spit balling, AC gen on front of main engine..

[a64pilot]

Originally Posted by CassidyNZ

So it is presumed that the “allowable hp take-off” at the front on the engine is limited because of the smaller size of the crank journal vs the flywheel end?



Then it is said that the “allowable hp” is a linear relationship to RPM.



So presumably the front crank journal grows in size as RPM goes up allowing it to handle more horsepower? Of course it doesn’t so why the hp change? I still don’t get it.

Oh, and by the way, the crank journals on a 4JH engine are all the same size if this clip from the original Yanmar manual is to be believed (only one dimension shown). So that flies in the face of conventional thinking that the front of the crank is less capable of absorbing load than the back one. Yet the manufacturer insists that this is the case.

Maybe the PTO capability at the front of the engine has more to do with the multi-track pulley that sticks out 250mm in front of the engine creating a moment of leverage on the crank journal than it does with journal size. Oh, but wait, Yanmar says that placing devices on either side of the crankshaft centreline does not alleviate the problem!

Too many conflicting arguments here.

It’s not arguments, it’s pages taken directly out of the Yanmar installation manual, just read them, ignore everything else.

The reason the HP changes as a function of RPM is because the actual engine limit is a torque limit, it doesn’t change of course. However HP is torque x RPM, so if the torque is held the same and RPM increases, the HP goes up.
That is why the amount of HP that can be extracted changes with RPM, but in actual fact it’s a torque limit and the limit doesn’t change.

[a64pilot]

Originally Posted by Dockhead

Type A is all side mounting using belts of whatever type.


Type D is using a front PTO flange and pillow bearings.


Leece Neville school bus alternator is more like 60% efficient so maybe just barely not overloading it. At any rate it's original installation by the Moody works, or rather, by the Yanmar supplier, so I would think it is reasonably engineered.


But I would not install a bigger one.


I think on a new build it might make sense to mount a big Echo Tech or Humvee or similar big alternator off a PTO shaft -- Type D. Maybe the output could be regulated to avoid overloading the engine (see the shape of the curve vs propeller curve).


By the way, I think you have an Autoprop like I do -- note that the propeller curve for these is different and much fatter than that of a fixed pitch prop, leaving at different RPM less headroom for PTO. Worth being careful with.


Perhaps EGT monitoring would be sufficient to avoid overloading the engine.

The way I have my 165 amp alt derated, I only see 90 amps from it. I have it derated IAW directions on Maine Sails Marine How To site, with a belt manager of 4 and I imposed a 90c temp limit, which is conservative, but figure I’ll get lots more life out of the alternator by not letting it get smoking hot.
I didn’t intend for my alternator to be a primary source of charging, but if the engine is running, why not take advantage of free power?
As my stock alternator was an 80 amp, I feel comfortable with 90.
Plus I believe Yanmar is being conservative, that their motors may take a little more than they say, there rarely is a limit at which you barely exceed this and it goes bang.
I also never motor above 2000 RPM and the motor just doesn’t “feel” strained there, I know that’s an ignorant statement, but as a life long motor head I do believe that I can tell a motor that’s being stressed, as silly as this sounds but you can usually even smell one.
I believe Yanmar set that limit to ensure a good long service life, with a little fudge that any good engine guy leaves as a safety margin.

In my opinion it’s become apparent that at least a few people are exceeding those limits by a significant amount, and that is likely going to reduce their engines service life, maybe significantly.
What bothers me is that there is an industry if you will that is selling products that will damage your engine, they should know this, and have decided to continue selling anyway, without warning people that they should determine what their particular engine can handle, that all engines are different etc.

On edit, I believe that’s irresponsible and they should at least warn buyers that they need to ensure that installing their product won’t exceed the engines limitations, because apparently at least for Yanmar, it can.

[a64pilot]

Originally Posted by Fendell

Hi All, As the OP I just wanted to say I'm still following the thread closely, and thanks for the constructive conversation.

There seems a lot of engineering to overcome to make this a possibility, which is why I'm guessing its not the norm. I wonder if its not seen more because its not an 'off the shelf' set up?

If there are any aviation buffs watching, is there a down scaled version of a Constant speed drive, similar to the type aircraft use for power generation?

Cheers again

The CSU or constant speed unit your referencing on an aircraft, is the propellor Governor, closest correlation to it on a diesel is the Governor used on a generator that maintains the generators constant speed as load changes.
So yes, there is such a thing on a Diesel.

