Victron Phoenix off-grid huge DC draw with no DC loads

[standard.confection]

Hi all! My tiny cabin off grid setup consists of:

• victron phoenix smart 48v 3000W inverter
• mppt 150/35 victron controller
• cerbo gx
• victron lynx distributor 1000 DC
• dyness 5.12kwn 48v battery
  And 6 solar panels that round up to a total of around 2400W.

My problem is that I see huge DC power draw, when I only plug in AC loads. First picture shows an air conditioner running. Second picture is with no major loads connected (just Wifi router).

This load is not constant. If the battery is full, I see around 50w draw (which im assuming is the inverter itself and cerbo). But when charging or powering some AC loads, this DC load fluctuates and even goes to a negative value sometimes. I’ve seen it go between -50w to 350w.

Any idea why I’m seeing this DC draw?

Just air conditioner

No major AC loads

DC load gets smaller once the battery is almost charged

with a fully charged battery

[pwfarnell]

Have a read of this FAQ. It is on the FAQ category at the top of DIY.

The DC System Power on a Venus device is jumping, erratic or does not match other loads

This topic covers the reported power in the DC system tile as shown on a Venus device (such as CCGX, Cerbo, Ekrano or Raspberry Pi etc.) or on VRM dashboard. The symptoms are typically that the DC power does not match with a calculation using the power shown and the battery, solar and ac tiles and/or that the DC System Power is erratic or jumping about. [DC system tile] To see the DC System tile, it needs “Has DC System” enabled in the System Setup Menu of the Venus device. [Has DC System] I…

[standard.confection]

Thank you for that. But on the battery, the total discharge rate reported is the AC load + DC power. This means that the battery draw is inaccurate? Should I watch only for the AC loads?

[pwfarnell]

No, the DC power = Battery discharge - ac power.

You have no DC power meter so it is an estimate, that is what the FAQ described.

The AC load is accurate, the power flowing into or out of the battery is accurate and the power out of the MPPT is accurate. The DC load is not accurate, it is the calculated difference between the 3 accurate readings and will be a mix of any real dc loads, the inefficiency of the inverter, cable losses in the system etc.

[standard.confection]

that’s interesting, could inefficiencies and cable losses account for such a high wattage? thank you for all the answers

[pwfarnell]

If you do not have any DC loads other than the Cerbo then disable the DC loads display, they add nothing other than confusion.

Cerbo will take something like 6W. The inverter has a minimum 25W load and the losses are approx 10% for a resostive load, so for a 1000W load you have losses of around 125W for a resistive load. If the load has a poor power factor such as a motor the losses can be higher for the same ac power. Good cabling at 48V system should have < 10W losses. Your MPPT will be losing a few percent in conversion losses. Then there are the inherent errors in the measurements as well.It all adds up.

[standard.confection]

I just discovered something else. I am only powering one AC load through a smart plug that shows power draw.
Looking at the power draw reported by the plug (around 240-250w) and the PV charge, it makes sense to see around 16w on the battery.
It’s just the AC load reported in VRM that are off. Is this normal? Thanks again