Electrical motor maths: 25HP=8HP? [Archive]

mydauphin

03-03-2009, 09:50 PM

The advantage of electric is you get torque from zero rpm up, diesel needs to be operating at torque range of lets say 1500 rpm. So at 800 rpm 8hp electric has same torque and can drive same propeller as 25hp diesel.
But of course set both at same rpm and the diesel will give you same hp as electric hp all things being equal. But remember not all engines, motors, batteries or transmission are same. Neither are propellers or boats... that is why there are engineers and experimentation. Don't believe what people are trying to sell, Physics still rules our lives.

Alik

03-03-2009, 10:37 PM

Yes, true. Diesel is not efficient at idle speed, needs about 30% of max RMP to keep it running. The advantage of electrical motor is better use of power at idle speeds, but who compares propulsion/power at idle speeds??? Every comparision should be fair.

Rick Willoughby

03-03-2009, 11:49 PM

Looking at this:
http://www.youtube.com/watch?v=gP-WK2QArj4
just wonder if something wrong with maths here? The guy clearly says that 25HP diesel delivers only 8HP? Need advice.

There is no maths in the clip. He is providing limited factual information with no numbers. Basically little more than nonsense.

Most diesel have ratings given at the shaft. You have to determine what allowance there is in this for auxiliaries but these losses are typically small unless you have oversize alternator for example.

The diesel will be able to deliver peak power at close to peak rpm. The peak torque will be a tad higher than the rated torque but at lower rpm. If the load torque exceeds the peak torque then the diesel speed will collapse. Combustion is poor and there will be lots of black smoke.

An electric motor has a continuous rating based on how well it is cooled. Ratings are normally given in open air. However an electric motor can exceed its continuous torque and power rating by two or three fold. So if you have an electric motor rated at 10kW there is no problem getting 20kW from it if the power supply is up to it. It will deliver this power until it overheats. If the load torque exceeds the rated torque the motor will just draw more current until it trips or hits current limit. Most of the low end EV motors have a current limit around 2X rated current.

So a diesel has quite a narrow range of operation while an electric motor has a wider range.

Some of the high powered electric vehicles being built do not bother with gear changes because the motor has the torque to spin the wheels in the normal gear that allows top speed.

This is a good comparison of electric and IC torque:
http://www.youtube.com/watch?v=pm6gD6r3-cw&feature=related
The electric car has rated power less than half of the IC.

There are a few electric dragsters that take advantage of modern batteries and electronics. My favourite is Bill Dube's bike:
http://www.youtube.com/watch?v=GDHJNG2PngQ&feature=related

Rick W

Joakim

03-11-2009, 03:42 AM

The diesel will be able to deliver peak power at close to peak rpm. The peak torque will be a tad higher than the rated torque but at lower rpm. If the load torque exceeds the peak torque then the diesel speed will collapse. Combustion is poor and there will be lots of black smoke.

An electric motor has a continuous rating based on how well it is cooled. Ratings are normally given in open air. However an electric motor can exceed its continuous torque and power rating by two or three fold. So if you have an electric motor rated at 10kW there is no problem getting 20kW from it if the power supply is up to it. It will deliver this power until it overheats. If the load torque exceeds the rated torque the motor will just draw more current until it trips or hits current limit.

Since we are discussing marine applications it is important to remember that a propeller has a lot of slip during acceleration from zero. Thus the engine never needs to work hard at low rpm. Here is the curves for my engine: http://www.yanmarmarine.com/uploads/products/pdf/GM_YM/1GM10_TechData.pdf Note that the maximum torque is almost constant (16-18 Nm) between 1800 and 3600 rpm. With any decently chosen propeller the engine will take well over 1800 rpm during bollard pull or rapid acceleration from zero. Thus the diesel will always give about the maximum torque when needed in marine applications (this is not true for fast planning boats). The only problem with low torque at idle is that it takes a while to accelerate the engine from 800 to over 2000 rpm where the thrust starts to be good.

This is very different for cars, since the wheels are not supposed to slip thus you basically start from zero rpm, which is OK for an electrical engine, but bad news for a diesel. Thus the good torque at low rpm is a clear benefit for a car engine.

