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Old 19-06-2008, 06:44   #1
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Battery Cable Gauge

I recently hooked up our new house battery bank. The bank is charged by an Air Marine wind generator, and the generator is wired to an inline ameter with 10 gauge wire, approximately 18 feet long. Connecting the ammeter, stop switch, and circuit breaker board, is 8 feet of 1 gauge battery cable (1 gauge was cheaper than buying the smaller gauge marine wire). So, is my use of a heavy gauge wire going to result in a loss of efficiency? I read somewhere that using an over-sized wire will open up electrical flow such that voltage is lost.
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Old 19-06-2008, 07:35   #2
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Quote:
I read somewhere that using an over-sized wire will open up electrical flow such that voltage is lost.
Using an undersized wire offers more resitence as amps increase. Using a wire small enough with a load high enough will melt the insulation and cause a fire. When it's not that severe you get voltage loss based on the length of the wire. So a short wire one foot long carries a big load but one 50 ft for the same load will decrease the volatge at the far end.

Using a wire larger than required just decreases your bank account. There are tables that can give you the right sized wire based on amps and length. You need to count the length as both the red and the black. Normally you just double the distance.
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Old 19-06-2008, 07:49   #3
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Here's a link I use to calculate wire size.

Voltage Drop Calculator, Amperage Tables, Wire and Cable Technical information


What Paul said is spot on....you must count the total run of the wires, meaning the length of both the positive and negative wires.

I usually try to get voltage drop in the 3% or less range.
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Old 20-06-2008, 03:11   #4
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Quote:
Originally Posted by Wilmington Piper View Post
... So, is my use of a heavy gauge wire going to result in a loss of efficiency? I read somewhere that using an over-sized wire will open up electrical flow such that voltage is lost.
You heard wrong. Larger wire sizes increase electrical efficiency, reducing electrical consumption.
Excepting cost, weight, & difficulty in handling; BIGGER WIRE is ALWAYS BETTER.

For more information, and pre-calculated charts, see also:

http://www.cruisersforum.com/forums/...ats-372-2.html

and:
Wire Size Chart.1 - Read /w "Ohm's Law & You" Cruisers & Sailing Photo Gallery

and:

Wire Size Chart.2 - Read /w Wire Size Chart.1 & "Ohm's Law & You" Cruisers & Sailing Photo Gallery
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Old 20-06-2008, 10:13   #5
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Maybe you read that the "voltage drop" is LESS, not LOST. (Both would be true but lost would be terribly odd wording in USEnglish.)

Your only worry now is that marine wiring is tinned, regular wiring is not, and on a boat untined wires tend to corrode much faster. You need to pot, seal, protect, the ends of that non-marine wire, because corrosion on the main wiring can quickly cause more loss than a change in wiring sizes.
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Old 21-06-2008, 00:34   #6
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Don't forget our wire guides in our Study Hall Folks.
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Old 21-06-2008, 04:06   #7
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This reminds me of a discussion I had with a fourth year apprentice electrician who steadfastly refused to accept that a thicker cable meant less voltage drop for a given length. It took more than half an hour to only partially convince him, increadible.

Mike
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Old 23-06-2008, 08:44   #8
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Originally Posted by Whimsical View Post
This reminds me of a discussion I had with a fourth year apprentice electrician who steadfastly refused to accept that a thicker cable meant less voltage drop for a given length. It took more than half an hour to only partially convince him, increadible.

Mike
You have to look at these things logically - typically after imbibing a bit of alcohol; then it all becomes spectacularly clear:

Think of a wire as a passage out of your local watering hole. If the passage is nice and wide, with little hindering the way of your average drunk (electron), then the drunk tends to meander left and right on the way to the parking lot - or the marina in the case of us sailors. But if the passage is narrow, then you can only travel in a straight line, so you're forced to take the shortest path to your car (or boat in its slip). So, from this impeccable beer-goggle logic , one can make the intuitive leap that's usually reserved for winners of the Darwin award, and assume that a narrow gauge wire is more efficient at passing electricity than a wide, heavy wire.

Now, the more sober among us, only marginally so since we couldn't afford that last drink because we just filled up our gas tank, will quickly realize that narrow passage is fine when there's only one electron/drunk at a given moment, but at closing time when everyone's leaving the bar, there's a massive pileup, and everyone gets in a fight in the narrow passage through the parking lot. The same thing happens in electricity. The electrons all want to leave at the same time, and they get stuck in that narrow passage, and before you know it one makes some snide comment about another electron's wife - and it's shear bedlam. There's a complete meltdown, and the whole thing goes up in sparks and flames.

