Best BMS solutions for larger (120s LiFePO4 / 384V) strings?

[cboles]

I have several APC Symmetra PX UPS racks (40kW each in N+1 configuration) that I am experimenting with using LiFePO4 battery systems instead of the SLA batteries these usually come with. I have been using one with A Pylontech PowerCube M1 with success, but now I'm starting to play around with building various surplus battery packs to accomplish the same thing. Basically the APC expects a center tapped +192V | 0V | -192V battery, mainly to minimize potential to ground and it seems pretty good at discharging the battery halves fairly symmetrically.

I could build the BMS system out of a number of 15s or 20s BMSes, but I'm not seeing a lot of units that have isolated RS485 or CAN interfaces such that I can safely have them on a single comms bus while wired in series. Are there any BMS products out there people would recommend to either work with a 60s battery or are designed to be used in series with communications for higher-voltage systems?

 

[Samsonite801]

I had been thinking of using this solution for a 56s BMS for my Prius...

Starter Kit:

123SmartBMS G3 4S, 2x I-sensor 2020

123SmartBMS gen3 is an easy to use yet advanced, modular BMS to keep your lithium batteries in perfect condition, increasing the lifespan of the battery pack.

123electric.de

Scaleable add-on modules:

123SmartBMS Between Board

The 123SmartBMS Between Board is an additional module developed to be installed on each cell of the battery as an extention to the 123SmartBMS complete set (4 cells).

123electric.de

Smart Relay:

123SmartRelay dual relay module

123SmartRelay is a dual relay module with extremely low self-power consumption. It can be used to switch high currents or even small signals.

123electric.de

I guess you can string up to 255s with this setup...

I don't know if they are available in the US (my location), but I had this in my bookmarks from back when I found them. No problem to just make an overseas order...

I don't recall if they support communications or not, I might go read the description again... EDIT: Looks like it has an app though, and series data communications bus stringing all the modules on the same bus, not sure the protocol yet, as I don't have time to read the full manual right now.

Here is the link to a manual on it:
https://123electric.de/img/cms/123SmartBMS_gen3_manual.pdf

 

[cboles]

I had been thinking of using this solution for a 56s BMS for my Prius...

Starter Kit:

123SmartBMS G3 4S, 2x I-sensor 2020

123SmartBMS gen3 is an easy to use yet advanced, modular BMS to keep your lithium batteries in perfect condition, increasing the lifespan of the battery pack.

123electric.de

Scaleable add-on modules:

123SmartBMS Between Board

The 123SmartBMS Between Board is an additional module developed to be installed on each cell of the battery as an extention to the 123SmartBMS complete set (4 cells).

123electric.de

Smart Relay:

123SmartRelay dual relay module

123SmartRelay is a dual relay module with extremely low self-power consumption. It can be used to switch high currents or even small signals.

123electric.de

I guess you can string up to 255s with this setup...

I don't know if they are available in the US (my location), but I had this in my bookmarks from back when I found them. No problem to just make an overseas order...

I don't recall if they support communications or not, I might go read the description again...

Thanks. One problem with these per-cell systems is cost. The individual cell modules for these are 18.50EUR each x 120 = ~$2650 USD, which is about 1/2 the cost of the 35kWh battery pack it is attaching to.

123SmartBMS Between Board

The 123SmartBMS Between Board is an additional module developed to be installed on each cell of the battery as an extention to the 123SmartBMS complete set (4 cells).

123electric.de

 

[Samsonite801]

Thanks. One problem with these per-cell systems is cost. The individual cell modules for these are 18.50EUR each x 120 = ~$2650 USD, which is about 1/2 the cost of the 35kWh battery pack it is attaching to.

123SmartBMS Between Board

The 123SmartBMS Between Board is an additional module developed to be installed on each cell of the battery as an extention to the 123SmartBMS complete set (4 cells).

123electric.de

Yeah that's what is holding me back on that project, I have bigger fish to fry right now. Maybe they'll get cheaper into the future...

