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Build a 48 VDC Generator with a 50 hp electric motor

  1. Dec 25, 2015 #1
    You can select any type of motor. I'm going to spin it at a varying RPM and with a varying torque. The combination of torque and RPM will be capable of 50 hp intermittently. I can limit the maximum RPM but lower is better as I can leave out a gearbox.

    No different than what they probably use in a wind type generator.

    What all is required to covert this rotational energy @ 48 vdc with an electic motor?
     
    Last edited: Dec 25, 2015
  2. jcsd
  3. Dec 25, 2015 #2

    anorlunda

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    Wrong units on your question. You don't convert energy to volts, you convert mechanical energy to electric energy. Volts are not energy.

    Is this homework? If so, it should be posted to the homework forum.
     
  4. Dec 25, 2015 #3
    No, this isn't homework. I am converting rotational energy to electric power @ 48 vdc.
     
  5. Dec 25, 2015 #4

    anorlunda

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    You must specify how much power. Power is voltage times current. 48 volts and zero current is zero power. If you don't understand that, I'm afraid you will not be able to understand any better answers to your question.
     
  6. Dec 25, 2015 #5
    50 hp
     
  7. Dec 25, 2015 #6
    I'm not using the electric motor to turn a generator, I'm using a hydraulic motor. I want to convert the electric motor to a generator.
     
  8. Dec 25, 2015 #7

    anorlunda

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    The generic term for DC generators motors is Dynamo https://en.m.wikipedia.org/wiki/Dynamo.

    Some types can be used as generators or motors without modification. Therefore you must be more specific. Do you want to design a motor yourself ? Do you want the make/model of a motor to buy on EBay? Do you need only the name of the type of motor? What to you mean by "what is required?"
     
  9. Dec 25, 2015 #8
    I want to buy a manufactured motor.

    Can I simply buy a 48 vdc, 50 hp motor and spin it?
     
  10. Dec 25, 2015 #9

    jim hardy

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    A question well stated is half answered.
    I select a permanent magnet DC dynamo.
    A DC dynamo will act as either a motor or a generator, just the directions of current and torque reverse.
    A mechanical coupling between your hydraulic motor and your dynamo, a device to control speed, and a sturdy mount.


    Just what is your question?
     
  11. Dec 25, 2015 #10

    anorlunda

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  12. Dec 25, 2015 #11
    Looking at a Baldor catalog, 48 vdc might be too low for a large motor.
    I'm trying to select the appropriate dynamo for this application. I can design everything up to the dynamo. I was told on another thread that the best way to get power back to the grid is begin at 48 vdc and use a proper inverter. Once I select the dynamo I can size the hydraulic motor. But my expertise ends at the dynamo shaft.
     
  13. Dec 25, 2015 #12

    jim hardy

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    Have you looked into that claim?
    Induction generator has the nice feature it won't backfeed into a dead grid and electrocute a lineman, like a simple inverter can..

    In your shoes i'd try to cultivate experts like Anorlunda by sharing more details of your experiment.

    Like a dynamo, an ordinary induction motor will induction generate by simply overspeeding it slightly. Plus it has no brushes and is cheap. But that might need a gearbox.

    It's a helpful bunch here, just you gotta prime the pump and be polite.

    old jim
     
  14. Dec 25, 2015 #13
    Thanks Jim. Didn't mean to come off impolite. I'm having trouble asking the right question.

    Basically, I have up to 50 units of mechanical/hydraulic HP I want to convert and put on the grid. I've done the bulk of the conceptual design on the mechanical/hydraulic side and I'm trying to at least nail down the generator motor. Once I have those specs I can finish sizing the hydraulic motor and coupling. If there is a minimum RPM then I can configure the hydraulics to store the energy and release it to the hydraulic motor when there is enough to get it up to speed.

    Just hammering out the details but I have very little knowledge of electric motors beyond what is required to drive a pump.
     
