question

jontm avatar image

Single Quattro in three phase offgrid system

Hi!

I am currently planning to do some upgrade to my offgrid cabin. Today we use two 35 kVA three phase diesel generators (one in standby) to supply power to the cabin. The average power consumption is about 50-100 kWh per day, but most is used in the morning and evening. Peak power is just under 10 kW, during most of the day it is only 1-2 kW. I therefore want to install about 20 kWh of Li-Ion batteries to be able to shut off the diesel generators during the daytime.

There are only a couple of three phase loads in the system and none of them need to be able to run while on battery power. I got hold of an older 10 kW 48V Quattro 230 V that I am planning to use for this purpose.

Would it be possible to just connect the Quattro inline to two of the phases in the system and then run single phase when on battery and three phase while on genset ?

My initial thought is that it should in theory be possible as long as the inverter section in the Quattro never runs at the same time as the genset ? Then make sure i rewire the fuse box in the cabin to ensure that all the loads that i want to be able to power from battery is connected to the two phases coming from the Quattro.

I believe that my genset has contactors for the supply, so when the genset is not running, the third phase would be physically disconnected from the generator. I understand that i will also need some contactors with some smarts to ensure to disconnect the two live phases on the three phase loads when on battery to ensure that i do not damage the equipment. Running with 2 phases live on a three phase load is likely to cause problems :)


A bit unusual setup I am sure, but if anyone have some thoughts or have done similar things I would be very interested to hear about it. The simple solution would probably be to purchase two additional Quattros, but that would be very expensive since i do not really need three phase.

At the same time I would like to not change over to a pure single phase system as my gensets are three phase and it would be good to get some of the loads that i do not need to be able to power off battery to be on other phases on the genset so that I get a more even phase load on the genset while it is running

MultiPlus Quattro Inverter ChargerGeneratoroffgridquattro 10kva
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4 Answers
Alexandra avatar image
Alexandra answered ·

@jontm

One phase in one phase out.

You cannot mix two phases in, as they are out by 120° on sine wave and the inverter synchronises to grid. I did see you thought that is would be fine if you werent running the genset, but then how would you charge the batteries if you needed to?

You would have to separate out the circuits like lights and powerpoints you want to run on the battery only and it cannot include any part of a load with three phase needs.

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jontm avatar image
jontm answered ·

circuit.png


Seems like i forgot to include the schematic to illustrate how i propose to connect it.

I assume that i can charge the battery while the transfer switch is engaged, but i might be mistaken ? Can it not charge while the transfer switch in engaged ?

It should perhaps be said that i do not have a neutral in my current system. The generator is wired with in delta on the stator windings. Phase to phase voltage is 230 V. L1 would be connected to L1 on the Quattro, L2 would be connected to N.


circuit.png (159.2 KiB)
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shaneyake avatar image
shaneyake answered ·

The best way to do it would be to setup a single phase system for just battery.
You can still power the inverter from 3phase like you said L1-L2 input but the output should go to a dedicated L1-N wiring for all the loads you want on battery. You can't wire it like your diagram as there will be an imbalance between L1-Brown and L2-Black when running L3-Gray loads this will cause multi to think there is a ground fault and trip off.

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Rob Fijn avatar image
Rob Fijn answered ·

Best you can do this at your AC distribution box. Here you have fuses that supply 3 phase loads and 1 phase loads. Then simply supply the 1 phase loads via big switch and then to the Quattro and then to the 1 phase fuses... Use the Switch as a emergency when you Quattro system is not working..

Regards, Rob


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