Still can't figure out cable size needed to connect Pylontech batteries to Growatt inverter!

[YMcClean]

Hi we have a 6KW Growatt hybrid inverter and 4 x 2000c Pylontech batteries, we want to add 2 X 5000c Pylontech batteries as we are exporting a lot to the grid. So the question what is the best way to connect these?

So after much toing and throwing from Voltacon who sold us the cable and the folks who put the panels, and Pylontech, here is where we are at:
Pylontech cables are 4AWG, (peak current capacity 120A, constant 100A) so we understand the need to have the cables doubled up. Pylontech are clear from their point of view all the 6 batteries can be in one stack (UC5000 as master) and can double up their cables from first battery and from last battery and take these to a busbar.

Voltacon are suggesting the need to have the 2000s in one stack and 5000s in another... Either way the doubled up Pylontech cables will be going to a busbar and DC breaker then to the inverter. Can you someone tell me what size/rating cable is needed go from the busbar to DC breaker and DC breaker to inverter? Pylontech saying "you will need to do the calculation". Voltacon saying the 70mm2 cable they sent is needed and will need to be adapted to make the connections, but Voltacon not saying why it needs to be so large, just "that's what is needed"! Someone has kindly sent us a online calculator but we don’t understand enough to use it!

 

[MisterSandals]

Can you someone tell me what size/rating cable is needed go from the busbar to DC breaker and DC breaker to inverter?

What are the volts, amps and length of wire?

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

Keep voltage drop below 3%, looks like 4AWG or better:

 

[MisterSandals]

6KW Growatt hybrid inverter

6000W / .85 efficiency / 40V (?) cutoff = 176A

Wire and fuse for 200A or 250A.

 

[SplitUniverse]

The cables from busbar to inverter (and the associated breakers) are calculated based on the MAX that the inverter will draw from the battery. Look up the spec and start from there, if borderline go next wire size up. Breakers are there to protect the wiring.
If Pylontech states expressly that the batteries can be stacked in one bank then you can do just that, the inverter manufacturer is making assumptions on batteries (spec wise) and erring on the safe side as they don't want to take responsibility for making the wrong statement.

 

[Norwasian]

Personally, I would use the largest cable size that would be accommodated by the devices, e.g. the breaker. The larger the cable, the better: it runs cooler, with less resistance/line loss, and is less likely to be the source of problems going forward. I would also use only pure-copper cables, as those will have higher current-carrying capacity per their size.

Does the 70mm wire fit into the breaker? If not, is this the reason for Voltacon saying it would need to be adapted to make the connections? I suspect that is the case, as 70mm2 is large wire for the typical breaker.

 

[YMcClean]

Hi all, you guys have been fab! Really clarified everything. We will wire it for 250A, the largest cable that will fit and made of copper, does that make sense? Any suggestion for a good brand of DC breaker?

 

[MisterSandals]

Any suggestion for a good brand of DC breaker?

Is there any reason you want a breaker instead of a fuse? I do not see much reason to have switch on/off capability.
Midnite makes very high quality breakers if you are set on that.

Otherwise 250A-300A fuse would protect that wire.