Is a 100 amp Alternator Too Large ?

[btrayfors]

A Perkins 4-108 can handle a 100-amp alternator with a single 1/2" v-belt (Gates Greenstripe or equivalent) just fine. I've had one for more than 9 years. Mine doesn't eat belts anymore, after initial alignment problems which I found and corrected within months of the original installation.

The trick is to:

1. GET THE ALIGNMENT ABSOLUTELY RIGHT. Be very sure the pulleys (main drive, water pump, and alternator) are perfectly aligned so the belt runs true.

2. USE AN EXTERNAL SMART REGULATOR. Like the Balmar MC-612, which

• "ramps up slowly" after about 40 seconds when you first start the engine;
• can be set to limit the alternator output to any desired percentage;
• has a simple ON-OFF switch option which cuts alternator output in half in case you need additional engine power;
• can take temp sensors for both the batteries and the alternator; and
• can be programmed for any type of battery chemistry.

The alternator isn't going to put out 100 amps for long. As it heats up, output will be reduced, and as the batteries take a charge actual output will be more like 70-80 amps in the bulk charging stage.

Bill

[Marksman]

I have a Beta 28 with a 100amp balmar. Beta's solution was to use a groved belt to replace the v belt. You only have to hand tighted it and the extra contact area has plenty of grip. Works great.

[rebel heart]

How much time / experience do you have with the beta? I see them advertised around but am waiting for a 10+ year consensus opinion.

[Highlander40]

External regulator is a good thing. With a large bank, temp sensors on both alternator and battery bank are essential.

Think twice about retrofitting poly-V flat belts to an older engine. My Yanmars did not like it at all. the shaft allignment isn't there. The crank, water pump and alternator must be perfectly parallel and all pulleys must be in the same plane.
The refit was done by a major yard as a test prior to doing other customers boats.
The belts shredded, walked off the pulleys and messed with my life.
The only good thing was that they did not charge.

When the engine is designed for flat belts, they are great.

[DotDun]

I have a 90amp Mastervolt on a 3GM30 with a single belt and a Balmar 612 regulator. I have the field wire on the stock Yanmar 55amp alternator disconnected, it's my 'backup'. My house bank is 450AH of Trojan T-105s, I'm a little hot according to the recommended charge rate (10-13%). I'm going to look at turning the Balmar down a little.

Works fine. I only run one belt on the double pulley, the OP had it this way and when I bought a matched set of belts, there was so much belt dust all over the engine room I took one belt off. I haven't investigated it any further but I assume the setup was run with one belt long enough there is a size difference between the two pulleys. I know it would have wore in had I let it go longer, but I couldn't stand the belt dust.

[Vasco]

Have had a 100 amp alternator (Powerline and Balmar) with a 3GM30F for twenty years with a 3 stage regulator on a CS36M. No problems at all, a bit of belt wear and dust but I use good Dayco top cog belts. Never had a belt go.

[foggysail]

Well, I am frustrated! Just spent over 15 minutes explaining why operating an alternator at 100 amperes is not something that I could recommend only to have the reply TIME OUT and not get posted. My fingers are too tired to recreate that lost post.

Foggy

[Bright Eyes]

Thanks for all the advice so far. Let me include some more details.

Our house battery bank is 340amps. We also have a starter/spare battery on its own bank of 65 amps.

The reason we want a larger alternator is to charge the batteries while we are cruising. Our only other power supply is two 80 watt solar panels. And we ofcourse have minimized our energy usage.

[John A]

If you really want to see the fan belt smoke, and the altenator go to 1oo%, then use the microwave at full power while the engine is running!

[John A]

Originally Posted by foggysail

Well, I am frustrated! Just spent over 15 minutes explaining why operating an alternator at 100 amperes is not something that I could recommend only to have the reply TIME OUT and not get posted. My fingers are too tired to recreate that lost post.

Foggy

Bummer!

next time compose large posting in your word-processing account, and cut and paste it here.

[Dockhead]

Originally Posted by Bash

You also want to look at what you're asking your engine to do. You've got 24 HP pushing a 37-foot boat. That's not a lot of power to spare. Ask yourself how your boat would respond once you've only got about 20 available HP.

I'm not sure I'd want to be your engine at that point.

Remember, though, that the alternator will be drawing that kind of power only when it's giving max output. That will not necessarily be so much of the time.

[arisatx]

Originally Posted by delmarrey

If you need more power this would be the best solution! IMHO. You'll also have a backup system.

I've seen this setup in the Mack Boring catalog:

[Marksman]

Hey Rebel Heart,

I've only had the Beta for a year and only put about 16 hrs on it as there is plenty of great sailing just around the breakwater 30 yds. from my slip. So far, so good. Asways starts right up and runs well and strong. One of the selling points was how all the service items (filters, impellers, alternator, heat exchanger etc.) are positioned at the front of the engine in easy reach, and Beta published a cross reference for other brands of filters and such. Also very easy to install, geared for the DIY sailor with no waranty issues for DIY.

Oh yea, I don't work for Beta.

Cheers!

[Volition]

I have a 100 amp; the voltage regulator controls the voltage /charge going into the batteries. Should be no problem....have had mine 3 years with no issues. Currently using the same batteries and it had no problems keeping them charged. Do it.

[Marksman]

Oh, one more thing, take notice of the built in oil change pump, also at the front of the engine.

Viva!