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Old 02-12-2016, 11:44   #526
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Re: Oceanvolt Hybrid Motor

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Originally Posted by beiland View Post
...just wanted to return to this question one more time...





Here is where I posted that PDF on the OSSA Powerlite system
http://www.cruisersforum.com/forums/...ml#post2267370
...and here is a short excerpt...
So can someone explain all of the incorrectness in this PDF ??
Adding to the previous post there are some other "incorrect claims".

"OSSA Powerlite generators control the speed of the diesel engine to maintain a desired voltage as the load varies. This desired voltage can be fixed, or it may optionally vary to provide motor speed control to a brush type motor. The AC output is immediately rectified to DC, so that the frequency of the power is not a factor. Major OSSA Powerlite loads are designed to be non- inductive. This can cut the size of the engine required by half because the genset is sized for maximum load, instead of inductive startup loads."

There is no such thing as a non-inductive motor. All electric motors use magnets which are necessarily inductive. AC motors with variable speed drives do not have "inductive startup loads".

"The async operation of the engine means that it is always turning at the optimum speed for a given load. This eliminates wet-stacking and greatly increases engine life. It also reduces noise and increases fuel economy, since the engine is no longer required to turn at a fixed high rpm under light load conditions."

Wet-stacking of generators isn't a big problem. I'm willing to bet almost no cruisers have had this problem with their AC generators although they often run with light loading. And the solution is quite simple depending on how the system is configured. Battery charging/water making/heating water during light conditions can increase the load or simply dumping a small amount of heat into the seawater can handle the light load case if it is a real concern. But the reality is that light loading doesn't happen much because the generator is being used for propulsion which will almost never be a light load. If it is why are we motoring?

"If multiple gensets are desired for system redundancy and continuous operation during service, they can be staged to come on or off line as the load conditions change with no concerns about syncing the power frequency."

This is pretty trivial for AC generators as well. It's done all the time. Syncing the power frequency is a very simple process easily managed by a small controller.

My best guess on this is that OSSA/Glacier Bay just didn't have the technical competence to build systems with AC motors. So they made up some "deficiencies" to justify a DC system. The result is a system that is neither simple or efficient. It is often the case that the most simple and efficient system from the user's perspective requires more complex engineering by the designer.

And this is probably why there not so many successful electric drives on boats. Siemens tried to make this work and failed miserably. So what makes us think some small startup can succeed in a market as small as cruising boats. No matter how smart they are they can't defy the laws of physics except in the marketing literature.
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Old 02-12-2016, 12:10   #527
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Re: Oceanvolt Hybrid Motor

Should note that Siemens is a major marine supplier and is actively involved in air independent propulsion used in non-nuclear attack submarines. When financial expense is not the primary concern, AIP is viable but should also note that the primary focus is running silent and without snorkel requirements.

Where diesel generators are used to provide propulsion instead of mechanical drive, there's usually particular performance requirements such as massive sustained electrical demand like cruise ships, ships that service survey/drilling and need extended station keeping with active thrusting pods.

I think if diesel electric has a market future it'll have to be some sort of magnetohydrodynamics drive.

I'd like to point out as battery technology gets better, viability of electric drive might get better for costal uses like in a small daysailer - but ironically I think better battery banks would actually mean a moderately sized 800w solar array would be able to power fridge, freezer, radar/electronics/AP without the need for any generator. Which if anything makes it even harder for hybrid systems to survive in the market.
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Old 02-12-2016, 15:09   #528
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by transmitterdan View Post
Adding to the previous post there are some other "incorrect claims".



"OSSA Powerlite generators control the speed of the diesel engine to maintain a desired voltage as the load varies. This desired voltage can be fixed, or it may optionally vary to provide motor speed control to a brush type motor. The AC output is immediately rectified to DC, so that the frequency of the power is not a factor. Major OSSA Powerlite loads are designed to be non- inductive. This can cut the size of the engine required by half because the genset is sized for maximum load, instead of inductive startup loads."



There is no such thing as a non-inductive motor. All electric motors use magnets which are necessarily inductive. AC motors with variable speed drives do not have "inductive startup loads".



"The async operation of the engine means that it is always turning at the optimum speed for a given load. This eliminates wet-stacking and greatly increases engine life. It also reduces noise and increases fuel economy, since the engine is no longer required to turn at a fixed high rpm under light load conditions."



