electic kW / diesel kW

[CDK]

Originally Posted by Mr. Know-It-All

Efficiency and torque have no direct relation. Efficiency is how well you convert energy, such as the energy in diesel to movement, or energy in batteries to movement.

Wrong!
IC engines have max efficiency at max torque. Electric motors, series wound or permanent magnet types, have zero efficiency at max torque (blocked state).

[Mr. Know-It-All]

Originally Posted by CDK

Wrong!
IC engines have max efficiency at max torque. Electric motors, series wound or permanent magnet types, have zero efficiency at max torque (blocked state).

Well, an electric motor usually have it's efficiency peak at 75 % of max RPM. Max power is usually produced at 50 % of max RPM. For IC:s, the maximum efficiency is usually in the neighborhood of 70%-80% of peak torque.

[CDK]

Please explain these figures.
At least you contradict yourself here.

[Mr. Know-It-All]

The efficiency of a motor is how well it converts input power to output power. Here is an example which I found on Google: http://www.engineering.sdsu.edu/~hev/motor.html

Assuming the motor revs up to 12000 RPM, the efficiency peak for this motor is reached at 70%, which is close to 75%. Peak power is reached at 50% of max RPM. I said torque and efficiency is not directly related. And they are not.

The power for an electric motor is (usually) not increased if you rev it beyond a certain point. That is because there will be a linear drop in torque if you rev it. Torque will decrease at the same rate RPM increases, so no net gain in power.

For an internal combustion engine, you will usually see a decrease in torque as well if you rev it high enough. Some engines may produce LOWER power for a higher RPM, but that is usually only true if you are close to maximum RPM.

Lastly, we have the efficiency for an internal combustion engine. Again, there is no direct relation, but a rule of thumb, and these are always subject to change. Here is a chart: http://ecomodder.com/imgs/geo-1L-bsf...nstruction.gif (they were hard to find) describing torque, v.s., RPM, v.s. fuel consumption for a specific engine. As you see from the chart, there is no direct relation. Clearly the peak torque is reached at 3300 RMP and the best fuel consumption is around 2700 RPM. That is, max efficiency is reached around 80 % of the RMP where peak torque is produced.

[mydauphin]

Originally Posted by mydauphin

Also remember these Murphy's law,
A diesel is lot easier to keep dry than a electric motor...
A diesel fuel tank never loses charge...
The bad weather will invariably happen when your batteries are low, and you will wish the extra speed a diesel would have given you...
A diesel engine boat will always find a buyer and home port...

I can't believe this thread is still going. But let me add there should be a big difference between Marine and Non-Marine batteries. Marines batteries should be better built and take the inevitable pounding that a car or golf cart battery might not take. Remember you still need to charge your batteries. If anyone is serious about an electric boat you need something similar to what a Hybrid car has except regeneration circuits that wouldn't work. You need high voltage systems and batteries beyond just deep-cycle.

[CDK]

Originally Posted by Mr. Know-It-All

Lastly, we have the efficiency for an internal combustion engine. Again, there is no direct relation, but a rule of thumb, and these are always subject to change. Here is a chart: http://ecomodder.com/imgs/geo-1L-bsf...nstruction.gif (they were hard to find) describing torque, v.s., RPM, v.s. fuel consumption for a specific engine. As you see from the chart, there is no direct relation. Clearly the peak torque is reached at 3300 RMP and the best fuel consumption is around 2700 RPM. That is, max efficiency is reached around 80 % of the RMP where peak torque is produced.

When discussing electric motors, the drawing board figures from a company like AC-Propulsion have little meaning; these guys love to mix peak pulse currents with no load voltages. They either do that on purpose to impress the reader with large numbers or they don't know what they are talking about. You might as well use the Enterprise's warp drive to make your point.

As for IC engines, here is a graph for a modern diesel engine as built by Steyr in Austria. The point of peak efficiency is exactly where any engineer would expect it to be in a well tuned engine.

[Mr. Know-It-All]

From the diagram in your own example, peak efficiency is at 2500 RMP. For me it looks like peak torque is reached at 3250. Maximum efficiency is at 77 % of peak torque. I think you are reading the diagram in the wrong way. Peak efficiency is were the engine consumes the LEAST fuel per unit of power produced, i.e., in your diagram at 2500 RPM.

For the electric motor, 75 % of max RPM is only a rule of thumb.

Originally Posted by CDK

When discussing electric motors, the drawing board figures from a company like AC-Propulsion have little meaning; these guys love to mix peak pulse currents with no load voltages. They either do that on purpose to impress the reader with large numbers or they don't know what they are talking about. You might as well use the Enterprise's warp drive to make your point.

As for IC engines, here is a graph for a modern diesel engine as built by Steyr in Austria. The point of peak efficiency is exactly where any engineer would expect it to be in a well tuned engine.

