Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 15-01-2016, 05:41   #16
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,061
Re: Wire size on alternator

Quote:
Originally Posted by Wotname View Post
???
The negative side is usually the alternator case and the engine and then the BIG negative cable from engine to battery.
And often the negative side of the charging circuit has the most voltage drop due to the alt current passing through multiple poor conducting metals, rust, corrosion, gasket material etc. before it picks up the main engine negative cable.. Also many factory alternators are isolated ground, such as many of the Hitachi's, so they pass through quite a bit of very small GA wire before even getting to larger neg cable..

If one desires any sort of charging performance, where the alternator is not seeing absorption voltage prematurely, even a 3% voltage drop, without properly sensing the battery terminals, is too much voltage drop. Stack a 3% + drop on top of an alternator that cuts back the voltage limit, based on alt temp, and it can literally destroy your charging performance.

I wonder if anyone could tell me how much milk I have in my fridge. I am away from my fridge and don't know..
__________________

__________________
Marine How To Articles
Maine Sail is offline   Reply With Quote
Old 15-01-2016, 05:46   #17
Senior Cruiser
 
Sailmonkey's Avatar

Cruisers Forum Supporter

Join Date: Sep 2009
Location: Houston
Boat: '76 Allied Seawind II, 32'
Posts: 5,790
Re: Wire size on alternator

Quote:
Originally Posted by Maine Sail View Post

I wonder if anyone could tell me how much milk I have in my fridge. I am away from my fridge and don't know..

Sqrt 7^34 deciliters


Sent from my iPhone using Cruisers Sailing Forum
__________________

__________________
Sailmonkey is online now   Reply With Quote
Old 15-01-2016, 05:53   #18
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Wire size on alternator

Quote:
Originally Posted by Boatyarddog View Post
I'm not sure where you got that r

As stated by others, I used round trip for the calculation, so your 6' example is electrically 12'.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 15-01-2016, 10:34   #19
Registered User
 
deblen's Avatar

Join Date: Oct 2014
Location: Grand Manan,N.B.,Canada N44.40 W66.50
Boat: Mascot 28 pilothouse motorsailer 28ft
Posts: 1,405
Images: 1
Re: Wire size on alternator

Depends on max current per table.

https://www.bluesea.com/resources/1437
__________________
My personal experience & humble opinions-feel free to ignore both
deblen is offline   Reply With Quote
Old 15-01-2016, 10:53   #20
Registered User
 
Sailorman Ed's Avatar

Join Date: Jun 2010
Boat: Polynesia 40/42
Posts: 685
Images: 15
Send a message via Skype™ to Sailorman Ed
Re: Wire size on alternator

Quote:
And often the negative side of the charging circuit has the most voltage drop due to the alt current passing through multiple poor conducting metals, rust, corrosion, gasket material etc. before it picks up the main engine negative cable.. Also many factory alternators are isolated ground, such as many of the Hitachi's, so they pass through quite a bit of very small GA wire before even getting to larger neg cable..
So we should run a separate ground wire from the alt case back to the battery or only to the engine battery cable?


Quote:
if anyone could tell me how much milk I have in my fridge
This is easy, "not enough"
__________________
Sailorman Ed is offline   Reply With Quote
Old 15-01-2016, 13:30   #21
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Re: Wire size on alternator

Quote:
Originally Posted by a64pilot View Post
Silly question, usually the wire from the Alt does run to the battery bank,
But, three ft or less away from the Alt. is usually the starter solenoid, that has a HUGE wire that also goes to the bank. So why not just take your Alt wire to the solenoid?

I believe my stock Yanmar wiring harness had a 10Ga wire, though it may be an 8
The smaller stock Yanmar harness does indeed utilize the HUGE wire on the solenoid.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 15-01-2016, 13:33   #22
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Re: Wire size on alternator

Quote:
Originally Posted by Maine Sail View Post
And often the negative side of the charging circuit has the most voltage drop due to the alt current passing through multiple poor conducting metals, rust, corrosion, gasket material etc. before it picks up the main engine negative cable.. Also many factory alternators are isolated ground, such as many of the Hitachi's, so they pass through quite a bit of very small GA wire before even getting to larger neg cable..

If one desires any sort of charging performance, where the alternator is not seeing absorption voltage prematurely, even a 3% voltage drop, without properly sensing the battery terminals, is too much voltage drop. Stack a 3% + drop on top of an alternator that cuts back the voltage limit, based on alt temp, and it can literally destroy your charging performance.

I wonder if anyone could tell me how much milk I have in my fridge. I am away from my fridge and don't know..
Ahh yes, I forget that many don't their engine in a pristine state .

BTW, what's milk
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 15-01-2016, 14:20   #23
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Re: Wire size on alternator

Most manufactures recommend #8 wire for under 2' of length, and #6 for under 12' for an 80 amp alt. If your going to an isolator/combiner you'll need to read their instructions, for it matters.
__________________
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful! ........
A nation of sheep breeds a government of wolves!

