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Old 14-11-2011, 12:43   #16
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Re: Alternator Wiring ?

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Originally Posted by btrayfors View Post
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
Then lead the voltage sensor wire on the alternator to the batteries if a 3% voltage drop makes a difference.
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Old 14-11-2011, 13:02   #17
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Re: Alternator Wiring ?

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Then lead the voltage sensor wire on the alternator to the batteries if a 3% voltage drop makes a difference.
Yes, IF there's a voltage sensing wire from the alternator or regulator. This would help with efficiency (but wouldn't affect the 3% voltage drop or heat loss).
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Old 14-11-2011, 13:03   #18
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Re: Alternator Wiring ?

This is slightly off topic; although, does apply to Alternators.
I recently purchased a 120amp Alternator to replace my 55amp Alternator on a Yanmar 4JHE, 45HP Diesel.
The new unit only has one sheave and when installed becomes very hot which I believe is due to belt slippage. Charges well until it stops I believe due to heat~?
I read some time ago that it is possible to wire in a device that will restrict the Alternator output to say 80amp+- and perhaps eliminate the heat problem.
Does anyone know of such a device or have other suggestions short of dumping my new Alternator and purchasing a smaller unit~?
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Old 14-11-2011, 13:06   #19
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Re: Alternator Wiring ?

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Originally Posted by adlib2 View Post
This is slightly off topic; although, does apply to Alternators.
I recently purchased a 120amp Alternator to replace my 55amp Alternator on a Yanmar 4JHE, 45HP Diesel.
The new unit only has one sheave and when installed becomes very hot which I believe is due to belt slippage. Charges well until it stops I believe due to heat~?
I read some time ago that it is possible to wire in a device that will restrict the Alternator output to say 80amp+- and perhaps eliminate the heat problem.
Does anyone know of such a device or have other suggestions short of dumping my new Alternator and purchasing a smaller unit~?
A smart regulator, like the Balmar MC-612 or MC-614, can de-rate the alternator output to any degree desired.

That may be a good way to go, depending on your situation.

BTW, a 1/2" V-belt can handle up to about 100A. Much beyond that, you need either 2 belts or, better, a serpentine belt.

Bill
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Old 15-11-2011, 09:08   #20
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Re: Alternator Wiring ?

Thanks Bill:

Didn't realize the Smart Regulators were as readily available~~!!
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Old 15-11-2011, 09:11   #21
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Re: Alternator Wiring ?

Thanks everyone, I can't wait to test it in the Spring. On to new fuel hoses.
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Old 20-11-2011, 23:00   #22
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Re: Alternator Wiring ?

The regulators can be set up to adjust output two ways: amp manager or Small Engine Mode. The latter is much easier, just s simple switch.
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Old 21-11-2011, 03:23   #23
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Re: Alternator Wiring ?

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Originally Posted by btrayfors View Post
Yes, IF there's a voltage sensing wire from the alternator or regulator. This would help with efficiency (but wouldn't affect the 3% voltage drop or heat loss).
IF the regulator is a smart reg, it will have a battery voltage sensing wire and temperature compensation. Taking the sensing wire directly to the +ve battery post will compensate for the volt drop...thats the whole idea....so when you set 14.4V (or whatever) on the reg for the absorption voltage...that's what you'll get at the battery. The voltage at the alt out piut will be higher to COMPENSATE for the drop.....that's how these regs should work. If yours doesn't, you need a better reg. there's plenty on the market...I use Next Step II from Ample Power...works well.
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Old 23-11-2011, 18:32   #24
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Re: Alternator Wiring ?

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Originally Posted by Albro359 View Post
Taking the sensing wire directly to the +ve battery post will compensate for the volt drop...thats the whole idea....so when you set 14.4V (or whatever) on the reg for the absorption voltage...that's what you'll get at the battery...
Quite. So in this case the voltage drop is not relevant.
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