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Old 11-12-2018, 12:57   #1516
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by OldMan View Post
Exactly!

In my very poor attempt to illustrate the loss in a hybrid/EP system, I wasn't very clear.

In a cursory look, industry-wide, alternators on gensets have efficiency ratings around 85% - 95%. OV and other EP vendors claim 95% efficiency on their motors.

My earlier swag using a 1KW loss in a 15KW alternator (93% efficient) falls inline with the above numbers. Add to that a 750W loss in the 15KW EP motor and you now have a ICE putting out 16KW so the alternator can deliver 15KW to the EP. The EP then delivers 14.25KW to the drive train. This does not take into account any loss in cabling/controllers/etc.

The bottom line - if you connect the same ICE to the same drive train it only needs to produce 14.25KW to be equal, an 11% drop in load.
The most important efficiency aspect, by a large margin, is fuel efficiency.

Your argument completely ignores it. That's where it's gone off the rails.

A Yanmar 3YM20 can produce 15kW at the crank at about 3,100RPM. It will consume about 3.5L/hr at that rate.

A Yanmar 3JH40 can produce 15kW at the crank at a tick under 1,400RPM. It will consume about 1.2L/hr at that rate.

In other words, two engines, producing the same HP. One uses almost 3X as much fuel as the other.

Now guess what engine a genset for a comparable EP system might look more like? The 0.85L 3YM20, or the 1.64L 3JH40?

THAT is how an EP can be more efficient. That 3X efficiency gap leaves a mile wide margin for any conversion losses. They're absolutely meaningless in the face of that.

This "direct drive magic" efficiency argument needs to go away.
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Old 11-12-2018, 14:14   #1517
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Dockhead View Post

This whole issue is a big fat red herring. Maximum efficiency of diesel engines is usually at about 75% of maximum power. But the difference in specific fuel consumption between say 35% and 75% is less than 10% in the table posted earlier in the thread, and between 35% and 90% is about the same. You're going to have the same issue running a generator to run a hybrid drive -- if you use the generator wide open, it is NOT indeed going to be running in its most efficient regime, and anyway you're only chasing 10% or so -- and this is a waste of time. Neither with hybrid nor with conventional drive are you going to be able to easily get right into the maximum efficiency groove, and you certainly will never get there with a hybrid drive and intentionally undersized generator where you may need to add battery power during periods of high power demand.
Which table is that? I just skimmed the 100+ pages and didn't find a table. My best guess is you're referring to this post.

If that's the case, you're right - the engine shown has very similar efficiency for most of the propeller curve. But that's because it's restricted to the propellor curve, which is way off of the peak efficiency of the engine.

Here's a typical diesel engine - the one from the smart car a couple generations ago - 3 cylinders, 1.5L:



That constant curve with this engine would be running something like 260 or 270 g/kWh. The engine can do 206 g/kWh, though - at fairly low rpms and near WOT.

That's the thing. A hybrid/generator system can use that peak efficiency point for every power demand below that output by paying 5% or so to go through the battery and cycling the generator as needed.

The 30% lower fuel consumption pays for a lot of conversion losses...

Which is why I said what I did. At docking speeds, the efficiency advantage is huge (though efficiency there may not be terribly important and the control benefit matters more.) At maximum power output, a mechanical system is likely more efficient. In between, it varies.

If the stories I've read of cruising at ~5 knots using one engine at half to two thirds rpm are typical usage, the hybrid will likely return better economy in that regime due to the ability to run the engine at its most efficient point.

The fuel savings won't pay for the extra costs of a hybrid system today, let alone the cost of ripping out a working system to replace it with a hybrid, but the numbers say the savings will be there for folks who don't firewall the throttle all the time - and that doesn't count the other benefits (better control in docking, hopefully less maintenance, might never need the generator if you sail everywhere, can supplement drive power with solar/wind/shore charging, A/C with no generator running, etc.)
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Old 11-12-2018, 14:21   #1518
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by ssmoot View Post
A Yanmar 3YM20 can produce 15kW at the crank at about 3,100RPM. It will consume about 3.5L/hr at that rate.

