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Old 01-17-2005, 11:20 AM   #1
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Default Battery Cable Size

I am moving batteries to the console. Using the wire size chart:

http://bestboatwire.com/catalog/incl...uge_chart.html

I know about the "round trip" to calculate the length. The question is what do you use for the amperage number? Engine has a 60 amp alternator so my guess is using 60 is a safe decision. I can forsee no power draw or power input to the batteries that ever would really approach 60 amps. Your thoughts?
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Old 01-17-2005, 12:15 PM   #2
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Default RE: Battery Cable Size

The size should not be based on what the engine puts out, but rather how much power is required to start the motor (s). I suspect it's considerably more than 60 amps. So my question would be; "How many amps to start the motor?" Size accordingly, double the distance as you've stated. Then from the new battery location you would then calculate the power to a Bus for the electronics, etc. Size wire accordingly. www.bluesea.com is also a great source of information also...the catalog is priceless.
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Old 01-17-2005, 02:13 PM   #3
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Default RE: Battery Cable Size

MUMBLER-

Agree. Starter current draw is heaviest load. The best boat wire chart really wasn't made for battery wire and high amperages so I had to poke around for some better info. The million dollar question, what does a V6 outboard starter draw? I am going to use my starter fuse size. From my repair manual, the starter circuit fuse on the Honda 225 is rated for 150 amps.

CM=(K x I x L) / E
CM = Circular Area of Conductors
K = 10.75 (Constant representing the mil-foot resistance of copper)
I = Current (amps)
L = Length (feet)
E = Voltage drop (in volts) (.36 is accepted marine practice for 12V)

(10.75) (150) (20) divided by .36 = 89583 circular mil area

My cable size for a 20' round trip is rounded to 90,000 circular mil area. That equals 1AWG battery cable I have rounded up by at least a size (starter doesn't draw 150, rounded up to 90K circular mils, went to the next highest wire size on the chart) but better to be safe.


info from:
http://www.e-marine-inc.com/products.../boatwire.html
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Old 01-17-2005, 02:57 PM   #4
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Default RE: Battery Cable Size

Sleeper, I take the max starting amp hours that the battery says it can put out, then double the cable size to account for the copper sulphate that can easily cover 1/2 of the strands on the wire.
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Old 01-17-2005, 03:48 PM   #5
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Default RE: Battery Cable Size

Get pr-cut tinned marine battery cable here http://www.jamestowndistributors.com...NO=J1353425238
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Old 01-17-2005, 05:55 PM   #6
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Default RE: Battery Cable Size

Quote:
Bullshipper - 1/17/2005 1:57 PM

Sleeper, I take the max starting amp hours that the battery says it can put out, then double the cable size to account for the copper sulphate that can easily cover 1/2 of the strands on the wire.
Bull- they don't make battery cable that big. If I started out by using 1000 amps (Optima Blue Top) as an example, the wire would need to be over AWG 0000 which is as big as it comes (.785 diameter) , then double it?? You're not trying to sell me some Mexican welding cable are you, maybe a deal on some powerplant generator primary wire?


The accepted formula is stated above for figuring battery cable size. My original dilema was what to use for the amperage part of the formula. Since I have a 150 amp fuse link at the starter, it is easy to guess that the most amperage possible my engine can draw starting is something less than 150 amps. I need to do a test someday to see but I am thinking that starting current is no where near 100amps. On the output side (another cable size consideration), my alternator puts out max 60 amps. AWG 1 cable with less than a 20' (roundtrip) length is more than I need according to the math.
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Old 01-17-2005, 06:07 PM   #7
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Default RE: Battery Cable Size

Quote:
Kid Stuff - 1/17/2005 2:48 PM

Get pr-cut tinned marine battery cable here http://www.jamestowndistributors.com...NO=J1353425238
Yes, but much cheaper (30%) here:
http://bestboatwire.com/catalog/default.php?cPath=24

I have never found Jamestown to be a great deal, yes they have most everything you need but cheap they are not. I have found them to be an excellent source for West epoxy products though.
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Old 01-17-2005, 06:11 PM   #8
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Default RE: Battery Cable Size

For whatever it is worth, my 175 efi Mariner starter motor draws 175 - 180 amps.
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Old 01-17-2005, 06:15 PM   #9
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Default RE: Battery Cable Size

I would go no less than 1 AWG, but more preferably, 0 or 00(double-aught) AWG for batteries. I was taught to to use the largest size available for your purpose(mine, too). You need to be able to carry the starting load as well a providing power to the electronics and etc.
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Old 01-17-2005, 06:16 PM   #10
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Default RE: Battery Cable Size

Quote:
marinerman2 - 1/17/2005 5:11 PM

For whatever it is worth, my 175 efi Mariner starter motor draws 175 - 180 amps.
Thanks for that number, where did it come from? Have you actually measured the starting current or is that what the starter motor is rated for? I only ask because on the Honda 225 there is in fact a 150 amp fuse in the starter circuit. I am curious to know what a V-6 OB starter really draws @ 12V.
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Old 01-17-2005, 08:25 PM   #11
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Default RE: Battery Cable Size

