Sontex 749 emonHub Mbus

My ASHP is going live next week and I’ve had them install a Sontex 749/MBus heatr meter which I’ve connected to my emonpi with the mbus/usb interface purchased from our hosts.

I don’t see any direct support for that in the emonhub interface code.

Do I write my own code into a branch and submit to github for merge or are there any suggestions as to the configuration which works?

I’ve got a sontex 749 on my heat pump. Emonhub supports reading from it via mbus using the Sontex interfacer.

    Type = EmonHubMBUSInterfacer
        device = /dev/ttyAMA0
        baud = 2400
        pubchannels = ToEmonCMS,
        read_interval = 10
        validate_checksum = False
        nodename = mbus
                address = 0
                type = standard

However, one extra step is required with the sontex 749 which is currently not very well documented on our site. @TrystanLea figured this out, we need to get round to documenting it.

Basically Tlthe Sontex 749 has a few different pages of mbus data output, we need to tell the sontex to return the page of mbus data which has the data which interests us. This step only needs to be done one at the beginning, currently it’s a manual process which would be good to automate:

L402: emonhub/ at master · openenergymonitor/emonhub · GitHub

  1. change L402 0x5b to 0x7b
  2. restart emonhub
  3. change L402 0x7b to 0x5b
  4. Restart emonhub

Each change moves the meter on to the next page and it’s the 3rd page that we want

You’ll need a mbus reader

I have the MBUS to USB converter from the shop.

I’ve connected it up and changed the config. but not showing in the inputs yet.

2022-09-12 08:05:44,247 DEBUG    MBUS       Invalid MBUS data received 0 bytes 2005.2 ms
2022-09-12 08:05:44,449 DEBUG    MBUS       Decoded MBUS data: None
2022-09-12 08:05:52,086 DEBUG    MBUS       Invalid MBUS data received 0 bytes 2007.5 ms
2022-09-12 08:05:54,298 DEBUG    MBUS       Invalid MBUS data received 0 bytes 2010.2 ms
2022-09-12 08:05:54,499 DEBUG    MBUS       Decoded MBUS data: None

Where does that Python reside on an emonpi?

Found the code and went through the 0x5b/0x7b stuff but still no luck.

What’s the correct wiring for the interface board?

The shop page shows AABB for the four connections and I wired the Sontex to A and A - polarity is irrelevant according to the sticker on the cable.

I’m assuming the baud rate is 2400 - doesn’t seem there is a screen/display to say what it is.

You need to connect one wire to A and the other wire to B. Be sure to disconnect the mbus adaptor before adjusting the wiring, since its important the wires are not shorted.

OK, that fixed it and after doing the page adjustment am getting the following inputs.

Do you have any documentation of what these are (OK, some are obvious) and what Feed configuration to use on them?

Excellent! That’s the correct page, these inputs have all the data you need. The most useful are FlowT, ReturnT, Flow_Rate, Energy and Power. You should log these inputs to feeds with 10s intervals.

Finally had the ASHP fired up yesterday but some issues I think not helped by confusion over ‘flow’ and ‘return’.

For the Sontex values read over mbus, I’m getting FlowT higher than ReturnT. I’m thinking that’s wrong and maybe either the entire plumbing is wrong or the heat meter is installed incorrectly.

Any ideas?

Unless I have misunderstood, it’s normal for flow to be higher than return.

Flow is the temperature coming from the heat pump, return is after the water has been used by the house and going back to the heat pump.

I don’t think you have - that is the normal way of naming for a conventional boiler (oil, gas, wood-chip…) so I think going against that convention would be most unusual.

The only time it might be the other way round is if the heat pump is cooling – and while I understand some air-air heat pumps can do this, I wouldn’t expect a wet system to be capable of it - for obvious reasons!

That sounds normal

Thanks all. Everything seems correctly installed which is reassuring.