All four power channels show zero even during daylight. What is wrong?

First confirm the Modbus TCP server is active on the device. Some firmware versions require Modbus to be explicitly enabled in the app settings. Also verify the device IP address and that port 502 is reachable from the Gateway's network segment. A firewall or VLAN separation between the Gateway and the device is a common cause.

One channel reads correctly but the others return errors. Why?

Register reads for addresses 30037 through 30040 should succeed in a single contiguous FC3 request. If one register fails, the device may be returning an exception for that address. Check that the firmware version supports all four addresses; older firmware revisions have been reported to respond differently to contiguous block reads.

Values appear but seem implausibly high or inconsistent. What should I check?

These registers are uint16 with no scaling factor defined in this template. If the raw value does not match expected PV output, cross-check against the Marstek app reading for the same channel. A polling interval that is too short (under two seconds) can cause the device Modbus stack to return stale or corrupted responses.

The gateway connects but drops readings intermittently. How do I stabilize it?

The Marstek Venus D Modbus TCP server can serve only one client connection at a time. If another system (such as a home automation platform) is simultaneously polling the same port 502, connection resets will occur. Use a Modbus proxy or dedicate the polling slot to the ModbusCloud Gateway to avoid conflicts.

Free Modbus template: Marstek Venus D (pv)

The Marstek Venus D is an all-in-one balcony power plant with an integrated inverter, up to 4 kW of PV input across four independent MPPT channels, and modularly expandable LFP battery storage. This Modbus TCP template reads four PV channel power registers (power_a through power_d), giving your ModbusCloud portal per-MPPT visibility into solar harvest. Installers and building owners can track individual panel string output in real time, detect shading or soiling on specific channels, and feed the data into historical trend analysis without relying on the Marstek app.

Name	Address	Function	Type	Unit	Access
power_a PV input power on channel A, reported by the inverter.	30037	FC03	uint16	W	R
power_b PV input power on channel B, reported by the inverter.	30038	FC03	uint16	W	R
power_c PV input power on channel C, reported by the inverter.	30039	FC03	uint16	W	R
power_d PV input power on channel D, reported by the inverter.	30040	FC03	uint16	W	R