How does the torque (and thus efficiency) of a typical marine electrical motor behave at low rpm? I'm guessing it is relative to current, thus efficiency is very low at low rpm. Is that so?

Joakim

jehardiman

03-11-2009, 01:17 PM

Electric motors have thier maximum torque at stall and minimum torque at sync speed (the shape of the torque curve varys for each type but they are all similiar in this..see this site http://www.reliance.com/mtr/mtrthrmn.htm). The motor is rated for torque, and therefor HP, at a given speed. Normally, this rating is based upon continious operation and is a winding thermal or circular mil amp limit. It is important to notice that EM torque increases as rpm drops and torque decreases as RPM rises forcing a flat or negative HP curve.

ICE's have thier maximum torque at about 60-70% of thier maximum RPM, and it remains fairly constant as RPM drops to some minimum idle. Therefor ICE's carry thier HP lower into the RPM curve and have more HP available at high rpm.

Because the powering curve is exponential, ICE's are better suited to marine propulsion because their HP curve follows the powering curve. EM are not as well suited because thier HP curve cuts across the powering curve as RPM imcreases. This is why you need expensive motor controllers for marine propulsion, becuase you need to change the % of sync speed to RPM in the motor controler (either with MG-TG sets or solid state frequency generators).

All in all, an electric prime mover is heavier, larger in volume, and more complicated than an ICE. What you pay for in the light weight and size is slightly less efficency, but most of that can be recovered and usualy is in large plants.

drmiller100

03-15-2009, 02:38 AM

the lecture is nonsense with his definition of "designed horsepower".
further, I'm a little interested how the magic electricity gets created to run the electric motors across a large lake.

Rick Willoughby

03-15-2009, 03:31 AM

...........

How does the torque (and thus efficiency) of a typical marine electrical motor behave at low rpm? I'm guessing it is relative to current, thus efficiency is very low at low rpm. Is that so?

Joakim

Torque is proportional to current. My Mars PMSM, using the 4-quadrant Kelly controller, takes 260mA from a 24V (6W) to turn over at minimum speed. So no load loses are very low. Not too shabby for a motor/controlle combination able to deliver 9kW.

The only additional losses at full torque are copper losses. The winding resistance is 10mohm. So at peak current of 200A you need 400W to produce 27Nm of torque.

By comparison a Yanmar 2YM20 operating to spec will deliver 32Nm once it gets to 1800rpm and pulls 6000W to achieve it. This might give you an idea of the comparative pulling power. This is why electric dragsters do so well against IC motors. Instant on; with twice rated torque at zero rpm no problem.

Rick W

Joakim

03-16-2009, 08:45 AM

The only additional losses at full torque are copper losses. The winding resistance is 10mohm. So at peak current of 200A you need 400W to produce 27Nm of torque.

Where is this 200A? How much is taken from the batteries? 200A * 24 V = 4800 W. Or is there a boost circuit that creates that 200 A * 2 V = 400 W only using about 20 A at the 24 V batteries?

Joakim

marshmat

03-16-2009, 02:51 PM

The 400 W is the loss due to the resistance of the motor winding: R*I^2, for 10 milliohm resistance and 200 amp current.
If Rick is using a 24 V battery, you are correct that 200 A at 24 V is 4800 W.

Rick Willoughby

03-16-2009, 06:20 PM

Where is this 200A? How much is taken from the batteries? 200A * 24 V = 4800 W. Or is there a boost circuit that creates that 200 A * 2 V = 400 W only using about 20 A at the 24 V batteries?

Joakim

Joakim & Matt
These controllers all use switching mode DC-DC link. Losses are very low. I gather they use either MOSFETs or IGBTs but I have not opened either of my controllers to actually see what they have inside:
http://www.irf.com/technical-info/whitepaper/choosewisely.pdf

I have a 200A variable frequency variable current TIG welder and have had it open. The small size of the electronics to handle the current is impressive. My Kelly controllers are likely to have even smaller components given it is 120A continuous.

Most portable devices like computers and phones use switching mode power supply for battery charging. It gives much greater flexibility with input voltage so the same power supply can be used worldwide. The output voltage does not change irrespective of the input voltage. Also the power losses are almost independent of input voltage.

