Choice of electric motors as inboards for a catamaran.

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

  1. xellz
    Joined: Jul 2017
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    xellz Junior Member

    Currently researching possibility to build a fully electric catamaran and so far for my purpose and how it will be used, looks like it's a viable solution.

    Now i'm trying to find my way through rather big choice of options for motors. Since i don't have experience i most likely will miss something that can add large extra cost in the making.

    What i'm looking for are 2 electric motors in 8-10kw range. Will be cheap motors still cheap in the end or complete systems like Bellmarine make more sense? For example Lynch motors are considerably cheaper and also lighter, saw an electric conversion on youtube using Lynch motors. But what are major differences between brushed and brushless motors?

    Also recommendation for motors or links on this matter are welcome.
     
  2. BertKu
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    BertKu Senior Member

    Xellz, A brushed motor has an extra coil and uses energy via the brushes to create a magnetic field, the main coil is switched on via the brush making only contact with a particular coil which together with the other coil creates a torque when current flows. A brush less motor has magnets instead and no brushes. A electronic control system creates a turning field, which you don't need with a brushed DC motor. Advantage brushless motors only has 2 moving items, two bearings. High starting torque. Disadvantage, need electronic control system. Brushed motors, disadvantage torque is slowly build up, when the motor starts turning. Starting current can be up to 10 times the normal current. need brushes maintenance. Bert
     
  3. BertKu
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    BertKu Senior Member

    I forgot to mention. Brushless motors normally are smaller and lighter with the same power. You could look at Mars motors in China. I have their 4 Kw continious brushed motor here in my cupboard. Or look at this one for 850 dollar. . ME1202 Brushless Motor 24-72V, 6500 RPM, 10 kW cont, 24 kW pk, ATV / Golf Car / NEV Mount http://www.electricmotorsport.com/me1202-brushless-motor-24-72v-5000rpm-10-kw-cont-24-kw-pk.html Bert
     
  4. xellz
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    xellz Junior Member

    Do i understand right about motor efficiency rating? In link you gave rated efficiency is 84% and bellmarine for example are rated at 91-92% depends on model. So to move boat same distance i would use ~7-8% more electricity with less efficient motor?
     
  5. BertKu
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    BertKu Senior Member

    Hi xellz, my apology, but we have 12 hours or maybe more time difference and I could not reply in the morning. Yes, you are right. it depends whether it is a brushed motor or a bruhsles motor. I also am surprised that they quote 84 at the below and 92% at the top for a brushless motor. Maybe because of the cooling of the motor which is by the blower and it reduces the efficiency, maybe they included the controller in the overall efficiency. I cant answer that question. However, may I guide you on the right track.
    1) excellent decision on the catamaran choice.
    2) will you have a mast yes/no
    3) if yes, will you have a small sail yes/no
    4) picture yourself in the cockpit. Ask yourself the question, how do I switch the motors on and off and how do I do the speed control.
    5) Where do I place the batteries. IF my boat will be an AC 380Volt boat, no problem where the battery sits and my cabling does not consume to much energy. Control is with contacters, on/off and the control is with triacs, similar as a light dimmer, either with remote control or with a servo motor controlled from the cockpit. The batteries can be on a convenient place, with close by the converter DC to AC from household appliances. reasonable cheap and mass produced and a wide choice. But regeneration is problematic.
    However If I have a 36 or 48 or 72 Volt DC motor, my cabling has to be massive thick copper, otherwise I loose efficiency. or my batteries must be on top of the motor.
    6) Do I make a stainless steel container and place my motor in transformer oil for cooling and let the seawater cool the oil. ( I had that idea 6 years ago, it is very effective and I see that OceanVolt now also have copied this idea. In my case I made my own controller, wrote my own software, made my printed circuit boards, designed and populated my own pc boards and mount the motors in oil and made seal housings for them, place sensors in the motor. I even made my own propellers. I would not recommend this for you, thus you have to think about it where it is all coming from and how do they interact with everything else, motor etc. )

    7) Is it not better to save some money more and buy 2 OceanVolt 15 KW outboard system or from Torqeedo, with everything already matching and regeneration of energy when sailing with a sail. I think you are better off with 2 outboards than 2 inboard motors. If you beach with the boat, catamaran, the outboards you just lift up.

