Protocol Documentation

[scottdwyer]

Hello, I am looking at building my own battery monitor with an Arduino, and want it to communicate with a Growatt unit. I am confident I can handle the programming and hookup, but am unable to find documentation on how to communicate the data. In searching I found your software, which looks like it has the capabilities I would need, but I would need to reverse engineer it. Do you have, or could you point me to any technical documentation on communication protocol between the BMS and inverter? Thanks.

[scottdwyer]

I may have found what I think I need. I found a pylontech communication protocol document, and also a python script on here (github) that can communicate with a pylontech bms, both for RS485. I believe I can work with that. I think my next issue is that the standard Arduino is only rated to communicate at 115200, and by looking in your code the growatt is 500000. Lots of work ahead of me to see if I can do this, and while I think I have what I need, if you have anything more I would appreciate it. Thanks.

[ErikssonPer]

What growatt inverter do you have ?
There's tested solutions to interface bms and growatt inverters that talk via can protocol.

I run a emus bms on a growatt sph inverter for example.

[scottdwyer]

I have the LVM-ES SPF 3000TL 48v (actually 3 of them). I have 5 sets of 12v 100ah batteries, so there is no bms. I need to make my own bms, which is why I asked for documentation. So far I have found the most documentation on the pylontech rs485 protocol, so that is likely what I will use to attempt make my bms.

[ai-republic]

Do you really want to build your own BMS? Why not buy a cheap one like JK or Daly. Or are your batteries non-lithium? I guess so with 12V. And then you like to send the SOC, current and voltage via RS485 to the inverter? But if you just want to monitor them why don't you just connect the batteries straight to the inverter (configure lead-acid batteries) and connect your arduino monitor straight to the battery for voltage (& SOC) and connect to the battery cable to determine the current?

[scottdwyer]

I want my inverter(s) to switch based on remaining capacity, not voltage. To do that I need a BMS system to tell the inverter the percentage. That is really the only thing I need, the rest of the values will be calculated from total voltage and current, and I may fake the temperature. The inverters don't allow setting the cutoff voltage to a high enough level to suit my needs. It will allow running down the system to 20% or less when I want it to be higher. My plan is to use the arduino to monitor current with a shunt (already have a Renogy shunt monitoring system I can use to get the current from the voltage across the shunt) to calculate the remaining capacity, and send that information to the inverter.

You mention buying a BMS. Is there a BMS that could be used with a single shunt to calculate remaining capacity and send that information to the inverter? I don't have access to individual cells, only battery voltage and total voltage, and I really don't care about individual battery voltage because I already have balancers on each set. My batteries are 12.8v LifePo4, 5 sets of 4. Actually one set is 2 24v batteries. If there is something that would work for that, I would be interested. But my searching has not yielded any results that look like it would work for what I need.

[ai-republic]

Well, sounds like you got a little project there 😉
Hope I can help you with this Plyon documentation:
Pylon-RS485-protocol-V3.5.pdf

[scottdwyer]

Thanks for the documentation. Although it does have much Chinese and Russian in it and is very hard to follow. I found a version 2.8 that is all in English, so hopefully I can put it all together and figure it out.

[ai-republic]

Yeah, that how I do it too as decent documentation is hard to come by.