question

hummingbear avatar image
hummingbear asked

Negative DC Loads while charging, positive while discharging (increases with load)

Before I start I want to say I've read through quite a few posts already where folks are describing negative DC loads, however I have not found anything that quite explains what's going on.


Some background on my setup: I live off-grid and run my home off our solar/battery setup. I recently switched over to a new 48V battery system I build, we have all new hardware, Multiplus II 48V, two victron charge controllers, smartshut...etc.


I see negative load on the DC side (indicating a charge coming from DC). This is odd as other than our charge controllers we have no other DC charging sources. However if we have a large AC draw (3Kw when running our well pump) DC load spikes to around 100-200W.


I'm perplexed because I never saw this on our previous system. What could be going on? Below is a schematic of our system:

1664384315266.png



During the evening (no solar input):

1664387473762.png

During the day (solar input/net positive load to battery)
1664387542761.png


I am using my own graphing system but my Venus device displays the same data as well.

SmartShuntdc system
1664384315266.png (106.1 KiB)
1664387473762.png (71.9 KiB)
1664387542761.png (69.6 KiB)
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knissone avatar image knissone commented ·

This is quite similar to several other posts I've seen recently, including my own post here. Not that I have any clue what I'm really talking about here, but I'm really starting to wonder if there's a firmware issue, as widespread as this problem seems to be.

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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

The obvious question is to check if the shunt is installed in the correct orientation.

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hummingbear avatar image hummingbear commented ·
Yes...we have significant AC loads and they are reported correctly. But yes, system is on the system side, battery is on the battery side.
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bathnm avatar image
bathnm answered ·

How is the shunt configured? Is it as a shunt or a dc load or dc source. This can change how data is presented and reported

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hummingbear avatar image hummingbear commented ·

Can you expand on what you mean a bit? Configured where, in VenusOS? It is a DC Shunt on the last negative before our battery, before any system loads.

1664393503698.png

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