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Axpert 5k (73.00e) / Modbus Duo BMS / Pylontech US2000


Wulff
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Good day

I recently picked up a modbus duo BMS from our friends at Rectron which according to its literature is designed to be the intermediate between a 5K and a Li battery that communicates over RS485. According to the literature, connect inverter to RS-232 port, connect battery ( with supplied cable) to RS485 port on battery (has drawing of a US2000 in the literature) to the BMS port and if everything is lekker, the battery symbol on inverter should flash and its all good. To communicate with inverter it has a RS485 modbus port to connect up to PC. Sweet. official product, all should be fabulous.

However. few things I hope community can help with. Had to buy a USB to RS422/485 adaptor to get PC to talk to inverter. After setting up modbus comms in WatchPower, I could see the Inverter through the BMS module. Yay.
The supplied BMS cable to battery they give pinout is 1-2 to 4-5 , which is not RS485, so I used a good ol straight RJ-45 cable. thus far ive seen no blinky battery icon on inverter. 

So I'm curious, was there a change in the string structure from inverter with the modified 73.e firmware that the genuine BMS for this inverter no longer understands whats being said? [ WatchPower still works and all settings, etc work so I dont think so, maybe its just a passthrough ]

Is there some magic sauce I'm missing? No I'm not using ICC for few reasons, one being no trust, two is cost. This BMS is a 1/5th the price and I honestly don't need the extra bits that come with ICC

Is there some clever way of intercepting the comms to see if its talking to the battery and what I would be looking for? (Short of hooking up my Oscilloscope and sniffing the raw binary)

I wanted to pick up one of these when i bought the pylontech battery but Aunty Rona was causing nonsense with stock and supply.

Any help or Clues would be awesome.

 

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1 hour ago, Wulff said:

According to the literature, connect inverter to RS-232 port, connect battery ( with supplied cable) to RS485 port on battery (has drawing of a US2000 in the literature) to the BMS port and if everything is lekker, the battery symbol on inverter should flash and its all good.

I don't know how they'd achieve the battery symbol flashing.

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To communicate with inverter it has a RS485 modbus port to connect up to PC.

I'd be surprised if the PC connection is RS-485; I'd guess RS-232.

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Had to buy a USB to RS422/485 adaptor to get PC to talk to inverter.

Through this box?

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After setting up modbus comms in WatchPower, I could see the Inverter through the BMS module. Yay.

So Watchpower actually worked normally? Wow.

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The supplied BMS cable to battery they give pinout is 1-2 to 4-5 , which is not RS485,

? I think they know the pin-out of their box better than you do. The battery seems to have the RS-485 on pins 1,2 and 7,8, so I'd say you need the 1,2 end plugged into the battery, and the 4,5 end must be for the box's BMS port.

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so I used a good ol straight RJ-45 cable. thus far ive seen no blinky battery icon on inverter. 

I doubt that a straight through cable will work, and I also don't see how the battery icon on a PIP-4048MS is going to flash.

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So I'm curious, was there a change in the string structure from inverter with the modified 73.e firmware that the genuine BMS for this inverter no longer understands whats being said?

There are enhancements (new interpretations for previously illegal parameters), but it's completely backwards compatible. So that can't be the issue.

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Is there some clever way of intercepting the comms to see if its talking to the battery and what I would be looking for?

Since you have an RS-485 interface that the PC can see, you may be able to use a free program that talks to RS-485, and connect that in parallel with the cable to between the box and the BMS. I think I've used a program called QModMaster before. But I found modbus to be a weird protocol to use.

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(Short of hooking up my Oscilloscope and sniffing the raw binary)

So why aren't you doing that? 😈

In short: I think your main problem is the cable from the box to the BMS. Half duplex RS-485 only needs two wires.

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Hi @Coulomb

Sometimes, the obvious stares you in the face, as well as a great idea. 

I made up a cable. the one supplied most certainly wasn't going to work. the pylontech manual as RS485-B on pin 7 , A on 8 and GND on 6 with this magic box having A on pin 4, B on pin 5 and GND on 8.

So I made up said cable with a shaved portion mid sentence to see whats potting. With no plug in the battery, its dead silent. so I'm assuming the battery has to be polled to get a response ( more forum digging in future). However, when I connected up my funky cable, things lit up. 
from what I can gather , assuming;  baud 9600, 8 bit, NO party, 1 Stop bit, the strings being generated are long. 

(2 hours later) there will be a follow up post. I was pretty sure my cable was right that i made up. since 485 was giving grief, i happen to have a ICC cable for the RS232, plugged that in and at 9600 baud rate on BatteryView, it timed out. but i connected at 115200. Since the BMS box wants 9600 and my jumpers on the pylontech was 0000 and i moved to 1000, turned off battery and back on, id imagine that the baud would be 9600..  
Is there a trick to getting these batteries to restart?

 

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