Diesel/Electric Propulsion System Design - Have your say!

Discussion in 'Hybrid' started by CatBuilder, Sep 11, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    Gotcha. Now I understand what you were thinking of. I was hoping that my large, super huge generator (DC generator?) would charge up some batteries that could run house loads through an inverter. My thinking was this might be more efficient because the huge generator could stuff a lot of power into the main battery bank (house/propulsion), then I could simply tap into this stored energy to run house loads. Or... if I draw it down too far, the huge generator kicks in and tops them off quickly. I believe this is more efficient, but I have not finished my homework yet. One drawback could be weight though. Those might be some heavy batteries in my plan, while a smaller generator could weigh less with your plan.

    Your plan makes a lot of sense.

    I did also find out why the HP is different from diesel to electric motors. It's because the diesel engines are rated at brake HP, the maximum HP they deliver, while the electric motors are rated at shaft HP. The shaft HP is what you use to do prop calculations anyway, so that is why you can get away with "less HP" on an electric motor. It's just a different measure of HP, not actually less.
     
  2. CatBuilder

    CatBuilder Previous Member

    You may be missing something: The 10KW electric engine is equivalent to about a 20KW diesel due to different HP rating schemes used by both. (see above post to Teddy)

    EDIT: Here is a link from the link to emotion propulsion explaining the different HP ratings...

    http://www.electricmarinepropulsion.org/Pages/Technology_hptorque.html
     
  3. CatBuilder

    CatBuilder Previous Member

    To me, the one big variable here I haven't figured out is cash. That may be the diesel/electric killer, which will leave me with outboards as the default solution.

    I am thinking it will cost me less doing a diesel/electric, but I'm not 100% sure. I still need to add up all the parts to see.

    See, I think most people reading this look at the proposal from their own boat. That is, they have a boat and it's full of stuff. I have absolutely nothing inside my boat. In fact, I barely have a boat at all right now. :D

    So, by going diesel/electric, my thinking is that even if it's more expensive, how much more expensive will it be when you realize huge gains such as:

    *Having a real dishwasher
    *Cooking with electricity (no propane system or weight from it)
    *Buying $50 electric space heaters instead of installing complicated, heavy hydronic systems or Espar type diesel heaters (those cost a fortune for a cat this size)
    *Running air conditioners at anchor (more charters)

    Look at it this way: I still have to buy an inverter, a charger, a huge house bank, a generator, outboards, solar panels, wiring, Morse controls or similar for outboards, etc... etc...

    It seems on a brand new boat, this might just be a way to save money AND weight. Maybe. Like I said... still have to do all the numbers (and I'll post the results in this thread), but just from a very basic overview, this might be cheaper, more efficient and weigh less for a boat that has large house demands.

    I want to stress again, I'm not looking at overpriced systems, just a large generator, a couple electric motors with controllers, a batter bank and an inverter. I need half that stuff anyway for charters. Why not put it to work doing something more productive?
     
  4. michael pierzga
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    michael pierzga Senior Member

  5. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    E-motor salesmen have bad rep in hugely exaggerating the hp to hp differences.
    The article you linked to largely fell into the category of marketing crap.

    Yes e-controller works as transmission and thus huge torques can be pulled at low rpm. Show me a 2500rpm 10kw prop in e-system. And then show me 10kw (rated constant output as any marine diesel is) 2500 rpm motor that can't turn that same prop at 1500rpm.

    Certainly diesel would benefit from variable pitch for number of reasons. In many way this would be similar to speed controller of e-motor.

    10kw at the shaft is 10kw no matter what the source is. And kw or hp is much better unit than torque as torque# without rpm# is irrelevant. (and as torque # with rpm info is essentially power rating...)
     
  6. CatBuilder

    CatBuilder Previous Member

    Yep. That was a little bit on the marketing BS side, but there is a difference when someone specifies a 30HP diesel engine to power a craft and what you'd put in for an electric motor. One is rated at the shaft (electric) and the other is rated peak HP at max RPM using brake method (diesel). You use a 12KW or so electric motor to substitute for a 30HP (20KW) diesel engine. That's just how it's done. Different rating systems.

    The diesel engine rating system (Peak HP at max RPM) is a bunch of marketing BS too. :)

    They should rate that HP at the shaft as well.
     
  7. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    Just watching the owner of Harmony show off his system makes me cringe at the complexity, and then at the end to see the credits with all the suppliers and having to depend on all that stuff playing nice with each other, hmm.

    I don't remember why you nixed the outboards but there are ways to hide them while not using them, and I don't think weight wise and space wise you could beat a pair of outboards and something like an 8 kw genset.

    I saw a cat once where the twin outboards were on a center mounted sled and when raised they tucked up into the backrest of a seat across the back of the cockpit. Very clean, you could only see the legs hanging down.

