Misleading Magazine Article; Electric Propulsion

[kloudie1]

I was amazed at how misleading an article published in a major sail magazine is, concerning electric propulsion.. Article is in the January issue.
article states that the 7 kilowatt electric motor is equivalent to "..about 20 horsepower.." One kilowatt is 1.34 horsepower so 7 kw is 9.38 horsepower, not even close to 20.. The motor supplier limits the power to the motor to 160 amperes maximum so that is still around 10 horsepower; nowhere near 20.
The author states that he can expect to motor for approximately 8 hours without stressing the batteries. He is using a 185 ampere hour, 48 volt battery made of 4, 12 volt AGM batteries.. for conversation, say he can tolerate 70% discharge so that gives him (185 X .7) 130 ampere hours to mess with.. For 8 hours run time, he'd have to draw (130/8) 16 amperes every hour.. at 48 volts that is 777 watts or 1 horsepower to power his boat, a 30 ft,Irwin Citation. My bet is that he'd need more than 1 horsepower to drive that boat .. He also states that he probably could run a little under 4 hours at full throttle .. At full throttle that propulsion system would draw in the neighborhood of 150 amperes to supply 7 KW.. with a 185 ampere hour battery supply, the run time to a dead discharge would be approximately 1 hour, not close to 4.
I am disappointed that a major magazine would publish an article that is blatantly wrong and very misleading.
I am not campaigning against electric power; I am campaigning against blatant misleading articles.. Rant temporarily over..

 

[Stu Jackson]

+1

Truly embarrassing.

Will be interesting to note if they publish any Letters to the Editor on that one.

 

[Chief RA]

This type of hype concerns me as there are numerous people not versed in electrics that tend to fall for this. Using an electrical propulsion system requires a staggering amount of electrical source! Chief

 

[justsomeguy]

Whom do I have to pay to read this article?

 

[Joe]

Kloudie, did you send this comment to the magazine's editor? You should.

 

[Paul Mermelstein]

Kloudie, did you send this comment to the magazine's editor? You should.

I second that motion.

 

[kloudie1]

I just did.. didn't have the time to do that yesterday..

 

[Maine Sail]

The only thing I can say to help you keep everyone around you honest in any endeavor into electric conversions is to:

Trust Ohm's Law - Many here and elsewhere (magazines, resellers etc.) try to re-write it, but as of yet no one has been successful.. A useful calculation is below...

Convert Watts to Amps at fixed voltage:

Watts ÷ Volts = Amps

eg:
5000W ÷ 12V = 417A
5000W ÷ 48V = 104A
5000W ÷ 72V = 69A


Never Forget Peukert - When dealing with high load applications such as e-boats one simply can not ignore Peukerts Law when dealing with lead acid batteries. You will find very, very, very, very few e/conversion companies who are up front and honest about this point...

Don't Ignore DOD and Cycle Life - The depth at which you discharge to will impact how many cycles you get out of the propulsion bank. Get this wrong and batteries can become far more costly than diesel maintenance and fuel combined. 50% is still the recommended max DOD regardless of how you are using the bank. Many companies try to use calcualtions that use 100% of the capacity!

Don't ignore Coulombic Efficiency - Lead acid batteries require that more energy be put back in than you took out. This charge efficiency also changes as batteries age...

Don't Forget Changes In Capacity Over Time - A 100Ah lead acid battery is only a 100Ah battery when used at and loaded at 5A at 80F, when new or just broken in.... Every other load & temp range either above or below the 20 hour rate at 80F results in CHANGES the batteries rated Ah capacity. Cycle life and DOD also impact & change usable Ah capacity.. Anyone telling you otherwise is really not qualified to be doing so.

Consider Newer Battery Technologies - LiFePO4 cells have minimal Peukert's corrections but they are still not a Peukert of 1.0..... A 100Ah battery with a 1.0 Peukert would provide 100Ah at a 300A load and conversely 100Ah at a 0.5A load. This simply does not exist in the real world but LiFePO4 comes close and can deliver many thousands of cycles even at 80% DOD..... The reality is that a LiFePO4 bank might provide about 90Ah at 300A and 110Ah at 0.5A.. Minimal changes with high loads. Electric propulsion is HIGH LOAD USE....