Many believe that all diesels have such a Governor, but they don’t. The governor in a normal propulsion Diesel is of very limited authority, yes it can add or subtract fuel to try to maintain RPM, but it’s of very limited authority when compared to a generator’s Governor.

[Dockhead]

Originally Posted by a64pilot

The way I have my 165 amp alt derated, I only see 90 amps from it. I have it derated IAW directions on Maine Sails Marine How To site, with a belt manager of 4 and I imposed a 90c temp limit, which is conservative, but figure I’ll get lots more life out of the alternator by not letting it get smoking hot.
I didn’t intend for my alternator to be a primary source of charging, but if the engine is running, why not take advantage of free power?

I would not be as conservative as you are. You have a Mark Grasser alternator, right? Such a device should be capable of being run at something near its rated capacity, I would think. And why do you limit the temperature so low? I run my Leece Neville totally stock cheap large frame school bus alternator at full power with no derating for hours at a time. It is a fantastic source of power -- I can run the washer/dryer off it while motoring, do electric cooking, get a good charge in the batteries. 100 amps at 26v or so is up to 2.6kW, and 2kW plus even at low RPMs. I see case temperatures of 110C or so, but this is well within the rating, which allows the alternator to be used even in ambient temperatures of 110C.

Originally Posted by a64pilot

As my stock alternator was an 80 amp, I feel comfortable with 90.
Plus I believe Yanmar is being conservative, that their motors may take a little more than they say, there rarely is a limit at which you barely exceed this and it goes bang.
I also never motor above 2000 RPM and the motor just doesn’t “feel” strained there, I know that’s an ignorant statement, but as a life long motor head I do believe that I can tell a motor that’s being stressed, as silly as this sounds but you can usually even smell one.. .

I don't think there is anything ignorant about that whatsoever. I firmly believe that mechanical harmony can be heard, and that when a motor sounds good, it's in a regime which is good for it, when it sounds or feels strained, it is strained. All the more if it sounds good to a real motor head. I run my Yanmar in different regimes and even at redline on a regular basis -- following the Yanmar manual. It sounds most harmonious at around 2000 RPM +/- 200, in fact it sounds beautiful, and I think it is obviously less happy at 3000, so I feel quite sure that 2000 is better for it. If someone thinks that's "ignorant", well, I don't care.

Originally Posted by a64pilot

I believe Yanmar set that limit to ensure a good long service life, with a little fudge that any good engine guy leaves as a safety margin.

In my opinion it’s become apparent that at least a few people are exceeding those limits by a significant amount, and that is likely going to reduce their engines service life, maybe significantly.
What bothers me is that there is an industry if you will that is selling products that will damage your engine, they should know this, and have decided to continue selling anyway, without warning people that they should determine what their particular engine can handle, that all engines are different etc.

On edit, I believe that’s irresponsible and they should at least warn buyers that they need to ensure that installing their product won’t exceed the engines limitations, because apparently at least for Yanmar, it can.

I agree.

[Fendell]

Originally Posted by a64pilot

The CSU or constant speed unit your referencing on an aircraft, is the propellor Governor, closest correlation to it on a diesel is the Governor used on a generator that maintains the generators constant speed as load changes.
So yes, there is such a thing on a Diesel.

Many believe that all diesels have such a Governor, but they don’t. The governor in a normal propulsion Diesel is of very limited authority, yes it can add or subtract fuel to try to maintain RPM, but it’s of very limited authority when compared to a generator’s Governor.

Na I dont mean a governor on the engine, im referring to how an aircraft provides AC power. A quick google search tells me its a device that regulates the input speed to a constant output. to which my question was has anyone seen or heard of a down scaled version of this device? I fly regularly in a Fokker 100, which lead me to wonder how they generate power for air con/lights etc which is what lead me on this google rabbit hole...

[a64pilot]

Originally Posted by Fendell

Na I dont mean a governor on the engine, im referring to how an aircraft provides AC power. A quick google search tells me its a device that regulates the input speed to a constant output. to which my question was has anyone seen or heard of a down scaled version of this device? I fly regularly in a Fokker 100, which lead me to wonder how they generate power for air con/lights etc which is what lead me on this google rabbit hole...

