Steel wire carrying twelve volts ?

  Could I have some advice please.   I need to get a twelve volt, 1/2 amp supply five hundred metres up a hill. I do have a fence a metre high made from wooden posts and
seven runs of Num eight (4 mil) galvanised steel wire. Is it feasible to use two of these wires to carry twelve volts that distance ? Thank you.  
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grumpyoldhori writes:

No.
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On Fri, 25 Apr 2008 23:33:18 -0500, Richard J Kinch

I'd say yes.
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wrote:

Probably need to start with 24 volts to get 12 at the top. It will have about 15+ ohms total resistance (~3000 feet of wire). Is the load constant? Like a lamp or such?
Is the wire insulated from the wood post? He could use 24 volts AC to a transformer at the top and convert to DC at the end.
Tom
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wrote:

I figure 7.7 ohms for 1000 meters of 4 millimeter iron (steel) wire, so drop of about 3.9 volts at 0.5 amp. I'd find a source of 16 to 24 VDC for the drive end, put a 12-volt regulator (e.g. LM7812) on the load end. The regulator costs about a dollar. It'll need a bit of heatsink, perhaps a piece of ally 10 cm square or so. It can be bent as desired to fit in a space.
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On Sat, 26 Apr 2008 14:32:13 -0400, "Michael A. Terrell"

Yes, an 0.1 to 1.0 uF 50-volt bypass cap is a good idea. 30-volt TVS (transient voltage suppressors) would handle about all induced lightning surges. Example: 1.5KE30 http://www.microsemi.com/datasheets/SA4-15.PDF
About 90 cents each.
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On Sat, 26 Apr 2008 18:10:39 -0500, Don Foreman

I have not been following the calculations closely - but if he has 6 strands, and the resistance is 7.7 ohms per 1000 feet on single strand - if he parallels the wires into 2 conductors of 3 seperated strands each, the total resistance is only 7.7/3=2.56 ohms per 1000 feet.
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On Sat, 26 Apr 2008 22:59:32 -0400, clare at snyder dot ontario dot canada wrote:

It's 1000 meters (round trip) rather than feet ... but you're certainly correct that loop resistance will drop if he uses more wires.
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wrote:

Indeed. AC up, convert to dc to avoid the losses
Gunner
Political Correctness is a doctrine fostered by a delusional, illogical liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
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grumpyoldhori wrote:

If it was me, I run some trials. Id get a 12 volt car battery ,connect the positive to one of your galvanised wires then at the 500 meter point conect this wire to one say 2 strands down,come back to the battery and put a volt meter between the retun wire and the battery negative. this will show you the voltage losss/drop over the 1000m length. what ever this is, lets say for example 12 volts, youll then have to add another 6 volt battery to make the input voltage 18 to get 12 volts at the 500 meter point. Run the trialand let us all know what the values are. Even tho its up hill that shouldnt make much difference to what you get out. To replace or run a copper line 1000meters is a much better way to go. tho the cost wold be high. Depends where you are.
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wrote:

ted what has going up the hill got to do with it? please explain that, it really has me interested.
Stealth Pilot
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Stealth Pilot wrote:

I put that in just for fun to see if anyone might query it. Water wont flow up hill unless pushed. Tho as an afterethought, there might just be a miniscule slowing of the electrons uphill . Effect caused by gravity, if electrons hace some mass. Probably un measuable Thanks for responding Ted Dorset UK
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Ted Frater wrote:

You have to supply the intended load for there to be any voltage drop.
Jon
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Like the others said, experiments will give you the answer for sure. But you can get a reasonable answer by calculating things ahead. For instance:
I shall make an assumption that resistivity of steel is the same as iron (1xe-7) and that your wire has a diameter of 2 mm (easy on the calculations and probably generous). This gives the resistance of a 500 m long steel wire as 16 ohms, give or take. Thus passing 0.5 Amp current will cause a drop of 8 V, leaving you with only 4V up the hill...
A copper wire of the same diameter and length is about ten times more conductive, thus the drop would be only 0.8V.
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Michael Koblic wrote:

If the duty cycle was fairly low, I would look at using a 12v SLA battery ( or maybe an old car battery), a small solar panel and a trickle charger to keep it toped up. As others have said, the resistance of the steel wire would be too high and the cost of running large enough copper conductors ( to minimise volt drop) that distance, would be too expensive. What is the application and estimated amount of use per day?
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Stephen Robinson wrote:

Running a Linksys wireless router on a hop for a microwave link. The output power is only 100mw. but the router draws five watts on average to power it's board etc. Running 24/7. Looked at solar and running copper wire, both came to around NZ $600 Which is why I am keen on using the steel wire if possible.
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On Sat, 26 Apr 2008 19:09:04 +1200, the renowned grumpyoldhori

Okay, the router comes with a 'universal' SMPS wall-wart, yes?
How about using TWO 230:24 (eg. 1A rating) transformers to send the power down your wires at 24VAC/50Hz, and step it up at the other end. The wall-wart will tolerate as low an input as 100VAC or so, so if the numbers we have for resistance are in the right ballpark you should be okay (easy enough to short them at one end and measure the (loop) resistance at the other. If it's around 35 ohms you should see around 150VAC at the output of the downstream transformer with a 6W load (if the 6W is from the nameplate, rather than measurement, expect to see a fair bit higher than that-- mabe 180 or 200VAC).
Although this may appear to be a more complex and expensive answer than some others, it should give you a stable regulated supply for the router, and at least has a good chance of surviving a nearby lightning strike (put an arrestor at each low voltage end, before the tranformer, as well as fuses or circuit breakers to protect against shorts). Going directly in with DC, I think you'll be buying, and configuring, a new router after every few electrical storms. The transformers provide isolation against common mode voltage (assuming the arrestor breaks down before the transformer insulation) and will saturate when presented with a high normal mode voltage.
Best regards, Spehro Pefhany
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On Sat, 26 Apr 2008 19:09:04 +1200, grumpyoldhori

