DC motor no output also AC question

I am attempting to build my first wind powered generator. Experimenting and doing a bunch of reading everywhere says a DC motor will generate electricity without being excited. I got excited but the motor didn't need to be :) So as I progress I find a 12V motor from a hydraulic unit and check it with 12V. It runs! I started trying to spin by hand but got no output reading so I connected a variable speed drill to the shaft and spun it starting slow watching the DVOM and nothing.

What am I missing here? I realize if I am going to do DC I need a motor greater than 12V but I am just trying to make one generate power at this stage.

I have also read that you can match a capacitor to an AC motor and it will excite the motor just don't disconnect under load or you will have to excite the motor again with 12V. This would allow generation of 60 cycle AC thus eliminating the need for batteries / inverters. Ideas or thoughts?

Comments

  • mike95490mike95490 Solar Expert Posts: 8,573 ✭✭✭✭✭
    Re: DC motor no output also AC question

    A couple of thoughts for you, if you are going to do much in this field, get yourself a laser tach. You will need to be measuring RPM's, not guessing at them.

    Understand this too, this is dangerous, get a sleeve, finger or necktie caught in something, it will be painful.

    DC motors. If you can feel the magnet "cogging" when you turn it by hand, it will work as a generator.

    AC Induction Motors - these are NOT all types of AC motor. When an induction motor is spun up by AC power, and then you add mechanical power, as if you are trying to overspeed it, it turns into a synchronized generator, and can produce about half it's nameplate power, back int the grid. you will need fully automatic disconnects and such to legally connect this to the grid, and generate. Nobody wants Fried Lineman.

    You can also use *most* induction motors, with a suitable cap, to locally generate AC power. If you size pulleys right, you can get close to 60Hz. Don't apply DC to an AC motor.

    Car alternator. Can work, but very uneconomical, they need lots of RPMs to get their lame cooling fan to work, and are low efficiency, generally.

    There are lots of sites you can look up about using motors to generate with, but it's a bit beyond what I want to get into here.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2System2 Posts: 6,290 admin
    Re: DC motor no output also AC question

    Thanks for the tip on the laser tach. If I understand what you are saying here not all DC motors generate? I will check this motor but believe it felt relatively smooth when I turned it by hand. I am only at the stage of trying to figure out how to make one work. Once I have an operational model to play with I will get a bit more serious about what I actually want to do with it all. I am in southern IN and wind is not really existant here except in winter months.

    I have been collecting solar panels for installation one day & wanted a smallish wind generator to compliment them. Gives me something to do to keep me off the streets and out of trouble :)
  • mike95490mike95490 Solar Expert Posts: 8,573 ✭✭✭✭✭
    Re: DC motor no output also AC question
    elgemcdlf wrote: »
    ...not all DC motors generate? I will check this motor but believe it felt relatively smooth when I turned it by hand.

    Some DC motors have field coils, not magnets. If it has magnets, it WILL generate. But if it turns evenly and smoothly, then there are not likely magnets inside.

    Check out the toys at
    http://www.scoraigwind.com/
    http://www.otherpower.com/guemes_notes.html
    http://www.forcefieldmagnets.com
    http://www.otherpower.com/
    http://www.coilgun.info/mark2/inductorsim.htm
    http://www.qsl.net/ns8o/Induction_Generator.html
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 29,988 admin
    Re: DC motor no output also AC question

    Take a look at the site OtherPower.com for information on home built wind turbines. You will find much more information there for your project than here.

    Regarding DC motors as generators--there are many types of DC motors (series, shunt, permanent magnet, etc.) and 30+ years ago, cars used generators--which were a form of DC motor--and because they have a bit of residual magnetism in the field, so they can self excite enough to generate enough power to power the field windings, which then can generate full current/power. And, before you start an engine with a new generator the first time, you have to "flash" or "polarize" the generator to make sure the residual field is the correct polarity (or the generator "generates" in the wrong polarity and fries the wiring/generator when connected to the battery by the regulator).

    Here is a good starting point for how DC (and AC) motors work.

    For wind turbines, using DC motors / AC Alternators with permanent magnets solves several issues... 1) More efficient as you don't have to generate a field with part of the power generated. 2) Simpler controller--don't need a field controller. 3) Don't need to flash/polarize. 4) No brushes/commutator/slip rings needed--longer life.

    The major downsides for any standard wind turbine design is that they can very easily self destruct in high winds and/or if the alternator/controller fails. A horizontal wind turbine always needs some sort of load/brake/furling device to limit rotational speed.

    And most designs used to charge a battery bank need two independent charge controllers to prevent overcharging of the batteries (normally, all of the wind power goes to the battery bank to charge it--and any excess power is removed by turning on a "dump load" to discharge the battery bank when more charging current is coming from the wind turbine than needed). So, if the first dump load fails, a second system is needed to prevent overcharging (another dump controller+load, or braking system on wind turbine, etc.).

    You can drive a typical AC induction motor faster than it normally turns and generate electricity--but, in the end, this will probably more trouble than it is worth (between regulatory requirements of the utility company, setting the motor up so that is is only connected when it is turning fast enough to generate useful power--or else your wind turbine turns into a giant AC powered fan, etc.).