[Mr. Know-It-All]

Originally Posted by mydauphin

I can't believe this thread is still going. But let me add there should be a big difference between Marine and Non-Marine batteries. Marines batteries should be better built and take the inevitable pounding that a car or golf cart battery might not take. Remember you still need to charge your batteries. If anyone is serious about an electric boat you need something similar to what a Hybrid car has except regeneration circuits that wouldn't work. You need high voltage systems and batteries beyond just deep-cycle.

To hopefully kill of the thread, I will post a table containing energy densities: http://en.wikipedia.org/wiki/Energy_density

If you look in the table, diesel contain 46.2 MJ/kg. Lead acid batteries is at 0.13 MJ/kg. It it not feasible to use lead acid batteries. It never will be. If you can use 25% of the energy in diesel, it is still, by weight, 100 times the energy stored in a lead acid battery. You clearly need Li-ion batteries or better. These batteries will probably not be available, at reasonable prices, for a very long time.

[FAST FRED]

The problem with the Styer info is there is no info on weather the 2500 fuel consumption number is for max load at that rpm , or the minor power of the prop graph.

Big difference between having 80 hp for loads or 36hp.

Again a Fuel Map or BMEP graph is needed , not a prop graph.

FF

[Mr. Know-It-All]

As you say, optimize everything is not possible using this information. Since you know the torque (from the diagram) at the maximum efficiency, you know the power output. The engine will only run maximum efficient at that power output.

It is also impossible to say if 2500 RMP:s is most efficient for your particular boat. So this information alone is quite useless.

Originally Posted by FAST FRED

The problem with the Styer info is there is no info on weather the 2500 fuel consumption number is for max load at that rpm , or the minor power of the prop graph.

Big difference between having 80 hp for loads or 36hp.

Again a Fuel Map or BMEP graph is needed , not a prop graph.

FF

Anyone remembering the original question?

hy
i am looking forward for an hybrid drive for an sailboat. i have seen on many articles from electric motors, that for example an electric motor of 10 kW can easely replace an diesel up to 40 kW.

I just can't find the right answer for that... ?

i just think maybe if the electric motor is forced and overheated, otherwise i can not see how an electric motor of 10kW to give the power of an diesel of 40 kW..

The simple answer was:

the statement is false, and hybrid systems on boats are not feasible at present.

Period

[COOL Mobility]

Well that would be a surprise to the many members of the Electric Boats Forum http://groups.yahoo.com/group/electricboats/ of which many have successfully converted their stinky deisel yachts to clean electrics. These range from small yachts to 50 foot catamarans in the Bahamas, clean, green and fully tested and functional.

Established in 1998, it now has nearly 4,000 members and a wealth of information in over 15,000 postings.

Have a read and you'll find many 30' yachts with 5KW to 20 KW motors that are now electric powered. Some use the numerous commercial kits, other home built but real functioning examples, with pictures and performance data. If they were not feasible, why are people with full electric and hybrid (using gensets) yachts happy?

Also how are the various manufacturers of commercial systems surviving, let alone thriving?

Lead Acid batteries are the norm, but some have invested thousands in LiFePO4 battery packs.

Read their stories, look at photos and videos and decide for yourselves.

That is all nice.

And all worthless.

None of these boats have a comparable performance to IC engines.

But it is mute to discuss Hybrid systems again and again.

There are the believers which simply ignore the fact that it is impossible to store enough energy on board, and the professionals which are not as blind.

Hybrid propulsion does not exist on boats capable of coastal cruising. period

Regards
Richard

Originally Posted by COOL Mobility

Well that would be a surprise to the many members of the Electric Boats Forum http://groups.yahoo.com/group/electricboats/ of which many have successfully converted their stinky deisel yachts to clean electrics. These range from small yachts to 50 foot catamarans in the Bahamas, clean, green and fully tested and functional.

Established in 1998, it now has nearly 4,000 members and a wealth of information in over 15,000 postings.

Have a read and you'll find many 30' yachts with 5KW to 20 KW motors that are now electric powered. Some use the numerous commercial kits, other home built but real functioning examples, with pictures and performance data. If they were not feasible, why are people with full electric and hybrid (using gensets) yachts happy?

Also how are the various manufacturers of commercial systems surviving, let alone thriving?

Lead Acid batteries are the norm, but some have invested thousands in LiFePO4 battery packs.

Read their stories, look at photos and videos and decide for yourselves.

[mydauphin]

Dude even electric bow thruster are more unreliable than hydraulic. There is a difference between boutique boats and crossing open bodies of water and surviving the inevitably little storm.

[marshmat]

Has this thread jumped the shark yet?

What started as a straightforward engineering question with a straightforward technical answer has turned into name-calling and accusations of stupidity and ignorance. Please, guys, we're all above this sort of bickering.

It was established within the first six posts that electric drive can work if well engineered, that it has certain limitations that must be understood, that it's ideal for some applications and useless for others, and that a kilowatt is a kilowatt regardless of what type of device is connected to the shaft.

Let's stick to logical, technical discussion on the thread and take the bickering to private messages. OK?