Rick W

Joakim

03-17-2009, 03:46 AM

Rick Willoughby

03-17-2009, 05:42 AM

Yes I'm well aware of switching mode power supplies and I have even designed and built them, but only for <1A currents.

You said your system can provide 9 kW. At 120 A that would be 75 V, thus much over the supply of 24 V. This would require a buck-boost system, which is able to both increase and decrease the voltage.

I have some doubts about the efficiency of the controller designed for >>24 V 120 A at 2 V 200 A. They don't typically do well on such a wide voltage range and most likely they are optimized for the higher power outputs.

Is your controller one of these: http://www.kellycontroller.com/mot/KellyPMUserManual.pdf ? After fast reading it looks like a PWM controller NOT a switching mode one. That means it only switches on/of the voltage you have and thus it takes the full 200 A from 24 V (or whatever batteries you have) when using the full torque and can not provide 9 kW unless you have much more than 24 V batteries. Or did I miss something?

Joakim

Joakam
I have a Mars PMSM with a regenerative Kelly controller. I checked the spec per attached. It is the KBL48210. The peak current is 200A. The continuous current is 100A not 120A.

PWM is one form of switching mode operation. All of these controllers use energy storage in the switching cycle so the power output is not much less than the power input. That is the big feature of switching mode. The current is multiplied in relation to the voltage reduction ratio. Effectively an interchange of magnetic and electric energy similar to a transformer. It is only at full voltage where the battery current equals the motor current or its 2-phase equivalent given that they are 3-phase motors.

My intention is to use a supply voltage between 40 to 50V. I was intending to use 4 x 12V VRLA batteries but lithium are looking more promising. I may end up buying a 10S lithium battery of about 6000mA rating and 20C power rating so I can do more serious testing with my test outboard. My current 12Ah VRLA batteries limit output to about 270W:
http://www.boatdesign.net/forums/attachments/boat-design/20726d1209288392-electric-boat-data-drive_leg_test1.wmv

Rick W

Joakim

03-17-2009, 06:36 AM

PWM as such is not a switching mode supply as I see it.

But in this case the PWM uses the inductance of the motor to make it work like a buck converter. http://www.4qdtec.com/pwm-01.html

Thus it can reduce the voltage, but not increase. And it short circuits the motor while PWM state is "off".

The PWM ratio needs to be very low in order to reduce the voltage to 2 V. . Still skeptical about good efficiency at 200 A 2 V. Any measurements or more detailed specifications available?

Joakim

Rick Willoughby

03-17-2009, 05:49 PM

PWM as such is not a switching mode supply as I see it.

......
Joakim

You are in a very small minority if you think PWM DC-DC supplies are not switching mode. Last sentence in the attached might help explain.

Rick W

Rick Willoughby

03-17-2009, 06:40 PM

..........

But in this case the PWM uses the inductance of the motor to make it work like a buck converter. http://www.4qdtec.com/pwm-01.html

Thus it can reduce the voltage, but not increase. And it short circuits the motor while PWM state is "off".
.....
Joakim

Uncertain why you included this, It is not related to my motor. My Mars motor is a 3-phase synchronous motor. So the switching mode DC-DC link is separate to the motor side. The motor is driven by a 3-phase bridge.

I have not checked the no-load losses in the controller at full current. The losses on the DC side will be low because the current in this side is low at zero speed condition even at current limit. The losses on the AC bridge side probably around 200W.

If I get around to it I will do some torque testing with the little batteries to see what is possible with 280W from these.

Rick W

Rick Willoughby

03-23-2009, 06:05 PM

I did the torque tests on one of my Mars motors. My calculations are very close. The best I could get from the little batteries before going into undervoltage control was 11A at 19.5V. This gave a torque of 11.2Nm.

I have attached a photo of the test set up that shows the peak result. I did a number of lower current test to get a good curve. The curve is almost linear as you would expect. Extrapolating indicates you would get twice rated torque of 28Nm with 600W.

There is also a video of the motor running up. If you take a look at current during creep speed the value is 0.27A with 23.6V. At full speed the current is 6A with 20.5V.

This gives a good idea of the losses in the motor and controller. They are not very high for something able to deliver 9kW on 48V.

