36-2 Alternator

Sea Story · Feb 7, 2011

Greg,

I have a P39 with the same engine. A few years back, I took out the 55 amp, stock alternator and had a motorola 107 amp installed. It took a while to find out why that was a bad idea, and I ended up without electrical power off Cabo San Lucas in the middle of the night... Turns out, you need a two-belt setup to drivefor that big an alternator, otherwise the belt starts slipping when the alternator starts working. Luckily, I found another boater in Matzalan with a spare 85 amp, stock Yanmar alternator, and it worked fine when we installed it. It's still in operation, and does well in keeping my battery banks charged.
The 85 amp isn't manufactured by Yanmar, (I think it's a Mitsubishi), but it is the one they provide as a stock item. My expert mechanic tells me that the 85 is as big as you should go with a single belt.

Hope this helps...
Jerry

Ariel · Feb 8, 2011

Greg,

Good to hear from you again. I was thinking you and Ann must have sailed away looking for warmer weather.

We have a 135 amp Balmar alternator. Its that large only because I got a good deal on it about fifteen years ago. I have it limited to 65 amps by the regulator.

Keep two things in mind as you go through this excercise:

1. The flooded batteries will only accept about 20% to 25% of their rated capacity. Your three house batteries and start battery through a isolater or combiner will accept about 100 amps COLD. It will decrease as the batteries heat and drive the batteries above the gassing point if the charge is to high.

2. Get a regulator with temperature compensation for boh the batteries and the alternator. It is good insurance for protection of the batteries and the alternator.

3.Check on the HOT rating of the alternator. Capacity of the alternator is reduced about 20% when it is hot.

4. You will most likely need to replace the wire to the batteries for the higher amps and install a seperate negative wire and not use the path through the engine as the negative path.

5. A single pulley is adequate if you don't go over 100 amps. The Yanmar belt does not work well and I use a Gates "greenstripe" belt from an auto store. It has a cog like backside. The current belt is about eight years old and does not make dust as the Yanmar belt did.

6. I do not like the isolator because of the voltage loss in the isolator. A combiner is better, or as I use, an isolator eliminator from Ample Power to charge the start bat from the house bank. Because of the windlass a combiner may be better for you.

Ample Power is a good source if information and data. The owner, David Smeed, is a former cruiser and has two very good books for referance, "Living on 12 Volts with Ample Power" and "Wiring 12 Volts for Ample Power". The latter is the most understandable unless you are an electrical engineer.

If I can be of any more help, just ask.

Oh! We will be in the Chesapeake this summer and not sail to New England as we usually do. This year I am the fleet captain for our club and will be staying close by. Maybe next year

Dave
s/v ARIEL

Sea Story · Feb 15, 2011

It was a Hitachi and not a Mitsubishi. Got my Japanese manufacturers confused....!

Jerry

36-2 Alternator

NYSail

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Sea Story

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Ariel

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NYSail

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Sea Story

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