Wet-stacking of generators isn't a big problem. I'm willing to bet almost no cruisers have had this problem with their AC generators although they often run with light loading. And the solution is quite simple depending on how the system is configured. Battery charging/water making/heating water during light conditions can increase the load or simply dumping a small amount of heat into the seawater can handle the light load case if it is a real concern. But the reality is that light loading doesn't happen much because the generator is being used for propulsion which will almost never be a light load. If it is why are we motoring?



"If multiple gensets are desired for system redundancy and continuous operation during service, they can be staged to come on or off line as the load conditions change with no concerns about syncing the power frequency."



This is pretty trivial for AC generators as well. It's done all the time. Syncing the power frequency is a very simple process easily managed by a small controller.



My best guess on this is that OSSA/Glacier Bay just didn't have the technical competence to build systems with AC motors. So they made up some "deficiencies" to justify a DC system. The result is a system that is neither simple or efficient. It is often the case that the most simple and efficient system from the user's perspective requires more complex engineering by the designer.



And this is probably why there not so many successful electric drives on boats. Siemens tried to make this work and failed miserably. So what makes us think some small startup can succeed in a market as small as cruising boats. No matter how smart they are they can't defy the laws of physics except in the marketing literature.

Output voltage varies with field supply voltage, changes to engine speed effect frequency.
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Old 03-12-2016, 14:14   #529
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by Cap Erict3 View Post
That is a broad and inaccurate statement.

You may want to look at the different capabilities of series, shunt, compound, induction, synchronous, universal and stepper motors.
No, it is not "broad and inaccurate". You need to have todays technology!

Nowadays the performance of an electric motor just depends on the way of controlling it. Mounting a sensor which is giving exact feedback about the current rotational position allows to implement a so called "field oriented control".
(works with DC, AC, asynchronous, synchronous and all the derivatives you mention)
With this you can control torque, speed or whatever you like and consequently people get the flat torque curve we are talking about. (up to the rpm where the maximum power - often defined by the electronics, not by the motor itself - is reached)
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Old 03-12-2016, 18:50   #530
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Re: Oceanvolt Hybrid Motor

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Originally Posted by myocean View Post
No, it is not "broad and inaccurate". You need to have todays technology!



Nowadays the performance of an electric motor just depends on the way of controlling it. Mounting a sensor which is giving exact feedback about the current rotational position allows to implement a so called "field oriented control".

(works with DC, AC, asynchronous, synchronous and all the derivatives you mention)

With this you can control torque, speed or whatever you like and consequently people get the flat torque curve we are talking about. (up to the rpm where the maximum power - often defined by the electronics, not by the motor itself - is reached)

Pm me ur resume and maybe I'll set u up with a service call the next time I get a request for an expert in the field. Do you have tools and a passport or just an Internet connection and access to Google?
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Old 03-12-2016, 19:11   #531
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Re: Oceanvolt Hybrid Motor

Capt,

Is all you've got ad hominem attacks? If you're going to refute something, let,s here it. As in references or evidenced argument please.


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Old 03-12-2016, 20:12   #532
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Re: Oceanvolt Hybrid Motor

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Capt,

Is all you've got ad hominem attacks? If you're going to refute something, let,s here it. As in references or evidenced argument please.


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Pot calling the kettle black?
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Old 03-12-2016, 20:38   #533
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Re: Oceanvolt Hybrid Motor

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Capt,

Is all you've got ad hominem attacks? If you're going to refute something, let,s here it. As in references or evidenced argument please.


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Feed 120 volts @ 60hz to a shaded pole 3/4 hp motor and I'll hold the shaft. Try that with a comparable series wound motor and we'll discuss the result. After you get a wrist brace for the sprain.
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Old 04-12-2016, 01:36   #534
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Re: Oceanvolt Hybrid Motor

How does this refute myocean's comments on motor controllers? Your point is some types of motors have more torque than others? So?


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Old 04-12-2016, 01:51   #535
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
How does this refute myocean's comments on motor controllers? Your point is some types of motors have more torque than others? So?


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His original statement read:
---

Every electric motor can operate with maximum torque over the whole range up to the speed where the maximum power is reached - not further! In this example at 700 rpm max power is .