  15. Dec 25, 2015 #14

    russ_watters

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    50 hp is 37 kW. That's a pretty powerful system (mechanically and electrically) for a novice to undertake. It will be complex, dangerous and expensive. You can't design it just by getting vague/disconnected one-liner questions answered.
    You aren't using anything yet, are you? Have you purchased this hydraulic motor? What is the make/model of it and where is it getting its hydraulics? [Edit; oh, this is your wave power thing]

    Does your house even have a big enough electrical service to handle this? Have you talked to your utility about setting up the metering/service?

    I think you may need to hire yourself an electrical engineer if you want to have much of a chance of this working.
     
    Last edited: Dec 25, 2015
  16. Dec 25, 2015 #15
    It's just a matter of scale. I've designed much larger and more powerful systems. This is relatively simple other than the fact I've never created electricity before :)
     
  17. Dec 25, 2015 #16
    I haven't sized the hydraulic motor yet, I need to get the RPM range. I'm designing something on a slightly larger scale than a single household. Targeting remote villages on the AK coast. I won't be hiring an electrical engineer anytime soon. I want to have a solid design laid out for the generator platform before I begin soliciting an electrical engineer. Otherwise, like yourself, I'll be talking to people who will be just be rolling their eyes at the whole concept.

    This thing is getting designed and costed to the last bolt. But, I need to specify the generator motor.

    Thanks for your input, Russ.
     
  18. Dec 25, 2015 #17

    russ_watters

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    I don't see how you can size the generator until you've gotten the hydraulic motor (and maybe even tested it).

    And fyi, the eye rolling you are getting is mostly about your approach. This is a serious project and you don't seem to be approaching it very rigorously.
     
  19. Dec 25, 2015 #18
    What is your "rigorous" recommendation? I'm not sure what you mean by "your approach". You start with an abstract concept and work out the details.

    The hydraulic motor is determined by the output specifications, not the other way around. Cmon, Russ. You don't specify components without the application parameters. The hydraulic motor output depends on the gen motor input RPM range and torque requirements.

    FYI, I expect this will cost much less than an equivalent kW wind turbine generator system.
     
  20. Dec 25, 2015 #19

    russ_watters

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    All we see are the disconnected bits and pieces and half-finished thoughts posted here. I sincerely hope there is more detail than we are seeing. Have you made any drawings/schematics? Have you designed the wave energy harvester? An electric generator is a common thing, but a wave power harvester would be quite an invention. All I've seen of that was a couple of hypothetical numbered pulled out of the air - nothing about how to capture it.
    No, since this is an experimental power generation project, the driver is the amount and type of available power: the flow rate and pressure of the water. At this point, that part of the system should be functioning. Then you select a hydraulic motor based on that input, then a generator to match the motor and electrical requirements.
    Highly unlikely but in either case, have you priced-out any of the components yet? The actual wave energy gathering device in particular. It's the "special sauce" in this recipe.
     
  21. Dec 25, 2015 #20
    Yes, I have the general schematic completed but the components aren't yet specified. See attached. But, you see my point, you want to see details. That's what I'm working on.

    I agree, there are a lot of half-finished thoughts here. I'm debating whether I should just put this up as a PF group project or not. If there is actually something that's patentable in the system, I'd be killing that ability by publishing it in a public forum. I haven't seen any designs in my research that take my approach. So, I'm asking questions that don't reveal the entire "sauce" recipe. There's a buoy, a mechanical to hydraulic conversion, a simple hydraulic system, and a gen motor. From that gen motor the interface to the grid is no different than with any other generator system. Probably nothing patentable here but I want to make sure I can put something out there first.

    I don't want to debate hydraulic design with you but, you don't create a hydraulic system (or any system) and then try to make it work on an application. The application defines the system components. Then prime mover, the "input", is the ocean wave action, the application is the gen motor. Moving on from that...

    I haven't done a lot of costing yet but based on the simplicity of the system and the fact that most of the components are "off-the-shelf", I can say with confidence that it will be cheaper to construct and maintain than a wind turbine equivalent. A buoy is cheaper than a set of precisely engineered props, for example.
     

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