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BMS requirements for energy storage.

How do you store and manage your electricity?
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francisco.shi
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BMS requirements for energy storage.

Post by francisco.shi »

I just got my solar panels installed and running. I got a Goodwe hybrid inverter. I am about to connect the battery. The inverter is designed to run on a 48v battery. Maximum voltage is 58v which will be good for 14S NCM pack.
My question is what does the BMS need to do other than balancing the batteries?
The inverter has settings for max charge and float voltage and DOD. The inverter has a maximum capacity of 100A and the battery is 180Ah so there is no chance of overheating.
It appears that once the cells are balanced the BMS doesn't need to do anything.
The inverter has BMS connection. Has anyone ever worked out what the protocol is for batteries?

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coulomb
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Re: BMS requirements for energy storage.

Post by coulomb »

francisco.shi wrote:
Thu, 30 Apr 2020, 05:23
My question is what does the BMS need to do other than balancing the batteries?
It's like a breaker in your house switchboard: if all goes well, it should do nothing. But apart from balancing, it should check for over- and under-voltage on all cells, over-temperature, and it should prevent charging when too cold (0°C for LFP, I don't know the figure for NCM).
The inverter has BMS connection. Has anyone ever worked out what the protocol is for batteries?
The Pylontech protocol is well known, and that brand of LFP batteries is one of the most popular, so most inverters support that protocol (if they support any at all). Here is the RS-232 version; the RS-485 version is slightly different:

https://www.photovoltaikforum.com/core/ ... 61216-pdf/

The BMS sends packets with information like accurate SOC, suggested charge voltage, maximum charge current, and a few specials like Do Not Charge. I don't know the Goodwe BMS interface implementation, but with Axpert Kings and Growatts, the BMS overrides the normal fixed settings for charge voltages and maximum current.

Even though your cells appear to be balanced now, it's likely that they'll drift off balance in a year or two. Manual monitoring and balancing is a pain, and there is good chance you'll be too busy to do it, or merely forget to do it, when it's actually needed.
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jonescg
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Re: BMS requirements for energy storage.

Post by jonescg »

I just emailed you a copy of the standard, AS5139:2019 which your battery will need to comply with.
Not all inverters need an input from the bMS, particularly if they are told to run on a lead-acid profile where the absorption voltage is the same as the float voltage. I understand Victron does this.
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francisco.shi
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Re: BMS requirements for energy storage.

Post by francisco.shi »

Thanks. I will have a read.

reecho
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Re: BMS requirements for energy storage.

Post by reecho »

francisco.shi wrote:
Thu, 30 Apr 2020, 05:23
I just got my solar panels installed and running. I got a Goodwe hybrid inverter. I am about to connect the battery. The inverter is designed to run on a 48v battery. Maximum voltage is 58v which will be good for 14S NCM pack.
My question is what does the BMS need to do other than balancing the batteries?
The inverter has settings for max charge and float voltage and DOD. The inverter has a maximum capacity of 100A and the battery is 180Ah so there is no chance of overheating.
It appears that once the cells are balanced the BMS doesn't need to do anything.
The inverter has BMS connection. Has anyone ever worked out what the protocol is for batteries?
The CAN bus protocol used is a barstardised version of Modbus originally used in the SMA Sunny Island inverter.

You can use aftermarket BMS such as ZEVA with Goodwe (which I currently have). I choose LG RESU battery on the Goodwe. It doesn't care what battery I choose as the CAN BUS ID's are all the same.

francisco.shi
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Re: BMS requirements for energy storage.

Post by francisco.shi »

I am going to use my own BMS. I have the cell top boards working. I can measure voltage and temperature for each cell and can balance the pack. What I need to sort out is the behavior for the main controller. For the car I have control over everything but for the home storage I don't know how much I can rely on the inverter and how to talk to the inverter. From what I can understand from the stuff that jonescg sent me I have to have a contactor as well as current measurement on my side and tell the inverter when to stop. If the inverter doesn't follow then I guess I disconnect the battery using the contactor.

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