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Old 26-05-2015, 18:41   #1
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Alternator Output Lead Sizing

I'm preparing to install my new Mark Grasser alternator, which is rated for 140A, but will be "detuned" to around 120A (per Maine Sail recommendations). Regulation will be via a Balmar MC-614 external regulator, with battery sense wire physically connected to battery bank.

I have plenty of 1/0 AWG cable and lugs left over from another project, as well as lots of 4 AWG and lugs (but nothing in the middle). I was planning to use the 1/0 for the alternator, even though it's overkill, but I recently discovered that there isn't enough space in my desired cable path for two 1/0 cables.

According to the BlueSea Circuit Wizard app, the 4 AWG is large enough based on ampacity, but not quite enough to prevent exceeding 3% voltage drop (gives about 4% drop at 120 amps). The app says I should use 3 AWG to stay under 3%.

But I'm thinking that the voltage drop threshold isn't really too important here (within reason), since the regulator will bump up the alternator output as necessary to overcome any voltage drop. Plus, the alternator will rarely, if ever, be running at 120 amps (it's feeding a 4x6V bank).

So on the one side, common sense seems to say that 4 AWG will be fine, and since I have materials on hand, I should go ahead and use it. But on the other hand, I spent quite a bit of money on the alternator and regulator, so it seems dumb to "cheap out" on the wiring.

Suggestions?
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Old 26-05-2015, 18:49   #2
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Re: Alternator Output Lead Sizing

Since you already have it, I'd use 1/0 and find room for the two cables. Just 'cuz :-)

In things charging w/12VDC, overkill is good!

Be sure to add appropriate fusing near the batteries.

How long is the run?

Bill
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Old 26-05-2015, 18:52   #3
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Re: Alternator Output Lead Sizing

#4 got hot on our boat with the alternator putting out. I would go bigger.
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Old 26-05-2015, 21:48   #4
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Re: Alternator Output Lead Sizing

Run is about 15 feet (round trip). I did come up with another possible cable route, so it looks like the 1/0 is probably the way to go (those fat cables are hard to manage).
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Old 26-05-2015, 21:55   #5
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Alternator Output Lead Sizing

I'm planning to land the alternator on the house bank bus bar, which is connected to the house bank with a short run of 1/0 through a MBRF fuse (I can't recall the size offhand - 250A? - was sized for the 1/0 wire), so I should be good with regards to fusing.
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Old 26-05-2015, 22:57   #6
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Re: Alternator Output Lead Sizing

#4 is ro small, #1/0 is overkill, they don't make #3

I used #2 AWG for a 100A alternator with 25 foot round trip.

Why not use what's right, even if yo have to buy some wire?
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Old 26-05-2015, 22:57   #7
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Re: Alternator Output Lead Sizing

Run a short 1/0 jumper over to the engine block ground and use the starter return for the alternator return. It is just along for the ride most of the time. If you use the #4 it should be fused appropriately where it connects to the battery bank/ switch.

If the starter wire size is smaller might want to just replace the return with that 1/0. Not carved in stone anywhere that positive and negative cables have to be the same size.

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Old 26-05-2015, 23:40   #8
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Re: Alternator Output Lead Sizing

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Run a short 1/0 jumper over to the engine block ground and use the starter return for the alternator return. It is just along for the ride most of the time. If you use the #4 it should be fused appropriately where it connects to the battery bank/ switch.
Except if he has the AO run directly to the house bank, this ain't gonna work.

And besides, why run the AO thru the switch anymore, that's so old school.
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Old 27-05-2015, 08:44   #9
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Re: Alternator Output Lead Sizing

Following
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Old 27-05-2015, 09:36   #10
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Re: Alternator Output Lead Sizing

Keep in mind that the fuse needs to be sized for the wire not the output of the alternator 1/0 cable should have a fuse around 150-170amps not 250
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Old 27-05-2015, 09:59   #11
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Re: Alternator Output Lead Sizing

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Keep in mind that the fuse needs to be sized for the wire not the output of the alternator 1/0 cable should have a fuse around 150-170amps not 250
1/0 105C wire can be fused at 285A at 100% of ABYC max ampacity outside an engine space and 243.2A inside an engine space, both at 100% of Table VI single conductor max ampacity. You are also allowed to go to 150% of Table VI, in certain situations, if necessary..

Rusty, you can also just stack the 1/0 alt neg lead directly onto your engines 1/0 neg lug (don't use the rusty block as a path). Just make sure both lugs are clean...

Also don't forget that the regulators black wire is part of the voltage sensing circuit so both the red/v-sense and regulator black wires need to sense the bank directly.
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Old 27-05-2015, 10:23   #12
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Re: Alternator Output Lead Sizing

0 can be awful stiff, just make sure it isn't so stiff that it will break the alternator lug or loosen up a lot with vibration. It's a perfect situation for large flexible welding cable.
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Old 27-05-2015, 11:18   #13
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Re: Alternator Output Lead Sizing

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It's a perfect situation for large flexible welding cable.
Sure if you have an old leaky engine that keeps everything nice and oily so the ends don't corrode and you're not going to keep the boat for another 30 years because that's about how long it takes for the insulation to fall off welding cable
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Old 27-05-2015, 12:06   #14
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Re: Alternator Output Lead Sizing

this is a repeat on balmar! i was an ample power fan for years, till i bought the hype that balmar was spewing at at the local commercial boat show here in seattle...bought the balmar regulator in 02/03, it never charged the same from day to day! when we got back from alaska, i faxed my records to steve, at balmar, they sent me a new model, the 612...for 5 yrs, i got a new one every year! i finally went back to ample power, shoulda never left!, got their V3 model, set it for flooded deep cycle, and never looked back! just go to 'amplepower.com' and do some reading. on the wire sizes, all wire in the charging system, should be the same size/both ways, or damn close! remember dc current flows like water in a pipe! different wire sizes, restricts the flow! larger is better! i have 6 6v, and use 2/0 all around...clyde
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Old 27-05-2015, 12:39   #15
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Re: Alternator Output Lead Sizing

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this is a repeat on balmar! i was an ample power fan for years, till i bought the hype that balmar was spewing at at the local commercial boat show here in seattle...bought the balmar regulator in 02/03, it never charged the same from day to day! when we got back from alaska, i faxed my records to steve, at balmar, they sent me a new model, the 612...for 5 yrs, i got a new one every year! i finally went back to ample power, shoulda never left!, got their V3 model, set it for flooded deep cycle, and never looked back! just go to 'amplepower.com' and do some reading. on the wire sizes, all wire in the charging system, should be the same size/both ways, or damn close! remember dc current flows like water in a pipe! different wire sizes, restricts the flow! larger is better! i have 6 6v, and use 2/0 all around...clyde
On the HC 38 in my Avatar, I had a Balmar regulator (admittedly that was years ago and I think it was a series 3 or 4 reg.) and I had a Ample power regulator. I used the Balmar for quite a while then decided to go to the Ample Power reg. The difference in out put was huge with the Ample Power.
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