I have an SDM120MB meter (MBus variant) connected to an ASHP that is dropping it’s Mbus connection to my emonpi every few days. I have to reset at the CU (flipping the breaker) to restore.
The meter continues to operate fine locally and is connected to the OEM Mbus reader with screened, 0.75mm2 CY Control cable. The screen is appropriately grounded. The Sontex Heat Meter on the same MBus circuit is never affected and continues to operate fine, suggesting it’s isolated to the meter itself. I am using the OEM interfacer here.
The dropouts are random but typically occur every 4-10 days over the past 5 months, requiring the CU reset mentioned above to get data moving again.
Interestingly, switching out with an identical meter results in the same problem. Is this a known issue with SDM120’s or is there something that would be causing this intermittent freeze?
Unfortunately I have also noticed this on a couple of systems, not all, but exactly as you describe, sometimes it can be few months, other times a few days. It seems there is a reliability issue with the MBUS variant of the SDM120. I tried a few different things such as slowing down the readings and reducing the number of retry attempts but no luck in getting better reliability. I also haven’t been able to reset the meter when it has crashed via a software fix, as you say it requires a breaker reset. We’ve started to recommend installing the Modbus version with a separate modbus reader, that one seems to be rock solid from our experience so far. I realise I need to update our documentation to reflect this, I will do that now. I wonder if the supplier might take the MBUS version back and exchange for a modbus variant?
Sorry I should have posted up here about this sooner, I appreciate that the issue is more than a bit frustrating!
Thanks @Trystan, that’s helpful insight and should be quite easy for me to rectify. I understand the SDM120 Modbus variant is reported to work fine and actually have an unused one which I can switch out. Thankfully also have a couple of spare cores in the cable back to the emonpi which i will now make use of!
Thanks for this info, which saved me from ordering an MBus SDM120 (from a different supplier ) and then battling with reliability issues post-installation.
It’s frustrating though - I want to add a sub-meter on the electrical input to my central heating circulation pumps (for full reporting against the SPF H4 system boundary) and my MBus cabling goes right past these pumps on the way to the heat meters. All my other metering is on MBus too (water meters and some electrical meters with pulse outputs connected via Relay-brand S0-to-MBus adapters) and I’d prefer to keep all the metering in one place rather than adding Modbus into the mix.
I’m inclined to try a different manufacturer’s MBus-interface kWh meter; looks like Rayleigh Instruments might be worth a go (as long as they’re not re-branded Eastron units…!)
Just in case anyone is looking for a reliable single-phase electricity meter with an M-Bus interface, I’m happy to report no issues with models from Rayleigh Instruments after several months of use:
I’m using an RI-D175 which is one module wide and handles up to 45A (single phase)
One complication which is no issue for me but which did cause a problem for integration with a Loxone system is that this meter only appears to support Primary M-Bus addressing, not also Secondary addressing (which Loxone relies upon)
The larger RI-D35-100 is two modules wide and handles up to 100A (single phase)
This appears to be a rather better-engineered unit than the D175, with a much larger display and many more configuration options - and it supports Secondary addressing
Since it’s only a little more expensive than the D175, it’s probably the better choice for anything needing more than about 16A - provided the extra DIN rail space is available
Both models are MID-certified and are available in M-Bus and MODBUS variants, so the usual care is required when ordering to ensure the right one is selected.
) and then battling with reliability issues post-installation.