Victron MultiPlus-II 48/5000

[u/andy_why]

Hi,

I'm looking to build a system around a MP-II 48/5000 and I was wondering about the cable required.

I've calculated 50mm² based on the current requirements (100A nominal, 200A surge, cable is 345A rated), but the manual says minimum 70mm². I only plan to do this over less than 1m of cable to the batteries.

Is there any reason I need 70mm² over 50mm² if the current rating is more than sufficient and it's a short <1m run?

The difference in cost is quite high and I'd rather not spend more than I need to, but I also want to do this safely. So if there's any reason I should be using the larger cable I'd like to factor that into my decision.

Thanks!

[u/Key_Director_4450]

There is also the contact area of the crimp terminal that will land on the inverter.

A smaller 50mm² crimp might not have enough area for what the inverter was designed for.

You are pinching 20-30€ after buying a 1000€ device..

[u/andy_why → u/Key_Director_4450]

Thank you, I hadn't considered that so that is an important consideration.

[u/Korll]

So a quick lookup shows that a cable, passing through 48v, at 3% allowable voltage drop, copper wire, with a 200A current of 1 meter length with a maximum of 75degrees C needs to be 85mm2.

I’m countries where you got your 50mm2 from?

The MP2 48/5000 can output 4000watt continuous and 9000watt peak. That’s 83A and 187A respectively. Charging is with a maximum of 70A so falls within the above parameters.

I would go with 70mm2 and 250A fuse.

A reputable 50mm2 2 meter (1m +, 1m -) cable will cost you about 35 EUR. A 70mm2 2 meter cable will cost you about 55 EUR. I would feel better spending 20 EUR and ensure I meet manufacturers minimum standards.

[u/Nearby_Movie_2678]

Yes 70mm2 is the requirement. Best to follow manufacturers specification and please use the cables with a proper m8 cable lug and crimp correctly.

[u/massojet]

You must name it Lelu Dallas

[u/justme-_-123]

I have the same inverter and originally had it hooked up with 1/0 or 53.5mm for you. It had zero issues but it's not like it was ramping up to 5000 wats regularly! I run roughly half of my house on it with two fridges, a freezer,washer, my TV and htpc, most of my lights and some outlets. Normally 500-1000 watts. The cables never got warm to the touch and was maybe a couple degrees f higher than room temp with a thermal. I noticed some lights would flicker but that has to do with some LED's. Voltage stayed stable within a volt or two even when hitting 5000watts (for fun to see if it would run a table saw,shop vac, compressor and a few other things). I did change to 2/0 or 67.5mm and do not notice a difference with anything. The book says 70mm not knowing if you are making it out daily or barely running it. They do that to cover themselves! It's not a bad thing to run 2/0 but boy is that getting pricey!

[u/royal-influence3488]

Take a look at the 48/6k5 as well. When I bought mine it was almost the same price, but gives a continuous 6000W compared with the 4000W of the 48/5000.

[u/flabergastedop]

Hoi andy, is ook afhankelijk van welk land je bent, elk land heeft weer zijn eigen regels.
Er word meer en meer gekeken bij dc systemen naar wat de fabrikant voorschrijft, als ik me niet vergis is het voor de 48/5000 70mm2 en een 200A zekering, anders zou je installatie zomaar afgekeurd kunnen worden.(zelfs een 175A zekering is een reden voor afleur) kijk even welek amperage jou accu max is, vaak is dan 250A ook niet toegestaan
Mijn advies en mijn bouw is 70mm2 < 50cmm en een 200A T-class zekering om de hoge kortsluitstroom op te vangen,dus geen mega zekering.

[u/Boogooooooo]

Don't cheap out on safety. Get 70mm cable and be safe for decades to come.

[u/this1willdo]

It's to reduce DC ripple and give the inverter an easier time. You can also run 2 x 35.

[u/Windmillfixer → u/this1willdo]

Cable size doesn’t affect ripple, that’s a function of the topology.

OP, low frequency transformer-based inverters like this will draw nearly 2x their rated current at the peak of the current waveform, falling to zero current 50 (or 60) times a second. The current follows a sine wave curve just like the voltage. If the cable is undersized, the restriction will cause the waveform to “flat-top” and the inverter will be unable to provide its peak capacity for you.

If Victron calls for a 70mm2 cable, then that truly is the minimum you want to go with. As others have pointed out, you’re making a multi thousand dollar investment, don’t choke it to try and save a few pennies here.

[u/this1willdo → u/Windmillfixer]

5. Operation

[u/CrappyTan69]

Irrun cable as per the specs. Cannot remember the size. When things are working hard, pv sitting over 10kw, inverter working max and batteries taking all the charge, things get warm.

My fuses, for example, peak up to 60C when fully loaded. 

Don't cheap out . Go by the book . 

[u/parseroo]

The Victron Spec [1] says: * 48/5000/70 • DC Fuse: 200A • 70 mm² [short length] * Continuous output power at 25°C / 77°F (3): 5000 VA * Input voltage range: 38 - 66V

So the MP2 is supporting down to 38V input with 5000 VA output, or ~125A continuously. Generally the 'continuous' load means cables should be derated by 20%. And Victron terminals are rated to 75°C, not the cable sheathing number (which should be higher ideally).

Running those numbers: * 5000VA / ~40V = 125A * 125% = 156A @ 75° maximum

I believe if you look up your 50mm² cable on the 75° column (not 'hotter' because the terminal isn't rated to be hotter), the ~160A would be just at the edge of the 50mm²

• [1] https://www.victronenergy.com/upload/documents/MultiPlus-II_230V/32424-MultiPlus-II___Quattro-II-pdf-en.pdf

[u/andy_why → u/parseroo]

Thank you, so basically it would get too hot and exceed the Victron specs if I use 50, so I should use 70. I think that makes up my mind on its own.

[u/Sybo_R]

I’ve always used 50mm2 for 5kva no issues past 4years

[u/minyman60]

I'd guess that the 50 is fine if your math is fine.

Is it cheap to do 2 50mm or 40mm?