Choice of electric motors as inboards for a catamaran

Discussion in 'Electric Propulsion' started by xellz, Jul 16, 2017.

  1. Rumars
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    Rumars Senior Member

    I think you need to research some facts. Start with storm tactics for a catamaran.
    Electrical generation is indeed that easy in theory. Any electric motor will generate electricity if moved by an external force. If that output is stable and usefull is another thing. I would not recomend trying to do regen with a series DC motor (Reihenschlussgleichstrommaschine).
    Just imagine this: you have a motor designed for an output of 10kWh at 1000rpm and 48V. Now you spin this motor at 100 rpm. It most definetly will not put out 2kWh. If you want a specific voltage and power output at a specific rpm you build a generator for it. Windmill motors are designed for low speed high power applications. You also need electronics that convert the variable input voltage to a stable output for charging batteries. That is exactly what solar controllers do. Most solar panels have an open voltage of around 70V. The controller transforms this up or down as needed. Whoever told you a 24V system is difficult on board does not know what he is talking about.

    Safety at 48V is a myth in your case. A 45kWh battery is capable of delivering 1000A at 48V. Ask your electrician what will happen to you if you recieve 1000A DC shock at 48V. Ask him what happens if you recieve only 200A wich is normal amperage for your motors.
    You select the voltage of the battery according to the motor and controller you buy. Cheapest way is to go with popular industrial battery traction applications. Wich for your power range means forklifts and floor sweepers. Second cheapest is road EV stuff from the DIY crowd.
    For regeneration the cheapest way is to use a separate system designed for the average speed range of your boat.

    A self sufficient electrical boat means an operator capable of understanding and maintaing or repairing it. Without it it will be hopeless.
     
  2. BertKu
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    BertKu Senior Member

    Yes over the 48 Volt there is a DANGER of hanging and get stuck onto a connection and die, if you are barefoot or wet.
    1. Iskip, we need to know whether you can with a, 120 Dollar Hobbyking 130 Kv motor, could rev up. i.e. if you are able to push the revolutions up to 7800 rpm you have a 3Kw generator which can charge your batteries. Those motors can run to 72 Volt i.e. 72 x 130 = 9360 rpm for 10 minutes, air cooled. I have read that people run them non-cooled at 3 kw as a motor. You may have to buy 3 very good quality bearings and as you are a mechanical engineer, it will be a piece of cake to replace the bearings. The very same motor I have running in transformer oil as cooling for some 6 years, but I am running them at 24 Volt i.e. 3120 rpm. The bearings seem to have lasted so far. It takes me 10 minutes to dis-assemble a motor and 10 minutes to re-assemble. But I have 4 of those motors and have not had to replace bearings. However people who use them at very high revolutions have complained that the bearings does not last. What I have done is with shellac ensured that the winding's are not vibrating. But for 120 dollars, you can buy a few spare. Not all hobby products are bad quality. All what I try to say is, just rev your rpm up with a rib belt or nylon gears or V belts. Have some bearings on board, some extra motors for that price and you have a winner. Bert
     
    Last edited: Aug 29, 2017
  3. BertKu
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    BertKu Senior Member

    Iskip, you have to consider modern lithium batteries. Like in other threads, where they suggest to look for second hand lithium electric car batteries and are not too heavy and you could discharge the battery without consequences up to 10 or 20% of battery power. I have bad news that HobbyKing is no longr selling the inexpensive 3 Kw (6.4 KW at 72 V - 130 KV brushless motors). I had a look and google around and could only get the 152 Dollar (+transport and import costs) Turnigy RotoMax 1.60 Brushless Outrunner Motor 231 KV - 1 Kg each with bracket and hardened shaft 10 mm. Put 3 on the same shaft and have your propeller revving up the speed of the shaft while sailing and you have 9 Kw maximum coming out of the 6 x 3 = 18 Shottky diodes of 40 Ampere each and you have at all times enough power to put some ESC's to drive those motors and your catamaran from the battery. You can select 1, 2 or all 3 motors. The same apply to select 1 or 2 or 3 alternators from the same set up. I am only a little concerned about the light shaft of only 10 mm. Mine are 12 mm and because I drive the propeller from the casing and that is 50 mm type of shaft and not from the 12 mm shaft + an extra high quality bearing. Thus I can easy produce more than the 1 to 3 KW, I only use on my boat. But you are a mechanical engineer and will come up with some solutions. But 3 motors on one shaft is not a bad solution. I have seen many speedboats driven by more than 1 or 2 brushless motors. Bert
     
  4. Rumars
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    Rumars Senior Member

    Bert how do you suppose he is going to put 10 kW continuous on a 10mm shaft? Or better yet how is he going to gear up from 100-200rpm to 11000rpm? RC motors are good value for what they are, but this application is not for them. By the way if you want a low kV RC motor they are still available. Alienpowersystems sells a copy of the popular C80100 and other low kV RC motors.

