question

eyub avatar image
eyub asked

3 PHASE SYSTEM WITH GENSET ( STARTING CURRENT)

we have a customer requesting a solar system for oxygen pumps in his fish farm, he has 4 oxygen pumps each of 2.2 kW rated power and they are three-phase he needs to operate them 24/7 there is also grid in the site for 8-10 hour per day and there is also a generator, he wants to operate using solar during the day time and about 2 hours battery backup at night or during a cloudy winter day, and the Genset will start when the batteries are empty and there is no grid.

can we offer him a solution with Victron at this big back-up capacity, also note that there is no suitable place for the battery so we have to create a small cabin and cool it with a small 12000 BTU AC

I thought of :

19.44 kWp solar (54 panels 360 watts divided for three sets each 18 panels for each inverter)

3 x 5 KVA Quattro

3 X 250/100 MPPT charger (1 for each inverter)

24.576 kWh battery ( 12 X LiFePO4 Battery 12,8V/160Ah Smart ) considering 85%DOD


SO MY QUESTIONS ARE:

1- can this combination (especially the inverter) stand the starting current of this load ( I don't know the starting current the pumps are installed and I couldn't find their datasheet online but I attached the nameplate photo)

2. can I replace the batteries with LONG LIFE GEL OPZV 2V with considering 60% DOD, will they stand the discharge current of the load since the load during the battery back up?

- I attached the load calculation and the motor nameplate

thanks

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MultiPlus Quattro Inverter Charger
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Alexandra avatar image Alexandra ♦ commented ·

@eyub

The 5KvA Quattros may not be quite enough. The start up currents on motors can be heavy if they do not have great power factor correction on them. Or at least soft start devices. we have even seen motors installed with electrical wiring that is too small making the whole situation even worse.

So 2200W is active the power rating but the apparent power may be very different.

Watts law for three phase is easy to work out the active power though.

Current (amps) = power (watts) ÷ voltage (volts) ÷ square root of 3 (1.732) ÷ power factor

2200÷380÷1.732÷0.8 = 4.18A. 0.8 as a power factor is generous for motors.

Also on another note, is there a reason why you are choosing to build battery banks with 12V batteries instead of a 48V system? Battery balancing will become an issue and not all batteries can be series parallel connected.

Is the site running are you able to power log it?

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eyub avatar image eyub Alexandra ♦ commented ·

- related to the staring current, I will try to get the datasheet from the owner he said he can find it if not I will try to go to the site run the motors and clamp the phases to measure the starting current, but the question is that what is the peak starting current for Victron inverters and for how many seconds it last because I couldn't find this in the manuals.

- related to the soft-start can I use them to solve the problem if yes what type should i select I am not familiar with them

- the battery we can go with any batteries, even with GEL OR AGM if they stand this discharge current? fo they ? or it is preferred to stick with lithium

-the last thing is that I got the logic o how you calculated the real current but why you did that.


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Alexandra avatar image Alexandra ♦ eyub commented ·

@eyub

Amperage determines cable size. And what your base load should be. Also working it out will help as knowing what you should be drawing verses what you are actually seeing and helps in diagnosing issues.

Sometimes a site has unexpected major electrical issues which will give you a headache after you install the system and a make a very disappointed customer. (Speaking from experience)

And you should work out your inverter size so the max of the inverter is able to handle the peaks. Anything drawn over that is classed as an overload. Repeating an overload is not really the best for longevity of a system. I have seen a Victron take a 100% overload but don't forget that the battery and the cables have to be able to support that overload as well.

Lithium is better for high current discharges if the battery is rated for that. So check your battery C ratings.

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1 Answer
tilo avatar image
tilo answered ·

As Alexandra said, if 4 pumps start at the same time, the startup current may overload the system. You may install a time delay relay to 3 of the 4 motors so they do not start at the same time.

Do not make a separate battery bank for each inverter. You must use one battery bank for the 3 inverters.

The 12V 160Ah Smart can be series connected to 48V. In any case use 48V.

What is the temperature in this place?

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