Do that with a flooded lead acid 100Ah battery:

100Ah Battery 300A Load = 33Ah
100Ah Battery 0.5A Load = More than 100Ah

*Learn the MATH and DO NOT trust others to do it for you

*Define your BOX/REALISTIC USE

*Be HONEST with yourself and your MATH

If you do those three things you will have a good outcome... Ignore the MATH, don't be HONEST with yourself, and don't clearly DEFINE your USE and you will not be as happy as you should be...

Here in Maine with 10-20' tides, tidal rivers with strong currents, the vast majority of vessels residing on moorings, light summer winds and cold water that reduces usable battery capacity, e-conversions fit into a pretty small box. Still there are boxes where they fit into, even in Maine.

The point I think that needs to be considered is to clearly define your box, your real use and your expectations. Once you've defined that use Ohm's Law/math to see if what you want to do can work.. In many instances it can and in others it simply becomes a fairytale.

I have consulted with numerous customers over the last 4 years who wanted to do an e-conversion. Every single one of them had been rather grossly mislead on the realities, math and capabilities of e-propulsion. This I find extremely frustrating!!

Two did convert but they had boxes that were perfect fits for an e-conversion...
I find many in the e-propulsion world, whether re-sellers or buyers, fall into two categories:

Dreamers - These folks operate on the fantasy of "clean quiet e-power", and believe in their hearts, not their brains, that this will work, because they want it to..

Realists - These folks come to me with a realistic view of an e-conversion and understand the math involved. They have done the mathematical homework before even reaching out to me. They don't have unrealistic fairly tale expectations and have clearly defined why and how they plan on using the boat. They use their BRAINS not their HEARTS......

I suspect this author falls into the Dreamers category not the Realists category....


What magazine is this in?

 

[RichH]

So Maine .... I take it you dont own an all electric automobile?

Those 'numbers' dont work out either.

 

[Maine Sail]

So Maine .... I take it you dont own an all electric automobile?

Those 'numbers' dont work out either.

I drive my hybrid 99% of the time, and a pick-up truck 1%.

The numbers on a boat can be made to work but no one I've met is willing to pay for it for any sort of real usable range.

The Lagoon 420 we just chartered was one of the much applauded hybrid fleet. It was a MISERABLE FAILURE. It was soooo bad, Lagoon took it back and converted it to diesel.

Apparently the engineers who told the owners they could do 4 hours before the 22kW hybrid genset would kick in never heard of Peukert, the effect of heat on batteries etc.... According to the owner of the charter company the boat could barely make it to the outer Road Harbor buoy before the 22kW genset kicked in. That genset, which is still installed, is TWICE as loud as both Yanmars at full cruise!!!! 22 THOUSAND WATTS is a LOT of diesel and genset. Remember this was a factory engineered (by the French) hybrid boat that was supposed to do 4+ hours on electric and it barely made 30 minutes and only got worse as the batteries aged in the Caribbean heat..

My neighbor has the Mac Daddy MuskMobile, (as he calls it) we chat cars quite a bit, and no the numbers quoted for range don't line up, especially when it is cold. Yes the batteries have heaters and coolers but when cold, we're in Maine, they don't heat up instantaneously. Hell he can barely make it to his dealer on a charge and this is a car that is supposed to go 265 miles and his dealer is about 130 miles...... It is a very beautiful car, Gawd awfully expensive, but as he fully admits it has limited mobility compared to the claims. He drives his SUV to the ski condo for a reason....

A friend has the Leaf and the stated range on that has also been a fallacy for him. For his use the Leaf works, he drives 12 miles per day, he fits into that box, but he takes his wife's car for any real driving. Still, he loves it....

Again, EP can work but you need to be realistic and use real math not fantasy math as is done so often..

If I had a day sailor, tied to a dock after each use, I would go EP in a heart beat, I like the technology, but it would be LiFePO4 batteries never lead acid....

 

[Daveinet]

One of the big problems with comparing electric to gas or diesel is that most gas and diesel are not direct drive. So there is some loss in the gearing. So to equate a power equation to actual usable output is not accurate. Most electric drives are specified in lbs of thrust, which I would imagine is the basis for the magazine article. That doesn't work either, because an electric motor develops the greatest amount of torque under locked rotor. The faster the motor turns, the less output thrust it has.

