discrepancies in cable section recommedations among victron manuals

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raul-v asked May 7, '24

discrepancies in cable section recommedations among victron manuals

I just upscaled to a phoenix smartsolar 12/1600 VA inverter.

English manual recommends to use 70 mm2 cabling

Spanish manual recommends to use 50 mm2 cable

My understanding is that 50 mm2 cables may stand up to 134 A and 70 mm2 171 A when ventilated what in either case does not seem enough for the maximun 3000 V at 12 V.

I understand that maximum time at peak power is around 0.5 seconds? even considering a power factor of 0.8 means 3000 VA/ 12 V gives the 250 amp fuse?

The purpose of the fuse is to protect the cable or the inverter or Both?

I´ve researched the kind of time reaction curve that the mega fuses have (even in victrons datasheet) but dont have it very clear.

I cant evaluate if a 50 mm2 cables in a 1.5 m lenght will be adequate enough or energy losses and overheating will became a potential risk?

Phoenix Inverter

70-mm2.jpeg (184.2 KiB)

50-mm2.jpeg (1013.5 KiB)

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dognose commented · May 07 at 03:49 PM

According to some calculators, running 250A through a 1.5m 50mm² will result in 2.23% loss. (70mm² would be 1.59% and 90mm² would be 1.24%)

Fusing that with 250A is way to much, that fuse will never open in a timely manner.

If you take a look at this "mega fuse" datasheet, A 125A Fuse operated at 200% will last between 1 and 15 seconds. (Time/Current Characteristics top right)

https://m.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/bolt-down-fuses/littelfuse_mega_datasheet.pdf

Given you want to allow some "peak" currents, but generally operate with the inverters continuous power of ~ 1300W, i'd take a 125A Fuse. (Running at 135%, so 168 Amps, it will still allow that for 120 - 1800 seconds)

If you notice that fuse getting destroyed to often, you could increase it's rating. But starting with a 250A right away may just lead to issues, because it will allow 300A or more for way to long.

Better blow some fuses and increase them step-by-step than starting "to big" and toast your wires ;-)

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Answer 1 · 2024-05-07T15:14:01Z

Guy Stewart (Victron Community Manager) answered · May 07 at 03:14 PM

Hi @Raul V,

It’s such a big topic that we have written a whole book about it

https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

If you still have questions after reading that let me know and we can go over what else is missing.

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Answer 2 · 2024-05-07T15:45:01Z

raul-v answered · May 07 at 03:45 PM

Thanks a lot, ill go over it.

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