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## DonGould

3888 posts

Uber Geek

Topic # 114195 11-Feb-2013 20:23

Ok, so pushing 5v down cat5 doesn't go far, 12v is better, more and more stuff is using 24v and some stuff uses 48v.

So, understanding this theory I get that more volts you have the less copper you need to push it.

Well I want to push some power around the farm, I don't need huge amps but I don't want to spend bucket loads on copper cables to get the amps where they're needed so it strikes me that I need to up the volts then drop them again when I get where I want to go.

Seems to me that I want 500 or 1000v so I can push a few watts where I want them?

I guess I'm looking for 300 to 1200w at the other end.

Ideas?

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## gregmcc

1572 posts

Uber Geek

You are looking at it the wrong way, the power at the end of the line is what you need, Power = Volts x Amps

More amps= bigger copper (otherwise it over heats and butns up)
Move volts=better insulation (otherwise the insulation breaks down, you get a shock, the wires short out)

As soon as you want to use a voltage above extra low voltage 50VAC, 120VDC (ripple free) then you have to comply with the electrical regs, Use the right kind of cable etc.

## knoydart

852 posts

Ultimate Geek

Trusted

Losses caused by large currents (I x I x R is the formula to go hunt for), so for instance the national grid here typically run at 220Kv, 110Kv and the HVDC link which I think is run at 400Kv DC.

Suggest if you want to provide low level DC you try and keep it at 230V AC and then transform and rectify when you get to your destination. Remember to get a sparky to install any work above ELV as Greg notes.

Mods - suggest a move to home workshop?

## oxnsox

1923 posts

Uber Geek

May have to run 'Mains' in there really. Our get geeky and use wind/solar.....you know you want to

1076 posts

Uber Geek

How far are looking to go, a kilometer or two? Higher voltage does mean less current therefore less copper, but as Greg mentioned it means more insulation (and danger).
If you only want 300W you can go about 600m on 2.5mm2 TPS before the voltage drop exceeds 6%.

Edit: but if you have a switchmode power supply as the load, a much bigger voltage drop (ie longer cable or lighter cable) would work.

## richms

21235 posts

Uber Geek

Trusted
Subscriber

Just make sure its a permanently connected load or you have appropriate over current on the run to be compliant. And I don't think you can get a 1.75A breaker.

Funnily enough, according to a sparky I was dealing with, a permanent connection unit with an IEC cable in it counted as a permanently connected load. Thats one way around stupid bloody RCD regs ;)

Richard rich.ms

## DonGould

3888 posts

Uber Geek

Hi Guy,

At this stage the questions are as much academic so I can build up a better understanding of what can be done.

As far as regulations are concerned, no, I'm not thinking of attempting to do stuff that I'm just not allowed to.

I'm keen to understand different things I am allowed to do. I'm keen to understand the most cost effective things that I could ask a sparkie to do.

Some of this is about using the power we might generate off a wind turbine. At another farm we looked at putting 240v to a shed, but it was going to cost \$10,000 just in cable.

If we generate power then I want to understand if it's worth moving the power or moving the use closer to the generation.

Solar down the back end of the farm has issues for a whole pile of reasons, but yes, getting the geek on does appeal.

I didn't know about the insulation issues. So now I'm starting to understand why lower voltage is used.

ya... I'm more a 1's and 0's guy, I normally only care if the power is on or off, not how much there is, how fast it's moving or how hard it will bite :)

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## Goosey

1550 posts

Uber Geek

Subscriber

What kind of Farms?

1076 posts

Uber Geek

Commercially available (small) grid-tied wind turbines like the Skystream3.7 ('2.4kW' ~\$15k) are not as good a payback as grid-tied solar (eg '2kW' \$8k), for Canterbury weather conditions. We get very little wind in winter.
If you're building your own for much less, or the site is particularly windy then it may make more sense (economically).

## DonGould

3888 posts

Uber Geek

Skolink: Commercially available (small) grid-tied wind turbines like the Skystream3.7 ('2.4kW' ~\$15k) are not as good a payback as grid-tied solar (eg '2kW' \$8k), for Canterbury weather conditions. We get very little wind in winter.
If you're building your own for much less, or the site is particularly windy then it may make more sense (economically).

Farm in this case is in Wellington not Christchurch.

Wind blows 24/7, even on a clam day.

Interesting comment about the return on solar though.

Flat land to put a panel farm is a bit of an issue.  How much sqm do you need to generate 2Kw?

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1076 posts

Uber Geek

DonGould: Flat land to put a panel farm is a bit of an issue.  How much sqm do you need to generate 2Kw?

Approximately 13m2 (250W panel is ~1.8x0.9m)

## oxnsox

1923 posts

Uber Geek

Wind, or solar, will be costly if grid tired (because you still have to run Mains in) but of course you do get some payback from your excess. (know people in Not. with a solar grid tired system, which impressed me much over Christmas).

Lower cost option given remote AC would be a DC based solar/wind system charging a battery bank. Probably your load is DC based anyway so you could delete the in efficiencies of DC-AC conversion. However my experience with wind and solar is that neither is a reliable source, so its important to match the reserve power and input power ability to the only real constant in the system....the load.

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