And that, my friends, is the God's honest truth about why you want big fat wires - so that any snide comments from passing electrons won't be overheard, because they're too far away across the width of the wire to be heard!
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Old 23-06-2008, 09:07   #9
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Ah, Beau! But you need to prove that the logic applies only to really drunk electrons. So, first you take a power cord and cut the end off and insert it in a bottle of beer. You see, not much happens. Npow you do the same thing with a power cord that is allowed to soak for a while in a bottle of Everclear, ensuring it is REALLY DRUNK before you apply the power to the cord.

WHOOSH!

Darwin award, theory proven.<G>

Or, maybe not. Line for the lab sessions starts over there ===>>
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Old 23-06-2008, 09:29   #10
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This is a bit off thread, but apropo, I think...

When we have a narrow question that shows a complete ignorance of a complex and subtle topic (like wiring a boat) are we doing a dis-service by answering that narrow question instead of refering the questioner to a good reference book?

The chance of the original poster getting a good safe wiring project even after he has had the basics of Ohm's law explained to him seem to be pretty remote. There are an awful lot of questions he/she doesn't even know to ask. If someone dosen't have a clue about the basicis of wire sizing, do you think there is even an inkling of the grounding/bonding issues in the marine environment (for example)

I am trying not to be disrespectful or unhelpful, after all we were all ignorant once, but there is a minimal base of knowledge needed to do a safe electrical job. Without that base it seems counter productive to answer such questions.
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Old 23-06-2008, 11:52   #11
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Nigel Calder's book on boat systems offers a VERY good overview as well as specifics on wiring and electrical systems. Highly recommended!
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Old 23-06-2008, 12:18   #12
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... When we have a narrow question that shows a complete ignorance of a complex and subtle topic (like wiring a boat) are we doing a dis-service by answering that narrow question instead of refering the questioner to a good reference book? ...
... there is a minimal base of knowledge needed to do a safe electrical job. Without that base it seems counter productive to answer such questions.
Three quotations come to mind, which seem to address & resolve (for me) the question you pose.

1. “A little Learning is a dang'rous Thing; Drink deep, or taste not the Pierian Spring.”
2. “If a little knowledge is dangerous, where is the man who has so much as to be out of danger?”
3. "A journey of a thousand miles begins with a single step."


1. I am often concerned that many of us undertake projects, for which we are woefully unqualified.

2. I am often concerned that, whilst I know and understand a lot about some subjects upon which I comment and/or advise, my knowledge is incomplete.

3. I am resolved to help inquirers in beginning their education, as far as I am able.
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Old 24-06-2008, 17:24   #13
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When did you guys start sounding like my dad? Being a man who learned LONG ago that the pursuit of knowledge ends only in death, I asked this question looking for a direct answer. In the meantime, I have read the pertininent sections of Nigel Calder's Mechanical and Electrical guide and consulted the tables on voltage drop. What I want to know is what everyone else uses for that (hopefully) short run of battery cable in their boat. Also, I have read that 16 gauge is usually standard for running lights, fans, etc. On even a boat as small as mine, I could improve the voltage drop from 10% to 3% by jumping to 12 AWG. Is it worth it in cost of wire over voltage drop?
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Old 24-06-2008, 18:44   #14
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Most likely, yes. Some pertinent questions might be: When used, how long is the circuit in use? How long is the wire run?

I discovered that after being at anchor over night, my frig would start short cycling and not cooling well. The culprit was too small wire on a long run in a circuit that ran alot. Factory had used 12 or 14 gauge wire on a 40' (total) run. When the battery voltage neared 12.2 +/-, the voltage at the compressor was about 11V. Rewired with #6 and the loss is in the 3% range and frig now is happily runnning and cooling the beer!
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Old 24-06-2008, 19:28   #15
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When did you guys start sounding like my dad?
Depends on how old you are.

Is it worth it for lights. Probably not 10% to 3% however could be more than one volt. The lights don't burn as bright. Where this will kill you is a Windlass or any other high amp load. When the load is 50 or more amps the 10% could fry the wire. This is DC amps not AC amps. In AC current the voltage drop is pointless. The downside here is fire. It's a big deal.

Tell your dad we said Hi! You don't have to tell him he was right.
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