BMS DIY

[ironman]

No, this is one shunt for the whole pack, measuring amperes and Ah (~charge) going in and out. This way you can find out the state of charge % (SOC). I want to be able to know that SOC at a given moment and to instruct the bms to cut the charge relay at a certain %, say 90, or cut the load relay at another certain %, say 20. The code for that is already in place and tested; now I need to get the SOC out of that chip I bought.

[jtaylor]

Check out Stuart Pittaway’s DiyBMS on Github
https://github.com/stuartpittaway/diyBMSv4

He has open source hardware design that you can build yourself through JLCPCB. Controller is an ESP32 and the cell monitors are using either individual cell boards or an all in one up to 16S. One controller supports up to 128 cells which can be arranged in pareille banks or all in series. I use two on my boat, a 16S for propulsion and a 4S for house 12v.

The controller board has a INA229 (or 228?) for coulomb counting using a user-provided shunt.

The individual cell monitors are optically isolated and use a serial communication buss.
The 16S board uses the same communication buss as well.
The individual boards each have two temp sensors, one for resistive load temperature and another detachable one for making a cell terminal temperature measurement.
The controller has two SSRs (2A load) and 2 mechanical relays, with configurable rules for opening closing these.

Also, the controller supports CANbus and speaks Pylontech and victron.

On my boat, both my batteries talk to my CerboGX and can control the charging from my Multiplus II.

I am *very* happy with DiyBMS on my boat.

That said, the latest JKBMS is supposed to very nice. Definitely worth checking out. Integrated active balancer is a very nice to have feature.

[dreuge]

There is plenty for one to DIY, and with the good quality and very affordable BMS's that are available, a DIY a BMS is not worth it. I have been happy with JDB BMS's. I current have a JBD SP04S034 200A BMS. It has bluetooth, UART, RS-485, and a heat circuit(if one needs). I use the iOS bluetooth app and also use a simple python program for reading out the BMS data and generating simple plots for a web page. I have also recently integrated this into OpenPlotter too.

For a DIY project, build smart Battery Combiner using a cheap VSR and an ESP32 to switch the VSR on/off. I have done this for charging with my 120A Alternator. Recently I upgraded my smartBC to include SensESP and have data pushed to the Signal-K server as part of OpenPlotter.

I have an early write up of this on my blog. It contains everything except for my recent development with SenseESP & OpenPlotter (coming soon).

DIY 560AH LifePO4 (running great for 2.5 years now)
https://svjohannarose.blogspot.com/2...e-battery.html

Charging LiFePO4 via solar, shore, and Alternator w/ smartBC (great 2+ yrs)
https://svjohannarose.blogspot.com/2...m-w-solar.html

JBD BMS (purchased from LLT Power Electronics
https://jiabaidabms.com/products/jbd...42191951102114




Paul
S/V Johanna Rose
svjohannarose.blogspot.com

[Dave9111]

Originally Posted by Kettlewell

This guy's BankManager is an interesting concept for a hybrid bank of Lithium/lead. Not exactly a BMS, but could be a way to go.

That isn't a BMS. He doesn't release a lot of details on what that device is doing, but I'm guessing its mostly hype. For $380 I can buy two new 100AH LIFEPO4 batteries.

For a HYBRID system that operates at 12 or 24 volts, this device works well. And its $50. There is another variant of this that is rated at 250 amps.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I have one of these installed in a vehicle that keeps a 12 volt LIFEPO4, 100ah battery charged. The LIFEPO4 battery runs a small portable refrigerator (BougeRV) 24x7. This device connects to the car battery with a 30 amp fuse.
It works really well and its very simple. The alternator has sufficient voltage to almost fully charge the LIFEPO4 battery. If I don't run the car for 4 days or more in warm weather, I have an onboard LIFEPO4 battery charger that I plug in. That fully charges the battery. But I have only done that twice in 6 months. That device has a button on it so that if your lead acid battery needs a jump, you can pump it up with your LIFEPO4 battery by disabling the isolation. I haven't needed that yet, but its a clever feature.

There are some good reasons to keep a lead acid battery for your start battery.

[Dave9111]

I think that having a balancer in the BMS is a must. You might not need it right away with high quality cells, but they should be good for 3000+ cycles and eventually as they degrade they will need a balancer. That makes the BMS design a lot more complicated.
If you are going to do a new BMS design, don't stop at only protection.
I have no problem building a BMS, but it has to be better than what I can buy, or else I have better things to do and build. My project lists estimated time of completion already extends beyond my death. :-)

Edit: I'm mostly a software guy. Industrial stuff mostly. I would try to turn this into "mostly" a software problem. Figure out some basic measurement circuits and balancing circuits that can be controlled and attach a controller to all of it. That will give you the utmost in flexibility.

[kyriazis]

Originally Posted by ironman

Hey all,

While waiting for my first set of prismatic cells, I'm musing on the thought of building my own BMS - just because I think I can and to jog my brain. Anyone around here who's into this type of stuff, feel free to have a look at https://github.com/marcobergman/bms. Current question that's on my mind is the following:

• I think the voltage measuring could be done smarter. All multi-channel AD converters I can find are limited to their input not exceeding the Vdd, which forces me to use voltage dividers, and even with high-precision resistors it would require calibration. Surely there's better solutions for that?

I think that by rolling your own BMS you have no-one to blame if you have a fire that costs you your boat, and worst case somebody else's boat, too. There are may too many things that can go wrong while charging batteries, especially lithium. Why not leave the responsibility for someone (ie. a company) that has insurance.

[Dave9111]

Originally Posted by kyriazis

I think that by rolling your own BMS you have no-one to blame if you have a fire that costs you your boat, and worst case somebody else's boat, too. There are may too many things that can go wrong while charging batteries, especially lithium. Why not leave the responsibility for someone (ie. a company) that has insurance.

Good luck suing a battery manufacturer that is based in China or a BMS maker that is based in China. That will get you no where.

When you are rolling your own, creating battery packs from raw cells, you are taking some risks even if you buy a BMS system. Wire size, fuse size, etc is now all of your responsibility. If you are not confident in your own abilities, don't do it. Also, providing mechanical protection for your cells is important.
What if you drop a wrench on your cells bus bars? Is that possible?

I've seen picts of DIY batteries made using 2x4's for the case. The tops of the cells are left exposed with nothing to prevent the bus bars from being shorted.

Use fuses properly. And don't oversize them excessively.
Buy good fuses from a known company. If you are concerned about their quality, I would test them. Blow a few fuses under controlled conditions.

I'm a ME/EE with 40+ years of experience. I would make my own BMS if I thought it was superior to anything else available. But for now, I am buying packaged batteries. They have a warranty. The cells and bus bars are protected. But will the company be in business in 2 years? We will see. China companies are almost untouchable from a legal standpoint.

[ironman]

For closure, the new LiFePO4 battery and BMS are in the boat now, interfacing to SignalK, in intensive care period. I made a telnet CLI to adjust settings. No balancer yet, but the hardware is set up to cater for one, either commercial or diy. Those interested: https://github.com/marcobergman/simpleBms