Cable Sizing for High Amperage Applications

[CJT]

I am trying to size up the cabling for all of my electrics.

Now these calculations are assuming absolute maximum load on the winches or the twin compressors.

Chances are that they will not actually ever need to run at full load anyway.

I am currently leaning towards running the 33 mm² cable for all aplications however I am a bit concerned on the possible voltage drop on the longer cable runs, however even at maximum load the rear winch would still bet getting 11.22 volts if you assume 12 volts from the battery.

I have shown some larger cable sizing in red although I am not too sure if it is in fact needed or warranted.

https://www.aulro.com/afvb/images/imported/2012/08/135.jpg

Anyone out there running rear winches etc and are able to share their setups and experiences.

[Homestar]

Hi Chris, what sort of cable are we talking about here, and where did the voltage drop calcs come from?

I have a 6 metre run of 35mm squared cable and their is no noticeable voltage drop over that length. Just went and measured it - 12.38 volts at the batteries up front, and 12.37 volts down the back. Not sure if this changes when loaded - maybe we need Drivesafe to chime in here.

Not sure if I'd run 338 amps through it - mine is just to run a compressor, fridge and lighting - overkill for my application, but I had it lying around.

Cheers - Gav

[CJT]

Gav,

Sounds like the same cable or very close.

The voltage drop was through an online calculator, I can sit down and work it out manually to check the values.

Mine is cable stamped with 32.15 mm2 (2BS) I purchased from Springers Solar.

The 32 mm2 cable size is more than adequate for the dual battery charging, I am just unsure in regards to the winch cables.

The standard winch cables are that size but are only around 600mm long.

[Mick_Marsh]

Hi Chris, what sort of cable are we talking about here, and where did the voltage drop calcs come from?

I have a 6 metre run of 35mm squared cable and their is no noticeable voltage drop over that length. Just went and measured it - 12.38 volts at the batteries up front, and 12.37 volts down the back. Not sure if this changes when loaded - maybe we need Drivesafe to chime in here.

Not sure if I'd run 338 amps through it - mine is just to run a compressor, fridge and lighting - overkill for my application, but I had it lying around.

Cheers - Gav
The cable has resistance.
No current, no voltage drop.
Once there is current, there is a voltage drop. V=IR
What is the rated resistance of the cable?

[Vern]

i did the calcs years ago for my old rangie which had battereis in the back and obviously the winch up front, i had to run 70mm2 cable, was good for 400A at that distance all day long.

[CJT]

The cable has resistance.
No current, no voltage drop.
Once there is current, there is a voltage drop. V=IR
What is the rated resistance of the cable?

That is correct, hence the reasonable voltage drop through the 33 mm2 cable at 338 amps.

A 6m length of 33 mm2 with no current draw has a resistance of 0.0031 ohms, meaning basically no voltage drop, at 100 amps voltage drop is 0.31v and at 200 amps it is 0.62v etc.

These are generic calcs using the natural resistance of copper.

[Homestar]

The cable has resistance.
No current, no voltage drop.
Once there is current, there is a voltage drop. V=IR
What is the rated resistance of the cable?

The stuff I have is 0.554 ohms per Km...

Your making my brain hurt Mick, I haven't had to work this stuff out since I was at trade school....

[CJT]

i did the calcs years ago for my old rangie which had battereis in the back and obviously the winch up front, i had to run 70mm2 cable, was good for 400A at that distance all day long.

Thanks,

I went through the calcs tonight and I agree with the 70mm2 cable.

50mm2 rated to 300A and voltage drop of 0.541v over 5.0m
70mm2 rated to 400A and voltage drop of 0.372v over 5.0m

My preference is to keep the voltage drop to below 0.5v so the 70mm2 cable will be the way to go.

[Vern]

Could always go conductors in parallel if you have plenty of the 33mm2 cable

[joe.woods]

Thanks,

I went through the calcs tonight and I agree with the 70mm2 cable.