A Yanmar 3JH40 can produce 15kW at the crank at a tick under 1,400RPM. It will consume about 1.2L/hr at that rate.

In other words, two engines, producing the same HP. One uses almost 3X as much fuel as the other.

Now guess what engine a genset for a comparable EP system might look more like? The 0.85L 3YM20, or the 1.64L 3JH40?

THAT is how an EP can be more efficient. That 3X efficiency gap leaves a mile wide margin for any conversion losses. They're absolutely meaningless in the face of that.

This "direct drive magic" efficiency argument needs to go away.
Help me out here.
You pick a modern, common-rail ultra-efficient diesel for your EP system and compare it with an old-fashioned less-efficient diesel for the direct-drive, then tout the 3X efficiency gap between the two diesels as somehow demonstrating EP efficiency?
Not trying to troll- just looking for what I'm missing.

Newton might smile at the "direct drive magic" if he were alive.
I think a better efficiency argument might be to list:
1. friction loss of direct-drive transmission
2. friction loss of direct-drive alternator
3. better prop power curve of EP variable-pitch prop
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Old 11-12-2018, 14:47   #1519
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cyan View Post
Help me out here.
The point is to design the system around a specific output. Then pick the engine that's most efficient at it.

If the number you want to hit is 15kW for an EP system, then your generator is probably 1.5L to 2L. The generator can run at peak efficiency 100% of the time. Not 30%, or 50% or even 80% like the diesel propulsion. 100%. Because it can pay a small conversion loss and store excess energy in the batteries.

EP systems can play a game of Horsepower Arbitrage if you will, which is how they can be more efficient.

If you want to optimize for efficiency in a pure diesel system, you aren't choosing a 15kW engine because it'll be wildly inefficient at that output. You're going to size up. If you pick the 40HP Yanmar to get that efficiency now what have you got?

At that point you're comparing a 30kW diesel solution to a 15kW EP solution. Sound familiar? Maybe even a bit "magical"?
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Old 11-12-2018, 15:18   #1520
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
The most important efficiency aspect, by a large margin, is fuel efficiency.

Your argument completely ignores it. That's where it's gone off the rails.

A Yanmar 3YM20 can produce 15kW at the crank at about 3,100RPM. It will consume about 3.5L/hr at that rate.

A Yanmar 3JH40 can produce 15kW at the crank at a tick under 1,400RPM. It will consume about 1.2L/hr at that rate.

In other words, two engines, producing the same HP. One uses almost 3X as much fuel as the other.

Now guess what engine a genset for a comparable EP system might look more like? The 0.85L 3YM20, or the 1.64L 3JH40?

THAT is how an EP can be more efficient. That 3X efficiency gap leaves a mile wide margin for any conversion losses. They're absolutely meaningless in the face of that.

This "direct drive magic" efficiency argument needs to go away.

This comparison ludicrous from the onset. You pick 2 engines, one 1/2 the size of the other, quote power/fuel consumption on the smaller engine from beyond the manufacturers suggested continuous usage range. Then suggest to use the larger engine at a less than optimum loading, probably resulting in wet stacking and an early demise the engine. I wouldn't chose either of these engines for a 15KW load.



I never suggested an engine model. My example is using the same engine, yet TBD, for both hybrid and direct drive. My only point is the loss in the alternator and EP motor, which are necessary components of a hybrid system and not found in a direct drive system. Not sure how that scenario can "go off the rails". The 15KW load was dictated by BigBeakie's use case. The number can change to meet any application, the amount of loss will vary accordingly.



Is there some law that one can't use the more efficient engine for direct drive?
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Old 11-12-2018, 15:19   #1521
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by ssmoot View Post
Peak HP is what diesel-only fans keep claiming as the most important point of comparison.

I think that's silly, but nobody arguing that EP is viable is making the argument that you need to match peak diesel HP. They're making exactly the opposite argument.

In short, you agree with the EP proponents and disagree with the Diesel proponents. Claiming you would size a Diesel for peak HP is at best an unusual strategy and at worst dishonest.

