r2000 avatar image
r2000 asked

What is the Multiplus output voltage?

Hi all, my first post here.

Does anyone know how to calculate the output Voltage of Multipluss II inverter?

For example, the Voltage at the property (distribution board) is exactly 230V.

If Inverter would be charging batteries from the grid then there would be some voltage drop dependng on cabeling and load, say 2%, so Voltage at the end of the circuit where inverter is connected would be 230-230*0.02=225.4V

If now we wanted to export the energy from the battery, we would have to have higher voltage at the property than on the grid side (>230V) so the output Voltage should be at least 230V + whatever voltage drop (lets say we export the same power and it is again 2%). Would that mean that Voltage at output terminals of inverter would be 230+230*0.02=234.6V? Or that plus X% or X Volts ?

Basicaly I am trying to understand how inverter decides what voltage to output when outputing AC current - is it matching the grid+X% by consistantly monitoring voltage at the terminals and making sure that generated Voltage is higher?


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1 Answer
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wkirby answered ·

You need to think about the Power. Power is the product of Volts and Amps.
Also the resistance of the cable between the MultiPlus and the distribution board is reasonably constant. The Voltage drop over this cable will depend upon how much current is flowing through it.

So let's choose a constant current of 10A (2.3KW) and continue to assume that the Voltage at the distribution board is 230V. If the Voltage at the MultiPlus terminals is 225V when charging with 10A mains, then the resistance of the cabling is (230-225) / 10 = 0.5Ω.

Now with a constant cable resistance or 0.5Ω we can then calculate the Voltage at the terminals at any point in time for a given current and distribution board Voltage.
If MultiPlus is back-feeding 10A (2.3KW) into the distribution board then 0.5 x 10 = 5. MultiPlus needs to raise its Voltage by 5V to get 10A to flow, so the Voltage at its terminals will need to be 235V. With 5A, the Voltage would be 232.5V.

These calculations are very basic, backfeeding will cause the distribution board Voltage to increase also as there is more cable between it and the local substation.
Also the grid Voltage is constantly changing so those calculations are merely for a snapshot in time.

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·

Great answer!

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