Rick W

kroberts

03-23-2009, 07:25 PM

Ignoring the current debate right now, I will address the original poster.

I have heard many different numbers for horsepower conversions between electric and some sort of internal combustion engine.

The truth is, a horsepower is a horsepower is a horsepower. Watts is watts is watts.

It becomes a little more clear if you have ever tried to design a piece of industrial machinery. If you go through something like the Dodge power transmission handbook (not cars, industrial machinery) and calculate the rating for a belt or a gearbox, you will see where they take into account the smoothness of the power source and adjust power accordingly. In other words, the drive system reacts differently to different power impulse ratios.

Also, consider the torque curves and power curves for various engines and motors -- two stroke, four stroke electric, diesel, etc. Also consider that any application has curves for power and torque demand, and the lines go in all sorts of directions. The normal procedure is to find your required operating range, and then make sure your power source can supply the necessary torque at the necessary speeds, and that there is adequate reserve torque at any RPM up to and surrounding that range that all possible environment changes are accounted for.

Now, figure some guy is trying to get his pump working. It had a gas engine on it, and now he wants electric. He gets the handbook, and it's been decades since he ever used algebra. He was never good at it. He agonizes through the whole thing, and figures out that in his case the pump needs 1/3 the power of his gas engine. He gets his motor, sets it up and it all works.

Next time, this guy is not going to use the book. He needs a motor for an entirely different application, and rather than trudge through all that painful math, he just divides by 3 and goes with it, no matter how far off he is. Not only that, but everyone he talks to is going to hear about it, and some of them are just going to take his advice.

People always seem to think that horsepower is all there is. It's NOT TRUE, even if you are talking about gas engines in cars. Any number of variables come into it, even in one application like car engines.

Joakim

03-24-2009, 07:58 AM

Rick Willoughby

03-24-2009, 08:19 AM

Joakim
There is not much point in a boat motor having good low down torque or fine speed control. The purpose in doing the test was to verify my quick calculations above and provide you and Matt with understanding about these motors and controllers. You both assumed there could be no current multiplication through the controller.

With hindsight the phase locked synchronous motor is overkill for a boat. I would have looked more closely at open loop controllers had I known they were readily available when I purchased the Kelly controllers. Irrespective the motor and controller are a nice combination. Very smooth power delivery and heaps of torque down low.

My aim is to swing a prop up around 0.5m diameter using about 4:1 gearing. It will usually operate at less than 5% slip. Even in severe conditions I will not have to worry about the motor bogging down. So I will have heaps of grip efficiently applied. Bollard pull will be over 1.2kN.

Rick W

2farnorth

03-24-2009, 09:31 AM

All in all, an electric prime mover is heavier, larger in volume, and more complicated than an ICE. What you pay for in the light weight and size is slightly less efficency, but most of that can be recovered and usualy is in large plants.

If I read this correctly, you are saying an electric motor is more complicated than an ICE? One moving part versus dozens? I can see maybe the wiring a bit more complicated but nothing different than wiring all the accessorys on a vessel. From my knowledge, an ICE wastes anywhere from 60-70% of its energy in heat loss, where as electric motors are losing 5-10%.

jehardiman

03-24-2009, 11:55 AM

If I read this correctly, you are saying an electric motor is more complicated than an ICE? One moving part versus dozens? I can see maybe the wiring a bit more complicated but nothing different than wiring all the accessorys on a vessel. From my knowledge, an ICE wastes anywhere from 60-70% of its energy in heat loss, where as electric motors are losing 5-10%.

It's a matter of prespective and size, but it what I say is true.

Lets say you want to consider a small 8 kW shp main proplusion unit a 6 hour day boat with a maximum 6 amp hotel load.

You could just throw a 9.9 HP 4-stroke OB on it with a 5 gal tank so say 5 cubic feet and 200 lbs total including a 12 volt start/hotel battery.

For a comperable electrical system you need 2000 lbs of lead acid batterys or even 600 lbs of Li-ion. The battery weight alone can exceede the entire vessel weight of an ICE powered boat. Oh, and did I mention the 50Mw coal fired plant needed to charge those batteries (I won't even go into the energy-negative world of solar cells :rolleyes: )?

