Node-red and EVCS modbus TCP

Q&A and troubleshooting EVCS
1

Hi guys.

I have a victron ev charger and node-red on a PC. Nothing more. (no other victron items etc)

I want to use modbus tcp in node-red to control the charger amps based on info I have coming in on node-red from the import/export.

But I currently can’t seem to get any data from the EVCS on modbus into Node-red.

In nod-red when I try to read on the modbus-tcp, I have FC set to 4, unit-id 1, address 5010, quantity 1.

this gives an error: “Error: Data length error, expected 7 got 5”

Any ideas as to where I am going wrong?

2

Advise use Mqtt instead off modbus.

Send this info to the Mqtt out node via function node :

let Site = VRM number from your installation ;

let Current = Current value you want;

msg.topic = “W/” + Site + “/evcharger/40/SetCurrent”;

msg.payload = {“value”: Current}

3

Thanks for the reply. I don’t understand.

I have 1 victron device, the EVCS, no other victron hardware.

How does the EVCS communicate to MQTT as it won’t know the server address…

4

Hi @cqw .
Modbus function 4 is Read Input Registers.
The EVCS contains only Holding Registers.
Please try Modbus function 3 (Read Holding Registers) — it should work.

P.S. I think @Sdb is referring to the GX device. The EVCS does not contain an MQTT broker. This is only possible if you have a GX device in your system. Through the MQTT broker on the GX, you can control the EVCS also.

5

Many thanks, that sorted it.

but there must be some sort of bug in node-red, using a modbus flex getter, I have to injet via a function node, not via the inject node directly(as that causes an error)

Anyway it works.

Is it fc 6 to alter the max charge current value, that’s what I need to work on next.

Regards

6

Just looking at the modbus xls table:

I’m controlling the charging current via node-red using register 5016 ‘charging current’

what is 5129 ‘charging current limit external’ for ?