider making a similar DIY Arduino BMS (using your suggestion) that uses the X2 BMS diagram and just ignores ABYC?
X2 BMS Comparisons

I believe it is in that yaBMS thread. It’s all very simple because these modules (voltage measuring, display) all communicate using an I2C bus so you simply wire power and bus conductors and are done.

The trick is that I, for simplicity, use an algorithm that doesn’t require galvanic isolation for the voltage measurement. Each module measures between battery negative and cell positive so you actually get these four values: 3.2, 6.4, 9.6 and 12.8 Volt. So cell 1 is the only correct one. I use a simple loop:

for n = 1 to 4
  cell[n] = ReadVoltage(n);
cell[4] = cell[4] - cell[3]; // 12.8 - 9.6
cell[3] = cell[3] - cell[2]; // 9.6 - 6.4
cell[2] = cell[2] - cell[1]; // 6.4 - 3.2

That’s it, very simple coding. The ReadVoltage function is one I made up just now but the library you get with the module has one very much like it.

I think you know I would not do anything like in that diagram mixing LA with LFP, let alone putting them in series. You don’t have to: when your Arduino sketch wants charging to stop you simply flip an output pin that has a relay which takes the regulator offline. Or switch the MPPT controller off.

I have since bought even nicer LFP cells that fit the AA holders exactly. You have a 4s battery for just $15 : https://www.amazon.com/gp/product/B07RGQX6W7

[rgleason]

Regarding balencing, as I recall with your huge wonderful keel located battery, you just balenced initially and check it once a year?

[s/v Jedi]

Originally Posted by rgleason

Regarding balencing, as I recall with your huge wonderful keel located battery, you just balenced initially and check it once a year?

True, I never got to hook up the balancer because there’s still nothing to balance. But the following is the type of balancer to get:

https://www.amazon.com/Cywhrvzsf-Equ.../dp/B09G74WDN5

When you look closely at the picture, you see a solder bridge labelled “Run”. When you remove the solder blob, you can connect a switch or relay contact… which you drive from the Arduino

[rgleason]

See jedi's diagram in this thread:
https://www.cruisersforum.com/forums....php?p=3797954