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Old 11-11-2011, 14:28   #1
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Alternator Wiring ?

Installing a Balmar 80 amp with the MC 614 regulator. Running 2awg from the alternator to the house bank and I can't figure out what size fuse to use from the alternator to the battery in-line of the 2 AWG?

Spoke to some people that never installed a fuse, but the literature says you should have one.
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Old 11-11-2011, 14:37   #2
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Re: Alternator wiring?

Same size ground? How are you going to protect the alternator diodes if the fuse goes?
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Old 11-11-2011, 14:41   #3
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Re: Alternator wiring?

Why should the fuse go? It is likely to be a super duper size anyway (?).

Can two fuses be installed to avoid such risk?

b.
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Old 11-11-2011, 14:48   #4
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Re: Alternator wiring?

I fuse the cable going to the alternator from the battery, otherwise you have a large cable capable of welding with, connected to the battery unprotected.

I size the fuse to protect the cable, I size the cable to 150% of the nominal of the alternator.

I would rather blow the diode then burn the boat down. It's unlikely that the fuse will blow unless it's a dead fault/short. So not much worry of blowing the diodes if the wire is installed and supported properly.

Just remember breakers and fuses are to protect the cable not the load. If the load also require protection, then fuse the load at the device.

Lloyd
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Old 11-11-2011, 14:54   #5
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Re: Alternator wiring?

Balmar recommends circuit protection rated at approx. 140% of the alternator rated output.

Eric
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Old 11-11-2011, 15:32   #6
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Re: Alternator wiring?

I'd use a 130A ANL fuse in that circuit, located close to the batteries.

Note that ABYC specifications call for fuses with at least a 5,000 ampere interrupt capacity (AIC) for wires connected directly to large battery banks. Only three types of fuses in common use on boats meet these specs: ANLs, the new MRBFs (terminal fuses), and the large Class-T fuses.

IMHO, ANLs are preferable in this case because they can take considerably more amperage than their rating for quite some time before blowing, and as noted above you really don't want to interrupt the alternator charging circuit and blow the diodes or burn up the field windings in your alternator.

Also, depending on the length of cabling, I'd consider using larger than AWG2 cable to minimize voltage drop. I believe that in many instances AWG1 or even 1/0 would be a better choice.

Bill
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Old 11-11-2011, 15:49   #7
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Re: Alternator wiring?

Quote:
Originally Posted by btrayfors View Post
Also, depending on the length of cabling, I'd consider using larger than AWG2 cable to minimize voltage drop. I believe that in many instances AWG1 or even 1/0 would be a better choice.
Yes, the bigger the cable the better. You can also add a fuse to the ground.
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Old 11-11-2011, 15:49   #8
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Re: Alternator wiring?

Quote:
Originally Posted by btrayfors View Post
I'd use a 130A ANL fuse in that circuit, located close to the batteries.

Note that ABYC specifications call for fuses with at least a 5,000 ampere interrupt capacity (AIC) for wires connected directly to large battery banks. Only three types of fuses in common use on boats meet these specs: ANLs, the new MRBFs (terminal fuses), and the large Class-T fuses.

IMHO, ANLs are preferable in this case because they can take considerably more amperage than their rating for quite some time before blowing, and as noted above you really don't want to interrupt the alternator charging circuit and blow the diodes or burn up the field windings in your alternator.

Also, depending on the length of cabling, I'd consider using larger than AWG2 cable to minimize voltage drop. I believe that in many instances AWG1 or even 1/0 would be a better choice.

Bill
That's true, I should have been more clear on the voltage drop. Every DC circuit should take consideration of voltage drop. All of the inverter manufactures recommend Class T fuses, and that's what I use when installing high amp alts. Most alternator manufacture recommend less then 4% vd.

One thing to note, the terminal fuses are a good option for somethings, but I have found them to be a poor choice when installed to flooded lead acid batteries directly. They corrode from acid fog.

I spoke with Blue Sea engineer's and they said they agreed, and were looking into a better plating that would resist the acid corrosion, but I haven't heard back from them.

Also the Class T fuses have the lowest voltage drop across the fuse.

Lloyd
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Old 11-11-2011, 15:54   #9
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Re: Alternator wiring?

Quote:
Originally Posted by Seahunter View Post
.....You can also add a fuse to the ground.
Oops...no. ABYC calls for no fuses in the ground system.

I agree, except for SSB radios on their own circuits, where fusing both the positive and negative power leads is a good idea.

bill
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Old 11-11-2011, 16:04   #10
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Re: Alternator Wiring ?

Quote:
Originally Posted by aland3800 View Post
can't figure out what size fuse to use from the alternator to the battery

Alan,

A circuit breaker is used to protect the cable and a fuse to protect the source. Now, if you distance from the alternator to the battery is greater than 20 feet, the AWG2 cable its ok. I think you can use a smaller cable for your 80Amp alternator.