To get the distance at lower voltage drop, use 50 Hz or 60 Hz AC dropped down from mains power - I would start the experiment with a 24 VAC input using the top (#1) wire as a "guard wire" grounded lightning sink, with a ground lead going down the back side of the post to ground rods at all the high points along the route. If lightning is going to hit, you want to try and divert it from your power leads.
Make the #2 and #3 wires from the top your power leads, taken loose from the fenceposts and mounted on ceramic insulators, and see how the voltage is at the far end under load. The insulators will cost a bit, but increase efficiency a lot - especially with the existing wire stapled to wooden posts, when it rains the power will /all/ go away as it leaks between the wires at 200 high-resistance shorts. When you are only starting with 50 VA or less at the feed end it doesn't take much loss at each post to suck it all up.
Anything below 50V with a current limited source is considered Class 2 Wiring in the US, and IIRC the rest of the world is about the same. It will give the cows and sheep a tingle if they touch it, but that's about it - much lower voltage than a fence shocker generator, but you still want to use only enough voltage to get the job done.
At the feed end, my best guess for a starting point would be a 240V to 24V at 50VA transformer meant for running Air Conditioning controls, they are reasonably cheap. Fuses on both sides, and a healthy lightning arrestor tied to a good ground rod.
Telephone lightning arrestors should work perfectly for that voltage and be reasonably priced, they have about a 150V strike-over because ringing voltage is around 120V AC 20 Hz. And the newer three terminal gas-tube arrestor devices form a plasma and clamp both lines of the pair to ground at once, to avoid sneak current failures.
If your area gets nailed by lightning often, you could also put arrestors at all those mid-run ground rod locations. But due to added expense you might want to wait till the first time it all gets "blowed up good" and you realize it wasn't enough. Your call...
Wherever there is a gate, bury a length of PVC Plastic conduit with the long sweep ells between the fence posts and under the opening. Take the two power and one ground lead and convert to heavy gauge stranded copper wire for the short run, then back to fence wires. Might be a good location for a ground rod.
At the top of the hill you attach another healthy lightning arrestor across the two power leads connected to a ground rod, then rectify and regulate to the 12V DC the Ethernet repeater is going to want. And put a healthy crowbar zener on the 12V DC output, to try and save the repeater from a lightning strike or regulation failure.
If it all works as planned, go to a local print shop and have simple warning signs made up - Print them two-up on A4 Goldenrod or Red paper and cut in half (5" x 8") then heat laminated with a large border, and staple them to every fourth or fifth fence post through the laminated border. They will last several years if the paper remains sealed off.
"Warning - avoid contact with insulated fence wires. 24 VAC Class II Current Limited power for Wi-Fi Ethernet repeater system on top of hill for the (Name) residence. Safe for accidental contact. Please do not short or ground fence wires. Enquires contact Hori at (address/phone)."
Nothing fancy, but keeps the kiddies from playing with it, the local loons from inventing UFO conspiracy theories (Yeah, as if that would be enough to stop them...) ;-) and the local Law Enforcement/ Fire/ Wildlife authorities from freaking out about exposed wires.
--<< Bruce >>--
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grumpyoldhori wrote:

Ohh, this is different. Hopefully the router isn't too expensive, because any lightning anywhere nearby will be picked up by the long run of straight wire and deliver a massive ZAP to the router. You will need to clean and solder any splices/joints in the wire. I'd look carefully at rigging a low-voltage transformer at the source end to run something like 24 - 36 V AC on the wire, and then converting to DC with a transformer/rectifier at the router. This might give you a little isolation at the router end, too, which might keep lesser lightning events from frying it.
This can definitely be made to work, but due to the high resistance of the wire, it takes just a little more complexity to do it. The 24 or 36 V transformer at the source end (remember to fuse it to protect against something shorting the fence) should be easily found, might even be able to find a wall-wart with that kind of output. For the router end, you could use a transformer with a tapped secondary as an autotransformer (although that defeats the isolation mentioned earlier) to bring the 24-36 V from the fence down to the ~12 V needed for the router. Also, a transformer with both 12 and 24 or 36 V secondaries could be used, connect input to the higher secondary, output from the lower one. Leave the 230 V primary disconnected and taped off.
Jon
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On Sat, 26 Apr 2008 19:09:04 +1200, grumpyoldhori

Do your calcs for voltage drop at .4 amp and see if you can just put higher voltage in to counteract the drop. I'd throw 24 at it and use a 7812 regulator to control the voltage at the router. Also be VERY carefull if you are in a thunderstorm area. Non twisted pair is a GREAT antenna. A friend was loosing his fence charger every time lightning struck within 2 miles untill we installed a surge arrester (air core choke and spark-gap) His 3 miles of fence was picking up several 10s of thousands of volts (at low current) blowing the outputs on the fence charger. With the choke installed it's been trouble free for over 5 years.
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