    And a comment about power vs drag. I know of many a boat, monohull and multihull both, where the owners have opted for a fixed 3 blade vs the folding or 2 blade they had to make the boat power better. I can't remember anyone going the other way.

    Good luck, Steve
     
  8. pdwiley
    Joined: Jun 2008
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    pdwiley Senior Member

    Some engineer friends and I kicked around the idea of using a 3 phase motor, VFD and 3 phase gen set to do something similar. Skip the batteries because the amount needed to drive the motor was unfeasible.

    Advantage of the motor/VFD is you can get industrial units easily, the VFD gives you speed control plus braking, reverse etc. Pick a 6 pole motor and you've got around 1000 rpm@50 Hz, the VFD can go from 20Hz to 120Hz without dramas so you have speed control (I've got them on my machine tools).

    You can get VFD's that will take single phase in & give you 3 phase out but I don't think they go up to the 10kW size whereas the 3 phase units certainly do.

    We decided that it was a feasible system. I shelved the idea at the time for reasons which now escape me (probably to do with electric anything and salt water) but as I also have an empty hull perhaps I might have another look.

    PDW
     
  9. CatBuilder

    CatBuilder Previous Member

    That's exactly the idea, Steve. I want 3 blade fixed props, but I want them out of the water when I'm sailing. I can't think of any other way to do that aside from electric.

    Were those outboards you are talking about that tucked up into the backrest actually *under* the bridgedeck then? What would happen to them, as they floated on the sleds and the bridgedeck bottomed out? Wouldn't they slam up into the boat in that case? I had been considering a similar mount, but was figuring I'd have to have a pivot arm on the very aft part of the crossbeam to allow the sleds to ride up higher than the bridgedeck in the event of the deck belly flopping.

    The outboards and the geneset are definitely the fall back plan if this electric stuff doesn't work out. They are the "safety." The only issue I'm having with the outboards, other than gasoline use, is that they tend to overheat in wells and tend to go underwater when mounted outside. The exception being the sled, of course, but that thing has to go way back aft of the aft beam in order to keep the outboards from slamming into the boat in bad conditions.

    I agree with the complexity being a little stupid on that video. Too many switches. I would be looking at a much more basic, simplified, less redundant setup. Generator, electric motors, motor controllers (like Morse), inverter to get house power from the system and a battery bank. All regular stuff we all use every day, except the electric motors.

    The outboard thing still hasn't lost all hope, but I can't seem to find an acceptable way to mount them where they won't overheat or suck in water, or slam the bridgedeck.
     
  10. CatBuilder

    CatBuilder Previous Member

    Yes, that's exactly what I was looking it. I did see some PWM controllers out there as well that seemed to make some sense, but of course, that's a battery thing.

    Using 3 phase, 240V VFD's and the right motors to go with seems to be something very workable. I envision the batteries mostly for the house and a true diesel/electric (generator always on) when motoring. This could work well with a 3 phase 240V system. Then, you just get a good charger to work with the 3 phase 240 and charge up a monster house bank for the large house loads I have. If you use similar batteries to electric cars for the house bank, you can charge them up at C/4, I believe. Not bad... and with a huge generator like that, you have no problem charging them up quickly.

    That was the basic idea I had been looking at recently. Again, you'd need the same house bank, a generator, charger, inverter, etc.. anyway, so my logic is, "why not make them do something more?"

    Thanks for the post. Very interesting.
     
  11. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    There's allways substantial loss charging and discharging batteries among other issues.. Take a good look at my book recommendation, you won't regret it ;)
     
  12. pistnbroke
    Joined: Jan 2009
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    pistnbroke I try

    you will not charge your batteries at more than 25A reducing per 100AH and should not go below 50 % discharge or battery life much reduced ...do your research on www.canalworld.net it is not as easy as you think.
     
  13. CatBuilder

    CatBuilder Previous Member

    That's exactly what I said. New batteries are can be charged at c/4.

    I'm not a *****. I understand electrical systems inside and out .

    Just looking to do electric propulsion.

     
  14. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Cat,

    I would point out that traction batteries can be regularly discharged down to 20%, though they are much heavier for the AH. I haven't done the calculations to see if it is better/lb or by volume however.
     

  15. masalai
    Joined: Oct 2007
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    masalai masalai

    Hi CatBuilder,
    I baulked at electrics for drive motors on my Oram39C and on the bigger versions (44C) one tossed out the useless E-motor 'pods' as they would not honour the warranty or respond to emails/phone-calls for support, He eventually went for a 60hp outboard midships in a pod slung under the bridgedeck... Another 44C has a pair of 4KW Torqeedo outboards and should be back soon to wait out the Australian cyclone season... I will be keen to see how he is doing...
     
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