Cable Long Runs.Experience,Theroy - Page 3

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Re: Cable Long Runs.Experience,Theroy


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but it wont reduce the inductance. and the inductance governs the
overall velocity of the cable.

the context was the reduction of inductance.


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Re: Cable Long Runs.Experience,Theroy


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that I'd believe.

I did a pair of 15m cable runs in the loung of my last hous (it was a
BIG lounge), 4mm^2 twin cable. I worked out the inductance (I forget the
cable dimensions), and at 10kHz it was a sizeable chunk of my 4Ohm
speaker impedance - about 10% IIRC, so perhaps 6uH. compare that with
the 0.165Ohm DC resistance....

So I ignored it, and was still happy. I could have twisted the speaker
cables, but that required effort, and climbing up a scaffold.


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OK, assume resistivity of copper = 22nano-Ohm-meters (pure Cu is 18nOm).

R = rho*l/a = 22e-9 * 25.4e-3/1e-6 = 0.558 mOhms

0.558mOhms/(2*pi*3e3Hz) = 29nH

yep, thats about right, 1nH/mm


1mm^2 = 1.13mm diameter.

skin depth at 3kHz = 1.2mm, so the effect is negligible. bit of a straw
man, really.


but if you were trying to build a 29nH inductor, it would be very lossy
at 3kHz.

and if you were trying to build an 0.558mOhm resistor, it would be
horribly inductive - the magnitude of its impedance is 41% higher than
expected, and its step response would be evil :)


lets make it a real test, at 20kHz. skin depth = 0.47mm, so Fr = 2.5 and
Rac = 1.35mOhms

Xl = 3.6mOhms

now that is a seriously piss-poor 0.558mOhm resistor, but only a
moderately shitty 29nH inductor.

Xl starts to overcome Rac, because it increases linearly with f, whereas
Rac increases as sqrt(f), so a lot slower.

Cheers
Terry

Re: Cable Long Runs.Experience,Theroy


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DC is used for the really long runs

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no, but for 1200 miles perhaps

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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...

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ohm's law will help you answer that.

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auto electrical suppliers, welding suppliers.
industrial electrical suppliers

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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.

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that depends.

Bye.
   Jasen

Re: Cable Long Runs.Experience,Theroy



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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



Re: Cable Long Runs.Experience,Theroy


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




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Re: Cable Long Runs.Experience,Theroy


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Are you suggesting that at the power source(water trubine) convert it
to AC 240V via invertor,conduct it a couple hundred meters .....I do
want AC 240V at the destination....I can live with a slighly dodgy AC
power supply....been there many times over 100m with extenstion
cords...?


Re: Cable Long Runs.Experience,Theroy


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You could probably experiment with some older Fisher and Paykel washer
motors driven as alternators to get some higher voltages, they are three
phase though.

http://www.thebackshed.com/Windmill/assembly1.asp

They claim 0 to 300V unloaded at 2-3 amps for an unmodified winding.
You could probably bung a few on the one shaft and transmit high voltage
low current on three wires and use a 3 phase transformer at the far end.

Re: Cable Long Runs.Experience,Theroy



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Yes I am saying use an inverter to convert 12 volts dc to 240v ac


If the turbine produces a regulated 12 volts, then a 12v dc to 240v ac
inverter, such as the jaycar pn  MI5088 1000watt inverter is the ticket. 10
or 15 amp 3 core wiring over 400 meters is no problem at all if done
properly, forget extension leads, use 3 core flex from the electrical shop
with connector boxes, will be cheapest to buy 4 drums of 100 meter flex I
think, but enquire.

If the turbine's output voltage follows rpm, its not going to be so easy. Do
you have any data, pics, etc of the turbine?


Regards,
Mark



Re: Cable Long Runs.Experience,Theroy


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What turbine??, the OP's turbine?. Even using 240V flex will lose you
87.9 Volts based on the original poster's power requirements, 14 AWG 15A
copper wire and 800M round trip distance, this is 37% power loss. If he
could go as high as say 480V at half the current to 240V the power loss
would be 9% using the same resistance wire.A couple of 240V transformers
wired together could bring it back to a lower voltage suitable for
batteries and an inverter at the far end.




Re: Cable Long Runs.Experience,Theroy



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Calculations based on what load ?

What were the OP power requirements. They only wanted lights and power
and maybe a TV. This maybe as little as 300 Watts if they are careful
with what is installed.

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Re: Cable Long Runs.Experience,Theroy



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Well, He said 12 volts at 130 Amps = 1560 Watts which I think
is optimistic for a car alternator. 14 AWG is 1.69 Ohms per
100 metres

Re: Cable Long Runs.Experience,Theroy


Thanks...
It dose produce regluated output however could be set not to by
removing the voltage regulator.
It is a car alternator,and requires about 920rpm to kick in as a guess
as for power vairation above this speed I have not got there yet,just
at finding out if I can do this cost vs. commercial so to speak.
I like this idea to get started....upgrade to more volts(better
trubine/alternator) down the track.


Re: Cable Long Runs.Experience,Theroy


Yes....like this idea,however for first time setup it is alittle bit of
an overhead due to some unkown factors such as turbine speed,I may be
lucky to get 920 odd rpm out of it to power my car alternator however
will try,I have seen people claim upto 3kva from 30rpm on homemade
models using custom magnets and windings/parts.


Re: Cable Long Runs.Experience,Theroy



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So what is it you are farming that you want the power for 24hrs/day and dont
want a big increase in your power consumption from the mains?

Sorry....couldn't resist with the OP's name :)

James




Re: Cable Long Runs.Experience,Theroy


Yeah........It is about $4k-$5k to get the commercial stuff,also
already pay one bill and with a roaring water course,it is worth a good
hard try,also have the option to pipe water for a possible 10foot
fall,however gallons per minute would be limited to about 4 gpm.
I will attempt to use water current to power an under running water
wheel for a first time attempt.


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