Why a generator?

[Cheechako]

Originally Posted by a64pilot

No you would not need a set speed as long as it was fast enough to supply power demanded, RPM could vary with load just like a little Honda does.

The Honda uses an invertor right? That's what I've heard. If the speed varies with a plain old AC generator you get different voltage with speed.

[a64pilot]

Make another post cause the app doesn't give me room when I quote, anyway the Prius PSD is a planetary gear system that allows wildly variable speeds between the motor- generator and engine compared to wheel speed, I see all the time 900 RPM on my gasoline motor at highway speeds going down hill say and 4000 RPM going up hill, RPM varies with demand it's a constantly variable system.
You could do this with a marine engine drive system, instead of motor-gen, wheels and the internal combustion engine, you would have the prop, the generator and the engine, increase load on the generator and the RPM to the prop is reduced to keep motor load within limits, reduce or turn off the generator and 100% of motor output goes to prop.
Anchored then the engine would only turn the RPM required to make the power requested, like the Honda suitcase generator.
It's doable, has been done, question is would there be enough demand to pay for the design?

[a64pilot]

Originally Posted by Cheechako

The Honda uses an invertor right? That's what I've heard. If the speed varies with a plain old AC generator you get different voltage with speed.

Yes, the Honda makes DC, sort of and runs it through an inverter to get stable 120 VAC at 60 hz, just like your inverter makes AC power from your battery bank

[a64pilot]

I say sort of, cause I suspect the Honda may actually be an alternator that put its output through a diode bank that is I believe actually pulsating DC at that point not real pure DC. But that is what a regular alternator does.
Pretty sure that an alternator is lighter and more efficient than a pure DC generator, or we would still have DC generators on our engines

[John Holbrook]

Because converting rotary motion to electricity and electricity back to rotary motion is inefficient, expensive and complex.

My personal view is the engine should directly drive the prop but having it provide electricity to would save having a generator. The engine needs to be loaded properly if not propelling the boat so a 10kw output of electricity would be solid and a large Lithium Iron battery bank could accept that charge. From that all electrical needs bar Aircon could be handled. Perhaps even Aircon if just run at night in one sleeping cabin.

Originally Posted by Crazy Talk

I was thinking why not scale the engine back and add an electric propulsion sytem instead. Someone on this board has one and i saw a pictuee pisyed sonewhere. The engine would be a generator for all the on board power hogs, batteries for daily consumption and batteries for propulsion. It achieves my original thought of one fuel for propulsion and power generation as needed.

[brianlara 3]

John, think of Wynns as STP (scientifically treaped petroleum) . Both products, STP in the US and Wynns in other countries, produced a 'viscosity index improver' (an oil thickener) which had the thickness of honey. STP's track record with the US courts and other authorities was shameful. In Australia, whilst those products were not withdrawn from sale many executives Porsches were traded for low end Ford products.
Now, diesel abuse.
And my motives are purely protectionist and educational.
Surely you'll agree that a diesel engine, irrespective of aspiration, if used in light duty, will tend to create soot. And if you have overhauled a lot of injectors you'll know that dribbly injectors are usually not seating efficiently (carbon lodging) as distinct from injector needles and seats bieng pitted ( usually water ingestion).
And a dribbling injector is over metering, yes.
I will always contend that, as you've agreed, lightly loaded diesels will eventually glaze because of fuel over supply and reduced BMEP's (low chanber temp). And I agree, well run-in / well aged engines are less prone to glazing because the cross hatch has all but disappeared and as a result the varnish particles have no ledge available.
Enough huh? My ptsd prefers a stress free life. Nearly a year ago I intentionally abused a Moderator with the hope of bieng banned from CF for life. At 70 years of age I need as few disagreements as possible.
Cheers John

[Steven UK]

i didn't read every post so forgive me if i'm repeating, contradicting or confirming what someone else has said. a small diesel engine are generally a tractor engine marineised. the PTO that people refer to is generally an output from the timing cover (Power Take Off) and is generally used for auxiliary oil supply or air brakes. taking power from here is a bad idea unless its for hydraulic purposes. however alternators on the crank pulley will work, large alternators on each side in the 100+A range would charge batteries fast if they can take it. also the front pulley generally has four bolts that will fit a flanged universal joint, you could pretty much power anything you want from there as long as the engine will turn it. of course it will likely end up in the galley.