But in your words, nobody actually does that. Finally some common ground.
You're being extremely dishonest. Nobody is saying you'd size a diesel for peak HP.

We're saying you'd size a diesel for CONTINUOUS HP.

It's just that some are claiming that continuous HP is about 1/2 the rated output. This too, has been proven to be dishonest. (It might be true for very large engines, but not the sizes we use in sailboats.)

The EP faithful will claim:

1: That you can only run a boat motor continuously at about 1/2 power. Or less.

2: But if that same motor was bolted to a generator, then all of a sudden it's fine to run it at 90+% power continuously.

3: That even though marine diesels are supposedly only good for 1/2 their rated power, you can replace them with electric motors of 1/3 the rated power because you can run the electrics at 100% all the time.

4: Then you can size a generator that might only allow the electric motors to run continuously at around 50-60%, (with the genset flat out) and STILL get equal performance.

So basically, they're claiming that a 12-13 kW diesel is equal to TWO 30 kW diesels, IF instead of connecting it directly to a propeller, you connect it to a generator which is connected to electric motors.

It's pretty easy to see where the word magic arises.
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Old 11-12-2018, 15:30   #1522
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by ssmoot View Post
The point is to design the system around a specific output. Then pick the engine that's most efficient at it.

If the number you want to hit is 15kW for an EP system, then your generator is probably 1.5L to 2L. The generator can run at peak efficiency 100% of the time. Not 30%, or 50% or even 80% like the diesel propulsion. 100%. Because it can pay a small conversion loss and store excess energy in the batteries.

EP systems can play a game of Horsepower Arbitrage if you will, which is how they can be more efficient.

If you want to optimize for efficiency in a pure diesel system, you aren't choosing a 15kW engine because it'll be wildly inefficient at that output. You're going to size up. If you pick the 40HP Yanmar to get that efficiency now what have you got?

At that point you're comparing a 30kW diesel solution to a 15kW EP solution. Sound familiar? Maybe even a bit "magical"?
Well, yeah it sounds familiar. There seems to be an ongoing argument regarding the way diesel engines are rated and the way electric motors are rated. I think we have established that those numbers are not directly useful for comparing the two. I doubt there is any magic in that.

I like your aim of designing around a specific output. There are lots of use cases, but my cruising interests are easy to nail down. My direct-drive diesel is used 99% of the time at one carefully-selected RPM with a carefully-selected prop, as we will hours of doldrums for every minute of docking. Why can't I simply run it at "peak efficiency" 99% of the time like a gen set? (I admit that a fabny variable-pitch prop might be needed for that)

Dispensing with the start/stop debate (for me) as I encounter far fewer stop signs than a Prius does, the efficiency argument seems to be simply comparing fuel burned for the two systems at a steady hull speed. Newton seems to win every time, but I'm still rooting for him to lose.
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Old 11-12-2018, 16:33   #1523
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Re: Oceanvolt Hybrid Motor

On my system I limited max revs on the motor to 3000 of the possible 6000 and even so when I use full throttle the motor will overheat after 1 or 2 min.
You don't have to underestimate the heat created when you put 300 or 400 amps at 72V in that motor.
It is good to have full power for an emergency stop or manoeuvring in a harbor but you can't use it for extended times.
By the way at full power it would kill my battery bank in about 15 minutes.
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Old 11-12-2018, 17:05   #1524
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by ssmoot View Post
The most important efficiency aspect, by a large margin, is fuel efficiency.

Your argument completely ignores it. That's where it's gone off the rails.

A Yanmar 3YM20 can produce 15kW at the crank at about 3,100RPM. It will consume about 3.5L/hr at that rate.

A Yanmar 3JH40 can produce 15kW at the crank at a tick under 1,400RPM. It will consume about 1.2L/hr at that rate.

In other words, two engines, producing the same HP. One uses almost 3X as much fuel as the other.

Now guess what engine a genset for a comparable EP system might look more like? The 0.85L 3YM20, or the 1.64L 3JH40?

