Bluetooth BMS and microcontrollers

[hour]

Anyone ever used one of these BT BMS units? A lot of them seem like junk visually and are often for more than 4S batteries, but I've seen a couple.

I write mobile apps (iOS and Android) for a living, mostly Bluetooth LE stuff at this point including firmware for microcontrollers so apps can talk to them.

It would be extremely easy to assemble an ESP32 powered unit that operates a relay directly tied to your charging input for about $8, knowing when to operate the relay based on individual cell voltages pulled over bluetooth from the BT BMS. This could be configured wirelessly from a simple app. Also ten cents to add temperature monitoring and also use that to disable the charge input if too cold

All the photos for the BT BMS units show a crap-app to accompany it, almost always in Chinese. What are the odds of their BT being accessible by third parties - anyone investigated yet? There's a couple many-thousand dollar bluetooth sniffers at work but I'm not familiar with them. Could get a coworker to help me out but best would be someone responding "Yes, I've researched this, and X company has a github"

I'd build the unit and have it directly capable of reading cell voltages - just mount in the battery box - but I'm less confident on hardware assembly and the few projects I've found on the internet are over my head. Also no clue if one could tap in to a cheap exposed board BMS and read voltages from certain solder points with a microcontroller.

Thoughts, knowledge, experience?

 

[Rando]

This should help:

Generic-Chinese-Bluetooth-BMS-communication-protocol

There are a number of generic Bluetooth BMS units based around the TI BQ76940 BMS controller with a number of different configurations. I am not sure if they are manufactured by one or a number of different manufacturers. The thing they have in common is that they can be used with an Android app...

endless-sphere.com

Endless sphere would be a better place to pursue this - far more battery and BMS knowledgable folks there.

 

[hour]

This should help:

Generic-Chinese-Bluetooth-BMS-communication-protocol

There are a number of generic Bluetooth BMS units based around the TI BQ76940 BMS controller with a number of different configurations. I am not sure if they are manufactured by one or a number of different manufacturers. The thing they have in common is that they can be used with an Android app...

endless-sphere.com

Endless sphere would be a better place to pursue this - far more battery and BMS knowledgable folks there.

Thanks, been researching since posting and have spent most of my time in that thread and links. Should be doable either with bluetooth or directly monitoring via pins, hard work already done in many githubs.

Can get a 30amp 4s BMS for about $40 so total cost would be maybe $50 to be able to cut PV input to charge controller based on cell voltage, and before BMS kicks off and results in potential spike. And since people have already done the heavy lifting I could roll my own software to monitor everything that the goofy chinese software can as well as allowing for setting params for triggering the relay.

 

[Rando]

I have been running a 150Ah LiFePO4 battery with an el-cheapo 50amp BMS and have not seen any issues with PV charge spikes. As far as I know, I have only had the BMS kick in once when I was messing around with a balancer, and nothing bad happened - the solar controller went to the float voltage and picked up the loads when the battery disconnected. I am not sure why folks seem to be concerned about this. Program your charge controller correctly to stay away from the cut out points of your BMS and call it good.

If you are really concerned put a 15V clamping diode across the PV charge controller - it is a $1 fix.

However I would be interested in a bluetooth BMS to keep a loose eye on cell voltages - so much encouragement to get this working,

 

[hour]

I don't know what the rules are for all charge controllers, but the Victron SmartSolar line says to not disconnect the battery before the PV is disconnected. Someone else on here was talking about voltage spike killing some of his accessories when BMS shut things down. So the cheap solution (forget who posted the diagram, Jonyjoe?) was a voltage disconnect and a relay, so a couple bucks. That solution makes sense but is of course based off an overall voltage. I'm sure that works just fine when you avoid the upper end of things but I'd happily spend a little more money for control, and a new nerd project.

I'll update when I receive the BT bms I just ordered and get to tinkering.

 

[Rando]

A low cost BMS with a good ios/android app would be huge, so please don't let me discourage you from that!

However for the perceived voltage spike issue, the fail safe way to protect against this is something like this ($0.64):

1.5KE16A Littelfuse Inc. | Circuit Protection | DigiKey

Order today, ships today. 1.5KE16A – 22.5V Clamp 67.6A Ipp Tvs Diode Through Hole DO-201 from Littelfuse Inc.. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

This will guarantee the voltage on your main bus does not exceed 15.2V with almost no added complexity.

 

[hour]

A low cost BMS with a good ios/android app would be huge, so please don't let me discourage you from that!

However for the perceived voltage spike issue, the fail safe way to protect against this is something like this ($0.64):

1.5KE16A Littelfuse Inc. | Circuit Protection | DigiKey

Order today, ships today. 1.5KE16A – 22.5V Clamp 67.6A Ipp Tvs Diode Through Hole DO-201 from Littelfuse Inc.. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

This will guarantee the voltage on your main bus does not exceed 15.2V with almost no added complexity.

Not doubting you, just wondering why people have gone to extra lengths if this were the ultimate solution? Spose it still doesn't address the possible results of the charge controller having PV input and no battery connected.

Worth mentioning though that this would just be using an existing BMS and extending its capabilities by allowing it to cut charge source off if a cell goes too high, or cutting load off if a cell goes too low - with customized parameters and no risk of cc damage. Wondering why electrodacus hasn't been ripped off yet and in MPPT flavor - its been years and there's definitely a need for solar balance chargers.

 

[Rando]

I would argue that the vast majority of folks don't go to any extra lengths and everything works fine. There have to be thousands if not tens of thousands of folks running Battleborne batteries connected to solar and AC chargers - all of which are relying on MOSFET based BMS built into the battery that just cuts the charger if the voltage goes too high. I have not heard about voltage spikes killing equipment in these set ups any more than then they have in my personal setup. I think what you are seeing in the forums is an echo-chamber effect rather than engineering analysis.

I also think that most of the cheap MOSFET BMS already do exactly what you are suggesting (many are based on this guy: http://www.ti.com/product/BQ77915) .
But only some with a UART/Bluetooth interface have configurable set points.

I also think it is odd that there isn't more of a DIY/Opensource effort for a small embedded BMS like electrodacus. It does seem like mating a UART capable BMS (that has all the MOSFETS etc already good to go) to a bluetooth enabled microcontroller would be a good start. I can imagine that it would also be pretty easy to add coulomb counting SOC charge measurements as well, which would replace the BMV-712 most folks are using.

Interested to hear how your tinkering with the BT BMS goes.