-----

VFDs have come a long ways in the control of induction motors. The improvements in the drives have required changes in the design of motors.

The every electric motor comment is pure bs.

Read up on the required insulation changes, temperature monitoring and heat generated by these motors.

NFPA 70 is a good source of accurate info.
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Old 04-12-2016, 02:22   #536
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by Cap Erict3 View Post
VFDs have come a long ways in the control of induction motors. The improvements in the drives have required changes in the design of motors.

The every electric motor comment is pure bs.

Read up on the required insulation changes, temperature monitoring and heat generated by these motors.

NFPA 70 is a good source of accurate info.
My statement remains the same and can be complemented with a discussion of what exactly is in the end the limit for torque or power of a specific motor: This can be the power electronics
(->temperature), the voltage ratings and obviously the motors temperature limits or cooling. So the best is to tailor an entire system for a dedicated application.
We can just conclude, that just distinguishing between DC, AC and the frequency is in modern electric drive systems with DC intermediate circuit not sufficient anymore.
But I think this is a bit OFF TOPIC for this thread.
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Old 04-12-2016, 03:51   #537
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Re: Oceanvolt Hybrid Motor

It is illuminating to understand which electric motor is most efficient and most reliable. The highest efficiency in a drive system comes from proper selection of the motor and the controls. A DC system is neither the simplest nor the mot efficient. That is why you don't see a Tesla with that kind of system. DC is the choice when the designer may not know how to design with modern AC induction motor controls. Or it could be the buyers who don't understand the trade offs. Either way a DC system can not compete on cost or performance with a good AC induction motor system.
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Old 04-12-2016, 05:21   #538
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
It is illuminating to understand which electric motor is most efficient and most reliable.
...and which is lighter, more compact or which is easy to produce. Teslas decision to use asynchronous motors is wise because they do not need rare earth magnets in the vast quantities they are planning to produce and production gets simpler at the same time.
Regarding so called "DC motors" which are nowadays brushless motors working with AC currents it might be useful to update some old-school thinking which is still around.
For everything beyond dc motors with brushes, this is may be a useful short read:

The BLDC motor is dead. Long live the Brushless motor! - MAGicALL

and this

automotive - Why does a Tesla car use an AC motor instead of a DC one? - Electrical Engineering Stack Exchange
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Old 04-12-2016, 06:38   #539
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
Good heavens!

I was simply pointing out one of the unrealistic (and physically impossible) claims the electric motor evangelists make.

That they can make the boat sail faster by using one motor in regen, and feed that power to the other motor.

Obviously doing this would make the boat SLOWER, not faster. If every component were 100% efficient, the best result you could possibly achieve would be no loss, no gain.
Unrealistic yes, physically impossible no.
Your last sentence is incorrect for the reasons given in my post you just replied to.
However the greatest promise comes when regeneration is not done at the same time as propulsion. In such a case it can be close to working in practice too, but severely limited by the size of the battery bank. It would still be cost inefficient solution though, but some people just don't care about that.
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Old 04-12-2016, 06:58   #540
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Re: Oceanvolt Hybrid Motor

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With respect, I'm calling BS on this one. I have been in more than a few sailboats that were motoring at cruising RPM into big waves. When the boat was slowed I noticed no perceptible change in engine RPM. If a boat was so underpowered that this happens then it should be fixed ASAP.

What happens in a properly powered boat is the prop slips more when the boat slows and may cavitate. An electric system would have to be amazingly smart to sense this condition and slow down the prop to the optimal RPM to stop the cavitation and create maximum thrust. I don't think any EP solution on the market has such a feature. M

So, with respect, I think your ship building engineer is doing the proverbial hand wave.
When a prop slips more with given RPM, it requires more torque. A properly working engine control unit proves this torque as long as the engine is not already at max torque allowable for that RPM. Hence no perceptible change in engine RPM exists, but a change in torque, power and fuel consumption does exist. A controller for diesels is usually designed to deliver the user required RPM, not torque or power, hence your controller works as intended and quite accurately too.

Cavitation should not be a problem, if it is the prop is too small for the task, and it's dimensions should be changed and possibly the gear ratio too.
Even during a static thrust test the prop should not cavitate, it might stall though. But stalling is not necessary a problem if the boat is not intended to work as a tow boat.
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