THAT is how an EP can be more efficient. That 3X efficiency gap leaves a mile wide margin for any conversion losses. They're absolutely meaningless in the face of that.

This "direct drive magic" efficiency argument needs to go away.
Huh? ICE efficiency has not much to do with whether it drives a genset or a transmission. If the delivered HP and RPM are the same how can the ICE tell the diff between a prop load and an alternator/generator?

It seems silly to say that only EP gets to use modern efficient engines. Look at a modern common rail turbo engine and check the fuel burn per HP at different RPM. The curves are not 3:1 apart at useful HP.
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Old 11-12-2018, 17:17   #1525
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
You're being extremely dishonest. Nobody is saying you'd size a diesel for peak HP.

We're saying you'd size a diesel for CONTINUOUS HP.
Seems the tune has changed. That's ok, it's more reasonable, but still not the whole story. Sizing for max HP is still done today. Buyers look at HP on the spec sheet. They don't ask questions about duty rating. They think they are buying that magic unachievable ICE HP. It's ok, it's tradition and the competition is doing it.

Quote:
Originally Posted by 44'cruisingcat View Post

It's just that some are claiming that continuous HP is about 1/2 the rated output. This too, has been proven to be dishonest. (It might be true for very large engines, but not the sizes we use in sailboats.)

The EP faithful will claim:

1: That you can only run a boat motor continuously at about 1/2 power. Or less.
Depends on the engine. For some duty ratings, some engines, yes, 1/2 power. For others, 89% for 30 minutes every 8 hours. For John Deere M1 rated, 100%, M5 below 35%. Each engine is different.


Quote:
Originally Posted by 44'cruisingcat View Post
2: But if that same motor was bolted to a generator, then all of a sudden it's fine to run it at 90+% power continuously.
No no no. No one is saying that you'd use the same engine on the genny. You'd choose the generator system for the best efficiency at the maximum continuous output you wanted for an "infinite" cruise duration. You'd then size your batteries for full power at maximum cruise. You'd increase both for any reserve you wanted if you wanted it at all. No one has supplied me a formula for reserve power yet, I'll be waiting for that forever...

Quote:
Originally Posted by 44'cruisingcat View Post
3: That even though marine diesels are supposedly only good for 1/2 their rated power, you can replace them with electric motors of 1/3 the rated power because you can run the electrics at 100% all the time.
Answered already, and not sure where you got the 1/3rd. Again, not all engines are pleasure duty rated, but the real actual engines we have talked about here so far have been PD rated, and therefore should not be run continuous for more than 30 minutes every 8 hours (I think it's 8, hard to find). In my book continuous means continuous, but not in that engine's specifications. Again, not all engines are the same.

Quote:
Originally Posted by 44'cruisingcat View Post
4: Then you can size a generator that might only allow the electric motors to run continuously at around 50-60%, (with the genset flat out) and STILL get equal performance.
Genset's are not designed to run "flat out". They are designed to run at a certain load continuously (the ones being discussed here, there are light duty generators too). Since the generator only needs to meet the steady speed demand, and not the WOT demand (batteries can make that up) AND since they are decoupled from the load, we can pick the right duty, right efficiency, and right output for our application. Not as much need to compromise.


Quote:
Originally Posted by 44'cruisingcat View Post
So basically, they're claiming that a 12-13 kW diesel is equal to TWO 30 kW diesels, IF instead of connecting it directly to a propeller, you connect it to a generator which is connected to electric motors.

It's pretty easy to see where the word magic arises.
No one is saying this. You are misrepresenting the discussion. I am earnest in my answers, as I hope you are in yours.
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Old 11-12-2018, 17:38   #1526
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Re: Oceanvolt Hybrid Motor

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Originally Posted by saghost View Post
Which table is that? I just skimmed the 100+ pages and didn't find a table. My best guess is you're referring to this post.

If that's the case, you're right - the engine shown has very similar efficiency for most of the propeller curve. But that's because it's restricted to the propellor curve, which is way off of the peak efficiency of the engine.

