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cruisey1987 avatar image
cruisey1987 asked

Pylontech batteries 100A discharge limit

I was reading the Pylontech manual and noticed that they battery cables they supply are rated to 100A. So it would seem that if I have 8 Pylontech batteries which could supply 8x25A for 200A total, I'm still limited to 100A because of the cable

I wonder would breaking the battery into groups of 4 be a good solution here. Each group would be wired back to a DC busbar through it's own 125A fuse and then the busbar would have a 250A fuse to the Quattro

Someone at Victron seems to have a similar idea to be as I noticed the batteries in the example diagram are in groups of 4, but it doesn't say anywhere in the guide to do that

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom#example_wiring_diagram

Does anyone have any advice on this?

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wkirby avatar image
wkirby answered ·

That diagram demonstrates a good way to overcome the cable limitation.
Another way is to string all 8 together and then take positive and negative off both ends of the stack, like in the Pylontech guide. I don't like this option as much because the end modules are more likely to notice more current then the ones in the midddle.
I personally prefer the option shown in the Victron diagram. Use the guides and your engineers intuition to make the right choice for the installation.

Not knowing what your system consists of, are you likely to have currents higher than 100A? For example, if you have a 5kVA Quattro, then it will be around 100A continuous at full power so one set of cable would be sufficient in that case.

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tom4x avatar image tom4x commented ·

Building two stacks, how do the single modules know they are allowed to output the full 25A and not 12.8A when wired like suggested? The CANBus cabling shown in the diagram is the same as for a single stack of eight modules. And there's no LV-Hub in place which would allow creating groups.


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wkirby avatar image wkirby ♦♦ tom4x commented ·

There is only one stack because the data cabling between the modules is wired as one stack. LV hub is only required when there are more modules in a data string than that particular battery model supports - either 8 modules or 16 modules for the "C" model.
The physical location of the modules and the DC cabling layout is not part of the data stream between the modules.

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cruisey1987 avatar image cruisey1987 tom4x commented ·

I think the maximum current from the battery would be set in the GX device, for the diagram with 2 groups of 4, you'd set the max discharge to 200A (or whatever the inverter limit is)

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tom4x avatar image tom4x cruisey1987 commented ·
Ah, OK. That makes sense!
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nickdb avatar image nickdb ♦♦ cruisey1987 commented ·
The BMS will set the limit, it is not aware of what cabling you use, so it is up to you to follow the manufacturers specs.

an 8kVA inverter is 6400W, so at 52V will pull a max continuous current of just under 125A.

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cruisey1987 avatar image cruisey1987 commented ·
I'm currently looking at an 8kVA Quattro with 6-8 Pylontech batteries. I believe that can pull something like 167A continuous (8000VA/48V=166.666A)


So if I have the batteries, it seems better to not be limited on the power available


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wkirby avatar image wkirby ♦♦ cruisey1987 commented ·
Indeed, 8x modules would be ideal.

Wire them up like the Victron diagram that you linked originally. Ensure that the tails from each stack to the bus bar are the same length and type of cable. If you plan to use the Pylontech long tails then you'll be set.

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