Almost all smaller aircraft most often have starter / generators, for a PT6 as an example they are most often 250 amp 28V although I have installed 400 amp starter / generators.
If AC power is needed it’s often inverted. Many times aircraft that use AC a lot use 400hz three phase AC.
The one aircraft that I have a lot of experience with that used AC power, had dual 60KVA AC generators, but it was a helicopter and these AC generators rain off of the transmission and the RPM, and therefore the Hz rate was fixed. They ran at slightly different RPM in order to prevent resonant harmonics from being set up.

I don’t know how large transport category aircraft do it, I would assume they pull power from the N1 or gas generator which of course operates at a widely variable speed, and therefore the Hz rate will be variable if there isn’t a large inverter somewhere to keep Hz rate constant, like a Honda generator as an example.

Even if they drew power from the N2 or power turbine, it’s also variable RPM.
I therefore assume there is a largish inverter, probably at least two in the system, but that’s a guess really.

[RaymondR]

From an engineering viewpoint it would not be that extensive a project to mount an AC generator of 2-3 kW on the front of a 3GM30. As there's not much to hang it on you would need a couple of rails along the side of the engine attached to the engine mounting brackets, welded maybe, and a flange plate across the front. I'd estimate 2-3 days work as a DIY project.

I don't see speed regulation as a problem, it's a decent sized engine and the inertial energy stored in the rotating mass and engine governor would probably handle the load shifts on the generator.

[CassidyNZ]

Originally Posted by RaymondR

From an engineering viewpoint it would not be that extensive a project to mount an AC generator of 2-3 kW on the front of a 3GM30. As there's not much to hang it on you would need a couple of rails along the side of the engine attached to the engine mounting brackets, welded maybe, and a flange plate across the front. I'd estimate 2-3 days work as a DIY project.

I don't see speed regulation as a problem, it's a decent sized engine and the inertial energy stored in the rotating mass and engine governor would probably handle the load shifts on the generator.

At the risk of being verbally assaulted by other “engineers” here, the governor on a normal Diesel engine only establishes the max speed that the engine can be run at, it doesn’t control engine speed at multiple RPM points.

I know little about AC generators but I believe that they have to run at a constant speed so the governor on a gen set can be set at a chosen RPM and will then throttle up or down to maintain that exact speed. It’s not the same as a standard governor.

And yes, the bracket to mount devices in front of but not on the engine is a simple task. I have one on my engine exactly as you describe, supporting two additional alternators in front of the engine, facing backwards.

[RaymondR]

Originally Posted by CassidyNZ

At the risk of being verbally assaulted by other “engineers” here, the governor on a normal Diesel engine only establishes the max speed that the engine can be run at, it doesn’t control engine speed at multiple RPM points.

I know little about AC generators but I believe that they have to run at a constant speed so the governor on a gen set can be set at a chosen RPM and will then throttle up or down to maintain that exact speed. It’s not the same as a standard governor.

And yes, the bracket to mount devices in front of but not on the engine is a simple task. I have one on my engine exactly as you describe, supporting two additional alternators in front of the engine, facing backwards.

AC grid frequency is held to high tolerances because many of the gadgets connected to it use the frequency to keep time and for timing purposes. Not much, if any, of the AC stuff we use on boats is mains frequency critical so it doesn't much matter if the frequency is off a bit as long as the voltage stays reasonably well up.

The speed governor on the AC genset I am using on the boat at the moment froze up a couple of years ago and when I turn the AC hot water system on the voltage drags down from about 230 to 185 and nothing kicks out. Does not even cause a flicker on the TV set as the heater cycles.

I would just put the brackets as described to avoid the alignment problems. I would probably salvage the generator from a portable genset and have an adapter machined up for a direct connection with the 3GM crankshaft and not bother with a front end bearing or flex coupling. Basically emulate the mounting of the generator to the gas engine on the portable unit.

I'm so taken with the idea I wish I still had a 3GM30 to have a go at the project with.

[valhalla360]

Originally Posted by Fendell

Wow! I too have often pondered this exact set up. would love to continue the conversation in a different thread as I think this is a great alternative to re powering with like/like engines, as long as you can overcome the difference in control. Thanks Val

No one uses full throttle docking (at least not with good results). So that shouldn't be a serious issue. At worst, might take a little getting used to but driving a twin engine boat, you don't get exactly the same output out of each motor anyway... you tweak the throttles as needed to get the boat to do what you want.

