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alexw avatar image
alexw asked

Different Cable lengths

Hello everybody!


I read through multiple articles and also Victron's documentation about cable length, but I am still not 100% sure, so I decided you bother you here with my questions :-)


I use a setup with 3x Multiplus II, 3x Skylla-i Chargers, 2x MPPT, 4x SmartLithium. Everything by Victron.


Everything (except the batteries) is connected to a generic bus bar and then connected to a Lynx BMS + Lynx Distributor. The batteries are connected to "the other" side of the Lynx distributor - all in parallel.


CerboGX:

I am using a CerboGX for managing everything. Everything is connected together. In the "System Setup" I use as "battery monitor" the "Lynx BMS". In "DVCC" I set "SVS - Shared voltage sense" to "Forced on". My idea behind that the voltage at the BMS is the "real" voltage that all the devices (Multiplus, MPPT, Skylla-i) should adjust to.


Batteries:

All batteries have the same cable length (plus and minus). Each of them are connected to the Lynx Distributor. I think this is okay, since the cable length is as it should be.


Multiplus:

I currently use a parallel single phase system, but will change it to a three phase system soon. However, they are running as one "cluster". Currently I have the same cable length, but it is pretty messy. I only have about 0.5 meters of length. The cables have 50 mm².

Question #1: Is it possible to have different plus and minus cable lengths between the Multiplus? Example: MP 1: 0.3m, MP 2: 0.5m, MP 3: 0.7m

Question #2: Is it possible to have different length of plus and minus cable? For example: plus cable: 0.5m and minus 0.7m?

Skylla-i:

The Skylla-i chargers are connected to a small busbar and then connected via a 2.5m cable to the "central" busbar. The three Skylla-i also run in a parallel cluster.

More or less I have the same questions as for the Multiplus, but the main question is: I have a way longer cable to the central busbar, than the Multiplus. More or less the Multiplus and the Skylla show the same battery voltage.


General question:

I currently also have the issue, that the Skylla-i is not charging, when the Multiplus is charging. Right now the Multiplus is Inverting and the Skylla is in Storage mode. I would like them to work in parallel mode. Is this because they see a slightly different voltage?



Sorry for that long explaination and thank you in advance for your ideas/experiences!


Best regards

Alex

Multiplus-IIMPPT SmartSolarLithium BatterySkylla
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Ants Kosmos avatar image
Ants Kosmos answered ·

Cables from batteries to distribution box must be the same length. Plus and minus. Battery A +2m and minus 1m. Battery B + 2m and minus 1 m ..... This is for voltage drops. I think you understand, my low english too.


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Lukáš Svoboda avatar image Lukáš Svoboda commented ·
Imagine I have stack of 2 Pylontech bateries A that sits on top of batery B.


If I connect both batteries directly to busbar with same 2m cable I understand that it is "perfect".

But when I connect pluses of A and B with cable X and then connect B with busbar with cable Y then batery B has "cable length" Y while batery A has cable length Y+X which is larger than Y.

Is there something I understand wrong or the 20cm jump cable between batteries is assumed to be negligible? What if I stack 4 batteries like that? Isnt there difference of 60cm between batery D and A?


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kevgermany avatar image kevgermany ♦♦ Lukáš Svoboda commented ·

It's fine if you reverse on the negative. Negative for A goes to neg busbar and neg of B goes to A.

Can do it for 4 batteries as well, this is the way it's shown in the Pylontech manual.

But be careful of current ratings. The standard Pylontech cables are rated somewhere around 100A. If you're going to exceed that, connect all the batteries direct to busbars.



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dognose avatar image dognose kevgermany ♦♦ commented ·

Or connect them in pairs of 2. Then your busbars only needs 2x4 ports for 8 battery modules instead of 2x8.

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Related Resources

MultiPlus-II Product page 

MultiPlus-II Manual

Multiplus-II GX Online Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes

Skylla-IP65 product page (12v, 24v)

Skylla-i product page (24v)

Skylla-TG Charger product page (24v, 48v)

Skylla-TG GMDSS product page (24v)


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Additional resources still need to be added for this topic

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