For the installation of a home battery system, I am considering one of the following two inverters. It will be either a Multi RS Solar 48/6000 or a Multi RS19 Solar 48/6000. They are essentially the same devices with the same specifications, only with a different enclosure.
I am now looking into the required cable size for the DC wiring, and I have run into a problem.
According to the Wiring Unlimited PDF:
25mm2 for up to 75Ah
35mm2 for up to 105Ah
50mm2 for up to 150Ah
Both devices have a maximum DC rating of 100Ah.
So I would assume that 35mm2 is required.
However, when I look at the Multi RS Solar manual, it states that a cable size of 35mm2 is recommended. That seems logical, but here is the issue: the Multi RS19 Solar uses Amphenol SurLok Plus 5.7mm connectors. These connectors are rated for currents of up to 120A, but they can accommodate a cable of no more than 25mm2. So the cable would then be undersized.
Am I missing something, or is the connection not suitable for the required power?
When on short distances, like inside a rack where the rack inverter will be very close to the rack batteries, then the cables are quite short and then 25mm^2 could be used for 100A.
Take a look at Pylontech cables that are rated 100A and have 2m and 4AWG cross section (less than 25mm^2)…
What kind of problems do you have in mind?
Distances are too short for creating too much heat.
I have 25mm^2 cables for Multi RS over about 1m distance and it doesn’t heat more than 40 deg.C when on full power.
The deltaV over that distance is about 0.35V also on full power.
The length of the DC cabling from the distributor to the inverter will not exceed 1 meter. I just find it so confusing that the manuals specify different cable thicknesses for the same power ratings…
Manuals are conservative. The reality is different.
The manuals specify bigger section for less voltage drop over the same distance.
You will be surprised that the entire current of 100A passes through a H-bridge inside, which uses only 4 FETs per leg.
And those FETs are in TO220 packages that have source/drain pins with no more than 1mm^2 cross section.
So the whole 100A passes through a total of 4mm^2 on the FETs section.
