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Old 12-10-2011, 13:04   #1
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Alternator Upgrade

Winter project will be to remove my stock 50 amp alternator and replace it with a Balmar 80 amp, 7 series alternator with the MC614 regulator. I'm still trying to figure if I need a 1", 2" or 3.15" foot set up for my Westerbeke 38B4. I would like to go bigger but I have a 3/8" belt, which seems to limit me to a 80 amp alternator. I have 3 house and 0ne starting battery. House is around 300 amps.

Has anyone done this upgrade and did you also add a Eco charge or a ACR?
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Old 12-10-2011, 13:22   #2
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Re: Alternator upgrade

Yeah, the 3/8" belt is limiting.

Hardly seems worth it, though, to go from 50A to 80A when for a few more bucks you could easily go for 100A or 110A....but for the belt limitation.

Two possibilities:

1. go ahead and get the larger alternator, and just de-rate it using the MC-614 (i.e., limit it's output to, say, 75 or 80% of capacity); or

2. get a pulley kit and install a larger belt. ElectroMaax makes some nice ones which would allow you to install a serpentine belt and an alternator up to about 180A. Other kits are available from, e.g., TransAtlantic Diesel, et. al.

The first alternative would allow you to prepare for the future, when you upgrade your house battery capacity and your belt arrangement.
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Old 12-10-2011, 14:43   #3
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Re: Alternator Upgrade

"I would like to go bigger but I have a 3/8" belt,"

How robust is your flywheel? Is there enough metal for a machine shop to stick it on a lathe and open up the groove for a 1/2" belt instead? that could be one way out, and cheaper than having a new flywheel made.

I'd also suggest running the numbers on your pulley sizes (ratio) and engine speed versus alternator output. Sometimes, all you need to do is put the correct size pulley on the alternator and you can double the output at idle-to-cruising rpm ranges.

And with perhaps 400AH of total batteries, if you are conservative and only cycle them to 50%, you'd need 200AH to recharge...let's say 160-170 unless you've really been working that starter battery down...and considering that the acceptance rate of the battery will also be a limiting factor, unless you're running AGM or gel batteries, wet lead may not show much benefit from going up to a 100AH alternator. The batteries would just boil--not charge--and the regulator would cut the power back anyhow.

Not knowing all your numbers, but guessing 3/8 will be enough, if the alternator speed (pulley size) is optimized.
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Old 12-10-2011, 15:23   #4
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Re: Alternator Upgrade

The acceptance rate of the battery bank is the controlling factor. The size of the charger/alternator doesn't matter a whit, so long as the charging voltage is the same.

Lotsa folks don't get this.

Example:

400 AH flooded batteries
100 amp acceptance rate @ 14.4 volts (when discharged to 50% or so)

Actual initial charging rate with a 100A capable alternator or smart battery charger with voltage limited to 14.4VDC: 100A

Actual initial charging rate with a 200A capable alternator or smart battery charger with voltage limited to 14.4VDC: 100A

Actual initial charging rate with a 500A capable alternator or smart battery charger with voltage limited to 14.4VDC: 100A

The size of the battery charger or alternator doesn't matter, so long as the charging voltage is limited. The batteries are going to accept what they're going to accept. Period.

And, so long as the recommended charging voltage isn't exceeded, they're not going to boil, no matter the size of the charger.

What causes them to bubble and boil (like a witches brew at Halloween) is higher voltage, e.g., when you're equalizing a 12V bank @ 15.5-16.0 volts.

So....with regard esp. to flooded batteries:

Can you have too large a smart charger? NO, not really. The batteries are going to take what they're going to take.

Can you have too small a smart charger? NO, not really....it just takes longer to fully charge the batteries.

Bill
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Old 13-10-2011, 12:45   #5
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Re: Alternator Upgrade

Thanks everyone. The stock 50 amp with an internal regulator starts out charging around 30-40 amps and then drops to around 16 amps. It is 1994 vintage. This should be a fun winter project along with new fuel lines and a fuel tank clean out.
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Old 13-10-2011, 12:57   #6
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Re: Alternator Upgrade

alan-
The internal regulator, like all "car" alternators, is actually not designed to charge batteries. It is designed mainly to "not overcharge" batteries during a long day on the road, when the starting battery is only lightly drained by the one start, and then charged for hours and hours on end by a cheap dumb charging system.
So going to a proper external deep-cycle-purposed regulator will change that 16 amp output to something more useful, regardless of belt and alternator size. A very effective winter project.
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Old 17-10-2011, 11:20   #7
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Re: Alternator Upgrade

Battery acceptance will determine the alternator output. It could well be that if you buy the 100A alternator, the 3/8" belt will be just fine. It works for me.

Instead of using the programmed amp management adjustment on the regulator, consider the easier-to-use small engine mode:

Alternator heat, Regulator Controls, Small Engine Mode

Those regulators have very neat features.
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