I've got a Sunsynk 5kW single-phase inverter. I've always noticed the CT coil was a little off (compared to the meter), but recently after adding more panels I decided to dig further. My only non-essential loads are a geyser and stove, and the geyser is on a timer, so most of the time I'm sure there is no non-essential load. However, the inverter reports non-essential loads of between 200W and 500W, varying slowly over time. What's convinced me it's the CT coil is that if I check my meter readings (just manually noting them down every hour) they don't match up with the coil readings at all. Basically, that "non-essential load" is the coil over-reading.

My installer keeps saying this is normal and that the Sunsynk coils are just not that accurate, or that it's electromagnetic interference (I've got about 10-15m of cable run between the DB and the inverter, and it's in the same conduit as the power cables). Is this sort of error really normal? It seems pretty high to me - if I wasn't correcting for the error by adjusting the trickle charge setting, I'd be exporting 5 kWh/day or more (and my meter charges me for export - still waiting for the AMI meter). Has anyone else had errors of this magnitude and managed to fix them? The two suggestions I've come across are to use a higher-quality cable (e.g. Cat 6 or 6A) between the coil and inverter, or to use a separate power measurement device with a Modbus connection to the inverter (e.g. https://www.sunsynk.org/post/eastron-meters-do-you-need-one). The latter sounds ideal, but could be difficult because my DB doesn't have any more space for such a device.

55 minutes ago, bmerry said:

I've got a Sunsynk 5kW single-phase inverter. I've always noticed the CT coil was a little off (compared to the meter), but recently after adding more panels I decided to dig further. My only non-essential loads are a geyser and stove, and the geyser is on a timer, so most of the time I'm sure there is no non-essential load. However, the inverter reports non-essential loads of between 200W and 500W, varying slowly over time. What's convinced me it's the CT coil is that if I check my meter readings (just manually noting them down every hour) they don't match up with the coil readings at all. Basically, that "non-essential load" is the coil over-reading.

My installer keeps saying this is normal and that the Sunsynk coils are just not that accurate, or that it's electromagnetic interference (I've got about 10-15m of cable run between the DB and the inverter, and it's in the same conduit as the power cables). Is this sort of error really normal? It seems pretty high to me - if I wasn't correcting for the error by adjusting the trickle charge setting, I'd be exporting 5 kWh/day or more (and my meter charges me for export - still waiting for the AMI meter). Has anyone else had errors of this magnitude and managed to fix them? The two suggestions I've come across are to use a higher-quality cable (e.g. Cat 6 or 6A) between the coil and inverter, or to use a separate power measurement device with a Modbus connection to the inverter (e.g. https://www.sunsynk.org/post/eastron-meters-do-you-need-one). The latter sounds ideal, but could be difficult because my DB doesn't have any more space for such a device.

For starters I would say merely comparing your power meter against the inverter value is not close to ideal. Looking at the inverter reading from the grid vs a plain clamp meter at the same instant in time is what the installer should have done and showed you the fault reading from the CT. Only then can one perhaps imply that over 5kWh would be exported through the meter and measure as power used during exporting. Again checking that the CT does give an exporting reading through your meter as shown by the Sunsynk. Not saying it is not possible but one needs to check than to use a general statement.

A lot of prepaid meters would trip if 500W was exported.

2nd point about interference - never a good idea to have it in the same conduit when we know interference can affect the reading of high frequency equipment. 

Have you switched off the stove and geyser to verify that you dont have any viper load on your non essentials accounting for this 200-500W?

Edited December 28, 20241 yr by Scorp007

1 hour ago, Scorp007 said:

For starters I would say merely comparing your power meter against the inverter value is not close to ideal. Looking at the inverter reading from the grid vs a plain clamp meter at the same instant in time is what the installer should have done and showed you the fault reading from the CT. Only then can one perhaps imply that over 5kWh would be exported through the meter and measure as power used during exporting. Again checking that the CT does give an exporting reading through your meter as shown by the Sunsynk. Not saying it is not possible but one needs to check than to use a general statement.

For a bit more detail, here's the plot I made, using a combination of data extracted from the Sunsynk telemetry and eyeballing the meter reading: each horizontal segment on the black line is the average power computed between two meter readings. Blue line is the CT coil reading (P-External-CT-L1), orange is grid power going into the inverter (P-L1), green is the absolute value of orange. If one ignores the large spikes (corresponding to the geyser running), the black line tracks the green pretty well. Also notice that at 2024-11-27 16:00, the coil value went up (I changed the trickle setting) while the meter usage went down. That's what convinced me that I've been exporting and the meter charges for exporting.