Unprepared boaters, end up as floatsum!.......
delmarrey is offline   Reply With Quote
Old 15-01-2016, 14:28   #24
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,071
Re: Wire size on alternator

Quote:
Originally Posted by Wotname View Post
The smaller stock Yanmar harness does indeed utilize the HUGE wire on the solenoid.
Didn't know that, I never traced the thing, just cut it off
__________________
a64pilot is online now   Reply With Quote
Old 15-01-2016, 14:30   #25
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,071
Re: Wire size on alternator

Quote:
Originally Posted by Sailorman Ed View Post
So we should run a separate ground wire from the alt case back to the battery or only to the engine battery cable?



This is easy, "not enough"


Biggest take away I got from his post, was to ensure your sensing the voltage of the battery bank directly, and while he didn't say this, if you have a good regulator, be sure your sensing both battery bank temp and alt temp, after you shelve the stock alt of course
__________________
a64pilot is online now   Reply With Quote
Old 15-01-2016, 14:36   #26
Registered User

Join Date: Jan 2013
Posts: 203
Re: Wire size on alternator

Stock engines run to alternator output to the starter post.

It is a common practice to run a new wire to the house bank. That's the bank you want to charge first. Then you can use a combiner to the start battery.
__________________
twinboat is offline   Reply With Quote
Old 15-01-2016, 14:54   #27
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,056
Re: Wire size on alternator

With a 60A alternator in most cars, they use a 10-SAE charging wire, last time I checked. BUT. There may be two wires to the batteries, one for charging and the other for voltage sensing, and while they are often both 10-SAE the sense wire can be lighter without any problem.


10-SAE is about equal to 12-AWG, and assuming you are not interested in "how cheap can we build a boat?" you really want to measure the length of the wiring run, use a voltage drop chart, and select a cable that will have zero voltage drop. Ideally.


Except, the pursuit of "zero" will probably mean a cable too thick to attach to the alternator or some similar problem. And you don't need to aim for zero. The more voltage drop that is in that cable, the more voltage the alternator has to produce in order to charge your batteries. So the cheap factory wire means the alternator will be running hotter than it needs to, and wasting power (and engine power, fuel) while a heavier cable will let the alternator run cooler, or charge the batteries faster.


You compromise with your wallet and what's available and eventually say "That's good enough for me", at whatever point you feel meets your personal needs.
__________________
hellosailor is offline   Reply With Quote
Old 15-01-2016, 15:05   #28
Registered User
 
Lars_L's Avatar

Join Date: Jul 2011
Location: Boat: West coast of Norway Winter: Höllviken, Skåne, Sweden
Boat: H 30
Posts: 156
Re: Wire size on alternator

Calculate the size of the wire:

Resistivity of copper ρ = 17.2 nΩm = 0.0172 Ω mm²/m
Total length between battery and generator (both ways) l = 2.0 m
System voltage 12 V
Allowed voltage drop 3%
U = 3% * 12 V = 0.36 V
Dimensioned current I = 60 A
Max resistance R = U / I = 0,36 V / 60 A = 0.006 Ω
Cable area A = ρ * l / R = 0.0172 Ω mm²/m * 2.0 m / 0.006 Ω = 5.73 mm²


A simpler way that’s easier to remember is:

Area = length one way * current / 10
1.0 m * 60 A / 10 = 6.0 mm²
__________________
Lars_L is offline   Reply With Quote
Old 16-01-2016, 14:59   #29
Registered User
 
Boatyarddog's Avatar

Join Date: Nov 2014
Location: Olympia, wa.
Boat: Mariner Ketch 32- 1979- hull 202
Posts: 632
Re: Wire size on alternator

Quote:
Originally Posted by Wotname View Post
???

The negative side is usually the alternator case and the engine and then the BIG negative cable from engine to battery.

Exactly! And a 60amp charging unit rarely peaks.
If your alternator is larger, you need to charge rapidly, the run is long or you have a lot of loads, then a larger size conductor would be good.


Sent from SV Cloud Duster
__________________
Boatyarddog is offline   Reply With Quote
Old 16-01-2016, 15:06   #30
Registered User
 
Boatyarddog's Avatar

Join Date: Nov 2014
Location: Olympia, wa.
Boat: Mariner Ketch 32- 1979- hull 202
Posts: 632
Re: Wire size on alternator

Quote:
Originally Posted by Sailmonkey View Post
Round trip.


Sent from my iPhone using Cruisers Sailing Forum

The calculations include 2 conduits.
Most boats run more than 1 negative conduit, or should be.


Sent from SV Cloud Duster
__________________

__________________
Boatyarddog is offline   Reply With Quote
Reply

Tags
alternator, size

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
wire rigging dyform, compact wire, rod RDW Deck hardware: Rigging, Sails & Hoisting 4 12-11-2014 03:51
What's the Best Way to Connect a 4mm Wire to the Middle of a 6mm Wire? mischief Electrical: Batteries, Generators & Solar 11 07-11-2013 10:31
New wire being made 5 foot battery wire to terminal strip sdowney717 Electrical: Batteries, Generators & Solar 3 20-08-2012 09:27
How to Wire a Battery Isolator with a Three Wire Alternator ? bazzer Electrical: Batteries, Generators & Solar 7 05-12-2010 13:47



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 08:15.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.