Technical Support

This is a follow up to my previous post "excessive load rate and battery drain"...

Please stick with me, especially if you have CT coil readings concerns, as it’s a bit of a story…

I was frustrated with the inverter grid import and app power flow figures being inaccurate and higher than the house load figure on the meter IHD, particularly noticeable when no PV or battery power available, even after taking into account inverter internal use, the difference was +300w.  I was also disappointed that the app daily grid import figures were vastly different to my supplier usage figures, mostly +6kW.

I was aware that these discrepancies were probably caused by the CT coil, as mine is approx 20m from the inverter, connected with CAT5e UTP, with wires twisted together… and so I decided to try to get the CT coil grid import figure as close as possible to my IHD grid use.

I first attempted to adjust the CT ratio down from 2000:1, knowing that some people have done this with good results.  My adjustments helped a bit with the power flow figures but caused issues with the inverter when adjusting lower than 1800, and I didn’t achieve my goal.

So, I decided to invest in an Eastron SDM120CTM meter and experiment without completely removing the original Sunsynk CT coil (at least initially).  I installed the meter temporarily in a module enclosure next to the consumer unit and connected it to the mains supply with a 3 pin plug to check it was working and all parameters were as expected.  Then I installed the supplied CT coil and checked the grid load reading on the meter against my IHD… they matched which was not unexpected but confirmed the meter was registering the correct grid load.  At this point I was happy that I had probably resolved the “phantom” 300w issue, and when the Eastron meter was finally connected to the inverter the inaccurate figure issues I was having would be fixed.

However, before it was connected I noticed something unexpected… whilst the battery was discharging to satisfy the house load (no PV or grid) the Eastron meter was showing feedback to the grid at 300w !!!  The inverter and app were showing 0 grid load, as was my IHD (which can’t display feedback figures). It seemed that the inverter was discharging the battery at a rate to satisfy both the actual house load, AND the “phantom” 300w which it was feeding back into the grid (what else could it do with it!).  This finding actually answered another seemingly unrelated issue I was having… my battery was only discharging for 5-6 hours per day when I was expecting it to last 8-10 hours based on historical house usage figures from my supplier !!!

And so I investigated a bit further and alarmingly discovered that when solely using PV power the excess over the house load was first being fed back into the grid at 300w BEFORE using anything remaining to charge the battery !!!

It seemed that whenever I was using PV or battery power only, probably for 12 hours per day at this time of the year, the inverter was constantly feeding the “phantom” 300w back to the grid.  This was bad news for me as I am currently not on a feedback tariff (another story!)

However, I was reasonably confident that all my issues would be resolved by finally connecting the Eastron meter to the inverter and giving it more accurate figures… which I did, and voila !!!  Everything is now working as it should, all readings are accurate and I am now NOT constantly feeding the “phantom” 300w from PV and battery back into the grid.

Next steps will be to move the meter into the consumer unit from its temporary enclosure and raise this problem with Sunsynk.

Hope my “story” helps others, and I just put it out there… if you have concerns about your CT coil readings don’t ignore, it could be costing you £.