[Dockhead]

Originally Posted by CassidyNZ

At the risk of being verbally assaulted by other “engineers” here, the governor on a normal Diesel engine only establishes the max speed that the engine can be run at, it doesn’t control engine speed at multiple RPM points.. . .

Not a verbal assault by any means, but I will very politely say that this statement is false. That is not at all how diesel engines work.


The governor on a diesel engine is not indeed like the governor on a lawnmower engine, just limiting the top speed. The governor on a diesel engine is the device which regulates the speed of the engine -- since there is no throttle plate like on an Otto cycle engine. When you move the throttle lever on a diesel engine, you are changing the set speed on the governor. At a given throttle lever position, the governor will inject more or less fuel in order to keep the engine as much as possible at the same speed. How much authority the governor has depends on the range of fuel injection volume of the injection pump, and may be more or less. But all mechanically injected diesel engines work this way -- speed controlled by the governor.


Further reading: https://www.quora.com/What-is-the-pu...engine?share=1

[Shaneesprit]

Different engines will have different limits, but I would suppose that pretty much none are designed so that large loads can be taken off the front of the crankshaft.
28[/QUOTE]
I know of a 16 cylinder engine where you can bolt the 2 together to make a nice 32 cylinder beast

So your right about following the manual, because that can push over 1000hp through the front of the crank and output double the Engine spec HP through the flywheel, 40,000 hours at full load before bottom end rebuilds at full load, with regular maintenance ( the sort of maintenance that requires heads replaced ) but that’s expected planned maintenance.

[Shaneesprit]

Originally Posted by Dockhead

Not a verbal assault by any means, but I will very politely say that this statement is false. That is not at all how diesel engines work.


The governor on a diesel engine is not indeed like the governor on a lawnmower engine, just limiting the top speed. The governor on a diesel engine is the device which regulates the speed of the engine -- since there is no throttle plate like on an Otto cycle engine. When you move the throttle lever on a diesel engine, you are changing the set speed on the governor. At a given throttle lever position, the governor will inject more or less fuel in order to keep the engine as much as possible at the same speed. How much authority the governor has depends on the range of fuel injection volume of the injection pump, and may be more or less. But all mechanically injected diesel engines work this way -- speed controlled by the governor.


Further reading: https://www.quora.com/What-is-the-pu...engine?share=1

Actually you are both partially right, depending on the Engine type, the throttle can simply control the amount of fuel injected, or in a more modern case be looking at the RPM, that’s why when you apply load you loose RPM when you don’t have speed control.
On a more modern Engine Electronic governor has RPM feed back and controls the speed and fuel delivery.

[Shaneesprit]

I know little about AC generators but I believe that they have to run at a constant speed so the governor on a gen set can be set at a chosen RPM and will then throttle up or down to maintain that exact speed. It’s not the same as a standard governor.

[/QUOTE]

Keep your RPM no More or less than 2.5 Hz above or below spec but closer to spec is better - if your governor is gone and you run highly loaded increase the throttle slightly, if your not converting it to DC
That’s how cheap Gens are set up

[CassidyNZ]

Originally Posted by Dockhead

Not a verbal assault by any means, but I will very politely say that this statement is false. That is not at all how diesel engines work.

Thank you, I learned something today.

But at the same time I’m left a little puzzled. So the governor reaches equilibrium at any speed set by the “throttle” lever. When the load decreases, it reduces fuel, when the load increases it provides more fuel. OK, I get that.

So why, when I switch in one of my alternators and increase demand for horsepower, does the RPM drop a few hundred and stay there? Why does the governor not compensate and lift the RPM back to the original setting? After all, the alternator is only drawing 4hp, hardly overloading the engine.

Another thing that bothered me with the article I read is that it said in the event of a loss of oil pressure the governor will shut the engine down, acting as a safety device. But if the pressure drops, surely the same drop will be experienced on both sides of the governor and equilibrium and consequently, engine speed will be maintained. I know the practicality of this to be true because I once had a total loss of oil pressure and had to dive for the throttle lever while the low pressure alarm screamed in my ears. So I guess the governor that acts as a safety device has more clever stuff than a normal one.

Anyway, clearly I don’t have the expertise to meaningfully engage in this discussion so I’ll bow out.