Sleeper...don't forget a new fuse within 1' of the battery. Here is some good info.

http://www.bluesea.com/Article_Detail.asp?ID=121&Page=0&section_Id=140

BlueSeas Wire Size Chart

Hope this helps.
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Old 01-17-2005, 08:27 PM   #12
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Default RE: Battery Cable Size

To know the draw, you refer to the stat listed under "Locked Rotor Draw"when you email Delco or whoever supplied you.
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Old 01-17-2005, 08:33 PM   #13
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Default RE: Battery Cable Size

I have been using welding cable for my wiring needs for the last few years. It is more flexiable, carries the amps better and seems to be a lot cheaper.
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Old 01-17-2005, 08:45 PM   #14
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Default RE: Battery Cable Size

Click below and download Wiresizer 2.0. It will make things soooooo much easier for you in the future.

http://www.midcoast.com/~aft/program/wiresz20.zip
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Old 01-17-2005, 09:36 PM   #15
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Default RE: Battery Cable Size

Quote:
mole2 - 1/17/2005 7:45 PM
Click below and download Wiresizer 2.0. It will make things soooooo much easier for you in the future.
http://www.midcoast.com/~aft/program/wiresz20.zip
Nice program, thanks. Came out with the same AWG size as the long hand calcs so I guess all is well.

randyt- Welding cable is not tinned and not the right stuff for a boat. Don't tell me you use Romex for smaller circuits
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Old 01-18-2005, 10:26 AM   #16
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Default RE: Battery Cable Size

I've been looking for this info for a long time. I could never figure out the current draw of the starting motor. The Blue Sea info never really comes out and tells you what the draw is. They talk about inrush periods of over 1000 amps and cranking periods of 9 and 3/4 seconds at what looks to be 200 amps (their graph). Now if you look at their battery switch info, they are rated for 1,600 amp (inrush), 700 amp (cranking period...9.75 seconds), 600 amp (intermittent), and 350 amp (continuous). Soooo, which amperage do you use to size your wire? I would have thought that 300 amps would cover the cranking period and would be enough. But I'm still confused. I really don't want to use 00000000 battery cable!

And the starting circuit is the only one exempted from fuse or breaker protection, although you still could.
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Old 01-18-2005, 11:41 AM   #17
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Default RE: Battery Cable Size

Sleeper, the current was measured using a digital ammeter. The kind that clamps around the ground cable.
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Old 01-18-2005, 05:55 PM   #18
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Default RE: Battery Cable Size

Quote:
marinerman2 - 1/18/2005 10:41 AM
Sleeper, the current was measured using a digital ammeter. The kind that clamps around the ground cable.
Thanks marinerman2, good source of info.

OK, now we have established that we have two data points:

A. an EFI 175 HP Merc actually draws 180 amps as measured with an ammeter during starting.

B. a Honda 225 has a 150 amp fuse right before the starter, so it draws less than 150 amps starting

Now the question needs to be asked, why does a V-6 Honda 4 stroke take so much less current to start than a V-6, 2 stroke? One would think that the valve train of a 4 stroke would take more current? On the four stroke, a whole lot more things must get moving. Actually, I believe the answer to be that the Honda is much harder to crank so I poked around as to what is going on here.

Looking at the exploded view of the Honda starter in my tech manual it appears to be a lot different than most starters I have had apart. It actually has three planetary gears that the starter gear as we know it engages into the center of and then the planetary gears run around inside a geared race if you will. Kind of hard to explain without you seeing the pictures. Not enough definition in the pics to try and count teeth and thus come up with a reduction %. Suffice to say there is a lot of gear reduction in a Honda starter assembly. Hope it is built well because it looks kind of expensive.
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Old 01-18-2005, 06:16 PM   #19
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Default RE: Battery Cable Size

Lock Rotor Draw is the maximum current draw an electric motor will use to start against load, and can be found in the tech specs if requested. The other way is just to ask the OEM what he recommends as a cable size so as to not void the warranty when you burm the rotor wire. But if this is unavailable, you consider using this as a guide:
A very heavy starting load is a piston compressor, that will momentarily draw 7 times the current on its rated nameplate, and I would use this as a guide for high compression gas or deisel engines, and maybe drop back to 5X for older used models.
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Old 01-09-2010, 10:05 PM   #20
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Default

I am in the midst of planning my boat rewiring (17 ft Arima Sea Ranger) which will have 1 of the batteries forward so I feel the wire needs protecton. Anyway, it was either Blue Sea or a similar site I came across where a rough estimate is 1 starting amp per CI of displacement. The new Suzuki DF90 and my old Johnson 90 have around 95 CID so I estimated at 100A starting, + 25% to be sure. I looked as the Blue Sea Terminal fluse blocks and the fuse time delay looks like it can handle over 200A for < a second.

For the 15 foot 1 way distance and this load I was planning to use #2 to minimize voltage drop.

With multiple batteries there can be a pretty big surge current when switching to both if one is discharged.

I would be very interested in seeing some marine electrician's replys.

Jay
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