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texascharlie avatar image
texascharlie asked

Matching Cable Lengths?

I'm looking for input regarding cable length when hooking up my Multiplus and SmartSolar.

I frequently see the recommendation to keep cables the same length. What cables does this apply to? For sure, match cables linking batteries. But what about others?

Must the POS and NEG cables from the respective buses to the MultiPlus be the same length? If yes, is there an acceptable tolerance for slightly different lengths?

I expect my longest single cable to be less than 30" long and the total path from the battery (+) to the inverter to be about 60" long. I'm wondering if short runs like this reduce the need for perfectly matched cables.



Multiplus-IIMPPT Controllerswiring
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Kevin Windrem answered ·

If you are paralleling up multiple batteries, the cables between the positive terminals and a positive common point should be the same length and wire size. Same for the negative side. Positives and negatives do not need to be the same length.

If you are paralleling multiple inverters, the positive cables need to match lengths and the negatives need to match lengths also but positive and negative cables don't have to be the same. This applies to inverters run in full parallel mode (AC inputs and outputs in parallel). Less important for split-phase/3-phase systems.

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Daniel Suchý avatar image
Daniel Suchý answered ·

Do you have to also match lengths of MPPT and Inverter cables? I need to install MPPTs with longer cables than inverters have.

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Kevin Windrem avatar image Kevin Windrem commented ·
The cable length/size matching is from paralleled inverters to a common point. This is necessary for proper load sharing between the two (or more) units. The reason is that both inverters are given the same instructions to the inverter core. If cable resistances are different then one inverter will supply more current than the other. This is explained in Victron documentation. It might be worth taking the parallel / multi-phase training on professional.victron.com.

It is not necessary to match cable lengths to other devices like MPPT.

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