i asked this question myself earlier in my couch sailing career and got some good feedback. and this was basically it...

i wanted to know why larger alternators couldn't be run from the engine and turned off when the engine was needed for propulsion. the answer was that is was done regularly. personally i like the 'school bus' alternator route (maybe 2x) and have the ability to turn one or both off. this way the engine can be run for a shorter time and get up to temp quicker.

when the engine is idling cold with a 65 amp alternator most of the fuel is being used to just keep it turning (and wash by the rings) not drive the alternator.

some of the good battery technology can accept charge quickly LiFiPo4 for instance so having relatively inexpensive (made for GM in the millions) alternators putting a charge into the batteries and warming up the water tank quicker using less fuel and allowing me to have a hot shower sooner is all good for me. plus they can be repaired anywhere for cheap.

of course this is easy to say from the couch but it will be my first experiment.

this is a ford model...

https://www.dbelectrical.com/product...FQyUaQodkngLfA

hope this helps

[John Holbrook]

Brain all good mate, I think we are on the same page.

Steve yep. The yanmar 45hp has a 125a alternator as std and a second 125a alternator as an option. Aftermarket 12v alternators go up to something like 300a. There can be a huge gap between the crankshaft hp and hp absorbed by the prop. At max rpm the prop will absorb all the crankshaft hp but at say 2000rpm it may only be half. 2000rpm may move a sailboat along at a decent speed and on a 45hp engine and easily handle 10kw or so on power generation.

[Steven UK]

Also the same tractor engines are often found in mobile power generating installations so running a generator / alternator direct from the front pulley is doable. Not sure how you get 50-60Hz from that though. And then there is packaging the thing.

[Crazy Talk]

Originally Posted by John Holbrook

Because converting rotary motion to electricity and electricity back to rotary motion is inefficient, expensive and complex.

My personal view is the engine should directly drive the prop but having it provide electricity to would save having a generator. The engine needs to be loaded properly if not propelling the boat so a 10kw output of electricity would be solid and a large Lithium Iron battery bank could accept that charge. From that all electrical needs bar Aircon could be handled. Perhaps even Aircon if just run at night in one sleeping cabin.

Understood. But having electric propulsion with a diesel generator means a few gains as well. You have one engine instead of two. You can still charge batteries using solar so the generator won't run daily. And you've created redundancy for both electric and diesel. If the electrical system dies you can run the generator for all systems to get you home. And if the engine dies you have your solar and batteries to get to port.

These are just thoughts. I don't have the technical knowledge to explore the details. I know that all of the systems exist and are used extensively so getting them all together in one system is really the only complexity.

[Crazy Talk]

After doing a little looking, I think the limiting factor here is cost. Electric drive systems cost more than a diesel engine as do diesel generators. Add in a bunch more batteries and it's pricey.

Call me a dreamer.

[brianlara 3]

Yamaha.

[ericoh88]

Hi Crazy Talk

I am no expert so take what I am sharing with a pinch of salt.

1. A Yacthie Friend runs his Perkins 4-108 each day to charge his batteries for the last 25 years. He is a Mechanic so I did asked him about this glazing thing and he says the secret is STP . Lol.

2. SV Shango did a rtw on with large solar panels to runs water maker and all.

I went the Kohler 3 cylinder 5kva to keep the water maker and air cond system running.

Your pick. To me the fun is just going out there with the sails up because I am no good at boat building .

[SDChristian]

Originally Posted by Steven UK

Also the same tractor engines are often found in mobile power generating installations so running a generator / alternator direct from the front pulley is doable. Not sure how you get 50-60Hz from that though. And then there is packaging the thing.

How about a remotely placed hydrolically driven generator? Solves the packaging problem and also the inherent innefficiecy of the hydrolic system will help "load up" the desiel a bit more than just a generator alone.

http://vanair.com/hydraulic-driven-generator.html