48V Battery Pack Wiring Options

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duncangardiner asked Aug 17, '23

48V Battery Pack Wiring Options

Hi I have recently purchased two RosenPV 48V 200Amp Battery packs. The versions I have are meant to be wall mounted as in Powerwall configuration. But I have them stacked due to space constraints.

My Question relates to the High Voltage cables that go from the external terminals on the batteries. Specifically when two or more batteries are working in a Master - Slave configuration.

Q: Is there any technical advantage using short link cables between the two batteries. Or are the shorter link cables simply for ascetics and tidiness?

I was not supplied with any short Link cables, and instead have two long cable pairs (exactly the same length). So without ordering a link kit I'll be wiring my batteries like this:

Not shown is the communication cable between the two batteries and the setup that has one of the batteries in Master mode and the other in Slave mode.

All answers greatly appreciated

Kind regards

Duncan

Lithium Battery wiring

cable-route-2.jpg (97.3 KiB)

cable-route-1.jpg (112.9 KiB)

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Answer 1 · 2023-08-17T09:54:37Z

matt1309 answered · Aug 17, 2023 at 09:54 AM

Hi @Duncan.Gardiner

You might find this useful. Particularly, page 18.

Wiring Unlimited (victronenergy.com)

tldr: For 2 batteries i dont think you'll see a notable difference in either option. For more you may want to make further considerations (but in my opinion both will again be fine).

What you should worry about regarding these things is distributing load over the battery by making sure the batteries are of equal resistances (same wire lengths). Different length cables will vary the resistance to each cell.

If you've only got two cells (or if you oversize wires) then in my opinion the concerns are less so than if you add more packs in the future.

For example in option 1 the wire runs are shorter (lower resistance so better) however if you add a third in that chain then the middle battery is "further" away so you could have less draw from that battery which overtime could cause the batteries to degrade at different rates.

Whereas Option 2 will have more wire length overall however the resistance is likely exactly the same between each battery (mainly if you have 3 batteries for).

Personally I feel these things are often over complicated and the impact in real world generally feels less so to me. We get the wires of perfect lengths but the internal resistances of the batteries themselves are never perfect.

(Also most Pylontech installs daisy chains the batteries and connect positive at top negative at bottom (diagonal connection) which in theory means middle cells have higher resistance/drawn from less). Many people I've seen on here overcome these conditions with busbars/oversized cables to make resistance differences negligible.

Given you've already got the wires I see no issue with Option2, saves you buy/crimping your own wires).

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duncangardiner commented · Aug 17, 2023 at 10:14 AM

Hi @matt1309

Ok this makes sense. This is my initial install. I have setup the system to allow for 2 more batteries in 12 months (4 batteries in total) after I use this 2 battery setup and collect some performance data.

RosenPV (which make clones of PylonTech Batteries) are very poor at answering customer support questions, so getting any meaningful and reliable information out of them is painful.

The longer cables will cost me an extra Victron fuse, but in the interests of moving forward I'll go with the two pairs of long cables and terminate both batteries at the Victron Lynx Distributor Buz-bar. All the cables are exactly the same length.

The cables supplied from RosenPV are much heavier than the PylonTech equivalent. 8mm with 150Amp plugs rather than the PylonTech 6mm with 125Amp plugs.

Making my own shorter Link cables is something I considered however like the rest of the pack RosenPV have used clone plug and socket fitting of the Amphenol Radsok fittings. So I can not order replacement plugs from Germany (as I am in Portugal) because the actual plastic housing don't match in diameters and thickness.

Upgrading to genuine Amphenol fittings would mean changing the sockets within the battery packs, and I am not sure I want to go rewiring my brand new packs just yet.

A long way round to say I think the RosenPV cables will be fine for now.

Thanks as always for your very helpful insights.

Take care

Duncan

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