question

Anthony Beebe avatar image
Anthony Beebe asked

VRM Display Math

Apologies, if this question has been asked somewhere before on the site. What I'm trying to figure out is the mathematical relationship, if any, among Shore Power, AC Loads, Battery Charge/Discharge, and PV.

If, for example, the AC Loads are 200 W and I'm not connected to shore power (so zero), the PV is producing 100 W, shouldn't the batteries be discharging at 100 W to make up the difference?

I guess the basic question is should the numbers net out? Roughly?


VRM
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2 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

Inverter efficiency needs to be included to make the DC and AC numbers add up. That is you 200 watt load will most likely look like 220 watts to the DC side of things so in your example would be providing 120 watts. Of course this is all approximate.

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Anthony Beebe avatar image
Anthony Beebe answered ·

So Kevin, Take a look at the VRM screenshot below. Batteries are charged. AC Loads are 75W supplied by 84W, but I'm generating 35W from PV. Roughly, then, can we say that of the 75W needed, 35W is coming from PV leaving the remaining 40W coming from Shore Power? If this is true, what report indicates this? Anthony

screenshot-20220409-111633-chrome.jpg


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Kevin Windrem avatar image Kevin Windrem commented ·

From the screen shot there appears to be about 35 watts unaccounted for. for 75 watts out and 84 watts in, that's an efficiency of 90% which seems about right for a low power condition.

It could be a DC load that isn't accounted for. If you have DC loads, you should enable "Has DC system" in the GX device System setup. If not then it's a mystery.

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