I wish electric propulsion would show a thrust curve, so one could accurately asses its usefulness. So for every speed, show the amount of thrust, rather than just peak thrust. Some day I want to tow my boat behind my brothers jetski and test the amount of thrust necessary for any given speed. Put a load cell inline with the tow rope and try to average the load. That would give me some sort of ballpark of the required effort to move the boat. I've wanted to convert to a trolling motor to replace my outboard. I figured I could have a low power generator as back up. Most of the sailing I do is pretty close to port, so the chances of needing backup power on any given days sail is slim.

Comparing usable HP from electric to gas is not one to one relationship of HP, but most write ups I've seen are way off. Most articles state that 30 to 40 lbs of thrust is equivalent to my 4 HP outboard, however I believe from seeing actual performance reports, its more like 80 to 100 lbs of thrust.

 

[Chief RA]

Daveinet: In your case you might be able to cope with an electric power outboard. If it were me I would still carry the 4hp gas unit in case of an emergency condition. I owned a long shaft 4hp Evinrude Yachttwin years ago and it was light, strong and overall great motor. Happy Holidays! Chief

 

[kloudie1]

Maine.. this is Sail magazine.. I would have expected them to run that by Nigel Calder since he has done a lot of testing of electric/hybrid propulsion..
Daveinet;
Yes, outlet losses are as you characterize but on the electric side, inlet losses are the killer.. as Maine says, Peukert is a biggie and they are totally ignoring the cabling loss and the motor controller loss .. cabling and controller losses are in the same ballpark as gearing loss .. This motor system also has a toothed belt reduction drive which has losses..why i chose to not comment on them.. inlet side affects the range but not the shaft output.. but very much limits how much horsepower you can develop. I truly believe that for some folks, electric propulsion is the correct answer, but it is a small box that has to be fit into..

 

[kloudie1]

More quick 'thumbnail" calculations.. My Yanmar 3GMF makes about 8.21 KW to the prop shaft at a cruise of 2800 RPM, using typical propeller input HP curves from the Yanmar manual. At that RPM it burns 1/2 gallon per hour and the boat has a 20 gallon tank.. so it will run about 40 hours on a tank full.. to duplicate that electrically using a 48 volt motor would require 8210watts/48V=171 amperes for 40 hours is 6840 ampere hours. If ya try to do that with golf cart batteries, it would require 6840/225=30.4 cells and since each cell is 8, 6V batteries, 248 golf cart batteries would be needed (double that if battery life and Peukert is considered).. Not practical to duplicate the performance of a simple old diesel system.. Granted, it is not often when I have to motor that much. But I can if I have to..
More appropriate might be to note that while cruising, a motoring run of 4 hours during a day would not be unusual.. to duplicate that, using a 60% discharge to let the batteries live a little would require 684 ampere hours which would require 50 golf cart batts.. Then they'd have to be recharged! again, say ya have a 300 watt solar panel installation as your means of replenishment.. For the 4 hour run, you'd have to replace that 684 ampere hours at a rate of 6.25 amperes of full panel capacity.. 109 hours or assuming full capacity for about 60% of a typical 12 hour day, 363 hours requiring about 15 days! (of not running lights or stereo or autpilot ) Not practical
Again, I am not anti-electric, I am against misleading information.

 

[Benny17441]

The calculations clearly tells us that electric power at this time does not work. It just confirms my other indicators that pointed me to the same conclusion; 1) electric power is too bulky and heavy. 2) It takes hours to re-charge a spent bank while minutes to fill up with diesel. 3) It is hard to precisely calculate fuel needs on an outing, limited range complicates logistics. 4) Costly conversion, would have to throw out a working diesel engine to install an E-motor, batteries and control unit. Nuclear power anyone?

 

[kloudie1]

I think that when fuel cells become more common and affordable, that will be the answer.. they run on hydrogen or propane or LNG but at very high efficiencies compared to either batteries or internal combustion. That is what I believe will make the quiet of an electric propulsion system feasible.. here is a link for some interesting reading. They can provide a lot of heat as a by product so adsorption refrigeration and hot water could be part of the system.
http://energy.gov/eere/fuelcells/accomplishments-and-progress