Pylontech battery cables

[ns31]

Hi all - I have 2x Pylontech US5000 batteries in parallel, each with their own set of cables (as the cables are rated at 120a). It seems to be a very common mistake that people use the supplied cable to connect 1x positive and 1x negative to the inverter with batteries in parallel, but with 2x batteries there would be a potential 250a flowing through cables which are only rated at 120a max. It seems a bit worrying how many people have this setup (look on YouTube).

I plan to connect each battery cable to a 100a fuse on the positive wires before connecting to a bus bar, which will then be on a 250a between itself and the inverter.

I have a Blue Sea 5502 250A T fuse in place, but I was just wondering what people use on the battery cables for protection? Do you prefer a t fuse or something like a switched fuse unit? I assume a fuse unit means the cables can be connected directly without the need for a copper cable lug?

Many thanks

 

[DIYrich]

Class T fuse.
What is the AWG of the cables provided? 1 AWG is rated for 119 amps in conduit, and 211 amps for chassis (open air). Connect each battery separately to the busbar, or get thicker wire to connect in parallel.

 

[ns31]

Class T fuse.
What is the AWG of the cables provided?

Would this be on the positive lead only? Or is the recommendation double pole protection?

 

[littleharbor2]

You need to shop around. Some fuse holders allow raw cable to be inserted, most others dont.

 

[jploh]

My top choice right now is a combiner box containing a MCCB with a bus bar having terminals for lugs. I saw a block distribution box which has a more secure cover but it didn't say how much current it's rated for. Options are limited where I am, having issues finding longer 4 AWG cables crimped with Surlok.

 

[DIYrich]

Would this be on the positive lead only? Or is the recommendation double pole protection?

Positive only is sufficient.

 

[SeaGal]

Hi all - I have 2x Pylontech US5000 batteries in parallel, each with their own set of cables (as the cables are rated at 120a). It seems to be a very common mistake that people use the supplied cable to connect 1x positive and 1x negative to the inverter with batteries in parallel, but with 2x batteries there would be a potential 250a flowing through cables which are only rated at 120a max. It seems a bit worrying how many people have this setup (look on YouTube).

The reason for the apparent 'common mistake' is that, in many installations, the multiple battery racks are used to provide more storage capacity rather than increasing peak load - the peak load is limited by the inverter itself.

Hence you can safely have multiple battery racks connected to an inverter, provided the DC fuse is correctly rated for the cable, of course.

I see in a separate posting that you are installing an 11kW off-grid system... you will need to check the specifications of your inverter to find out the the maximum draw of DC possible and size your cables and fuses accordingly.

Note also that:-

a) Not all inverters will provide the same power AC from battery as they can from solar - for example my Solis provides 3.6kW with PV input, but only max of 3kW from battery.

b) Inverter power from battery may reduce when the voltage is lower - Pylontech batteries are only 15 cells each, so lower voltage than the industry standard.

c) The US5000 is only recommended for 80A discharge and max of 100A. But even at 80A each, you will only be able to power around 7500W for an hour if you only have two of those batteries.

Hence, I'm not sure how you will be able to go off grid with that configuration unless your power demands are very low, but that doesn't tally with having an 11kW inverter.