High voltage DC generator

Discussion in 'Electrical Systems' started by prp25brad, Mar 22, 2005.

  1. prp25brad
    Joined: Mar 2005
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    prp25brad Junior Member

    Any know where to get a 144-240 volt DC generator in the 15kw range. I cannot find any.
     
  2. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    DC generator

    Try Glacier Bay's new Powerlite products
    <http://www.glacierbay.com/ossa_powerlite.asp>
     
  3. MattZ
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    MattZ Junior Member

  4. cyclops
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    cyclops Senior Member

    What uses 144-240 volts of DC? AC I buy. DC, show me. A 15 kw 120-240 AC generator can also produce DC with 2 Full wave rectifiers rated at 75 amps. each to take surges and trip a breaker when needed.
     
  5. brian eiland
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    brian eiland Senior Member

    New Generation DC Systems

    You really need to have a look at these new DC systems....definitely the future onboard boats, as well as future electric-auto technology. Lets see if I can post a few PDF files.
     

    Attached Files:

  6. cyclops
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    cyclops Senior Member

    What is the "Latest" reason to go back to obsolete DC power. The higher the frequency the lighter the self contained generator. That is why 400 HERZ power is used in the milatary. ---------Are the Power and Light Co. ? ----My Coleman 5 kw = 80# your DC's are 2-3 times the weight.-----------What about shore power hook ups? I do not see it flying.
     
  7. george allard
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    george allard Junior Member

    400 herz,[cycle] generators are no lighter in weight then any other same KW rated 60 cycle unit. The equipment that they operate, motors,etc are lighter.The only place that I have seen them in use is aircraft.
     
  8. marshmat
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    marshmat Senior Member

    Show me a 5 kW 400 Hz AC motor that is lighter or more efficient than an NGM or CSIRO 5 kW DC brushless unit. I doubt one exists.
    Yes, there are advantages to DC power on a boat. But the extra cost and low availability of specialized equipment and appliances, compared to cheap and plentiful 120 VAC gear, would seem to go against the logic of economics for anything except primary propulsion applications. What exactly is the system to be used for?
     
  9. StianM
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    StianM Senior Member

    I don't see anny advantage of DC at all.
    It's more agresive in eating up the hul if you get insulation faliure.
    The macinery is more heavy.
    And you have more options with AC
     
  10. Ike
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    Ike Senior Member

    Talk about high voltage DC has been going on now for about five or six years primarily in th auto industry. But they are not talking 144 or 225 or 400. They are talking about 48 volts DC. Hybrid cars use much higher voltages for propulsion but that is not what all the talk has been about. It' s a simple fact that with all the electronic gadgets in cars these days that 12 volt systems are not adequate to handle the power needs. So GM and Mercedes and others have been experimenting with 48 volt systems. But in 2004 Mercedes decided to put off any introduction of 48 volt system cars (they had planned on the 2006 model year) and GM has been dinking around with 48 volts in Cadillacs.
    Oh, and by the way, by ABYC and Coast Guard definition 48 volts is Low Voltage. It has to over 50 volts to be High Voltage.

    So at ABYC the electrical committee has been reviewing all of the stuff going on and looking at reports on this. They have also been talking with the National Marine Electronics Association concerning the proliferation of electronic gadgets on boats, even more so than on cars and what effect this will have on the electrical systems. So far there have been some boats built with high voltage DC systems, but they are mostly really large yachts, Mega-yachts. I haven't seen any of this trickle down yet to normal size stuff.

    Also, of course, there are those who are really into electric propulsion, the Duffys and the like. These require really huge battery banks and high voltage systems.

    Now the aircraft industry, and the Navy have gone the other way. They use high voltage AC systems. We're talking 400 volts here folks which is a lot of volts! It'll really burn your fingers (and everything else). The big advantage to high voltage AC is you can make everything smaller and lighter. Some of the electric motors that drive things in Gun Fire Control Systems on ships aren't much bigger than the starter in your car and these things move gun mounts that weigh many tons.

    Anyway, the stuff is around and being used to a small extent in boats.

    Personally, I'm a purist. Sails or oars, oil lamps. The only thing where I really advocate electrical power is nav lights. They bigger and brighter the better.
     
  11. StianM
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    StianM Senior Member

    Electrical DC propulsion is old fasion. Now it's AC with frequensy omformers that is the future. Smaler equitment.

    400V 3p AC is perfect for for marine use since you can have smal electric motors.

    The other advantag is that betwen N and anny off the 3 p you have 230V so if you live in a country or use 230V on your boat you don't nead a transformator. If you go for 380V you will have 219V betwen N and the 3 p.

    formula is voltage/root off 3
     
  12. Morgig
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    Morgig Junior Member

    There is some potential benefit to using a DC generator, combined with a battery and inverter system, that being to reduce impact of start-up loads. You can therefore size the generator for the running loads, not the start-up load and reducing the wear associated with running the gensets light.
     
  13. marshmat
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    marshmat Senior Member

    There is nothing 'obsolete' about DC power. Whether you choose DC or AC depends on your application requirements.
    The reason AC is used for the nation-wide power grid is that with AC, it is easy to exchange a high-voltage low-current transmission for a high-current low-voltage one, using only a simple iron yoke with a couple of coils of wire (a transformer). DC systems make converting voltage a lot harder (although not impossible) but have the advantage of allowing easy storage of energy in capacitors or batteries. There are both old-fashioned and modern high-tech examples of both in common use. Base your decisions on what is best for the application at hand, not what is perceived as 'trendy' this year.
     
  14. Ike
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    Ike Senior Member

    Also AC can be transmitted over long distances with much less voltage drop than DC. So AC is what you get from the power grid, but for a small electrical system on a boat DC is a good choice. It significantly reduces shock hazards and fire hazards of AC systems. However if you are running things like Refrigerators and Air COnditioning you'll probably want AC. But I would prefer a DC only sytem if it were my boat.
     

  15. Tim B
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    Tim B Senior Member

    It seems to me that there are people around the marine market who do not appreciate the fact that not everyone runs three fridges a freezer and constant air-conditioning.

    In the UK there is perhaps a few weeks a year when air-conditioning would be nice to have. Usually, it is when you are in a marina and the answer is often open the hatch. I grant you that in the Mediterainian and Carribean it is a slightly different story.

    In terms of on-board power requirements, it saves far more to be sensible and practical than it does to use every gimmick to make the system cheaper. On-board supply (in my view) should be DC-only, with an AC invertor to give power for laptops/mobile phone charging etc.

    We must remember that water and electricity do not mix. 12 volts DC (and 24 VDC) may fizz a bit, but 240 volts (and 120V) AC is lethal. To suggest using 3-phase with 450V between phases (at 240V/phase) seems to me to be lunacy for "casual boating use".

    You must remember that while Naval 400 VAC 3phase supplies will produce about 750Volts across two phases at very high current ratings, the men and women using these systems are very highly trained in fault detection and repair. They are not casual week-end sailors by any means.

    Personally, I'm with the DC boys. When a simple, reliable solution is needed it doesn't get any simpler than a battery and a pair of wires.

    Tim B.
     
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