Here's a typical diesel engine - the one from the smart car a couple generations ago - 3 cylinders, 1.5L:



That constant curve with this engine would be running something like 260 or 270 g/kWh. The engine can do 206 g/kWh, though - at fairly low rpms and near WOT.

That's the thing. A hybrid/generator system can use that peak efficiency point for every power demand below that output by paying 5% or so to go through the battery and cycling the generator as needed.

The 30% lower fuel consumption pays for a lot of conversion losses...

Which is why I said what I did. At docking speeds, the efficiency advantage is huge (though efficiency there may not be terribly important and the control benefit matters more.) At maximum power output, a mechanical system is likely more efficient. In between, it varies.

If the stories I've read of cruising at ~5 knots using one engine at half to two thirds rpm are typical usage, the hybrid will likely return better economy in that regime due to the ability to run the engine at its most efficient point.

The fuel savings won't pay for the extra costs of a hybrid system today, let alone the cost of ripping out a working system to replace it with a hybrid, but the numbers say the savings will be there for folks who don't firewall the throttle all the time - and that doesn't count the other benefits (better control in docking, hopefully less maintenance, might never need the generator if you sail everywhere, can supplement drive power with solar/wind/shore charging, A/C with no generator running, etc.)

This is exactly the core of the efficiency argument. Nice data, great analysis.
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Old 11-12-2018, 18:09   #1527
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by ssmoot View Post
The most important efficiency aspect, by a large margin, is fuel efficiency.

Your argument completely ignores it. That's where it's gone off the rails.

A Yanmar 3YM20 can produce 15kW at the crank at about 3,100RPM. It will consume about 3.5L/hr at that rate.

A Yanmar 3JH40 can produce 15kW at the crank at a tick under 1,400RPM. It will consume about 1.2L/hr at that rate.

In other words, two engines, producing the same HP. One uses almost 3X as much fuel as the other.
Personally I want to know fuel per mile.

Real world, pushing 8-10k lbs displacement monohull, say 20 miles over eight hours.

Direct drive vs genny+EP

And how heavy does the battery need to be to do that for say three of those hours?

And how costly for the EP vs the old-school direct drive?

And finally, how much solar panel wattage would be needed to contribute say 25% of that power, in a clear tropical solar day?

Sincerely would love to see those numbers.
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Old 11-12-2018, 18:17   #1528
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Re: Oceanvolt Hybrid Motor

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Originally Posted by OldMan View Post
Is there some law that one can't use the more efficient engine for direct drive?
Of course not. It's what the EP proponents have been doing since Page 1.

So tell me then: Just how much more horsepower do you think a diesel needs to be competitive with a 15kW EP solution?
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Old 11-12-2018, 18:39   #1529
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
Of course not. It's what the EP proponents have been doing since Page 1.

So tell me then: Just how much more horsepower do you think a diesel needs to be competitive with a 15kW EP solution?
I can answer this one. About 50hp of diesel to match 15kW of EP at cruise.

I don't understand why people don't get that rated HP is almost at WOT and your warranty barely allows you to use it, and even when you are briefly allowed to use it, you never would due to the fuel consumption at that RPM! No one cruises at max RPM or max HP or max possible fuel consumption!!! What is so hard to understand?

HP is the real magic here folks. But that is the past that people do not want to give up. I'm more interested in the future.
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Old 11-12-2018, 18:47   #1530
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
I can answer this one. About 50hp of diesel to match 15kW of EP at cruise.

I don't understand why people don't get that rated HP is almost at WOT and your warranty barely allows you to use it, and even when you are, you never would due to the fuel consumption at that RPM! No one cruises at max RPM or max HP or max possible fuel consumption!!! What is so hard to understand about this?

HP is the real magic here folks. But that is the past that people do not want to give up. I'm more interested in the future.
Who cares if a 15HP EP can "cruise" at max HP. So can a 15HP ICE. But if you think electric motors and the inverter drive and genset can run flat out max HP in cruise mode for days on end and last forever then you have a rude awakening in your future.
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