Looking for BMS that support series connection for high voltage battery setup

[sunshine_eggo]

From taking apart multiple EV batteries, it seems like the BMS they use do not actually balance the cells. Usually cells used for EV packs are matched so well that balancing isn’t needed. I think the BMS do have a cell level voltage cutoff using contactors. If cells get out of balance the packs are usually retired to the DIY battery community or the scrap bin

Have you ever disassembled the BMS to see if there is a bank of passive balance resistors? It's pretty much impossible to so perfectly match cells that they won't experience some kind of SoC drift over just a few years of use.

I've tested 588 C-Max Energi (7.6kWh PHEV) cells from 7 different packs. None of the 84 cells out of each pack measure more than 0.01V difference, yet there were notable capacity variations of cells within the same pack of 2-7%. If there are capacity variations, but NMC voltages are within 0.01V across 3.45 - 3.80V values, some balancing must be happening.

These packs came from varying climates and ranged from 2014 to 2017 MY with 20-80K miles on them.

 

[Cheap 4-life]

Have you ever disassembled the BMS to see if there is a bank of passive balance resistors? It's pretty much impossible to so perfectly match cells that they won't experience some kind of SoC drift over just a few years of use.

I've tested 588 C-Max Energi (7.6kWh PHEV) cells from 7 different packs. None of the 84 cells out of each pack measure more than 0.01V difference, yet there were notable capacity variations of cells within the same pack of 2-7%. If there are capacity variations, but NMC voltages are within 0.01V across 3.45 - 3.80V values, some balancing must be happening.

These packs came from varying climates and ranged from 2014 to 2017 MY with 20-80K miles on them.

No I never disassembled the bms. At one time I looked into using the EV packs for a high voltage inverter and came to the conclusion (what I read) that the bms in the EV didn’t do balancing.. I used 60 volt 2016 chevy volt batteries for 4 years and the voltage never drifted. I was using the SOC conservatively same as an EV. I guess if they don’t drift in voltage they are close enough in SOC to not cause an issue. My understanding was if the voltage does start to drift they no longer trust the cell/cells so the battery is no longer fit for an EV. Might be different using other battery chemistries that drift more easily than NMC.

 

[sunshine_eggo]

No I never disassembled the bms. At one time I looked into using the EV packs for a high voltage inverter and came to the conclusion (what I read) that the bms in the EV didn’t do balancing.. I used 60 volt 2016 chevy volt batteries for 4 years and the voltage never drifted. I was using the SOC conservatively same as an EV. I guess if they don’t drift in voltage they are close enough in SOC to not cause an issue. My understanding was if the voltage does start to drift they no longer trust the cell/cells so the battery is no longer fit for an EV. Might be different using other batter chemistries that drift more easily than NMC.

Pretty sure Volt is NMC as well.

 

[Cheap 4-life]

Pretty sure Volt is NMC as well.

indeed

 

[RichardRSB]

I think that might be different for HV vs. LV inverters.

It is. Sure as hell.

 

[da9el84]

It is. Sure as hell.

Although the majority of inverters utilizing HV battery setup probably needs comms with a BMS, the Deye inverter actually doesn't and offer a pure voltage setting, even for this 50kW beast.

 

[RichardRSB]

True, but comms adds an extra layer of security, and also the ability to read the battery data from the inverter for use in other devices like eGauge, SA, of HA.
I use the Voltage mode to at the moment, but i really want the comms up and running. I am currently very busy getting this done. (Deye HV and OrionBMS2.).

 

[da9el84]

True, but comms adds an extra layer of security, and also the ability to read the battery data from the inverter for use in other devices like eGauge, SA, of HA.
I use the Voltage mode to at the moment, but i really want the comms up and running. I am currently very busy getting this done. (Deye HV and OrionBMS2.).

Well.... If the BMS has the necessary protection, then comms to the inverter doesn't really add anything. You can most likely pull data easier just by talking directly to the BMS to whatever system you desire, be it HA, Node red etc.

Do you have the SG01HP3 currently?
I've sort of abandoned my idea again, since there is not much desire for it in my country and each inverter model needs to be government approved, which is sort of a hassle, so I'll probably not go down that road.

 

[Ampster]

I am currently very busy getting this done. (Deye HV and OrionBMS2.).

I posted on the other thread my success with a SolArk and an Orion JR2 BMS.

 

[RichardRSB]

I posted on the other thread my success with a SolArk and an Orion JR2 BMS.

I've seen this. Problem is that the default profile in the Orion is for LV batteries. HV has a complete other Id-set. I am currenly working with Ewert to get this clear.

 

[RichardRSB]

You should rebuild the battery, and use Orion. Orion has a fully programmable CAN, and it does balance the pack. It is (one of) the best BMS you can buy for HV systems. And it can talk to Deye / Sol-Ark / Sunsynk and perhaps Megarevo. I use an OrionBMS2 for a 96S Lithium configuration (Tesla model 3 pack) with a Deye 20kW HV hybrid. (See my other posts).

 

[RichardRSB]

I know, Deye unfortunately still have a long way to come on their documentation/communication side, but they confirmed multiple times that these can be series connected.

View attachment 120204

Not to mention their wrongly usage of units. There is no such thing as a Kwh. Heck even on the Deye display it is wrong. (KW).