Is there such thing as goin tooooo big on my alternator upgrade?

[philm]

Interesting work by Nigel Calder on using propulsion engine to generate serious power : https://www.victronenergy.com/blog/2018/10/03/nigel-calder-and-the-integrel-9kw-alternator-on-steroids/

[Talbot]

Lots of data on this thread, but one thing I did not see being addressed.

Yes you can up your alternator by a lot. But there is always a downside. The larger the alternator, the more power needed to run it.

Now belt slip has been mentioned, but thee are alternatives that assist in alieviating that problem, but this does point to the problem. The bigger the alternator the more power being required to create electricity and the less available to provide propulsion.

One solution I saw a few years ago was to keep the existing alternator for propulsion times, and have a much bigger one (in that case a 240v ac unit) driving through a clutch which could disengage the drive to this unit.

[Sidney777]

Maybe I missed it, but how many hp does high output alternator Take from your Engine ?

[Talbot]

Originally Posted by Sidney777

Maybe I missed it, but how many hp does high output alternator Take from your Engine ?

Taking the figures from the 3YM30.

Assuming you are running the engine at 2500revs for propulsion, this is approx. 7.5kw (10 HP). If your 350 amp/hr alternator is humming at full load, it is extracting 4.2 kw (5.6 HP). To maintain the same speed you would need power relating normally to 2950 revs at the engine.

Of course these numbers may not be exact per engine/boat/prop setting, but are sufficient to illustrate the point.

I used to have 3GM30s, and consider the 3YM30 to provide more power at lesser fuel consumption.

[rom]

Originally Posted by Talbot

Lots of data on this thread, but one thing I did not see being addressed.

Yes you can up your alternator by a lot. But there is always a downside. The larger the alternator, the more power needed to run it.

Now belt slip has been mentioned, but thee are alternatives that assist in alieviating that problem, but this does point to the problem. The bigger the alternator the more power being required to create electricity and the less available to provide propulsion.

One solution I saw a few years ago was to keep the existing alternator for propulsion times, and have a much bigger one (in that case a 240v ac unit) driving through a clutch which could disengage the drive to this unit.

Technically it would be much easier to have one single big alternator and to control its output (from 0% to 100%) with a "dimmer" on the field. Even simpler a big alternator that you can field switch on/off like I do, that should be fine for many cruisers.

[rom]

Originally Posted by Talbot

Assuming you are running the engine at 2500revs for propulsion, this is approx. 7.5kw (10 HP). If your 350 amp/hr alternator is humming at full load, it is extracting 4.2 kw (5.6 HP)

350A. and obviously 350A@12V. I am not familiar with such alternators but I guess you can expect 70% efficiency. So it's more like 8hp that's it is extracting at full power.

[wingssail]

It is easy to become "gadget enamored". Meaning that if we can just find the perfect "best alternator, regulator, belt system, rectifier, batteries, etc etc" and all the other "best" systems and components, then everything about cruising will be better.

But I am a proponent of simplicity, and the 80-20 rule. If I can get 80% of the results from 20% of the complexity, not to mention price, then I happily sacrifice that last 20% of perfection.

I prefer to focus my cruising preparations on my sailing and navigation skills, and in keeping my boat simple, SIMPLE, S I M P L E!

So for electrical, charging, et all, I have a good 80/20 solution. I have inexpensive wet cell batteries, 550ah capacity, and a single, small frame 110amp alternator and a good external regulator. Two railing mounted solar panels add to the total system.

Yes, we run the main engine to recharge the batteries, depending on the electrical loads. For example, in cold water we use less power (refer) and the solar pretty much keeps up with it. In tropical areas we run the engine about 1-1.25 hours per day to charge and make water.

Sure there are more efficient systems, but how much better and what does that efficiency do for you, and at how much complexity, cost, and weight?

LiFePo4 batteries? Why do I need them? They cost more (a lot more). They require BMS. They cannot easily be serviced or replaced in many third world countries. More efficient? Yes, but my wet cells do the job at less cost.

Second alternator or large frame alternator? For what propose? to reduce my charge time from 1-1.25 hours to 45 mins? Why is that so important, we're making water anyhow, and if we happen to be motoring somewhere, it's all included. Do I want a new pully or serpentine belt? Try fixing or replacing that in Papua New Guinea.

