Cable Long Runs.Experience,Theroy

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Hey I need to conduct 12VDC @ 130 AMP over 300-400m with minimal loss
and expense.(we all need to do this right?)
I have discovered that I may need some seriously heavy duty cable for
my power station.

Basics are understood that DC was no good for long runs therefore AC is
used.
7 to 12 miles for DC dose not ring bells!?

Questions:
Is It dumb to try to transport DC over such a distance?
What loss can I expect provided I can find a matching cable specific to
my requirments.?roughly(have been googling,but looking for been there
opinions)

What Cable has been used in the past for this type of
application......at a guess would it be right to assume,phone
cable?telegraph?amps rating? Old hydro cable?That copper cable they
used to run by the train tracks 20 years back?

Do I need to go 24VDC to get back to 12VDC at destination?(hate this
idea)

I can find 100amp cable in 100m rolls where do I look for bigger stuff
?

Finally is it worth AC over this distance?I would gather a similar
infustructure would need to be in place as with DC?

To tidy this up,what cable should I be looking at using?

Thanks in Advance


Re: Cable Long Runs.Experience,Theroy



"Magic Mushroom Farmer"
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** 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.


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**  Nope.

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**  Nope  -   DC is best actually.


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**  Thick cable.

     Get the point?


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**  100 amp cable is rated for 240 voltsAC.

    No good for 12 volts DC.


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**  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.



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**  Very, bloody thick.

  Bout 50,000  kilos of copper.




........ Phil



Re: Cable Long Runs.Experience,Theroy


 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.


Re: Cable Long Runs.Experience,Theroy


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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.

Re: Cable Long Runs.Experience,Theroy


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$4 a kilo buy price where I am

Re: Cable Long Runs.Experience,Theroy


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

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

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

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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.

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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 :)


Re: Cable Long Runs.Experience,Theroy


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.


Re: Cable Long Runs.Experience,Theroy


On 23 Mar 2006 03:40:13 -0800, "Magic Mushroom Farmer"

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


Re: Cable Long Runs.Experience,Theroy



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

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Re: Cable Long Runs.Experience,Theroy


Snip
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G'day

thats a huge cable you're cable you going to need, assuming you want a
voltage drop of <10%

AS3008 gives guidance on cable selection, gives both maximum current
carrying capacity and voltage drop and other properties for a large
range of cables in a large range of situations. Get a hold of this if
you want to calculate it properly....

Your cheapest way would be to bump it up to 240VAC at the supply end
and back down to 12V DC at the load end. Inverters and power supplies
would probably cost say around $1000 - $1500 maybe - just an order of
magnitude cost. You could use much smaller cable then and have better
voltage regulation by using the power supply.

To move 130 amps at 12  volts over 300 metres would cost tens of
thousands of dollars, maybe hundreds of thousands. You would need
multiple runs of say 240mm SQ Al cables.... That cable is about $15 a
metre and you would need a stack of them in parallel. You'd be able to
tow an aircraft carrier with the cable :)

If you step it up to 240VAC you can use standard off the shelf parts to
do it, standard cables, accessories etc. DC at even 240V in any sort of
quantity gets to become a pain to switch and fuse - you need high rated
parts.

Goodluck

Cheers


Re: Cable Long Runs.Experience,Theroy



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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


Re: Cable Long Runs.Experience,Theroy



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 > 12 volts at up to 130 amps?

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

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If I drew the right conclusion above, then I guess because the river is
400 metres from his house :-)

Peter

Re: Cable Long Runs.Experience,Theroy


Hey....It is a water wheel running a regulated Alternator from a car.
I have learned I can trick the alternator into giving off more volts by
removing a diode or so.
Maybe 18volt....also the possibility of running in AC,then regulating
it back to 12vDC for an inverter.....thats if I can get enough power to
the destination.

I think my distance was more like,150m-200m however playing it safe.
As it is a costly exercise to experiment over this
distance....technical information or personal experience is a plus.
This is supposed to be a quick and dirty way to get some
power..lights...maybe a TV.
300W at the destination would be a good start.

Most people that are doing this are based close to their water wheels.
I


Re: Cable Long Runs.Experience,Theroy


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if its a normal 3phase  alternator you should be able to get a usable ac
voltage from it , push it through a suitable transformer to step up and
deliver  to site.

Re: Cable Long Runs.Experience,Theroy



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even more by removing the regulator.

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I'm guessing it's running at a few thousand RPM in which case 50Hz
transformers aren't going to work with it really well.

BTW what sort of car altenator puts out 150A ?
I'm guessing that you have a 35A altenator and batteries right next to it.

here's an idea that could work at 12V ...

If you could put the batteries beside the house and a regulator there too
and run 100A wires from there to the altenator (for battery + and - ) and a
thinner wire from the regulator to the field terminal of the altenator
you'd probably have something that'd work.

(if you leave the regulator in the altenator it'll only see the voltage at
its end of the wires and that'll be higher than the voltage at the other end.
conseqently the batteries won't get fully charged. The built-in regulator
can be easily bypassed and an after-market external regulator is less than
$20)

There'd be losses in the wires but the altenator would just be asked by the
regulator to "work harder" to compensate.

a thermal switch cponnected in the field line, mounted on the body of the
altenator (or the heatsink of the rectifier) could be a good addition too.
(eg jaycar cat# ST-3825)  I killed the diodes in an alttenator once by
running it non-stop at full power for too long.

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With the batteries next to your house you'll have upwards of 400A on
demand. use plenty of apropriately sized fuses.  That sort of current
can make fires real well, and I'm guessing the firemen out there  are
volunteers.

Bye.
   Jasen

Re: Cable Long Runs.Experience,Theroy



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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.




Re: Cable Long Runs.Experience,Theroy



"Terry Collins"
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**  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



Re: Cable Long Runs.Experience,Theroy


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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)?
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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?

Re: Cable Long Runs.Experience,Theroy


On Fri, 24 Mar 2006 19:24:44 +1100, Terry Collins

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

Re: Cable Long Runs.Experience,Theroy


Close...Fossil fuel costs money......Water in a river is
free...strapped to a car alternator.


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