Cable Long Runs.Experience,Theroy

"Magic Mushroom Farmer"

** Yep - the cable needs to be about 100mm diameter of stranded copper, per conductor. That would give you about 1.6 milliohms overall for a 700 metre round trip. Voltage drop = 208 mV @ 130 amps. ** Nope.

** Nope - DC is best actually. ** Thick cable.

Get the point?

** 100 amp cable is rated for 240 voltsAC.

No good for 12 volts DC.

** Only if it is 240 volts AC.

Then convert down to 12 volts DC

Maybe use a big lead acid battery and a big charger.

** Very, bloody thick.

Bout 50,000 kilos of copper.

........ Phil

If you try and do it at 12V then yes.

Quite common. I've done a 500VDC distributed power system over 12km, it can be a very efficient way to do it actually.

No. DC is common for long cable runs such as this. Trans-continental cable runs that link power grids are DC.

You'll probably need the train tracks themselves! Long cable runs like this are almost always done at a much higher voltage to reduce losses.

You will have to use a higher voltage for the long cable run and then convert it back, you don't have much choice really. The higher the voltage the less copper you need.

130A is a heck of a lot though, you might need multiple DC-DC converters at each end.

Dave :)

I recall we took a truck load of copper, 1 ton of it for scrap 20 years ago and got $150 for it,must have trippled by now,as people go crazy flogging the copper leads off junk yard stuff.

50 tons is alot of money....lol.

I have some 7 strand IMAPI 10-20mm ,unsure what it was used for....hydro earths?just looked at the power pole and they use even bigger unsheilded stuff for their earths. It is sheilded conductor wire...possibly that stuff they run to your house from the transformer......cannot find specs on it. I need big battery cable......this is what I need to ask/look for.....I got the picture....thanks Think I might go and check out an era gone by power station, everything is long gone expect turbines sitting in a deep water filled hole,never know,they used to drop water on trubines which powered 3 giant alternators via belt drives....strange...thats how they did it though....I am doing the same thing....just small scale. Thanks again Phill.

Thanks Dave.....thanks for confirming down-conversion as the most efficent and proven,cheapest way to get this to work. Have a clear idea of what I am doing now. Got stuck on the idea that large cable was readily available and was commonly used. Not sure if I can find a cheap 24VDC alternator.

Snip

G'day

thats a huge cable you're cable you going to need, assuming you want a voltage drop of

I'm curious.

What's your application? What sort of load requires 12 volts at up to 130 amps? Why can't you have your load closer than 400 metres to your source?

David

I am thinking welding cables - perhaps you can get these in the size you want.

I think the OP kind of implied that it was a micro hydro system.

If I drew the right conclusion above, then I guess because the river is

400 metres from his house :-)

Peter

It is sold by the drum, but I'm not sure as to what lengths,

>

Last time (few months ago) I went to the recyclers, copper was $1/kg (non-stripped cables) and Al was 1.13(?)/Kg.

the copper was a bit of a surprise as I had just cobbled together some internal wiring from a sorting machine and internal computer cables. I was expecting to be told they needed all the plugs cut off, but they just picked up the full box, weighed it, dumped copper, weighed box and paid for the difference.

Is it economical to just runs some standard 240V heavy gauge cable in parrallel? I know you can pick up drums of 240V 20Amp cable at various places cheaply. Perhaps running 5 runs of that may give you what you want cheaper.

** Terry - I did the sums for you.

The OP needs 50,000 kilos of copper wire.

Get your calculator out and start with the fact that 1 metre of 1 sq mm copper wire has 18 millohms resistance.

......... Phil

$4 a kilo buy price where I am

Is that in one wire, or multiple strands? Or would he be better off installing copper pipe (skin effect where electrons prefer outside of strand to inside)?

I probably won't get far considering my brain is clearly aware that this is Friday afternoon/evening and it wants to relax {:-).

So 400 metres gives ( 400 x 0.018) = 7.2 Ohm in one wire therefore total resistance in one pair (there and back) is 14.4 Ohm And if V = IR where V = 24V and I = 160 Amps, there fore wire resistance needed is 0.15 Ohm, which means he needs 96 wires to get 160 Amps doing a nice loop out and back but no useful work at any point {:-).

Actually that whole 160Amps thing has my ming boggling. I'm wondering it it isn't easier to move the generator?

Plus, 160Amps must be something like welding 2" thick steel, so he is going to require some huge special switches, otherwise the poor sucker who has to throw that switch is going to want full leather kits (boots to top of head) and arc welding visor?

Did I miss the revelation as to what this is for?

DC is used for the really long runs

no, but for 1200 miles perhaps

no. "12V" is your problem, not "DC"

If you can go to 24V you'll get the same wattage of loss with 1/4 of the copper thickness, but you have to use 24V appliances or convert it back to 12V (figure 80-90% efficiency converting each way)

if you can make 48V work it gets even better...

ohm's law will help you answer that.

auto electrical suppliers, welding suppliers. industrial electrical suppliers

I'll assume you mean going to 100V or more if it was 1 mile i'd say yes, for a quarter mile I'm not sure.

it all depends on how much you want to spend and how much power you can afford to loose in trasmission.

that depends.

Bye. Jasen

I wonder what the application is. Perhaps a Genny or a briggs and stratton strapped to a modern car alternator is cheaper.

Tell me about what you are trying to do - where does the 160A at 12VDC come from? Is it an alternator with a rectifier, or is it a DC generator with brushes? This makes a big difference as to your options. If it is an alternator with a rectifier, then you could either (a) have it rewound for a higher voltage or (b) find a surplus transformer that can step the voltage up to something more sensible. You need to think about the frequency in this case because it will affect the spec of the transformer.

Also, what is your load? Are you storing the power in batteries? If so, this might offer other opportunities such as moving the batteries and inverter to the generator end of the cable.

Chris

skin effect is for AC only.

Bye. Jasen

Hello Magic Mushroom,

I've plenty of experience running 25-30 volts up to 200 amps up to 30-40 meters for cinema xenon lamps and its a big enough hassle.

Working through the numbers, 100 amps at 12 volts at 400 meters using 120mm tycab welding cable that has 0.161 ohms per 1000meters resistance and assuming you can live with a 1.61 volt drop over the cable you'll need 8 runs of it.

The 35mm stuff in pvc jacket runs at about 22 bucks a meter on a 50 meter drum. I've never used the 120mm2 stuff, but recall the 70mm2 stuff was a kings ransom.

As others have pointed out, its beyond silly to go down this path.

Maybe a coupe of dc to ac inverters are the trick.

Good luck,

Mark