VRM missing load - all inverter loss?

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Jim asked Jul 20, '21

VRM missing load - all inverter loss?

I have a DC solar setup with lithium batteries and a multiplus 3000/24. Everything is working well, but when looking at VRM, part of the load is missing. That is, the numbers do not add up. My AC load is primarily resistive, with a gas absorption fridge utilizing heating elements, the wiring is proper or oversized, and the load is low enough that wiring loss is negligible. Inverter efficiency, power factor of other small loads, and charging losses might make up the difference, but it would be really nice if the VRM portal numbers came closer to adding up. It would also be nice if the Multiplus could report power factor of the AC load. These things aside, though, am I missing something on why the load numbers are so far off? 100w on a 600w load seems significant. Thanks for any insight.

Jim

Multiplus-II MPPT Controllers VRM

1626787901185.png (79.2 KiB)

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marekp answered · Jul 20, 2021 at 03:47 PM

Efficiency of the inverting at that power level is circa 90% (power used by MP itself and GX device do lower the eff.)

430 x 0.90 +180 - 496 - 71 = 0

I do not see anything wrong with your numbers.

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Jim commented · Jul 21, 2021 at 08:36 PM

The numbers make sense. It would be nice to have them all displayed in VRM to give a net 0. Alternately, an inverter efficiency number could tell the story too. Thanks for the replies.

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Answer 1 · 2021-07-20T15:21:55Z

Alexandra answered · Jul 20, 2021 at 03:21 PM

@Jim

Did you also consider the power the system takes to run itself?

I have found with pv invters and mppts and gx devices people often forget they use power as well. Can be 100W on smaller systems, on larger 3 phase systems even more.

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Answer 2 · 2021-07-20T15:41:14Z

Jim answered · Jul 20, 2021 at 03:41 PM

Hi @Alexandra , thank you for the reply.

I did consider those loads, and they should show up in the DC load box as the power they pull would come from either the solar or battery, but either way across the shunt (BMV-712). There is 71w of DC load accounted for, which seems about right given things running on 12v DC, including the Cerbo, MPPT, WiFi, and some other parasitic DC loads.

Solar production + battery = all incoming wattage to the system. From the picture, 430w from battery and 180w from solar = 610w.

Displayed load would be DC Power + AC load = 565w

For this image, the delta then is 45w. It would still be nice to see the 45w called out in VRM as "system loss" or such to make the picture complete.

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Alexandra ♦ commented · Jul 21, 2021 at 07:00 PM

@Jim

MarekP Is right on the money there. Efficiency is also important, and I have seen systems with much larger "losses" than yours. Your figures look good.

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