question

mryoshii avatar image
mryoshii asked

AC loads not the same as DC load

Hi, my load values seems off.

bildschirmfoto-2023-08-30-um-225155.png

Why is my DC load lower than the AC load?
This changes when the load is above 2kw. Then it shows more DC load than AC as I would expect because of losses.

Is my smart shunt broken?

Multiplus-IIVRMSmartShunt
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seb71 avatar image seb71 commented ·
The inverter and MPPTs power values are less accurate.


You could check the SmartShunt zero current calibration to rule out that possibility (see the manual on how to do it). Especially if you clicked on the "Calibrate" button at some point.

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mryoshii avatar image mryoshii seb71 commented ·

i have not messed with that, but i will give it a try

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Bob K avatar image Bob K commented ·
You have both a DC side and an AC side in your system, yes? Isn't it possible to have DC loads and AC loads simultaneously that are at different levels? For example, the DC side has a load from a bunch of DC lights and a propane detector, while the AC side has a load from something plugged into an AC receptacle.
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mryoshii avatar image mryoshii Bob K commented ·
​At the moment I have no DC loads. But if so, the DC side should always show more or equal than the AC side?
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Bob K avatar image Bob K mryoshii commented ·

I'm not sure what I'm looking at in your graphic. Is it showing me that it's pulling power from the battery bank, through the inverter in the MPII and feeding an AC load...like this? I think that's what the little blue traces are showing but it's a small pic and, of course, they not animated in a screencap. :-)

1693486489358.png


If you're not putting power into the system anywhere else, then yes, these numbers do seem off. I would expect the power draw (from the battery, -153W in this case) to be greater than the output (200W to the AC side) because of inefficiency losses through the inverter. Plus, your batts discharge shows 6 amps. 25.53v x 6a = 153w, so that calculation is right. But the MPII line at the bottom says 25.52v at 9.1a. The calculations are off or the MPII getting a little extra power from someplace that's not being measured. Otherwise, you've just created a perpetual energy machine. ;-)

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1693486489358.png (230.1 KiB)
mryoshii avatar image mryoshii Bob K commented ·
Your arrows are correct :D

there are no other energy sources in my system. It's just MPPTs Battery with smart shunt and MP2.

I will check with my clamp amp meter later this day.

Is it off in your system to?


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4 Answers
buddhafragt avatar image
buddhafragt answered ·

Your Smart Shunt is not broken, it is simply only very inaccurate. The values depend extremely on the type of load, a 10 USD energy meter is much more accurate. I threw mine away.

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mryoshii avatar image mryoshii commented ·
What energy meter are you using, and can it be integrated in vrm?
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mscn avatar image
mscn answered ·

I do have the EXACT SAME issue and it's driving me crazy.

From one of the answers here the SmartShunt might be "broken" - how so, and how it breaks to always be like 50-80W behind?

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Christian Häusler avatar image
Christian Häusler answered ·

Hello,

has anyone solved the problem yet?

I have exactly the same problem.

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buddhafragt avatar image
buddhafragt answered ·

No, only the Smart Shint you can integrate in Venus (DC), for AC there are some other meters you can use.

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