Electric motors and generator on board

Discussion in 'Electric Propulsion' started by Pengyou, Apr 25, 2019.

  1. Pengyou
    Joined: Feb 2018
    Posts: 7
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    Location: North Dakota

    Pengyou Junior Member

    Has anyone looked at the feasibility of installing electric motors on a boat as well as using an onboard generator with some battery reserve to power it? Possible benefit - better weight distribution on the boat (generators can be placed anywhere), improved maneuverability (use 4 smaller motors with propellers instead of 2)...any thoughts?
     
  2. BlueBell
    Joined: May 2017
    Posts: 746
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    If you like to spend money, inefficiency and love heavy boats then it's a wonderful idea.
    Ya, it's been looked at before, do a search on this forum and you'll see.
     
  3. Dejay
    Joined: Mar 2018
    Posts: 324
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    Location: Europe

    Dejay Senior Newbie

    I'm interested in this for a (mostly) solar powered boat as a backup / range extender. I've read that there are potential advantages for efficiencies for "diesel electric hybrid" somewhere, but from what I've learned in the case where you optimize your engine RPM, propeller and gearing for a specific cruising speed there is no advantage at all to this.
     
  4. The Q
    Joined: Feb 2014
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    Location: Norfolk, UK

    The Q Senior Member

    I have almost that on my 27ft Motor boat, a 4kw Diesel generator, 500Amp hours of lead acid batteries and a 10Kw Electric motor (3 phase). 4 solar panels on the roof.

    The maximum speed limit on the river is 6mph, and much of it 4mph. Max hull speed is acheived long before full power is required.
    I use just battery power from the moorings to the clubhouse across the river and back, or up to the nearest broad (lake) and back, just over half a mile away. The solar panels look after the charging for that.

    In theory at least I could go up to about 10 miles without the generator. But I don't, If I'm going anywhere, I start the Generator first, it saves taking lives out of the battery pack.

    Also many public moorings around here have electricity posts where you can plug in and charge for the same amount as your home bill per KW would be.

    Is it more economical, yes Vastly mostly because of the short trips using no diesel at all and the old engine was nearly 50 years old to a design 20 years before that. (The boat is used to support my sailing)

    As for ballast distribution. it's made my boat worse, as it's centre cockpit, and the engine compartment in the middle so all that lead is too far forward. Putting it under the bunks in the back would be better, but would require some long heavy duty cables which would increase losses..

    I'd like in future to change to AGM batteries with more AH, as they would weigh less and take less space. This would require some changes to the electronics of the generator as the charge voltages are different, going to modern lithiums or the like, would just be too complicated and expensive..
     
  5. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    18650 lithium NCR batteries like e.g. a used Tesla S battery pack can be gotten for ~270€/kWh now. If you take usable capacity and total charge cycles into account they are already cheaper than lead acid. But definitely way more complicated and higher investment. There is a huge price difference between those easy to use smart batteries and the raw batteries at the moment.
     
  6. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

    Lead acid doesn't do this:


    Not saying lithium is inherently dangerous but they do involve risks that might be harder for DIY person to clear.

    LiFePo is safer AFAIK
     
  7. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    Yeah I'd prefer lifepo too except they are a more expensive (400€/kWh) and heavier. But much less work to string together 8 prismatic batteries!

    I think the NCR 18650 are ok safety wise (better than pouch packs) as long as you have individual fuses, only charge to 4.1V, have proper balancing and keep discharge current low enough. That is how tesla builds theirs (plus cooling). I'll have to look into their safety record.
     
  8. Artem Klochko
    Joined: Dec 2018
    Posts: 19
    Likes: 10, Points: 3
    Location: Ukraine, Dnipro river

    Artem Klochko Junior Member

    Hi,
    this is my cheap DIY DC on board generator with wet exhaust.
    [​IMG]
    How it work:

    Cost:
    $150 - 6,5 hp 4-stroke engine.
    $100 - BLDC generator/motor.
    $30 - rectifier.
    $20 - water pump for exhaust cooling.
    It charging sailboat 36V 180 Ah battery.
     
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  9. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    That is so awesome Artem! I'd love to learn more how one goes about building something like this. 5kW DC generators are insanely expensive.
    How much power output from motor do you generate?
     
  10. Artem Klochko
    Joined: Dec 2018
    Posts: 19
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    Location: Ukraine, Dnipro river

    Artem Klochko Junior Member

    I don't know exact power yet. In few days I will install a wattmeter and post numbers there. I think it have less than 5 kW of power. For 5 kW it will be bigger and more expensive than this one.
    Detailed article how to build similar generator I will write in few weeks.
     
