question

marekp avatar image
marekp asked

VRM math problem

I have a math problem reading a VRM numbers.

See for yourself.

screen-shot-2021-06-04-at-102132-pm.png

Total consumption = 1353W

Grid = 20W

From battery = 677W x 0.90 = 609W (90% inv eff)

So VRM math is as follows.

1353 = 20 + 609 ?

Same here.

(this pict was removed to simplify the problem)

Any comments?

Where is the problem?

VRM
screen-shot-2021-06-04-at-102132-pm.png (108.7 KiB)
screen-shot-2021-06-04-at-102002-pm.png (93.4 KiB)
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3 Answers
Phil Gavin avatar image
Phil Gavin answered ·

Grid CT reversal?

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marekp avatar image marekp commented ·

There is no CT.

Grid is measured by EM24 power meter in the first pict.

I will remove the second pict because it is confusing the problem because it shows intermittent behavior when inverter/charger is used as grid power meter.

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markus avatar image markus ♦♦ marekp commented ·

Hi Marek,

I am pretty sure your EM24 is miswired.
BR

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marekp avatar image marekp markus ♦♦ commented ·

There are only 3 input wires and 3 output wires.

How one can miswire this?

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markus avatar image markus ♦♦ marekp commented ·

Consumer side wired to grid and grid side wired to consumers.

Or phase mismatch.

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marekp avatar image marekp markus ♦♦ commented ·

And EM24 display is up side down.

I thing I would noticed that. :)

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markus avatar image markus ♦♦ marekp commented ·

Maybe it’s inserted correctly and miswired nevertheless?

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marekp avatar image
marekp answered ·

Just to update.

There was a simple reason for the wrong numbers.

Problem was fixed by swapping phases L1 and L3 on the LM24 power meter.

Below the numbers after fixing this problem.

screen-shot-2021-06-05-at-92850-pm.png

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Phil Gavin avatar image Phil Gavin commented ·

Thanks, for the report back, I thought those grid meter readings looked dodgy.

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Murray van Graan avatar image
Murray van Graan answered ·

Which batteries are you using? In both instances, the battery discharge rate is roughly half the load?

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marekp avatar image marekp commented ·

Winstons (LFP) with "2 signal BMS" in both, but lets concentrate on the top one only.

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