    If you want to us an AC motor to generate power--it can be done--and legally, if done with by back driving an off-grid AC inverter... Some (most, all???) AC inverters, when back driven will actually charge the battery bank. Southwest Wind Power actually sells their Grid Tied AC wind turbines into this type of application (or at least they say they can--don't know if they have any real installations in the field yet with all of their other problems). This can also be done with using a Grid Tied solar inverter to back feed a off-grid AC inverter (again, need some sort of battery charge controller).

    There are some posts on this forum about back driving / back feeding (or as Outback calls it, "AC Coupled") AC inverters from Solar power sources--but no cookbook instructions (that I remember).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: DC motor no output also AC question

    Update: The motor spins smoothly so I am off to hunt down another DC motor :) Thank you for the info. I have absolutely no clue when it comes to electricity but am trying to learn a bit as I go. Now that I know what to look for in a DC motor I should have better success.
  • KevinbKevinb Solar Expert Posts: 26
    Re: DC motor no output also AC question

    In general to use a dc motor for a wind generator, you want high voltage at low RPM. The old Ametek dc servo motors that were used in large computer tape drives are popular. The best one is the 99V model, most others will just give you a trickle charge. The big disadvantage over an A/C alternator is that brushes wear out, and it takes much larger wire to get the power where it's going with DC as opposed to A/C.
  • mike95490mike95490 Solar Expert Posts: 8,573 ✭✭✭✭✭
    Re: DC motor no output also AC question
    Kevinb wrote: »
    it takes much larger wire to get the power where it's going with DC as opposed to A/C.

    Please explain this. Or document it.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • KevinbKevinb Solar Expert Posts: 26
    Re: DC motor no output also AC question
    mike90045 wrote: »
    Please explain this. Or document it.

    I thought it was pretty well known in the solar world that AC is much more efficent to transmit over distances than DC current. That's why Edison lost out with his desire to run the grid on DC, and Westinghouse prevailed with AC. There are simple calculations out there but I don't know any off the top of my head, I'm sure a search would find you some. Here's a start- http://en.wikipedia.org/wiki/War_of_Currents
  • BB.BB. Super Moderators, Administrators Posts: 29,988 admin
    Re: DC motor no output also AC question

    Actually, no, for "BIG STUFF" DC can be more efficient (both power, $$$ wise, and for bi-directional power sharing between regions) than AC--even when the conversion at both ends is taken into account.
    High voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is required to be transmitted over very long distances, it is more economical to transmit using direct current instead of alternating current. For a long transmission line, the value of the smaller losses, and reduced construction cost of a DC line, can offset the additional cost of converter stations at each end of the line. Also, at high AC voltages significant (although economically acceptable) amounts of energy are lost due to corona discharge, the capacitance between phases or, in the case of buried cables, between phases and the soil or water in which the cable is buried.

    HVDC links are sometimes used to stabilize against control problems with the AC electricity flow. In other words, to transmit AC power as AC when needed in either direction between Seattle and Boston would require the (highly challenging) continuous real-time adjustment of the relative phase of the two electrical grids. With HVDC instead the interconnection would: (1) Convert AC in Seattle into HVDC. (2) Use HVDC for the three thousand miles of cross country transmission. Then (3) convert the HVDC to locally synchronized AC in Boston, and optionally in other cooperating cities along the transmission route. One prominent example of such a transmission line is the Pacific DC Intertie located in the Western United States.
    More details here.

    While for "local" energy management, AC has been nice because of the low tech transformers and ease of designing/building AC switching equipment... The advent of cheap and efficient DC switching power supplies (such as our MPPT type solar controllers), and true sine wave inverters (with bi-directional power abilities too), has certainly brought the whole question of HVDC vs HVAC (relative terms) down into our solar designs now...

    My grid tie inverter runs ~200-600 VDC--or at a higher voltage than my own internal home wiring (120/240VAC).

    And given the price of copper vs electronics--I sort of wonder if we are not approaching the cross over point where local AC/DC voltage&current converters may not be "cheaper" and "better" in the near future.

    "Intelligent" power distribution/monitoring/control on neighborhood power poles may become the defacto standard as we get into distribuited power distribution/time of use control. The are already starting to roll out utility meters with reatime monitoring, billing, and control (of shed-able loads--like A/C and electric hot water heaters--may save an estimated 20% of load--perhaps 10 years of growth in power demands based on current estimates).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KevinbKevinb Solar Expert Posts: 26
    Re: DC motor no output also AC question

    You just gave me a headache :confused: Maybe it depends on what the dividing line between low voltage and high voltage is.

    For an example lets compare a 1000 watt wind generator AC vs DC at 24-48 volts. If the line needs to be 300 feet to get the controller, will it not take a lot larger gauge (and weight in copper) when using 2 wires for the DC than it will take for the 3 wires for AC? Do you not lose a lot more power from the resistance in the wire transmitting the DC compared to the AC?
  • mike95490mike95490 Solar Expert Posts: 8,573 ✭✭✭✭✭
    Re: DC motor no output also AC question

    Nope, at the levels we would be seeing in a home/hobby/small industrial, there is no AC/DC advantage. There IS an advantage to using higher voltage, like many of the solar PV inverters run 300 - 600VDC, down to the grid inverter,
    where it's turned into AC for the grid.

    Lower VOLTAGE, requires more AMPS ( & copper) to transport the same Wattage (power). AC or DC, the same calculation. (till you get to RF frequencies of AC)
    AC circuit breakers are much cheaper than DC breakers.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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