    Iskip if you still think about regeneration with the main engines then you need to do following:
    Take the selected propeller and do a tow test. You can use a dinghy and mount it on a temporary bracket alongside. Then you can record the no load shaft rpm at different speeds. Then put a load on it (electric motor or car alternator) and record the shaft rpm at load.
    After you have the actual motors spin one up with the help of the other to see what rpm you need for generating 0,5-1-2kW.
    Then all you need is a transmission with two gears. One for driving and one for generation. You will probably have to modify an existing one (replace reverse with the gear ratio needed for generation) or build a custom one from scratch. Or find such a transmission from some industrial equippment like a lathe and build a separate thrust block for the driveshaft.
    Of course this is only the mechanical part. The electrical part is separate, and you have to ask the controllers manufacturer about that.
     
  5. iskip
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    iskip Junior Member

    I think more and more, it is easyer to split the system. Standard electric engines system with fold propeller and separate 2 or 4 generaters. Maybe the generaters movable (out/in the wather), so, that I can change also the generater propeller (on sea), for faster or slower drive. Also would be possible to repair something on road.
     
    Irie likes this.
  6. BertKu
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    BertKu Senior Member

    Hai Rumars, you musn't portray me as a fool. I have all the time said 75KV and (not 11000 rpm)maybe he could consider 160 KV . It is only 75 x 48 = 3600 revolutions. Divided by 200 = 18 times revving up. That could be done. Secondly you don’t read my threads, maybe because of my English, but an out-runner supplies the torque from the casing or better said the turning part. Secondly the torque is placed on the large 80 mm bearing and that is static mounted and are with 4 strong legs mounted, not on the 12 mm or 10 mm shaft. Thirdly In my case a 50 mm worm wheel is mounted on the out-runner and has an extra bearing placed on the shaft, what I also said. Have you ever taken a large out-runner apart? Also I am talking 3 x out-runners and that is only 3 Kw per out runner. But I agree that it may look flimsy but the whole mechanical constructions has condensed to smaller motors with higher torque. That said. I fully agree with your proposal to do some tests and get some facts in how the propeller actual turns and then look for solutions. Rumars, he is an mechanical engineer, he figurers out what can and cannot be done. Bert
     
    Last edited: Aug 30, 2017
  7. BertKu
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    BertKu Senior Member

    Now you are going into the right direction. Have an out-runner geared up, with a large propeller, which you can lower or lift from the water for charging batteries. Bert
     
  8. Rumars
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    Rumars Senior Member

    Bert I don't want to make you look like a fool. I apologise and assure you that any offense was not intended. Brushless outrunners are a wonderfull thing. It is only my opinion that for this application it is easier to use a bigger form factor motor like a ebike motor and not an RC one.

    Iskip you are going in the right direction. Altough I must stress again that a full electric vessel without a fossil fuel generator has limitations that you have to accept. It won't be possible for you to motor into the wind for along time for example. And generating that much electricity from hydrogenerators might not be possible without a very high powered craft actively sailed.
     
  9. DennisRB
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    DennisRB Senior Member

    "Safety at 48V is a myth in your case. A 45kWh battery is capable of delivering 1000A at 48V. Ask your electrician what will happen to you if you recieve 1000A DC shock at 48V."

    Your electrician will say that your question is based on the totally false assumption that 48V is enough voltage to deliver 1000A through the high resistance of the human body. Even with an infinite amount of power available a 48V system is highly unlikely to cause a dangerous shock and will allow a few milliamps of current to flow at the most which would be hardly noticeable if at all. The Australian standards deem 50V DC and below "extra low voltage".

    Extra-low voltage - Wikipedia https://en.wikipedia.org/wiki/Extra-low_voltage

    So Iskip. I suggest you keep talking to your electrician and be wary of bad info. Also I suggest you read the "are electric horses really bigger" thread in this section of the forum for some realistic criticisms of the state of the commercial marine electric propulsion industry.
     
