question

seriusrod avatar image
seriusrod asked

Why my MP2 doesn't draw up to the configured Grid amount?

Overnight I run all my big loads and charge the battery. The system never approaches the 32A configured grid limit. And when the HVAC starts heating the water tank at 5:20, the charge reduces.
Why this happens? Is there anything I can do to fix it?

[Battery is blue, EV is green, HVAC is orange, Grid voltage is red]

1701268068554.png

Edit: This is an ESS system, with smart batteries, but not configured as controlling.
SmartShunt as battery monitor. The environment temperature is 16ºC


Exhaust temperature, charge and grid draw

1701344433151.png

ESS
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1701344433151.png (66.0 KiB)
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1 Answer
nickdb avatar image
nickdb answered ·

That chart is difficult to read.

Is this an ESS?

What is the temperature?

Charging reducing at the same time of loads would indicate the inverter hitting limits and possibly derating. Specs are at an internal temperature of 25C, unless you have very cool ambient temps it may be reducing charge.

That is typically the issue, assuming the batteries aren't limiting charge.

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seriusrod avatar image seriusrod commented ·

Thanks @nickdb for your help.

What you say is so interesting. I've seen in the VRM that the exhaust temperature of the MP2 during the night starts at 31ºC, increases to 41ºC in a short time and ends the night charge at 47ºC. I have a temp sensor inside the top output air outlet.
Shouldn't inverter limiting temp be independent from the charger ones?

My battery BMSs (2p), while they are integrated in the Cerbo system, is not configured as "controlling BMS".


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nickdb avatar image nickdb ♦♦ seriusrod commented ·
The system is a converter, so if it gets hot both will be constrained.
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JohnC avatar image JohnC ♦ seriusrod commented ·
@seriusrod

The Multi's inverter and charger are essentially the same device, just running in 'reverse'. They don't run together, so if it's charging, the ac loads are in passthrough from the grid. And if it's inverting, there's not enough grid to serve loads, so no charging.

I can't pick out from the graphs enough to compare to that 32A limit. In practice there's a bit of a safety limit applied to allow for surges. This may be as much as 10%, so I wouldn't expect more than 30A, so like 6600W. Or even less if you have loads with a poor power factor.

Are you absolutely certain you have it set to 32A? It won't be set there by default.


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seriusrod avatar image seriusrod JohnC ♦ commented ·

It seems that it could be more that one single thing.

Yesterday I was with another PV-friend and he noticed that my MP2 is strangely quiet in comparison to his ones. It has modulating sound, but it's deep and low. Can't be heard if you aren't at the same room.
Also from time to time it has a screeching sound. It seems to come when loads change and after a minute or so it completely disappears.

I also noticed that the Grid limit was not responding to commands and it was set at the 30A configured in ve.configure (It has the override checked). There was some glitch between the Cerbo and the MP2 that after a couple of reboots went away. To me that doesn't explain why it behaved more like the limit was at 20A.
I'm on the Venus 3.11 and I've recently upgraded the multi to 508.

Also I forgot to mention that I have the blue CT clamp attached at the AC input of the Multis himself hoping to stabilize the grid setpoint. My friend, who also is installer thinks that my unit is defective, as it has been acting with the grid from some time ago. It doesn't have a normal grid balance and periodically (every 30s or so) it rampages and tries to import up to 1000w for 3s and then goes back to normal. Even when it's setup to an export setpoint.
I've noticed that when this happens, the frequency reading, that normally is frozen at 50hz, fluctuates a little.

This weekend I'll install a CarloGavazzi and try to open the MP2 and blow the interior.

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