Honda 2000? Nice unit, but where to I carry it? On the aft deck? (we carry nothing on the deck.) And it is extra weight. Plus noise in the anchorage.

A gen set? weight, cost, and it's just another engine to maintain.

We've operated this way for 34 years, it has worked perfectly to charge the batteries on the main engine. Our system is simple and relatively efficient. Our batteries last 6-8 years, the alternators about half that, and the engine is doing fine at 6500hours and 55,000 miles.

My advice is get your head out of the search for numbers perfection, keep it simple, and go sailing instead. So often people who spend all their time trying to find the "best, perfect, pieces of equipment to install" instead of sailing every chance they get, will be quitting cruising within two years, or motoring everywhere and their perfectly equipped boats will be up for sale.

[a64pilot]

I carry our Honda in the cockpit, immediately ahead of the binnacle. Sits on the floor out of the way. If weather is expected to be real bad, I’d ratchet strap it to the binnacle, luckily we have never been in weather that bad.

Alternators are I believe actually very inefficient, that’s where all the heat comes from, so I don’t think you can use the 750W per HP formula, a quick Google says they are on average about 55% to 60% efficient. I’m sure some may be better than others.
However there is usually a lot of room between the power curves of what an engine is capable of at a set RPM and what the prop absorbs, up until quite high RPM, so overloading an engine with an alternator doesn’t happen often, so long as your not tying to put a big alternator on a tiny motor that is.

Serpentine belt kit just isn’t going to break, it’s just solid pulleys, and if your afraid of that, carry your old pulleys.
I only had a stock 80 amp alternator and belts were always an issue, to keep it from slipping required it to be way tighter than I was comfortable with water pump bearing wise and maybe even crankshaft bearing.

I agree with simple, but not much simpler than a Honda, absolutely no install at all. If it breaks, toss it, or give it away, you should still have Solar and an alternator.

[tdgaffney]

Wingssail: Well said. Keep it simple. And as we used to say, "Time to shoot the designers and get on with production."

[wingssail]

Originally Posted by a64pilot

I carry our Honda in the cockpit, immediately ahead of the binnacle. Sits on the floor out of the way. If weather is expected to be real bad, I’d ratchet strap it to the binnacle, luckily we have never been in weather that bad...

Sometimes weather is boisterous. Unexpectedly so. The decks and cockpit get mighty wet, awash even. On-deck is no place to store equipment, Best be prepared for rough weather and keep the expensive stuff in a locker below, or don't bring it. Same for jerry cans, paddle boards, kayaks, and anything hanging from an arch on the stern.

The capability to sail in conditions like this define a blue water cruiser.

[wingssail]

Originally Posted by a64pilot

I carry our Honda in the cockpit, immediately ahead of the binnacle...

Just asking, where do you and your guests put your feet while sitting in the cockpit?

[a64pilot]

Originally Posted by wingssail

Just asking, where do you and your guests put your feet while sitting in the cockpit?

The cockpit benches are over 6’ long, long enough to lay down and take a nap. The Honda takes up I’d guess a little over a foot of that.
Never really have guests, but there is plenty of room.
Some cockpits are drier than others, to take water in ours I feel sure the boat would be in a survival situation. Of course there are downsides of such a high dry cockpit and freeboard, it’s windage I’m sure.

[Ya Ubetcha]

On some engines, too much sideload on the crank shaft will bend it one cycle per rotation along the axis of the shaft. Don't know the correct terminology for the bending. Can cause the crank to break over time.

[Capt. Mike Maurice]

The side load may cause the crankshaft seals to leak prematurely.

[Q Xopa]

Originally Posted by Capt. Mike Maurice

The side load may cause the crankshaft seals to leak prematurely.

Do you have anything to back that up?

I would say that the Crankshaft Main bearings which are designed to allow for a diesel 'explosion' every two revolutions per cylinder and the weight of pistons and con rods changing direction twice every revolution aren't going to be too fussed over a comparatively minor tension in mostly the opposite direction.

The bearings have something like 0.0015 clearance, but with oil pressure don't even move that much.

I could be wrong but I can't see it myself.