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Posted by Don Foreman on April 30, 2008, 11:34 am
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>grumpyoldhori wrote:
> What figure should I be looking for on a km of 4 mm
> steel wire in ohms ?
I figure about 7.7 ohms, based on 9.7 microohm-cm for resistivity of
iron.
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Posted by Bruce L. Bergman on April 30, 2008, 3:25 am
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On Wed, 30 Apr 2008 11:25:46 +1200, grumpyoldhori
>Don Foreman wrote:
>> 37 ohms per km of 4 mm iron/steel wire strongly suggests a splice
>> that may be mechanically strong but has poor conductivity due to
>> corrosion.
>
> Yes, good point, I will put 4 mm copper wire jumpers
> across all splices.
> What figure should I be looking for on a km of 4 mm
> steel wire in ohms ?
No, you should get a portable torch rig with some horsepower (Oxy-
Acetylene or Air-Acetylene or MAPP) and go silver-braze or silver
solder all the splice points - or even 60/40 lead/tin solder if you
don't worry about RoHS, but no acid flux unless you clean it up.
Get the resistance down enough, and 24V (AC or DC) at the bottom of
the hill will be enough to get 12VDC at the top (after regulating,
filtering and surge/lightning arresting).
I still say AC is better for longer distance work at low voltage,
but as always Your Mileage May Vary.
--<< Bruce >>--
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Posted by Joseph Gwinn on April 30, 2008, 8:54 am
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> On Wed, 30 Apr 2008 11:25:46 +1200, grumpyoldhori
> >Don Foreman wrote:
>
> >> 37 ohms per km of 4 mm iron/steel wire strongly suggests a splice
> >> that may be mechanically strong but has poor conductivity due to
> >> corrosion.
> >
> > Yes, good point, I will put 4 mm copper wire jumpers
> > across all splices.
> > What figure should I be looking for on a km of 4 mm
> > steel wire in ohms ?
>
> No, you should get a portable torch rig with some horsepower (Oxy-
> Acetylene or Air-Acetylene or MAPP) and go silver-braze or silver
> solder all the splice points - or even 60/40 lead/tin solder if you
> don't worry about RoHS, but no acid flux unless you clean it up.
I would soft solder it, using whatever is used on copper pipes, to avoid
overheating and de-galvanizing the wires, promoting faster rusting.
Tinners flux (zinc chloride in HCl) will be needed. Plumbers grease
flux will not work on steel wire. Wash the joint off when done.
The splice joints are probably already too corroded and dirty to solder,
but there is no reason one cannot add jumpers around the existing
splices. Starting with open wire allows one to polish down to bright
metal before making the mechanical connection that will be soldered.
The splice should be the same kind of wire as the wire, to avoid setting
up a galvanic couple at each splice.
> Get the resistance down enough, and 24V (AC or DC) at the bottom of
> the hill will be enough to get 12VDC at the top (after regulating,
> filtering and surge/lightning arresting).
>
> I still say AC is better for longer distance work at low voltage,
> but as always Your Mileage May Vary.
Another reason to prefer AC is to reduce corrosion. With DC, one strand
will soon be eaten away at the fence posts by galvanic corrosion due to
the inevitable leakage currents. With AC, the leakage is still there,
but there is no net transport of material.
Joe Gwinn
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Posted by Randy on April 29, 2008, 9:37 am
Please log in for more thread options On Tue, 29 Apr 2008 22:48:46 +1200, grumpyoldhori
>
>
> May I thank all that gave me advice on this.
> Went out today and we insulated wires two and three
> from the top by using some plastic conduit that we
> cut so as to slip it over before refastening the
> wires to the posts.
> Oh, and we insulated the wires of the posts at both ends.
> Luckily this is a straight run fence, no gates or corners.
>
> Put a jumper across the wires at the top of hill and got a reading
> of thirty seven ohms.
> So have decided to follow Spehro's plan and use two of
> these http://www.jaycar.co.nz/productResults.asp?FORM=KEYWORD
>
> And use the Linksys wallwart as well.
Your link is missing the keyword to search on.
> Am I right in believing that using two wires up and two
> down would drop the overall resistance to eighteen ohms ?
> Thanks again.
>
>
>
>
>
>
Thank You,
Randy
Remove 333 from email address to reply.
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Posted by on April 29, 2008, 2:20 pm
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>On Tue, 29 Apr 2008 22:48:46 +1200, grumpyoldhori
>
>>
>>
>> May I thank all that gave me advice on this.
>> Went out today and we insulated wires two and three
>> from the top by using some plastic conduit that we
>> cut so as to slip it over before refastening the
>> wires to the posts.
>> Oh, and we insulated the wires of the posts at both ends.
>> Luckily this is a straight run fence, no gates or corners.
>>
>> Put a jumper across the wires at the top of hill and got a reading
>> of thirty seven ohms.
>> So have decided to follow Spehro's plan and use two of
>> these http://www.jaycar.co.nz/productResults.asp?FORM=KEYWORD
>>
>> And use the Linksys wallwart as well.
>
>Your link is missing the keyword to search on.
>
>
>
>
>> Am I right in believing that using two wires up and two
>> down would drop the overall resistance to eighteen ohms ?
>> Thanks again.
>>
>>
>>
>>
>>
>>
>Thank You,
>Randy
>
>Remove 333 from email address to reply.
No it's not search on the part number 95000.
** Posted from http://www.teranews.com **
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