Even self-produced electric proplusion plants for ships are much more complex and massive than straight direct coupled ICEs, so unless you have specific hotel load needs, or need it for noise reasons, electric is not the efficient way to power a small vessel

2farnorth

03-24-2009, 12:02 PM

I see what you are saying, but if the energy storage weight can be reduced, would that tip the scales toward electric in your opinion?

jehardiman

03-24-2009, 03:13 PM

I see what you are saying, but if the energy storage weight can be reduced, would that tip the scales toward electric in your opinion?

Right now? Power generation in the way that the creator of the universe intended it...Nuclear.

Fission or Fusion, take your pick. All propaganda aside, from any dispassionate analysis, safer, cleaner, and more efficient in thermal and volume than any other soruce.

In the long term? Atmosphere supplied hydrocarbon fuel cell.

Rick Willoughby

03-24-2009, 03:33 PM

It's a matter of prespective and size, but it what I say is true.

Lets say you want to consider a small 8 kW shp main proplusion unit a 6 hour day boat with a maximum 6 amp hotel load.

You could just throw a 9.9 HP 4-stroke OB on it with a 5 gal tank so say 5 cubic feet and 200 lbs total including a 12 volt start/hotel battery.

For a comperable electrical system you need 2000 lbs of lead acid batterys or even 600 lbs of Li-ion. The battery weight alone can exceede the entire vessel weight of an ICE powered boat. Oh, and did I mention the 50Mw coal fired plant needed to charge those batteries (I won't even go into the energy-negative world of solar cells :rolleyes: )?

Even self-produced electric proplusion plants for ships are much more complex and massive than straight direct coupled ICEs, so unless you have specific hotel load needs, or need it for noise reasons, electric is not the efficient way to power a small vessel

Many sailing boats carry more than 2000lb of lead just for ballast.

If you design right you can get a 10m boat to cruise at 8kts with a little over 1kW. This means for day cruising you can get away with 500lb of lead acid or half that with lithium. Batteries can be stowed to improve stability.

Add solar and wind energy collection and you have a boat capable of long distance cruising, only limited by human provisions.

You need to design from scratch not just replace the engine component.

Rick W

jehardiman

03-24-2009, 04:40 PM

Many sailing boats carry more than 2000lb of lead just for ballast.

We were not discussing a sailboat, which doesn't need a motor at all, so electric is out also, not to mention the toxic and hazardous materials used in batteries don't make the vessel any more eco friendly.

If you design right you can get a 10m boat to cruise at 8kts with a little over 1kW. This means for day cruising you can get away with 500lb of lead acid or half that with lithium. Batteries can be stowed to improve stability.

And if I design it right, I can build a ICE powered boat that gets 10 knts on 1.0 kW without having to carry around a quarter ton of lead, and goes for a week at 8 knts in the same displacement. Your argument there is apples and oranges. You can only compare propulsion relative to other transport requirements the vessel must meet.

Add solar and wind energy collection and you have a boat capable of long distance cruising, only limited by human provisions.

True, but why cause all the pollution and waste all that energy to dig up that copper, lead, and other rare earths for electric propulsion when you could just go to wind directly (i.e. natural fiber sails) and accieve the same result without pollution or wasted energy. FWIW, because of the material requirements, vehicle electrical propulsion systems never return any energy over ICE systems, they are always more enegry negative...it is always better to burn the fuel directly. If global energy effiency is the basis for your argument, then arguing for another process inbetween burning the fuel and applied power is counter to your tenent if you carry it to it's logical conclusion.

Most of what many people today is espouse as "energy effiency" is just a very NIMBY view of the world. They want thier electric cars, but not be downwind of the power plants that produce the electricty. They want the Li-ion battery or solar cells for thier Nano, but deride the strip mine in Bolivia that produces the rare earths.

Rick Willoughby

03-24-2009, 05:00 PM

John
Most practical sailing vessels require an engine. Seems sensible to use electric. If you are going to carry lead ballast why not keep it in a form that can be useful when there is no wind.

Recycling of most metals achieves up to 80% in some cases. Could be better but it gets down to how much it costs to mine versus recycle. As cost of mining goes up recycle proportion increases.

Lithium is not rare, just hard to handle.
http://lithiumabundance.blogspot.com/

A boat using solar and wind collection does not rely on a power station.

