Atomic 4 -- generator conversion

[LordGothington]

Ahoy!

Like most sailboats, the engine in my Tartan 27 is designed to provide a lot of propulsion and a little bit of electricity.

But a vast majority of the time, I only use the engine to motor in and out of the harbor. But I do want to have a lot of electricity for things like radar, an induction stove, refrigeration, computers, maybe even HVAC or a dive compressor, etc.

There ain't room for an engine *and* a generator on this boat. So, it is tempting to go diesel electric. Install an electric motor for propulsion, and a diesel generator (plus some solar/wind) for generating electricity. For long distance motoring that is clearly less efficient. However I do not usually motor long distances, but I always want a lot of electricity. And, unlike pure solar electric boats, I still have the option to motor long distances by running the generator.

But that is a pretty major overhaul to commit to in terms of time and money -- especially since it is unproven. That has got me wondering if I can do a quick and dirty trial run.

Here is my thought.

Disconnect the drive shaft from the A4 and install a 5-10KW motor to drive the propeller. I believe I have enough room to do this with out moving anything -- I just need a shorter propeller shaft. I would, of course, need to add mounts for the electric motor.

Install a big 100-200A 48V alternator using the hanley method,

http://www.moyermarineforum.com/foru...2&postcount=12

Make sure the transmission is 'locked' in neutral. (I am assuming the flywheel spins whether or not the transmission is in gear). Disconnect the existing transmission gear shifter and convert it to control the electric motor.

Install a 48V LiFePO4 battery bank and charge controller. One advantage of LiFePO4 batteries is that you can go from fully discharged to fully charged in an hour. (Lead Acid batteries prefer a much longer charge time). So, the engine only needs a short run time to top off the batteries.

The advantage of this hack job is that it is trivial to undo. If it turns out I it is a terrible idea, I can reverse the changes and sell off the alternator and electric motor. I'd probably keep the 48V battery bank, since I'll still be power hungry. And I'd probably just install a smaller 48V alternator.

If it mostly works great but the A4 isn't really up to the job, I can fully commit by replacing the A4 with a proper diesel generator. This also allows me to break up the costs of two time periods. A high output alternator is a lot cheaper than a whole generator. And quicker to install despite the custom mods required to the A4.

Another Tartan 27 owner did do an electric motor conversion and used a 5KW electric motor. They claimed it was strong enough, but that seems underpowered to me. Later models of the Tartan 27 used a 12HP diesel instead of the 30HP atomic 4. So I think 10KW is probably the upper limit of what is required.

In a perfect world, a 200A 48V alternator would require (200A * 48V) / (750 W/HP) = 12.8 HP to drive it. So that A4 should be plenty. But I am wondering what a real world limit would be. Keeping in mind that the A4 is not *also* (directly) driving the propeller anymore.

What else am I overlooking? It is a bad idea to run the A4 for hours on end with out engaging the transmission?

Does this seem like a viable experiment? Or am I overlooking a huge glaring flaw? Has someone already tried this?

(The battery system will be hella expensive, but let's assume I am going to end up buying that either way).

Also, I just want to reiterate that I am fully aware that when motoring this will absolutely be less efficient than a direct drive system. I am willing to make that sacrifice because I want to have a generator on board but don't want to install a second internal combustion engine. And, a majority of the time, motoring will just use the batteries and be topped off using solar or shore power. I am also aware that this will be less efficient than a true generator -- but this is just a stepping stone to that.

Another shortcoming is that a true generator will have a feedback loop that adjusts the throttle to match the current load. In this hack job, I'd have to control the throttle manually. While annoying, I don't think it is a deal breaker. The batteries will make up for any temporary shortcoming. After all, in theory, everything can be powered off the battery bank alone. Though, running the HVAC while motoring is probably a bit excessive.

[ndutton]

Interesting idea and I haven't digested it all to respond intelligently but my first thought is this sounds like a Tartan 27 with the heart of a Hinkley 48.

[Al Schober]

Interesting idea - convert to electric drive.
I don't think hanley's drive is going to hack it. That Balmar is 1.5 Kw, while you're talking about an alternator that almost 10 Kw! More belts, more belt tension, etc. I can see you breaking off the front end of the crankshaft.
I think you need a direct drive to the alternator - more like the vehicle mounted welding generators.
Besides, electric drive is not trouble free. Cleaning carbon dust out of the motor and dodging fireballs from the electrical controls will be in your future.

[Dave Neptune]

Perhaps a cog belt to drive it, no slip and far less tension. Set the A-4's max output RPM at around 22~2400 RPM for the alt' output rating. I think that at that RPM transferring 13+Hp via the front should not be a big deal. And at lower RPM's the alt won't load the drive. I've seen huge "blower loads" on the end of many cranks with "cog drives". Belts and drive pulleys are also readily available.

Also check to see that the RPM's you drive at are within the thermal ratings IE so the alt won't overheat.

Dave Neptune

[romantic comedy]

You say that there is no room for a gen and an engine, but yet there would be room for a dive compressor and HVAC, and a large battery bank , (and additional tankage)?

I have a 100 amp alternator driven off the crank (like Hanley) and I worry about the load on the main bearing.

What size battery bank and how would you charge it? It would need to be quite large if you were heating, cooking, running radar, running computers, and running air conditioning all off electric.

My question is why...

[ndutton]

OK Lord, it's clear you have given this a lot of thought although I'm a little confused on whether or not you plan to run a 48V 200A generator/alternator off of the A-4 or install a diesel genset instead. I read intentions for both. My thoughts anyway are:

1. The electric drive alone does not save much, if any, space. If space saving is the goal I think you'll be disappointed.
2. Space again, Romantic Comedy's comments about dive compressor, air conditioning, etc. are noted.
3. If intending to use the A4 to power a generator/alternator, the Hanley drive requires an early model head and cooling system.
4. Converting to electric drive will cost somewhere around $6K. If fitting a diesel genset, figure another $10K by the time you're done. Big money in my opinion for an electric range and air conditioning.
5. If driving a gen/alt with the A4 or a diesel, a 200A 48V genny is about the same size as an A4, maybe slightly smaller so I'm not seeing the space savings.
6. I think driving a big gen/alt off of the output end of an engine, any engine, is preferred to a belt drive off of the flywheel if for no other reason than avoiding side loads on the crank.

[joe_db]

Basically you are trying to create a miniature version of a diesel electric tug, cruise ship, submarine, or locomotive.
You certainly can do this and thousands, if not tens of thousands, vessels with electric motors exist and work well all over the world. The modern way to design a cruise ship is with 2 or 4 electric motors driving the props and 4 or more generators to run them and supply the ship. Losing an engine hardly impacts the ship, just a little less top speed. You still have both/4 props turning and in low speed low load conditions no need to run all the gensets.
That said, there are reasons this is not common on small boats:
1. Engine to prop is more efficient than engine to generator to motor to prop, every transition loses power.
2. You don't have engineering staff onboard and this is a lot more complicated than a driveshaft.
3. It takes up more space.
4. Specific to A4s, the Atomic 4 is about the worst engine I can imagine for this job. The A4 was NEVER intended to do anything but move boats. Gensets on boats use engines with standard bell housings that make adding a generator quite easy. Diesel engines are better suited to be generators for the most part, although there certainly are gasoline marine generators. In either case these will be WAY more reliable and efficient than kluging a generator onto an Atomic 4.