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johanneshovda avatar image

Victron toolkit cable calculator - what does length mean?

Trying to use the Victron toolkit app to determine cable size.

What unit of measure does "length" refer to? Is this the distance measured PER cable in a run?

E.g a 6 meter physical distance to the battery, is this 12 meters cable "length"? (Calculating both the positive and negative run).

In my case, I plan on running negative via the chassis. How does this affect the measure of cable "length" in terms of the Victron toolkit app?



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Mark avatar image
Mark answered ·

Hi @Tim from Eat Sleep Van, sorry I don't think that your feedback is correct.

I just calculated the loss myself and can confirm that the cable calculator assumes that the distance entered is the 1 way length for a 2 conductor cable.

Accordingly it automatically doubles the length to determine the 2 way length and the total resistance/voltage drop.

If you want to use this calculator to determine the voltage drop for a single conductor/1 way length, then you can simply work around the logic by entering half the length.

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Yeah I think you're right. I just tested the forumla listed here:

https://www.redarcelectronics.co.nz/how-to/calculate-voltage-drop

(50*10*0.017)/4 = 2.125 while the app reports 4.4 volts. So yes it assumes a return cable. Not ideal I'd say, and it really should say in the user interface. Or not do it all.

Mark avatar image Mark ♦ Tim from Eat Sleep Van ·

I just calculate it from scratch (V=IR) using an approximate resistance for actual multi-strand copper cable;



1560490626404.png (14.7 KiB)

So, are you saying that if I want to use the calculator app to size up only the positive run (since negative run is chassis), I should only enter 3 meters length (for a 6 meter physical distance)?

With that calculator - yes.

But that also assumes that the resistance through the chassis is 0Ω, which is probably a reasonable assumption.

This is an old 13 meter touring bus, so it's 8,000 kilos of steel tubing... that should make for a decent conductor..

Well the conductivity of steel is only ~3 to 15% that of copper - so you may want to re-think of it as ~240kg to 1200kg of copper... :-)

Tim from Eat Sleep Van avatar image
Tim from Eat Sleep Van answered ·

[edited] It's for double of wire. And yes if you're a single cable you should halve the cable length. If you're using the vehicle chassis then I think you can think of it as a very big fat cable that has low resistance? Not an expert, don't trust what I say. This person sounds like they know what they're talking about https://mechanics.stackexchange.com/questions/57206/when-to-use-chassis-and-when-to-wire-to-battery-neutral

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Thanks for sharing the link, interesting read on chassis ground