Solar panels are already commercially viable against other forms of power production. Just no large scale applications yet.

Liquid hydrocarbons are diminishing resource and need to be kept for applications that are currently hard to substitute. You seem to forget that your little IC motor will be eating this precious resource with no chance of it being recycled.

Rick W

jehardiman

03-24-2009, 06:05 PM

John
Most practical sailing vessels require an engine. Seems sensible to use electric. If you are going to carry lead ballast why not keep it in a form that can be useful when there is no wind.

Yes, but of the flip side, why not make the power more dense so I have to carry less weight which means less hull structure which means less petrochemicals and offgassing and also which means less weight which allows me to reduce power which....etc, etc, etc. There is no single answer so electric only cannot be end all. (and we better stop this before the cat and foiler people jump in about the ballast comment...:p )

Recycling of most metals achieves up to 80% in some cases. Could be better but it gets down to how much it costs to mine versus recycle. As cost of mining goes up recycle proportion increases.

Another comment that is not really here or there, but if we look at energy expenduture to reform materials, I think you would agree that the more material required, the more energy expended. Battery lead is very hard to re-process BTW, it is poisoned with sulphates that are difficult to extract.

Lithium is not rare, just hard to handle.
http://lithiumabundance.blogspot.com/

I never said Lithium was rare, in fact I was thinking of gallium, neodymium, and cadmium. These like lithium are not really "rare", they were called rare because they were difficult to extract, and still are.

A boat using solar and wind collection does not rely on a power station.

Ok, but that wasn't my point. If you are concerned about energy efficient propulsion why have a motor at all? For the size of vessel that could main propulsion powered by wind or cells, I can row it for all the upwind work I would need.

Solar panels are already commercially viable against other forms of power production. Just no large scale applications yet.

Not for vessel main propulsion, which is the topic here. There is not acres of deckspace to place them, and the environment/motions are not conducive to optimum power generation, even setting the need for heavy batteries to store the night reserve aside.

Liquid hydrocarbons are diminishing resource and need to be kept for applications that are currently hard to substitute. You seem to forget that your little IC motor will be eating this precious resource with no chance of it being recycled.

That statement is absolutely wrong. Biofuels are far more viable today than solar for a marine prime mover. Plants are far more efficient converting solar energy than even 3rd generation cells as well as being carbon neutral. And existing ICE technology fully supports it. Liquid fuels are here to stay Rick, get with the program instead of being one of those toxic polluting electric dinosaurs...:D .

Rick Willoughby

03-24-2009, 06:19 PM

That statement is absolutely wrong. Biofuels are far more viable today than solar for a marine prime mover. Plants are far more efficient converting solar energy than even 3rd generation cells as well as being carbon neutral. And existing ICE technology fully supports it. Liquid fuels are here to stay Rick, get with the program instead of being one of those toxic polluting electric dinosaurs...:D .

So you are one of these people wanting to take essential food production from the starving billions. These crops need huge water resources which is now having to be produced using desalination in many parts of the world. My understanding is desalination is not too far off on the west coast of USA either. Hard to have biofuels when there is no water for crops.

Solar energy production is the long term future. I am just staying ahead of the game. Besides I like the music of modern electric over the thud of crappier technology.

Rick W

jehardiman

03-24-2009, 06:27 PM

So you are one of these people wanting to take essential food production from the starving billions. These crops need huge water resources which is now having to be produced using desalination in many parts of the world. My understanding is desalination is not too far off on the west coast of USA either. Hard to have biofuels when there is no water for crops.

Sighhhhh,

http://images.yuku.com/image/pjpeg/ab825c689c95c4237323cc3198b9263fe8b618e.pjpg
One word....algae!

Rick Willoughby

03-24-2009, 07:42 PM

...

One word....algae!

Now you're just plumbing the murky depths to sustain an implausible position.

Rick W

jehardiman

03-24-2009, 11:24 PM

Now you're just plumbing the murky depths to sustain an implausible position.

Rick W

LOL, no, now you are then one who won't accept the correct answer because it doesn't fit your narrow view/expectations.

But, you don't have to believe me....