 

[yabert]

Are there any BMS products out there people would recommend to either work with a 60s battery or are designed to be used in series with communications for higher-voltage systems?

I had good result with Zeva BMS.

Also, at that voltage range (around360-400V) you can maybe take a look to buy a used EV battery (from Chevy Bolt, Tesla Model 3, Nissan Leaf or other).
The main advantage I can see is for around 3000-5000$ you can have a complete, super nicely package 50-60 kWh battery with a BMS integrated.
The downside is you will need to find how to activate the BMS without the rest of the car. Maybe those guys can help with that if you think it's interesting.

 

[curiouscarbon]

i’ve looked seriously at batrium, not sure how high it scales

 

[cboles]

I had good result with Zeva BMS.

Also, at that voltage range (around360-400V) you can maybe take a look to buy a used EV battery (from Chevy Bolt, Tesla Model 3, Nissan Leaf or other).
The main advantage I can see is for around 3000-5000$ you can have a complete, super nicely package 50-60 kWh battery with a BMS integrated.
The downside is you will need to find how to activate the BMS without the rest of the car. Maybe those guys can help with that if you think it's interesting.

That's part of the plan. If I have good success with these I was going to build a larger battery at another site consisting of several Tesla Model 3/Y batteries and just center-tapping that and using the built-in BMS and perhaps even their charger, instead of the built-in charging circuits on the APC inverters.

These batteries are going inside businesses and homes, so I feel more comfortable with LiFePO4. The Tesla packs will be in a shipping container in a remote location where a battery fire wouldn't easily spread or be life threatening.

 

[LeRoy Christensen]

I have several APC Symmetra PX UPS racks (40kW each in N+1 configuration) that I am experimenting with using LiFePO4 battery systems instead of the SLA batteries these usually come with. I have been using one with A Pylontech PowerCube M1 with success, but now I'm starting to play around with building various surplus battery packs to accomplish the same thing. Basically the APC expects a center tapped +192V | 0V | -192V battery, mainly to minimize potential to ground and it seems pretty good at discharging the battery halves fairly symmetrically.

I could build the BMS system out of a number of 15s or 20s BMSes, but I'm not seeing a lot of units that have isolated RS485 or CAN interfaces such that I can safely have them on a single comms bus while wired in series. Are there any BMS products out there people would recommend to either work with a 60s battery or are designed to be used in series with communications for higher-voltage systems?

Look into Orion BMS's, they are very comprehensive controllers. Also can communicate via CanBus to unlimited devices.
Good luck.

 

[cboles]

Thanks. I was getting close to building my own boards based on the LTC6812, when I found this open-source project that also sells built hardware:

ENNOID - BMS GEN 1

Our configurable battery management system is engineered to offer a complete solution for monitoring high voltage battery packs. It consist of a Master board based on an STM32 microcontroller connected through an ISOSPI interface to one or several slave boards. The modular BMS can be configured

www.ennoid.me

I went ahead and purchased some boards and will probably make a few software tweaks for my particular application (center-tapped 384V battery with dual contactors). I'll let everyone know how it goes.

 

[Ampster]

Are there any BMS products out there people would recommend to either work with a 60s battery or are designed to be used in series with communications for higher-voltage systems?

As others have said, EV batteries are higher voltage and BMSs designed for them can handle many cells in series and often have CANBUS capability. Zeva and Orion have been mentioned.
I am currently using an Orion BMS and previously used an EMUS BMS on an EV conversion. I have not found a low cost solution for a BMS that can handle that voltage and provide CANBUS.

 

[cboles]

As others have said, EV batteries are higher voltage and BMSs designed for them can handle many cells in series and often have CANBUS capability. Zeva and Orion have been mentioned.
I am currently using an Orion BMS and previously used an EMUS BMS on an EV conversion. I have not found a low cost solution for a BMS that can handle that voltage and provide CANBUS.

The solution I ended up using based on the LTC6812 chips has an isolated bus (ISOSPI) for each 15s slave module and they connect to a master that also has isolated CAN.