50mm2 rated to 300A and voltage drop of 0.541v over 5.0m
70mm2 rated to 400A and voltage drop of 0.372v over 5.0m

My preference is to keep the voltage drop to below 0.5v so the 70mm2 cable will be the way to go.

I agree I did the calcs for my rear winch and came up with 70mm2; I'm using welding flex, nice and pliable, rear bar not quite finished yet but I intend to use an insulated post on the bar for the +ve then run 350Amp Anderson plug to get heavy power at the rear for jump starting on freeways and such (me's think a little safer).

[slug_burner]

On your calcs you would be dropping about 300 Watts of heat on the 33mm2 to your rear winch per cable. A bit much, best go up in size as others have recommended.

[CJT]

On your calcs you would be dropping about 300 Watts of heat on the 33mm2 to your rear winch per cable. A bit much, best go up in size as others have recommended.

Yep,

I will run;


70mm2 for the rear winch (hopefully through chassis rail)
33mm2 or 50mm2 for the front winch depending on location of the control box and length of cable required
33mm2 for the compressor and rear batteries.
I am getting a price on wedling cable today.

I have not been able to find a local shop with the 70mm2 battery cable and most dont seem to have the 50mm2 either.

[Toppa]

Yep,



I have not been able to find a local shop with the 70mm2 battery cable and most dont seem to have the 50mm2 either.

I got my 70mm2 of ebay from a bloke up your way (QLD) his ebay name was sparkey000red

50mm2 is 17.50 p/m
70mm2 is 21.50 p/m

plus shipping

Better yet, if you have a mate who is a sparky, get him to put it on his account and you would get it much cheaper (wholesale) through stores like Middys.

[CJT]

I got my 70mm2 of ebay from a bloke up your way (QLD) his ebay name was sparkey000red

50mm2 is 17.50 p/m
70mm2 is 21.50 p/m

plus shipping

Better yet, if you have a mate who is a sparky, get him to put it on his account and you would get it much cheaper (wholesale) through stores like Middys.

Thanks for that.

I am getting a price on welding cable through my mate who owns a fabrication shop, so I will compare the prices from both.

[roverrescue]

I know its not maths but for a real world example:
-I have a length of 35mm2 welding cable from underseat batteries to towbar of the fender.
-175A Anderson that plugs to Warn9000 on the big boat trailer.
-Earth is to the passenger chassis rail - same rail as the main battery earths.
-Battery setup is two N70 marines in parallel NO switch/solenoid/black majic box.
-The tinnie weighs in at about 3500kg, retrieve is a double line pull over about 5m.

It winches fine, sure voltage drops but cable, connectors, winch motor do not get hot - it does the job perfectly well, certainly such that I have no burning desire to change things (pun intended!).

A pos and neg of 70mm2 would be a bear to run and what will you use to terminate it? Dinse connectors? Or will it be hardwired to a winch solenoid box - if so it will it fit???

Its also nice in that I have an ATV winch on the smaller boat trailer (it drives that with ease) and if I need to jump start someone I would have no hesitations off it either.

Anyways, back to the theoretical ;)

Steve

[CJT]

I got my 70mm2 of ebay from a bloke up your way (QLD) his ebay name was sparkey000red

50mm2 is 17.50 p/m
70mm2 is 21.50 p/m

plus shipping

Better yet, if you have a mate who is a sparky, get him to put it on his account and you would get it much cheaper (wholesale) through stores like Middys.

I recieved a price for welding cable;

35mm2 @ $7.85 p/m
50mm2 @ $10.60 p/m
70mm2 @ $13.50 p/m

All prices excluding GST.

[Vern]

really good prices there, i paid about that for 70mm 5 years ago, and i'm a sparky:(.
but copper was at a rather high price back then

[CJT]

I agree, about half the price of anything I found at retail prices.

[Toppa]

I recieved a price for welding cable;

35mm2 @ $7.85 p/m
50mm2 @ $10.60 p/m
70mm2 @ $13.50 p/m

All prices excluding GST.

Great prices Chris, next time i need cable, ill hit you up for your contact!



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