    Last edited: May 1, 2019
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  11. Artem Klochko
    Joined: Dec 2018
    Posts: 19
    Likes: 10, Points: 3
    Location: Ukraine, Dnipro river

    Artem Klochko Junior Member

    I got a 40A @ battery voltage 48V
    Sorry, no video yet, will do it later and post there.
    Currently working on auto-start ICE engine of generator using cheap ($20) BLDC controller from e-bike.
     
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  12. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    Thanks for sharing, sounds pretty good for the price!

    So what is the difference between this and some super expensive DC generator? I guess lower efficiency and compactness and work required to build this. If you only need a generator rarely then efficiency isn't that important for economics. But probably not for what OP envisioned.

    But would there even be a reason this would be less efficient? You'd have to tune the gearing so the RPM of the engine is most efficient and the RPM of the electric generator produces the voltage closest to what you need.

    I guess the ultimate test for efficiency would be to measure the fuel consumption and the energy output. Fill the tank and film the voltage and amp meter for one recharge cycle, then fill up the tank again to see how much fuel was converted into electrical energy.
     
  13. Artem Klochko
    Joined: Dec 2018
    Posts: 19
    Likes: 10, Points: 3
    Location: Ukraine, Dnipro river

    Artem Klochko Junior Member

    Dejay, I've never had an expensive generator, it is hard for me to compare.
    But I can describe issues with my genset.
    1) hard to maintain fixed voltage. Next issue result from first
    2) because if this, it cannot be used to charge lithium battery to 100%, as it sensitive to overvoltage. I will not rely on battery BMS.
    3) slightly noisy and require active cooling

    Despite of mentioned issues, it can be used to safely charge lithium batteries to 90% and also can be used when electric motor is working.

    I used a buffer property of lithium battery: even if you have charging dc current with higher voltage than battery full-charge voltage, after connection this current to battery, voltage will drop to battery current charge voltage, until it is not charged to 100%
     
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  14. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    That's brilliant! Charging only to 90% increases the lifecycles of the battery and the total energy you can store over the lifetime. The SBMS120 solar BMS / charge controller is doing it in a similar way, it requires the solar panel voltage to be close enough to the battery so you don't need an expensive charger and can get away with PWM with almost no loss. That is more economical than using switching power supplies / MPPT that will need to be replaced every 10 years or so.

    So did you look at the motor and select the right gear and motor to get the right voltage? Or did you "get lucky" that it fits well enough? I still need to learn more about electrical motors and generators.

    Do you have active water cooling? That would be interesting too, to be able to use the waste heat of the engine for heating water for showering or heating in the winter. That would be my ideal generator on board but if you look at water cooled DC generators it gets really expensive!

    Sorry for derailing the thread :)
     

  15. Artem Klochko
    Joined: Dec 2018
    Posts: 19
    Likes: 10, Points: 3
    Location: Ukraine, Dnipro river

    Artem Klochko Junior Member

    Currently I don't have genset auto-off function if battery changed to 90%. It will charge further and overcharge if I don't do a manual shut off a genset, as open-circuit voltage greater than battery full-charge voltage. Auto-off problem I have to solve - will add some voltage comparison relay, it will disconnect spark plug supply, when voltage will be 90% of full charged battery. This relay will be cheap.

    I know my ICE engine have 3000-3600 RPM, according to specs. I bought a BLDC generator, that provide 80V open-circuit at max RPM (3600). Under load, voltage will drop, but it still higher than battery full-charge voltage and charge work. I made a test with wattmeter at reserve 48V 75Ah battery, but my main battery is 36V 180 Ah. Test with main battery I will do later.

    Generator is connected 1:1 directly to ICE shaft, no belt or gear. No water cooling, except wet exhaust. I adding a water to exhaust tube using 12 V pump to reduce noise and temperature of exhaust gases. Engine body have air cooling system, that why I wrote it need an air access with cooler. As you can see at picture above, my genset installed under the cockpit. This is reduce noise and made genset independent of rainy weather. Air is injected to genset compartment by the cooler and there is a passage outside of compartment for hot air.

    "Cheap" engines with water-cooled body have a price 2-3 times greater than with air-cooled body. Currently I'm not interested in high price engine, maybe I will change my mind in future, but not now.

    Use genset to warm a cabin I think it is a bad idea. It work not all the time, it work just to charge battery when you at long passage (case when no wind and you need long motoring), so you can warm up cabin a limited time only, this is not convenient. If you will run it several hours in a row, when battery fully charged, you will burn a lot of fuel just to warm up cabin.

    More optimal way to use air heaters as used at heavy trucks, like "eberspacher airtronic". It provide a 2 kW of heat just for 0.28 l of fuel per hour.
    [​IMG]

    Cheap ICE engines are not designed to have a lot of workhours until replacement, this is another reason to do not use them as heaters only,
     
    Last edited: May 12, 2019
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