    8) My apology, but in the middle of my reply, the system had some funny hiccups and I lost half of my reply to you. If I think about something what was lost, I will post that later on. Yes, one more point. Very clever, but they work with 125 Ampere AC which is in the controller converted to DC. It is much saver to have AC on board than DC for voltage greater than 48Volt. This may explain the 84% efficiency.
    Bert

    Bert
     
    Last edited: Jul 17, 2017
  6. BertKu
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    BertKu Senior Member

    Unfortunately I hade some strange hiccups with the computer connection to boatdesign and lost half of my info. Your reply is thus only a half reply. Please go to your thread and read my full reply.
     
  7. xellz
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    xellz Junior Member

    I got rather detailed answer from Woods Design and more or less everything fits my expectations, expect that i better forget about 9-10knots, most inefficient speed for Skoota 28 and Jazz 30, It's either 6-7 or 12+ knots. 6-7knot cruising requires really little energy, but i do want to have an option for higher speed for short period of time, so motors have to be in 10-14kW range.

    No sail, no regeneration, for my use it doesn't make much sense. Currently i'm making a list of options, when i can understand myself to some extent what i'm trying to achieve, i'll contact company or someone who could complete necessary calculations and work. Make final adjustment to cost, weight, output etc and start preparing for boat building.

    Battery location, if possible somewhere to help with boat stability. I can't really tell now how far away from engine i could move them.

    From your answers and also efficiency of dedicated motors for marine applications make more sense. Especially since they also usually come with controllers and all kind of converters that would be needed. I would love to have more precise control over output. I also want to have an ability to plug in additional source of energy without too much trouble. Diesel generator, that could be easily removed (storage space and small crane near boat docking) and at some point solar panels.

    What about permanent magnet brushless motors? One of options i saw was Marine | tema.hr http://www.tema.hr/marine/ and they promote 95% efficiency rating, pricing is unknown.

    As for outboards, while it's most simplest solution, it will be my last choice. First of all, they can get in the way of fishing, a bit of concern for bad weather and acid rain, that is fairly common here, due to active volcano (lowest danger level, but constantly degassing). Then there is noise issue, electric motors sure are more quiet, but inboard will still have large advantage. And it's one of biggest reasons, why i'm going with electric.
     
  8. BertKu
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    BertKu Senior Member

    O.K.
    O.K. Xellz, I agree with you concerning inboards. I really like the idea of AC in and then converting to DC at the motor itself. I control my motor with a 5 volt system (my microprocessors are running at 5 volt. ) The control works from 1 rpm to + 3000 rpm. 0.1 Volt to 4.9 Volt. The cable is a screened cable to avoid external interference and 5 meters long. I assume other manufacturers has something similar. I control with my N Mosfets with opto couplers, thus I can go inexpensive to 100 or 200 Volt DC if I want., but really like to transmit AC to the controllers and have the controllers on top of the motor.
    Well, any question we will try to answer. Yes a small diesel generator of 5 KW will do no harm. With petrol you have all kind of safety issues. Bert
     
  9. BertKu
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    BertKu Senior Member

    Hi Zellx, you have two type of controllers with a permanent magnet brushless motor. (all modern brushless motors have permanent magnets also the modern DC motor). The quoted efficiency is probably without the loss in the controller and cooling needed for a large motor/

    a) with sensors build into the motor and the sensor senses the position of the coils versus magnet. Normally 3 sensors. I have placed 3 sensors in my motors as I am not experienced enough and not have the equipment to do a controller which senses the back voltage. Advantage from sensored controller and brushless motor, it runs from 1 rpm to maximum.

