sanity check diesel electric idea for tartan 30

Discussion in 'Hybrid' started by skkkkk, May 7, 2018.

  1. skkkkk
    Joined: May 2018
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    skkkkk Junior Member

    I must replace my tartan 30 diesel inboard.I want to go electric.

    Shore charged battery power would usually suffice for my sailing, but I want full diesel backup that will run long term if (when) necessary.

    Based on guess work and comparison I am sizing this as follows:

    6HP diesel air cooled engine -> Manta 3 generator -> 300 amp full wave rectifier -> GS 200 battery regulator -> 36V Lithium Ion battery ( 100 AH ) -> Speed Controller -> Manta 2 direct drive.

    Does this seem reasonably sized? I am under the impression the low end torque of the motor gives about double the effective drive of a diesel...?
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    No, unfortunately that is not correct. The conversion of diesel to electricity and back to mechanical power has many losses. A more efficient setup is a conventional diesel, with electric power inline. With the transmission in neutral, the shaft can be powered electrically.
     
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  3. skkkkk
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    skkkkk Junior Member

    Diesel efficiency is not my objective. I can waste power when under diesel power as long as I have enough drive to maneuver when on diesel alone. My main objective is to have a plugin electric battery bank only drive most of the time, with the added security of being able to fire up the diesel and motor through a storm.

    Am I wrong in assuming an electric inboard should be sized roughly 1/2 the horsepower of equivalent diesel?
     
  4. gonzo
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    gonzo Senior Member

    Yes you are wrong. It should be sized the same power. The power required is irrespective of the source. It doesn't matter what is producing it. If you are looking for an inefficient system, the combination you propose will fulfill that requirement. It will be more expensive, heavy and complicated than a conventional system.
     
  5. philSweet
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    So a comparable system might be:

    Sources - 50 amp shore power plug, Fischer Panda AGTPM DC 48V 6kW genset, and 4 x 200W solar panels. About $19,000 USD. (Plus fuel tank to suit. It needs to be 30% bigger than the equivalent straight diesel.)

    Motor - Electric Yacht System 20kW 48 VDC kit. About $9,000. A 15kW might work better, but I don't think they have one in 48VDC.

    Batteries - 24 Trojan L16EAC 6V AGM arranged in three banks of 8. You'll need six 4batt boxes and interconnects. This comes to about $6,000 for the batts and $2200 for boxes, hardware, and wire. The footprint is 36 sqft.

    Charger/inverter system - Three 48VDC charger inverters, such as Victron 2000 Multis (or one big one and some battery isolators.) About $3000 - $3500.

    That would be equivalent to a small diesel direct drive or a 35hp outboard in a well (plus any house electric supply).

    System weight is about 3700 pounds or so before fuel tank and diesel.
     
  6. skkkkk
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    skkkkk Junior Member

    The seaworthy argument wins this for the inline diesel every time regardless of efficiency either way. I want to peruse electric drive as well, linked to the diesel shaft as you suggested. I was looking at the manta II 10 HP motor. This thing is $650 and runs best (top speed) at 36V 3000 RPM. It seems to my naive mind that I can just get a 200 AH LI 36 V battery and hook it up with a battery protector and have a self charging ( off the diesel ) electric drive system, am I wrong? Why the fancy battery bank when you can get a single 36V LI...?

    Can someone post good links to diesel / electric driven linkage or any comments about gear ratio, etc?
     
  7. gonzo
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    gonzo Senior Member

    If you think that 10HP is all you need, then two 5HP outboards would work too. One important thing to consider with Li Ion batteries is to control the charge/discharge and the temperature. If they overheat they will go up in flames (Samsung phones). The setup is a bit more complex than with lead/acid. However, in a burdensome boat like yours, AGM batteries are a good option. Unfortunately, if you plan on charging from a generator, there will not be any savings but the contrary. You will use more fuel and carry a lot more weight.
     
  8. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    What was the rating of the little Farymann you are taking out? Can you post a photo of the mid-engine box? This is a huge packaging problem for you due to the odd layout. You will need compactness, and that pretty much means water-cooled everything. One last question - the simple way to do this means that when the electric motor is running and the diesel isn't, the pistons are going up and down. Yes, people really do this for short periods. No, I don't think it's a good idea either. But can you live with that?
     
  9. DCockey
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    DCockey Senior Member

    What engine are you replacing? What position throttle setting do you usually use?

    How will you use the electric drive? What boat speed will be needed? Do you need to recharge the batteries while being propelled by the Diesel engine? Being able to get on and off a dock or mooring and in an out of a harbor is very different from being able to make a passage under power against a strong wind for several hours.

    As others have suggested there are several possible arrangements. One alternative is a serial arrangement which has only the electric motor hooked to the prop shaft, and a separate generator can recharge the batteries. This would be the simplest for mechanical pieces and control system. Another option is a parallel arrangement which has both the electric motor and the Diesel engine hooked to the propeller shaft. This should be set up so that the electric motor can be used without the Diesel engine turning.
     
  10. skkkkk
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    skkkkk Junior Member

    so for the parallel case I envision a direct chain connection between the shaft and the electric motor. Put the diesel in neutral to drive with electric. Also the manta 2 10 HP motor 10 hp Permanent Magnet Motor Generator PMG Manta ideas 10 hp motor DC 8 hp electric 5 hp electric Dual Bicycle gokarts kart MANTA III THREE 3 3500 Watt electrical power generator http://www.hydrogenappliances.com/manta.html is also an 8000 watt generator so with a battery protector I can charge my 36V LI when I motor with diesel and drive on electric with the diesel in neutral, correct?
     
  11. gonzo
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    gonzo Senior Member

    Sure, you can do that. However, what is the reason for it?
     
  12. skkkkk
    Joined: May 2018
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    skkkkk Junior Member

    Here is my reasoning:

    #1 Seaworthyness - 10hp diesel is the stock motor size for this boat and diesel is the time honored and tested safest option with the bonus of having an effectively (for me) unlimited range. Before you convinced me of my folly I was going to replace the dead diesel with an electric drive with some kind of air cooled generator backup with enough juice to keep headway indefinitely at a albeit slow speed, since I would only be doing this (running on generator) for like 1% of all my motoring needs. However on reflection that those 1% are going to be the roughest and most critical periods. I think straight diesel inboard wins the day here.

    #2 I really hate diesels about as much as I fear gasoline engines. I kinda like an outboard, but not really in a big swell. I want 99% of my (modest) motoring needs to be covered by electric. When I sized based on actual examples I came to the conclusion that 100 amp hours of storage would probably be fine for me. Am I way off here, should I be thinking electric outboards? Is there a good reason for me not to charge the drive battery when the diesel is on? The motor I was looking at has the same HP as the diesel and roughly the same max RPMs at 36V which just happens to be the best operating point for this motor giving it a continuous 6HP over long periods of time. I am guessing that would be good enough to get in and out of the harbor....

    What is the best way to go?
     

  13. DCockey
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    DCockey Senior Member

    100 amp hours at 36 volts / 3.6 Kilowatt hours equals 3.8 hp for an hour at a combined controller and motor efficiency of 80%.

    When you talk about 100 amp hours of storage at what voltage is that calculated? Three 12 volt, 100 amp hour batteries in series to output 36 volts is 100 amp hours at 36 volts / 3.6 Kilowatt hours (not 300 amp hours at 36 volts / 10.8 Kilowatt hours ). Batteries usually should not be completely discharged before recharging so available electrical energy may be significantly less than the nominal battery rating.

    Efficiency of electric motors can vary from over 90% for a brushless motors with high efficiency converter, to much lower, perhaps 50% or lower.
     
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