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Old 27-08-2012, 13:55   #1
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Back for More Excellent Advice. Wire Sizing

Hello Gentlemen:
I am finally putting in my horizontal drum winch.
The run from the battery bank..(2 x 200 a.h. for 24V) is about 8 meters, lets call it 10 to be VERY conservative.
The winch is 1400 watts and the supplied breaker is 150 Amps.
How big a wire ????
Please do give me options, as my choices are limited and if you could do it in metric, well that would be that much better !!!
(Consider me on a remote island in the middle of absolutely no where. Which is where I am.)
There is no Amazon.com, no overnight delivery. Supply boat comes every two weeks, and no guarantee that what I order will be available...
Now I do have 100 meters of 2 mm, finely stranded copper wire...Could run ten of those in parallel....That might give you an idea how we have to do things..
In an ideal world a car battery cable about 5/8" in diameter would probably do it, but I would like to get it from somebody who knows.
Help please !
Thanks
Larry
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Old 27-08-2012, 14:06   #2
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Re: Back for more excellent advice. Wire sizing

Depends on how much voltage drop you can tolerate. I would use at least 0 gauge, 50 mm2 wire.
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Old 27-08-2012, 14:22   #3
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Re: Back for more excellent advice. Wire sizing

Hi Skipmac:
Thanks for chiming in..
Got the wire size at 50 mm, but how many strands and what size strand?
How much voltage drop is acceptable ?
THX.
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Old 27-08-2012, 14:37   #4
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Re: Back for more excellent advice. Wire sizing

0 gauge/50 mm2 would give about 4% voltage drop o4 +/- 23V at the load.

For boats the ideal is fine strand, tinned wire. Not sure the dimensions of fine strand but it makes a more flexible cable. Regular auto battery cable or welding cable is a larger strand, guessing 1-2 mm2 or 16 gauge. Marine
grade cable probably < 0.5 mm2.

Now this is the best and what is recommended but I can say that I still have a lot of original battery cables on my boat that are welding grade, not tinned and at 25 years old and still fine.
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Old 27-08-2012, 14:41   #5
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Re: Back for more excellent advice. Wire sizing

Something doesn't add up here. Is your boat's electrical system 24 volts? If so then the 150 amp breaker is way to0 big for a 1,400 watt motor. A 1,400 watt motor should pull 1,400/24 =58 amps. So a 90 amp breaker would be more appropriate.

Anyway, still assuming a 24 V system and a 10 meter run, and that a 5% voltage drop would be tolerable, then that requires at least #4 wire. If it is a 12V system then the current doubles and the gauge goes to 3/0 to maintain that same 5% voltage drop. Some installers believe you can accept a 10% voltage drop and that results in #1 gauge for a 12V system.

#4 gauge is a bit more than 5 mm in diameter, 5.19 actually. Since current carrying capacity goes up with the square of diameter, it will take (5.19/2)^2 = 6.7, or seven bundles of your 2 mm wire each way to be equal to #4 gauge wire. Not very practical. And you don't have enough 2 mm wire for this!!

David
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Old 27-08-2012, 15:51   #6
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Re: Back for more excellent advice. Wire sizing

Quote:
Originally Posted by djmarchand View Post
Something doesn't add up here. Is your boat's electrical system 24 volts? If so then the 150 amp breaker is way to0 big for a 1,400 watt motor. A 1,400 watt motor should pull 1,400/24 =58 amps. So a 90 amp breaker would be more appropriate.
I got the same results. 150 amp breaker seems quite oversized.

Quote:
Originally Posted by djmarchand View Post
Anyway, still assuming a 24 V system and a 10 meter run, and that a 5% voltage drop would be tolerable, then that requires at least #4 wire. If it is a 12V system then the current doubles and the gauge goes to 3/0 to maintain that same 5% voltage drop. Some installers believe you can accept a 10% voltage drop and that results in #1 gauge for a 12V system.
Don't you have to count round trip distance when calculating DC systems? If my understanding is correct then 4 gauge would only be sufficient for 5 M one way.
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Old 27-08-2012, 15:58   #7
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Re: Back for more excellent advice. Wire sizing

Quote:
Originally Posted by skipmac View Post
Don't you have to count round trip distance when calculating DC systems? If my understanding is correct then 4 gauge would only be sufficient for 5 M one way.
Never mind. It didn't say this but the calculator I was using apparently converts to round trip.
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Old 27-08-2012, 16:30   #8
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Re: Back for more excellent advice. Wire sizing

Thanks all for such fast answers,
I really appreciate the community you have here and only wish I knew enough to contribute.( I assure you that I do in those forums where I have the requisite expertise).
For the sake of clarity..
The boat starter and and the winch are on the 24 Volt system, all else is on the 12 volt.
The manufacturer spec`d the 150 amp breaker, I questioned it as well, I guess they figure if it is going into a dead short or overloaded motor is does not much matter, but it does, so I will put a 90 amp breaker in if I can get it, if not it will have to be 100.
Welding cable..never thought of that, it makes sense....DC, high current, super flexible...why am I not so smart ? Should be available on the supply ship !
And yes..I will start the boat first, then use the winch !
Next question, what is the best way to extinguish an electrical fire on a wood boat ?
hehhehe...
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Old 27-08-2012, 17:02   #9
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Re: Back for more excellent advice. Wire sizing

CM = (K x A x L) VD
Where:
CM = The Circular Mil cross sectional area of the wire
(See Table 1, and ABYC Section E-8, Table III)
K = 10.75 Representing the Mil-Foot Resistance of Copper Wire @ 78o F.
L = The Total Length of the wire in Feet
(This is the ‘Round Trip’ length of both Positive + Negative wires)
VD = Permitted Drop in Volts
(Ie: 3% @ 12.5V = 0.375 ED or 3% @ 25V = 0.750 ED)

See ➥ Wire Size Chart.1 - Read /w &quot;Ohm's Law &amp; You&quot; Cruisers & Sailing Photo Gallery

And ➥ Wire Size Chart.2 - Read /w Wire Size Chart.1 &amp; &quot;Ohm's Law &amp; You&quot; Cruisers & Sailing Photo Gallery

And "Ohms-Law-and-Boats" -372
"Ohm's Law & Boats"

And ➥ http://www.goodoldboat.com/reader_se...cal_wiring.php
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