    b) a controller which senses the back voltage when switching has no sensors but has a small software routine which kick start the motor. The routine creates a artificial rotating switching cycle whereby the rotor starts turning, because the coils get switched not by the position of the sensors but by a fixed rotating sequence. Thus it always has a starting speed before you can turn the speed up. The disadvantage is that such a controller is matched to the type of motor, while a sensored controller can be adapted to most type of motors and manufacturers. Moral of the story, don't buy this type of controller from the one manufacturer and the motor from another. With sensors you can do that. Bert
     
  10. Rumars
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    Rumars Senior Member

    Xellz I think first you need to decide how to mount the motors. You inboard options are shaft drive, saildrive and Z drive. Shaft and saildrive will need rudders, Z-drive not. Then you have the two outboard options, conventional and pod drive. Pod drive can be with or without rudders. Pod drive is what Bert explained, the motors are in the water. Self made is possible but complicated and limits you to long skinny motors. For all the rest any option is ok. The motors can be water- or aircooled, but they will need cooling. PM motors are lighter for the same power. Brushed or brushless, PM or conventional, is not important. What is important is that the motor has a continuous power rating in the desired range with the specified cooling. There are good ready made controllers for all motor options, that is not a problem.
    See what is available to you locally. It makes no sense importing something when there is a local product and support. As I said earlier start at the nearest forklift place for information.
     
  11. Caroute Motor
    Joined: Jun 2016
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    Caroute Motor Junior Member

    brushless motors have higher efficiency, can help to save energy. Another way to explain is for same shaft output power, brushless motor need less input power than brush motor.
     
  12. gregzw
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    gregzw New Member

    I am interested in electric propulsion systems for a pleasure craft in the 3o-50' range. I am driving my second Tesla and am sold on electric propulsion. The motor I believe are the most efficient available are from UQM Technologies. a link on their site: UQM Technologies - Products - Propulsion - Marine https://www.uqm.com/products/propulsion/marine/default.aspx. There is a company that has an electric trawler (35') and the specs/brochure ca be found at this link: https://www.yachtopolis.com/pdf/63516.pdf. The best value for battery systems may be the new powerwall from Tesla but I don't know what if any modifications would need to be made for marine applications. (My first Tesla went thru a flood without incident). Here is a link on the powerwall: Tesla Powerwall https://www.tesla.com/powerwall. a 14KWH runs about $6k. If you would like to discus you can reach me here: gregz@signsmart.com
     
  13. Ben Landgren
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    Location: Newcastle Upon Tyne

    Ben Landgren Junior Member

  14. xellz
    Joined: Jul 2017
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    xellz Junior Member

    Thanks everyone for answers, indeed, seems i tried to make it more complicated than actually needed. First i'll look for local brushless motors suppliers, i got too sidetracked by all "marine grade" marketing stuff :) But all the info i got through is helpful to make it work how i want in the end.
     

  15. BertKu
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    BertKu Senior Member

    No Xellz, you first sit down and decide what kind of batteries you can afford and how big they will be and at what weight. As soon you know that and you have a plan for a catamaran, you decide what the influence will be due to the weight of the batteries. If you have selected Lithium batteries, you have no real weight problem. As soon you have decided to do 2 separate systems, i.e. batteries, motor, propeller shaft and propeller in the one and a separate system in the other one. Or to have only 2 motors, but one battery bank. (Not recommended and is not advisable on the sea, only inland rivers and lakes)
    As soon you have made your mind up with the above, then you must make your mind up, what kind of generators you can get. i.e. 110 Volt AC output, or 48 Volt DC output or 230 V AC output, or whatever, then you can start selecting your motors. I recommend 2 systems, not one. Provided you can run both parallel when needed. Not before. Motors are the last worries, apart of your "how you will be affording it".

    I had a look at Marine | tema.hr http://www.tema.hr/marine/ and like what I have read and what is offered. Good choice. Bert
     
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