"CableChart" table helps you select the wire gauge
"FuseChart" table helps you select the fuse rate
Chears,
Nicolas
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Old 14-11-2011, 08:12   #11
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Re: Alternator Wiring ?

I know the fuse is to protect the battery cable and I will use a 150% of the 80 amps, never heard of fusing a ground and will not be doing that. I talked with many boaters that do not have a fuse in the battery cable to the batteries and was a bit suprised.

Thanks everyone. Should have it all done this weekend. A few more connections and it will be ready for next year. On to some new hoses and all new fuel lines.

Boat comes out on Friday for the winter. Very sad day
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Old 14-11-2011, 09:27   #12
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Re: Alternator Wiring ?

Quote:
Originally Posted by aland3800 View Post
I know the fuse is to protect the battery cable and I will use a 150% of the 80 amps, never heard of fusing a ground and will not be doing that. I talked with many boaters that do not have a fuse in the battery cable to the batteries and was a bit suprised.

Thanks everyone. Should have it all done this weekend. A few more connections and it will be ready for next year. On to some new hoses and all new fuel lines.

Boat comes out on Friday for the winter. Very sad day
The big concern is that you use over current protection (OCP) as close to the "source" as possible. In the case of an alternator the "source" is the battery bank. The actual standard is to be within 7" of the + battery post but 7" is often impossible unless using MRBF fuses (Marine Rated Battery Fuse) which mount directly to the + battery post.. The ABYC standards consider an alternator a "self limiting" device so no OCP is technically necessary at the alternator end of the wire.

The OCP is there to solely protect the wire in the event of a dead short, or other failure mode that creates high enough resistance to cause melting of the wire. The fuse would blow at the battery thus cutting off bank current to support a potential fire.

So with 2GA wire the max ampacity for a fuse on a single non-bundled conductor, rated at 105C (marine UL1426 wire is rated at 105C), are 210A outside engine spaces, and 178.5A inside engine spaces. Any OCP below these numbers is more than adequate to protect this wire. The ABYC standard also allows for the ability to go to 150% of the wires ampacity rating which I usually try not to do and is certainly not necessary in this case.


Remember to use the same size ground wire on your Balmar as your + wire. Most of these are no longer case grounded alternators and are isolated ground. I have solved numerous charging issues by simply fixing the alternator ground. Had one guy with a 125A alt charging AGM's using the engines factory wiring harness ground wire, 12GA, and could not figure out why he could not get anywhere near the alts rating out of it. Changed the alts neg wire to 1GA, same as the + wire, and it then worked perfectly..

Gotta go, heading out sailing, it's 60F here in Maine!!!
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Old 14-11-2011, 09:48   #13
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Re: Alternator Wiring ?

Gauge your cable to a 3% or slightly less voltage drop. This way you do not have too much of a voltage drop nor are you wasting money going overkill on the cable.

Base your cable gauge on your alternators maximum output and the wire run...at a 3% voltage drop.

This is as complex as it needs to be.


There is absolutely no point in fusing a negative DC wire...period. It is only the positive side of a DC system that needs to be protected against a short circuit. By definition, the negative side cannot be shorted.
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Old 14-11-2011, 10:31   #14
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Re: Alternator Wiring ?

While choosing your wire size according to the 3% voltage drop calculation is fine for many circuits on a boat, I believe there are good and valid reasons why this standard should not be applied automatically to alternator circuits and to battery combining circuits.

A 3% voltage drop is the difference between 14.4VDC and 13.968VDC. In other words, if your alternator is putting out 14.4V into a circuit with a 3% voltage drop, the batteries are seeing only 13.97V. Does this make a difference?

Yes, it can, in several ways.

Battery acceptance is largely a function of charging voltage applied to the battery. A battery which is under charge at 14.4V will accept more amperage than one charged at 13.97V. If you're concerned about full charges and, especially, keeping the charging times to a minimum (and reducing system loss due to heat), then you might well want to set up a charging circuit with less than a 3% voltage drop.

We're not talking about safety here, but efficiency. And, in my experience, anything you can do to improve the efficiency of charging your batteries on a cruising boat is well worth it. Choosing battery cable one or two sizes larger than the 3% solution will help contribute to the overall efficiency of your charging system.

IMHO,

Bill
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Old 14-11-2011, 10:37   #15
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Re: Alternator Wiring ?

The #2 wire you are planning will be fine--as long as you run your voltage sensing wire to the battery terminal, the regulator will be compensating for the wire losses in the positive side of the circuit. You can even compensate for losses in the ground circuit by running the regulator ground wire to the negative battery terminal, but its probably going to work well without that unless you have an extremely long wire run.
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