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sesshoumaru avatar image
sesshoumaru asked

Proper System Dimensioning

This question maybe sounds completly foolish, but the more I read about the system dimensioning, the more I got confused. So I would like to ask this, probably simple, question.


What does the 5000 of the Quattro or Multiplus II actually mean?
I get that its 5000 VA, which breaks down to about 4000W (-20% from VA). But what does it actually refer to?


Does it mean that the AC-out can only provide 4000W output? Even when the grid is connected or the battery can sustain discharge of, lets say 8000W? Or does it mean it can only take in 4000W provided from a PV inverter which is AC-coupled to it? Maybe both?


Sorry for the dumb question....

system design
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shaneyake answered ·

Looking at the Multiplus-II 48/5000/70-50
5000VA is the voltage amp rating. 5000VA with a PF of 1 should be 5000w but victron rates it's inverters with a power factor of 0.8 it seems. They have a note about Crest factor of 3:1.
I wouldn't really worry about this tho, I just think about the MAX being 5000W in perfect conditions.

The output rating is listed with temperature. As the inverter heats up the output goes down.
25C - 4000W
40C - 3700W
60C - 3000W
This isn't necessarily ambient temperature, as it is also airflow dependent.
My inverter outputs more than 4500W for minutes before it throttles down to 4000W.

AC-In to AC-Out is limited to 50A. Closer to 11 500W. So you can have 11.5kw of load on the inverter when grid connected. AC-OUT + AC-OUT2 can't be more than 50A tho. With AC-OUT2 limited to 32A.

Even if the battery can deliver 8kw the inverter won't push out more than 4000W.

Yes, you should not install a PV inverter on the AC output that is bigger than the inverter. 5000VA or smaller.

You can take 4000W from the victron inverter and 4000W from the PV inverter for 8kw total. However it isn't good practice to have loads on the output of the inverter that are bigger than the inverter is able to power. Because if you have 8kw of load on the inverter and you lose grid which might trip the PV inverter for a few seconds the Multiplus will be carrying the full load of 8kw and will overload after a few seconds.


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nickdb avatar image nickdb ♦♦ commented ·
The 48/5000 happily runs 4kW loads at the right temperature..

The temperature compensated output you mention is ambitious.

With a 32C ambient temperature it cannot do more than approx 3400W.

Tails off quite quickly.

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sesshoumaru avatar image sesshoumaru commented ·

Hmmm... okay, let me see if I got his right.


Assuming I have loads of about 8kW on the phase (let it be L1) with a Multiplus/Quattro rated with 5000VA and its nighttime (no PV). This means the Inverter can deliver about 4000W from the battery, the other 4000W will be pulled from the grid. Right?


If the power goes out in this moment, all loads fall to the inverter which will overloads and probably trip - power out / failure. I would need to switch off all loads and restart the inverter. Right?


As a sane person I would connect all heavy loads to AC2-out, and have a switch, so that I am able to switch the e.g. kitchen oven from AC2-out to AC1-out and then being carefully about how many hot plates I am turning on. Right?


Sorry for all that questions. I just try to understand the technical ratings better.

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nickdb avatar image nickdb ♦♦ sesshoumaru commented ·
Correct.

If I recall the inverter will try to automatically restart 3? times after overload, and if it can't succeed it will need manual intervention.

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shaneyake avatar image shaneyake sesshoumaru commented ·

AC-OUT2 is fully programmable. So you can have it turn off automatically when grid is lost and then have a switch on an AUX input that will turn it back on when you want.

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sesshoumaru avatar image sesshoumaru shaneyake commented ·
You mean even if the grid is off and the systems runs on battery (or generator on AC2-in) I could "force" the Quattro to switch-on AC2-out (while of cause keeping AC1-out on)?
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Paul B avatar image Paul B sesshoumaru commented ·
yes that is correct
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