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sam-carleton avatar image
sam-carleton asked

Venos OS showing a negative DC power

Have a look at the short attached video I took on my iPhone this morning. I am wondering what is going on with the DC load jumping around (in the negative range) all over the place when the Inverter is turned on.

The setup is very simple: It is a small RV with one 95Ah SLA battery, SmartShunt, MPPT 100/20, and Phoenix 800 VA. Everything is hooked together in a distribution block before it goes off to the RV panel and a smaller distribution block. The RV is NOT on shore power.

All the Vectron devices are connected to a BeatleBoard Black via USB dongles. The BBB is running Venos OS 2.93.

The ONLY DC load is what is needed to run Venos OS. When the inverter is not running it is 7 to 10 watts. When the inverter had the load you see in the video (150w~200w) the DC power is all over the place (from -8W to over -60W). Now that the load on the inverter is down around 12 watts, the DC power is positive and in a range of 18w to 21w. Once I turn off the inverter, it is back down to 7 - 10 watts range.

I am assuming something is wired incorrectly, but not sure. I did read some other posts and I have not grounded any of the VE devices, nor the battery. I am not sure how the RV panel is grounded, I did notice the other day some grounding bars behind the RV panel. Should I ground all the VE devices to it, including the load side of the SmartShunt?

RPReplay_Final1681302631.MP4

MPPT ControllersVenus OSSmartShuntpheonix
rpreplay-final1681302631.mp4 (9.7 MiB)
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2 Answers
kevgermany avatar image
kevgermany answered ·

Negatives of all the loads on the leisure battery must be grounded to the load side of the shunt. This must also be grounded to the vehicle chassis. Leisure battery is not grounded directly, but through the ground on the load side of the shunt.

Is there a load on the inverter when the jumping around happens?

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pwfarnell avatar image
pwfarnell answered ·

This is a common question answered many times.

The DC load is not measured, it is calculated from all other known information. The SmartShunt is the most accurate measure of current, the inverter is less accurate as it does not measure DC current directly but calculates it from the AC current and efficiency. The solar controller is reasonably accurate. The DC power is calculated as the difference between the SmartShunt power, the inverter power and the solar controller power so the DC power is the least accurate figure. Additionally, the measurement from the 3 devices may not occur at exactly the same time which causes the DC power to be variable.

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