SDM120 (MBus) Meter Freezing / Drop-out

Hi all,

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?

Many thanks

Hello Ben.

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!

Many thanks

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