question

JeanMc avatar image

Pylontech battery cable spec

Hello,


Can someone please clarify the following:


The Pylontech 2m external power cables (both + and -) is labelled 4AWG. The Pylontech US3000 manual (page 12) rates this as a 120A cable. AWG 4 translates to a 21.2mm2 cable with a current carrying capability of 70A at 60 deg C. (https://en.wikipedia.org/wiki/American_wire_gauge)


A Pylontech US3000 battery (page 4 of manual) has recommended charge/discharge capacity of 37 A. This cable should work fine with a single module. However 2 modules in parallel will double the current capacity while voltage remain at 48V. Are we really using a 70A cable on a 74 A supply source? Obviously the max current per single US3000 is much higher.

The Pylontech cables does not appear to be a copper cable. The wire strands are silver.



Thank you

Jean

Pylontechcable
5 comments
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Did you resolve the cable size issue @JeanMc?

I intend to buy 8 modules of US3000. According to Pylontech, you can use up to 8 battery modules without the need for a hub. Each module has 2 interconnection power cables. And each package has 2 power cables for connection to the inverter. These are however limited to 120 amps. Two questions:

1) Aren’t the cable connections severely limited for 3 modules or more? PolyTech recommends 37 amps charge capacity per module. That is potentially 37 x 8 = 296 amps in my case Yet Pylontech say their cable is rated at 120 amps. As Jean says, it doesn’t appear to be fit for the purpose.
2) For the same reasons above, aren’t the interconnection cables under speced by Pylontech?
I have read both Victron’s “wiring unlimited” and Guy’s comments but no answers.

Fideri

Hello @Fideri,

it is not just simple as it seems to be. I run a batteries block with 8 pieces USB2000B.

I connected to my bus bar one 2m cable from the very top unit and additionally one second 2m cable (each one for plus an minus) from the very bottom unit. But still all eight units are in daisy chain wiring. I am planning to change wiring and to work in two blocks whit 4 units in daisy chain and to have per block down and bottom one 2m cable to my busbar. So in total four cable sets per eight Pylontech units.

But there is another effect you have to think about. I recognized that depending on charging and on the temperature of the batteries, the Pylontech BMS limit in my system in the afternoon for hours the charging limit to 80 A for all 8 units. It make sense to think about wiring and cabling to use maximum current for charging - but keep in mind that the internal BMS has it's own demands and might regulates down the current. According to my monitoring the Pylontech BMS has always the final say and is the boss for the charge current. ;-)

Nevertheless I think it makes really sense to use as less as possible units in daisy chain. So the best would be, I think, to connect each Pylontech unit with it's own 2m cable directly to a bus bar or to use as best compromise as less as possible daisy chained units.

DayAndNight

That is one neat installation. Thanks for the pic.

I hear you when you say it’s more complicated. Certainly it is pointless to adhere to wiring standards if the input/output is going to be throttled by BMS.
I have ordered 8 of US3000. I will order 8 more when I get the cash. I will try to keep them in banks of 4. So 4 x 4 parallel.
There is one thing I don’t get in pic. As I understand it, your top “master” power cable (2 metres) is going to your positive busbar, unfused, then your busbar connects to the charger/inverter with your own cable which can be fused. The bottom “slave” power cable (2 metres) goes to your negative busbar, then the busbar connects to the charger/inverter with your own unfused cable. What about the extra orange power cable at the “slave” and the extra black cable at the “master”? Are those going to your loads?

Fideri

Hello @Fideri,

I think a picture say more than 1000 words! ;-) I did a drawing for you.

Of course I use fuses at the positive wiring. The three Multiplus-II (3-phase) are connected with 120 cm 35 mm² cables, for connecting the busbar to the victrons I used the Pylontech 200 cm 25 mm² cables. In the drawing I didn't show the net wiring, but this was done normally, with the serial cables delivered with the pylons and from the master to the Multiplus-II GX I used the special Victron/Pylontech CAN-Bus cable.

Here some photos of my busbar work:



Some more information about my first steps to realize my bus bar housing you can find here.

When I started, I didn't know the Victron Lynx system, which can be used for such an installation, too.

But I am satisfied with mine and I think I can upgrade each box for two additional Pylontech cables. I will guide one cable from the top and one from the botton into the housing and I will double connect the pyloncables to the busbar on the first and on the last terminal of the busbar.

DayAndNight

Hello DayAndNight,

As clear as night and day :)

Thank you.
Fideri

3 Answers
Guy Stewart (Victron Community Manager) avatar image

Hi @JeanMc,

The 4AWG cables supplied as part of the Pylontech cable kit have an insulation temperature rating of 105 degrees.

This allows for the much higher than normal current carrying capacity than you might be used to, or able to find in other cables.

7873-91c9dec5-c4c4-4002-b069-5cf7a70cd475.jpeg

7881-d230b1b6-2fdd-470a-b822-a176e59a49e7.png


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Thank you for your reply Guy.


Unfortunately it is no longer available as a free standing (offline) app.

But you can still access it via this website:

http://wirewizard.bambachcables.com.au

Most phones allow you to add a website as a web app to the home screen of your phone.

warwick avatar image warwick Guy Stewart (Victron Community Manager) ♦♦ ·

Thank you! Added.

kai avatar image

A related comment on current carrying capacities - the figures are based on stated conditions (free air vs in conduct, air flow, any adjacent cables (that may also contribute to ambient temp), etc) in the steady state - it takes a while to get up to the "rated" temp. Cable selection should consider those factors, including and up to what the cable enclosure can take. PVC has a max op temp of around 60C for instance, and would not be suitable as conduit material if the cable is expected to heat up to >60C.

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JohnC avatar image

Hi @JeanMc

Great you're concerned.

A quick answer might be just to suggest you use both cables. And that the silver cable is actually high-end tinned copper, usually specced for marine use.

But I won't. There's more to it than that of course, and I encourage you to take a look through this: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Come back if you have particular questions..

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Hi John,

I've read Wiring Unlimited.

Pylontech is approved for use with Victron products. This specific installation will use a Multiplus ii 5000 and MPPT 250/100 charge controller with these batteries.

Pylontech provides the shorter inter link power cables with each module and you have to buy the longer 2m set separately. The reason we purchase these cables is because of the connectors. You stay with the "theme" and the installation looks neat. Obviously you can buy a set of these cables for each module and that would solve the problem but that is not how these cables are advertised and sold. You require one of these cable sets with 3 x US3000 modules or 4 x US2000 modules. If you have 4 x US3000 modules you have to buy an extra 2m cable set. In a 4 x US3000 scenario, I would definitely use one 2m set on 2 modules and the other 2m set on the other two modules. I am however still concerned about the cable rating vs the module rating.

My specific question is: Am I missing something here? Or are these cables not suitable?

You can make your own cables:

https://www.mouser.de/ProductDetail/Amphenol-Industrial/SLPPA25BSB?qs=G2fvz%2F8gJKLF7L0%2F81ZKWQ%3D%3D&vip=1&gclid=EAIaIQobChMI-5vBk4uB6QIVGOd3Ch3uWAPaEAYYASABEgLbO_D_BwE

Unfortunately, the Radsock-Standard 5.7 plug is limited to 120A. Therefore, not only the 25mm²-Cables seem to be a bit unerrated. The Battery DC plugs are too.