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apophis avatar image

Multiplus -II frequency variation

Hy .

My friend has a system made from a multiplu-II 48/5000/70, mppt 150/100 and 19 solar panels of 300w , on the roof of his store , and a disel generator 2000w (he dosent have conection on the national network)

He has a house at 40m from his store but the cable of feeding the house has 60m between the house and the inverter . the problem is that when his water pump is starting (3000W) is making a power variation and a frequency variation very big :

-volt in faling from 230v to 180v for a second

-and frequency from 50Hz to 32 Hz for a second

and becouse of this variation the led lamps (8psc) has burn.

how can i help him to stabilize the variation

it is posible to and a (ups-with battery) stabilazer of 7000w near the house panel ?

please give me some ideas. Thanks.

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2 Answers
Alexandra avatar image
Alexandra answered ·

@apophis

How big is the cable between the house and the inverter setup? This is usually caused by undersized cabling and/or corroded joints causing more resistance.

You could always have a smaller inverter / ups setup on the pump to help. check the rating of the pump and size the inverter accordingly.

Final though there could be an issue with the pump wiring like an earth neutral leak? even on the pump control?

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alan avatar image
alan answered ·

This is classic overload behavior of a multi/Quattro (any battery inverter really)


A 3000w pump will have a startup surge of something like 6x nominal current.

So maybe 18kw, twice the surge rating of the inverter. What is the DC bus voltage when this happens? You are looking at a 375 amp draw, what sort of batteries?


You could try to add a super capacitor in parallel on the dc bus, to help with the surge.

https://www.fpv-power.com.au/super_capacitor/48V-16V-Maxwell-Super-Capacitor-Combo

Or switch the pump to a variable speed unit, these use inverter type motors with less surge.

Something like a grundfos CMBE or scala2

The other thing to check is to ensure the DC cabling is rated correctly and of sufficient size.

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