Here is a nice explaination from an academic sourcehttp://www.unh.edu/p2/biodiesel/article_alge.html

Or here from a more hyping commerical one...http://www.oilgae.com/

Don't trust me, do the numbers yourself. I could use a liquid fuel with half the BHU's in an ICE 2/3 as efficient and still be cost, weight, volume, energy and carbon balance ahead over a battery-solar cell system of the same power. Vessel efficiency is all about weight and volume and locking youself into preconcieved ideas about what is better takes alot of tools out of the toolbox.

Rick Willoughby

03-24-2009, 11:50 PM

The electric is all eminently feasible now. Your algae gobbler is many years away I expect.

I can harvest wind and sun anywhere on the ocean right now.

Rick W

Rick Willoughby

03-25-2009, 12:35 AM

Here is a nice explaination from an academic sourcehttp://www.unh.edu/p2/biodiesel/article_alge.html

Or here from a more hyping commerical one...http://www.oilgae.com/

These fuels do not suit pleasure boating as well as solar-wind power but they certainly offer promise for heavy duty transport.

These are the sort of projects that USA should have got into seriously about 9 years ago rather than continuing to make terrorists wealthy.

Think how much self-reliance you would have on fuel production if you had started farming algae instead of going to war with the terrorists about a decade back.

Rick W

FAST FRED

03-25-2009, 06:50 AM

"Think how much self-reliance you would have on fuel production if you had started farming algae instead of going to war with the terrorists about a decade back."

Over 85% of USA avaliable energy just waiting to be drilled or dug is "Off Limits" because of an insane congress.

Now they are busy putting solar in the middle of deserts , and wind farms as well OFF LIMITS .

'Fraid we will be funding terrorists far into the future.

FF

To be energy independant all the US needs is "permission" and a shovel.

FF

jehardiman

03-25-2009, 11:47 AM

The electric is all eminently feasible now. Your algae gobbler is many years away I expect.

I can harvest wind and sun anywhere on the ocean right now.

These fuels do not suit pleasure boating as well as solar-wind power but they certainly offer promise for heavy duty transport.

Algae fuel is available today, and is a vaiable candidate for a main propulsion energy source where solar is not (for me wind power = sails not a generator). I think the difference is that I do not see electric propulsion as a viable prime mover execpt in vessels where the hotel loads dictate the over-installation of power (such a cruise ships or drill ships).

For pleasure craft IMHO, they divide into two main types: a) fast mechanical powerboats which need power dense prime movers i.e. liquid fuels and b) "slow" sailboats which use wind power and only have small auxillary propulsion and hotel loads. In case b), you could make arguments for both power dense systems to save space and weight or weight innefficient systems such a electrics and have synergy with ballast requirements.

Like many things in vessel desgn there is no one "best" answer, there are only better choices based upon what you need to accomplish.

Rick Willoughby

03-26-2009, 07:21 AM

Thanks Rick. Is this the same motor you said would have 27 Nm at 400 W? If so and it would really produce that 28 Nm at 600 W, the efficiency of the power system would be about 70%, which is more than I thought.

So it can produce almost the same torque (28 Nm) at 600 W electrical power compared to Yanmar 2YM15 (not 2YM20 as you wrote earlier), which can produce 32 Nm at 1800 rpm thus producing 6 kW of power and consuming probably about 20 kW worth of fuel.

I don't quite know how to compare these two motors. They have about the same maximum power (10 kW vs. 9 kW) and about the same maximum torque (or is this 28 Nm about the maximum?). For propeller applications you don't need a lot of torque at low rpm, thus this benefit of a electric motor (or more of its controller) is not much of use. Probably it revs up much quicker while manoeuvring, but that is really not a problem for most marine diesels.

Joakim

Jaokam
It was pointed out to me that the relationship for power would be to the power 2 rather than linear. At the bottom end the controller voltage drop tends to linearise the relationship.

I did some cycling of the batteries to liven them up this week and have now got them producing 20A before stall. With this I was able to get 15Nm with a power input of 390W. The actual test data is attached as a photo. I also measured the weight of the torque arm and included half of this in the load for torque calculation. It weighed 0.3kg and is 505mm long.

The outcome is that it requires more like 1100W to produce twice rated torque because it is not linear.

Rick W