Electric meter SDM120M not talking to emonPi, baud rate issue?

Hardware
1

Good morning,

I’ve finally got round to installing my level 3 monitoring kit, but have come to find that the SDM120M isn’t talking to the EmonPi. I can confirm that it is wired up correctly as per the installation documentation (https://files.openenergymonitor.org/emonhp-pi2.pdf).

I have noticed via the display on the SDM120M that it is reporting a baud rate of 9600, when reading through the below document, this seems to suggest it should be 2400, could this be causing the issue?

2

In a word, yes.

What does your emonhub.conf file say? It doesn’t really matter what the baud rate is, but both ends (or all devices if it’s a bus) must use the same rate.

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3

Thanks @Robert.Wall will take a look at the emonhub.conf file tonight when I get home from work.

4

My SDM120 came with baud at 9600 but the documentation said the default was 2400 (I suppose, this explains the info in the doc link you gave).
Mine runs at 9600 with no problems.
Adam

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5

@Robert.Wall thanks for that, the emonhub.config file shows 9600, as does the display on the SDM120M so that isn’t that.

I have replaced the wiring between the SDM120M and the USB to RS485 convertor with Cat6 cable, additionally I have plugged the USB convertor directly into the EmonPi to rule out the USB lead.

This is the output from the log:

2025-04-29 19:40:41,198 ERROR SDM120 Could not read register @ 12: No communication with the instrument (no answer)
2025-04-29 19:40:42,301 ERROR SDM120 Could not read register @ 72: No communication with the instrument (no answer)
2025-04-29 19:40:42,402 ERROR SDM120 Could not read all registers
2025-04-29 19:40:42,403 INFO SDM120 Connecting to Modbus device=/dev/serial/by-id/usb-1a86_USB_Single_Serial_56EC022398-if00 baud=9600 parity=none datatype=float

6

You are using a twisted pair in your CAT6 cable for the bus? All I can suggest is you check absolutely everything, make no assumptions at all. As the page you cited is sent out with the heat pump monitor kit, and on-line support for this is included, if you can’t spot a problem (like you’ve counted terminals from the wrong end, the A & B (+ & -) legs are swapped), then go back to The Shop - [email protected].

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7

All sorted now.

I had wired up it following the installation documentation that was supplied with my order. This was v4 which showed:
8 to GND
9 to A+
10 to B-
Turns out that is incorrect and has been rectified in the online available documentation which is now at v4.9 this has been updated to:
8 to GND
9 to B-
10 to A+

Thanks for everyone help. :+1:

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