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sam-carleton avatar image
sam-carleton asked

Where are the missing 166 watts going?

I have a small system in my RV and I am trying to track down some missing power, or so I think it is missing. I have tried to attach a screenshot of my VRM, but the forum won't let me, so allow me to describe the situation.

I have the following:

  • Lithium Battery Smart
  • Lynx Smart BMS
  • two MultiPlus 3000
  • four different MPPTS
  • SmartShut is configured as a Power Meter between the above and the RV DC system

In the VRM screenshot the two MultiPlus's show 273 W, the DC Power is 46 watts, the charging is 381 W, for a total of 700W. But the PV Charger is showing 866W.

It looks to me like there are 166 watts which are not being accounted. Is that correct? I am guessing that is overhead from the two multiplus's and four MPPT, is that accurate? If so, it seems like a really big overhead to only be using 273 watts of the inverter.

Is there any way to get an accurate picture of where all the power is going? I ask because if my theory is correct, there is high overhead in the two MultiPlus, than I will look at wiring up the VE.Direct 800 VA I have for these smaller AC loads. But if it is somewhere else, I won't go the the trouble/effort.
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I have reached out to my installer multiple times over the last few days to get a good digital copy of the wiring diagram and have not heard back from the company (we didn't part on the best of terms), so I photographed the paper copies I have and you can see them here:

https://www.miltonstreetphotography.com/airstreamelectricaldiagram

VRMSmartShunt
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Kevin Windrem avatar image Kevin Windrem commented ·
No screen shot. Also a wiring diagram might be helpful.
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sam-carleton avatar image sam-carleton Kevin Windrem commented ·

Each time I try to add the image, I get a "Parcing error". The file is a small PNG file, don't know why it won't work, I do see a thumbnail behind the parsing error message.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ sam-carleton commented ·
It's a known issue with the community, try to upload the picture somewhere else and just share the link.
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sam-carleton avatar image sam-carleton Matthias Lange - DE ♦ commented ·
I think I found the missing power, I think that is the power used by the two MP 3000 inverters. The specs say max efficiency is 92%, 2608 watts * 92% = 2400 watts, so 208 watts. Right now it looks like the total power usage by the MP3000 group is 319 watts when it is producing 141 watts, that is a difference of 178 watts, which is below the 208 watts it uses when running at max efficiency.


All in all, I am thinking the power is going to produce the AC. Now if I was missing more then 208 watts when producing 2400 watts of AC, then I would be really concerned.

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1 Answer
jetlag avatar image
jetlag answered ·

The max efficiency is not at max power. So it could be only 85% at that low power output (it is only 138W per MP2). I could't find a curve showing this for the MP2 12V/3000 version, but I know a curve for the MP2 48/3000, and the peak efficiency is at about 400W there.

But nevertheless, this would still not explain the 166W missing. Even with the assumption from above, still about 100W are missing.

The DC power is also only a calculation of the system (if you don't have a separate smart shunt for that) to show the difference. And as such systems are often very dynamic, it might also be that the values of one "screenshot" are not allways directly correlating togehther.

It's difficult to follow without a picture and also a system diagram...

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sam-carleton avatar image sam-carleton commented ·
To clarify, I DO have a dedicated SmartShut as a power meter between the Lynx Distributor and the whole DC side of the RV, so the DC load is accurate ;)
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