Triskel power generation system on Distant Shores III

[Kenomac]

Originally Posted by Colin A

He does say a 10KWH battery bank which isn't small by most measures.

Watch the video, he doesn’t have a “MASSIVE battery bank” by any stretch of the imagination 780ah at 12v. But I guess that depends on where you’re coming from.

My point is, the system only provides one source to charge the “MASSIVE bank,” what if his engine is down? Then he has no backup plan.

The whole enchilada sounds good on paper to those who mostly sit at home dreaming and planning, but from our experience the lack of redundancy in the system will cost him dearly someday when it bites him in the behind.

[a64pilot]

Ken, assumption is that this Boat is a proof of concept, a mule in automotive terms, a prototype in aircraft.
The logical production system would have a massive battery bank, and a redundant electrical supply, meaning the other engine on a Cat.
The concept doesn’t make sense really at our levels of electrical consumption cause you can get there with current alternators, this has to be for the crowd that wants dock power at anchor or underway.
So far as using an engine at its efficiency peak to save fuel, forget it, there is an efficiency peak of course, just it’s not significant, it’s maybe 10% at best.
A turbo improves fuel efficiency probably more, as does common rail, but if you look at actual fuel consumption numbers, neither is really significant.

I’m in Jacksonville and just for curiosities sake went and visited the folks at Next Gen generators at the factory. One of the things I spoke with them about was a bigger inverter generator and why not? Well they had done it about ten years ago according to them and the fuel savings were insignificant, noise levels had to be lower, but a properly installed generator isn’t noisy anyway.

I had some very accurate instrumentation on my little airplane, an Electronics International MVP-50 that had been calibrated and monitored each individual cylinder head and exhaust temperature and had Gami balanced fuel injectors and had moved them around so that all 6 cylinders peaked within .1 GPH fuel flow.
On an airplane you can achieve the identical power output at different RPM’s by varying throttle and RPM, meaning that at full throttle and lower RPM you can get to 65% power for cruise, or you can turn the RPM up and lower the throttle and achieve the same 65% power. You know power is the same, when you achieve identical airspeed in level unaccelerated flight.
In theory the lower RPM will result in lower fuel consumption due to less engine and prop friction turning lower RPM..
I tested it and got no appreciable difference.
Then on an airplane you control fuel mixture as well. In theory if you have fuel injection and if your injectors are well balanced you can operate well lean of peak EGT and save considerable fuel that way, although you lose quite a bit of power.
There is quite a bit of mythology to support the lean of peak theory, Charles Lindbergh went to the South Pacific to teach our Aviators lean of peak operation etc.
Well, it’s a myth, there is nothing to it. I tested that too. You lose a lot of power lean of peak, and that lower power setting does save fuel, but duplicate that power setting at Lycoming’s recommended 50 degrees rich of peak, and fuel consumption is the same.

What it boils down to is that an engine, any engine will burn X amount of fuel to produce X amount of power, unfortunately there are no “tricks” to achieve significant reduction in fuel consumption.
We save fuel by slowing down, by reducing hull friction, not by operating an engine at its efficiency peak.

[Q Xopa]

Originally Posted by Colin A

In the detail video Nigel seems to imply that they can load at a low RPM to force the engine into an efficient curve. So running at anchor they can idle at 800 rpm but load up over 3KW on the alternator. He then says it would be as efficient as a AC fixed speed genset. It would be interesting to see the data on this to see how they match up at given electrical loads.

His graph aided explanation was saying that. I dont think 800 RPM was mentioned though was it?

It kinda does make some sense to increase the load and therefore efficiency at say 800 rpm.

I agree that would be an improvement over not doing it, ie running underloaded at 800 rpm.

However 800 rpm isnt a very fuel efficient rpm. Most engines run most efficiently at 1600 - 2000 rpm range. I know my 4JH4-TE runs most effiently at 1800-2000 loaded at around 55 HP.

The ideal at anchor or cruise should be somewhere around there. But of course not so practical trying to load our engine up at anchor that much with a alternator set up.

[a64pilot]

This is a BSFC chart for a typical 3600 RPM Yanmar engine. The belly of the curve is from 2400 to 2800 RPM with the lowest being 2500 to 2600.