  10. BertKu
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    BertKu Senior Member

    Dennis, it is not the 1000 Amp current what kills you. It is the 20 mA which could flow through heart and the low resistance your body has when wet and special salt wet. There are people who has such a low contact resistance that even by lower than 48 Volt potential, they are in danger. By DC your muzzles contract and does not let go. While by AC it goes 120 (60Hz) or 100 (50 Hz) times through the zero voltage and then, even by very higher voltages you have a chance to survive. Not by DC. Technical it is impossible for you to receive a 1000 Ampere shock. That would mean that your body resistance must be then 48 /1000 = 0.048 Ohm. get your Ohm meter out of the draw and just measure your body resistance and divide that with the 48 Volt. If it is more than 18 mA , you must be very concerned to work with electronics or electrical.
    Bert
     
  11. BertKu
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    BertKu Senior Member

    I know and I am not offended, but not everybody has lots of money and I am impressed what those very strong little motors can do. Provided Iskip ignore the 10 mm or 12 mm shaft which is actual only for keeping the out-runners magnets not flying through the air. You need to mount the shaft to the out-runner's casing and that would be up to 60 or even 80 mm in diameter. But everything has its mechanical limit and one cannot expect from a 3 Kw RC motor more than 60 to 70 % load, if used for a continuous period, This could exceed the manufacturers specification.
    I disagree that Iskip cannot prepare himself for the future. Electric boats will be in the next 5 to 10 years with solar panels which supplies energy round the clock travelling around the world. The Chinese has already some breakthroughs, it is just the price what will be the problem. just read: Can Solar Panels Ever Work At Night? https://www.thesolarco.com/can-solar-panels-ever-work-at-night/
    Iskip, keep on dreaming, although at present you still need to add a fossil generator, like Rumars wrote Bert
     
  12. BertKu
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    BertKu Senior Member

    That is a pity Rumars. Although it comes close to the C80100 of which I have 4 of them, the KV of mine is 130 and those of Alienpowersystems is all 180KV and higher. I bought 4 of them for under the 400 Dollar. That was inexpensive. I cannot trace the one which was from Czechoslovakia and had 75KV, that was a very powerful one. Also around the 120 dollar price mark. Thanks for the website. You know Rumars, as soon a product has a "marine label" , the price is sky high. For my electrical cable I use inexpensive copper welding leads, 80 mm2 . All what I do, is to make sure that the ends are tinned and that the ends are sealed with a very good product Star brite, "liquid electrical tape" I can without much loss push 400 Ampere through them. Bert
     
  13. DennisRB
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    DennisRB Senior Member

    World regulatory bodies have deemed 50V DC to be extra low voltage and safe. Yes its not impossible to get a bad shock, but the reason they deemed it safe is that 50V DC is extremely unlikely to cause electrocution, and 100% impossible to cause 1000A to flow through a human body as Rumas said it could. He recommended asking an electrician, as a licensed electrical contractor these are my answers.
     
  14. BertKu
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    BertKu Senior Member

    Fully agree with you. For that reason the earth leakage switch is set for 20 mA. but we are talking about a person on the sea, which is wet, probably may have bare feet and due to the salt water condition. Also maybe a small wound on the hands , whereby the danger trespass level could be reached easier . At present my resistance is 84 Kilo Ohm and that represent 0,5 mA at 50 Volt. However that is in a protective environment. No, over the 48 Volt DC , or 50 Volt when the generator pushes 4 x 14.4 Volt out is for me the maximum. If somebody wants a higher Voltage, I recommend AC and then convert it back at the controller/motor to DC if necessary with special warnings labels "high voltage" Bert
     

  15. BertKu
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    BertKu Senior Member

    Dennis, I copied some of the information from a research institute.
    The let-go phenomenon for low (<600 V) contact
    A factor that makes a large difference in the injury sustained in low-voltage shocks is the inability to let go. The amount of current in the arm that will cause the hand to involuntarily grip strongly is referred to as the let-go current.7 If a person's fingers are wrapped around a large cable or energised vacuum cleaner handle, for example, most adults will be able to let go with a current of less than 6 mA. At 22 mA, more than 99% of adults will not be able to let go.

    The “total body resistance” of the person is composed of the very low (approximately 300 Ω) internal body resistance plus the 2 skin contact resistances. The skin contact resistance will usually be between 1000 and 100,000 Ω, depending on contact area, moisture, condition of the skin,

    If the current path goes through the chest, continuous tetanic contractions of the chest wall muscles can result in respiratory arrest. Dalziel,6 who made measurements on human subjects, relates that currents in excess of 18 mA stimulate the chest muscles so that breathing is stopped during the shock.

    Dennis, one can easy understand that if somebodies body resistant is at 1000 Ohm + 300 internal at 50 Volt, he is a goner. 50 /1300 = 38mA. The person's muzzles are cramped around the connection and he has no chance to survive. Special if the Voltage applied is a charging voltage of 14.4 Volt per 4 x 12 Volt system This is 57.6 Volt Even at 1000 Ohm + 1000 Ohm + 300 Ohm, he has no chance (25 mA) Bert
     
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