I'm now using software and an RS485 connection to try to keep the orange line close to zero* by adjusting the trickle charge setting, and my meter is recording about 0.5 kWh per day (= 20W average).

1 hour ago, Scorp007 said:

A lot of prepaid meters would trip if 500W was exported.

2nd point about interference - never a good idea to have it in the same conduit when we know interference can affect the reading of high frequency equipment. 

What do you mean by "high frequency" in this context? Presumably both the power cables and the cables carrying the CT coil current are 50 Hz?

I've previously tried switching the non-essentials off at the DB, and it hasn't made any difference. There is a timer in the DB plus some LEDs for pilot lights/surge protection, but I'm pretty sure they're not drawing 200W (on the basis that I don't burn myself when I touch them).

38 minutes ago, bmerry said:

For a bit more detail, here's the plot I made, using a combination of data extracted from the Sunsynk telemetry and eyeballing the meter reading: each horizontal segment on the black line is the average power computed between two meter readings. Blue line is the CT coil reading (P-External-CT-L1), orange is grid power going into the inverter (P-L1), green is the absolute value of orange. If one ignores the large spikes (corresponding to the geyser running), the black line tracks the green pretty well. Also notice that at 2024-11-27 16:00, the coil value went up (I changed the trickle setting) while the meter usage went down. That's what convinced me that I've been exporting and the meter charges for exporting.

I'm now using software and an RS485 connection to try to keep the orange line close to zero* by adjusting the trickle charge setting, and my meter is recording about 0.5 kWh per day (= 20W average).

What do you mean by "high frequency" in this context? Presumably both the power cables and the cables carrying the CT coil current are 50 Hz?

I've previously tried switching the non-essentials off at the DB, and it hasn't made any difference. There is a timer in the DB plus some LEDs for pilot lights/surge protection, but I'm pretty sure they're not drawing 200W (on the basis that I don't burn myself when I touch them).

From another forum:

"Best accuracy AC current sensors are closed loop Hall effect sensors. They have a high frequency feedback loop op amp and additional winding on CT core to drive magnetic field in core to near zero."

I was under the impression the Sunsynk/Deye were using a high frequency Hall effect CT to increase the speed of throttling. Some pure AC CT inverters have a much slower response time from what I have seen mentioned.

There are ten of thousands of Sunsynks working correct without the Eastron meter. As the Eastron (SDM120CT) uses a comms cable (RJ45) it can easily be fitted say 10m away from the DB as per in your case where you don't have space in the DB. Also perhaps another 10m to the CT coil of the Eastron. These units are normally used where the distance exceeds the maximum reliable distance for measurement of power.

Thanks for the detail graphs. It does seem you have good data to have come to the correct conclusion that the CT is way out of it's intended accuracy. No further suggestions from my side.

Typical CT accuracy is 0.5% as used on a number of devices to measure grid power direction and magnitude.

50 minutes ago, Scorp007 said:

From another forum:

"Best accuracy AC current sensors are closed loop Hall effect sensors. They have a high frequency feedback loop op amp and additional winding on CT core to drive magnetic field in core to near zero."

I was under the impression the Sunsynk/Deye were using a high frequency Hall effect CT to increase the speed of throttling. Some pure AC CT inverters have a much slower response time from what I have seen mentioned.

The specific CT coil in my installation is a CTSA016. Unfortunately the data sheet doesn't say whether it is an AC CT or a Hall effect sensor.

50 minutes ago, Scorp007 said:

Typical CT accuracy is 0.5% as used on a number of devices to measure grid power direction and magnitude.

I'm curious how accurate CTs are at low currents (1A or less). The IEC 61869-2 accuracy classes only specify accuracy down to 5% of rated current, which for my coil is 5A.

39 minutes ago, bmerry said:

The specific CT coil in my installation is a CTSA016. Unfortunately the data sheet doesn't say whether it is an AC CT or a Hall effect sensor.

I'm curious how accurate CTs are at low currents (1A or less). The IEC 61869-2 accuracy classes only specify accuracy down to 5% of rated current, which for my coil is 5A.

Easton claim 0.5% and my own low cost power meter over a month of day time grid use of mostly 10W and about 60 kWh per month is not more than 2% out at any time. 

I eventually convinced my installer that there was a problem. They replaced the CT coil and ran a new cable in a separate conduit, and it's now much more reliable. There is still about a 40W bias, but it's pretty consistent and I've just set my trickle feed to 40W to cancel it out.