If your trying to maximize fuel efficiency, you need to be at those RPM’s, and of course have the engine optimally loaded.
The chart indicates fuel consumption differences in grams per hp. So if your so inclined you can calculate the difference

[Dockhead]

Originally Posted by Kenomac

Watch the video, he doesn’t have a “MASSIVE battery bank” by any stretch of the imagination 780ah at 12v. But I guess that depends on where you’re coming from.

My point is, the system only provides one source to charge the “MASSIVE bank,” what if his engine is down? Then he has no backup plan.

The whole enchilada sounds good on paper to those who mostly sit at home dreaming and planning, but from our experience the lack of redundancy in the system will cost him dearly someday when it bites him in the behind.

Redundancy is a very good thing with critical systems like these, but it's not the only way to achieve reliability, which is the final goal.


Diesel engines are reliable enough that even those cruising in remote areas might not feel that a backup is required. Certainly on a catamaran, which already has two diesel engines, adding a third is just silly in my opinion. No way would I have a separate generator on a cat, myself.


Redundancy in the electrical side is a good thing for sure, but you don't have to have a separate diesel engine to have this. You can run two alternators. Furthermore, you can carry a complete spare alternator without much trouble, and on top of THAT, alternators are extremely simple and you can repair them yourself with minimal tools and parts.


I have a heavy duty continuous duty rated generator plus a second, school bus alternator on my main engine. I keep a complete spare alternator in spares. If I had really good storage, like a large lithium bank, I would not miss the generator, personally. I don't think there's anything wrong with this concept. Only, as others have pointed out, there doesn't seem to be that much new, which this thing does, compared to using a normal big alternator plus good regulator.

[Dockhead]

Originally Posted by a64pilot

This is a BSFC chart for a typical 3600 RPM Yanmar engine. The belly of the curve is from 2400 to 2800 RPM with the lowest being 2500 to 2600.Attachment 178196

If your trying to maximize fuel efficiency, you need to be at those RPM’s, and of course have the engine optimally loaded.
The chart indicates fuel consumption differences in grams per hp. So if your so inclined you can calculate the difference

Come on -- the difference between best and worst on that curve is only 6%. The RPM you operate at is almost meaningless and certainly not even measurable in terms of cost per kW/h produced.


What is important is total engine hours used -- an hour of depreciation and maintenance will usually costs much more, maybe several times more, than an hour's worth of fuel. This is where doing propulsion and power generation at the same time really pays off. But also, as has been mentioned already, you've already paid the fuel overhead for having the engine running already, so the marginal cost of a bit more power to run an alternator is much cheaper per horsepower/hour than the average cost.

[Dockhead]

Another approach to systems architecture for power:


Maybe the main engine can have a normal school bus type alternator (2 or 3 kW) which runs all the time. Then, a massive one (10kW or something like that), which can be clutched in using a PTO, which is used only when the main engine is not being used for propulsion.


That's a lot of redundancy, and such a large alternator would certainly be enough load for any cruising boat sized main engine.



Then for someone really fanatical about redundancy (maybe those who cruise in really remote places), you could add a small emergency generator, maybe a small NexGen or something like that. But you would need the emergency generator only in some kind of real disaster where you've lost the main engine. For such a rare case, even a portable generator of some kind might be enough.

[Q Xopa]

Originally Posted by Dockhead

Come on -- the difference between best and worst on that curve is only 6%. The RPM you operate at is almost meaningless and certainly not even measurable in terms of cost per kW/h produced.


What is important is total engine hours used -- an hour of depreciation and maintenance will usually costs much more, maybe several times more, than an hour's worth of fuel. This is where doing propulsion and power generation at the same time really pays off. But also, as has been mentioned already, you've already paid the fuel overhead for having the engine running already, so the marginal cost of a bit more power to run an alternator is much cheaper per horsepower/hour than the average cost.

Yes the efficiecy might not be much difference. Probably not worth the hassle to chase.

I have heard the SFC difference from idle to best SFC RPM is often in the order typically half.

However as you say total engine running time is important to many.

This might also be a compelling reason to run at a faster engine RPM. Alternators work better too outputting more and better cooling airflow from their fans going faster.

Of course this assumes our batteries have a high enough Charge Acceptance rate.

[john61ct]

Originally Posted by Q Xopa

This might also be a compelling reason to run at a faster engine RPM. Alternators work better too outputting more and better cooling airflow from their fans going faster.

That's just a question of pulley ratio, the engine rpm just needs to reach a good point for the **torque** a large alt requires producing multiple kW.

Hence the soft start ramp up built into good VRs like Balmar's MC-614

[Dockhead]

Originally Posted by Q Xopa

Yes the efficiecy might not be much difference. Probably not worth the hassle to chase.

I have heard the SFC difference from idle to best SFC RPM is often in the order typically half.

However as you say total engine running time is important to many.

This might also be a compelling reason to run at a faster engine RPM. Alternators work better too outputting more and better cooling airflow from their fans going faster.

Of course this assumes our batteries have a high enough Charge Acceptance rate.

If you look at the curve A64 posted, you'll see that the difference from idle to optimum (which is near torque peak) on his engine is only 6%. My engine is similar, so I think that's typical.


You do make a good point about alternators and cooling, but diesel engines have a narrow enough rev range anyway, so they can generally be geared to be producing good power and flowing decent air from 1000 RPM already. Good alternators (large frame, hot rated) have plenty of cooling and should be cool enough at any RPM. Actually our use case is usually much easier than what schoool bus alternators are designed for -- they are designed to live under a bus hood where on a hot summer day the temps can be over 100C. On my boat, the ER temp never exceeds 30C with the blower on. That's an easy life for a school bus alternator.


See: http://www.prestolite.com/literature...ion_FL1212.pdf

[john61ct]

Originally Posted by Dockhead

Maybe the main engine can have a normal school bus type alternator (2 or 3 kW) which runs all the time. Then, a massive one (10kW or something like that), which can be clutched in using a PTO, which is used only when the main engine is not being used for propulsion.

Pretty sure both can be massive and physically online without a clutch.

Assuming we have the amps-output control in place to at least manually adjust that "live" if we're doing without the InTEGral automation in that regard,

the torque / resistance drag doesn't kick in until the VR / field current ramps up for the alt to start producing power.

That also means both alts can be matching for redundancy and "huge".

Yes the belt drive at a certain point likely needs to be more robust than the usual multi-vee serpentine.

Note if we really are talking 10+kW alts the Hummer surplus ones I've looked at are well over 300lbs each, so two mounted is more practical than carrying a spare.

[Dockhead]

Originally Posted by john61ct

Pretty sure both can be massive and physically online without a clutch.

Assuming we have the amps-output control in place to at least manually adjust that "live" if we're doing without the InTEGral automation in that regard,

the torque / resistance drag doesn't kick in until the VR / field current ramps up for the alt to start producing power.

That also means both alts can be matching for redundancy and "huge".

Yes the belt drive at a certain point likely needs to be more robust than the usual multi-vee serpentine.

Note if we really are talking 10+kW alts the Hummer surplus ones I've looked at are well over 300lbs each, so two mounted is more practical than carrying a spare.

Yes, maybe the clutch is not needed, but to transmit that much mechanical power you're going to need some kind of PTO in any case.


I would not want a spare 300 pound anything, so I think for me backup would be the schoolbus alternator or alternators, mounted in the normal places. That's 2kW to 3kW and quite enough to "limp home".

[Kenomac]

Originally Posted by Dockhead

Yes, maybe the clutch is not needed, but to transmit that much mechanical power you're going to need some kind of PTO in any case.


I would not want a spare 300 pound anything, so I think for me backup would be the schoolbus alternator or alternators, mounted in the normal places. That's 2kW to 3kW and quite enough to "limp home".

How do you “limp home” if your diesel engine poops out with something like a broken lift pump or air in the lines, where you’re unable to locate the source? Let’s also assume no wind and an imminent storm approaching, because that’s usually how things go. And you’re in the middle of nowhere wondering why you opted for only one source to charge your battery bank.

[john61ct]

Originally Posted by Dockhead

Yes, maybe the clutch is not needed, but to transmit that much mechanical power you're going to need some kind of PTO in any case.

I'm not up on the details once higher power than vehicle serpentine style, but in another thread a helicopter guy mentioned very robust belts driving their blades, also see rubber timing belts in engines.

[Kenomac]

Originally Posted by john61ct

I'm not up on the details once higher power than vehicle serpentine style, but in another thread a helicopter guy mentioned very robust belts driving their blades, also see rubber timing belts in engines.

John,

Just curious... do you own a boat? I don’t mean anything by it, I’m simply curious and thought I’d ask. Please don’t take offense.

Ken