Permanent magnet motor charging car battery

Discussion in 'The Projects Forum' started by msmith719, Nov 7, 2011.

  1. msmith719

    Thread Starter New Member

    Mar 29, 2011
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    Hi. I working on designing a power system one of my projects. There will be a 180V 1HP (746 Watt) permanent magnet motor (acting as a generator) rotating at 1800-2400 RPM. The motor will charge a 12VDC car battery. The power from the battery will be converted to 120VAC via a 500W+ power inverter like one used in a car. The appliance that will be plugged into the inverter requires 450W of power.

    I know that I will need a charge controller to insure the battery does not over charge. I have research several charge controllers. However, the charge controllers are for solar applications. I feel that those controllers are not suitable for this project. Does any have a charge controller that they would suggest for me to use? I want a controller that will work for this project while staying under budget.

    Also, does anyone have experience with a similar project? What issues should be considered in a project like this?

    Thanks in advance for your assistance. I look forward to your response.
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    PM generators are used almost exclusively on motorcycle electrical systems, you are basically duplicating the kind of generator system a bike uses to charge it's 12V battery. They are a pain because there is no graceful way to adjust the field current. They just crank out power and it has to go somewhere. Bike's use a shunt regulator that taps current to ground to control the battery voltage. That is very inefficient. Cars use an alternator with two windings (rotor and stator) and you can easily control stator current out by varying the current in the rotor winding. I am not sure if there are better regulator systems available for PM generators, but research bike electrics and you might find one.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Look into wind turbine projects. The wind guys deal with exactly the same issues, except that they suffer an even wider (though usually lower) rpm range.

    Does your generator really produce 180 volts AC at peak rpm? I think transforming that down to under 20v or so would be the first step. That'll give you much more current and a transformer is pretty efficient. A buck converter would be better, but a lot more complicated. I'd look for a transformer that will still give you a charging voltage (~14.5v) at the minimum expected rpm at the generator. BTW, rewinding the generator to give less volts, more current is an option also, but not practical for most folks.
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
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    The permanent magnet motor may be DC in the first place, in which case a transformer would not be an option. A switching converter would then be required, or the efficiency at full speed charging a 12V battery would be truly dismal.

    It will be useful to know if this thing is for instance a DC brush motor, or something else. NB some (brushless) DC motors cannot in fact be used as generators: their drive circuits won't work that way.
     
  5. msmith719

    Thread Starter New Member

    Mar 29, 2011
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    The motor is a DC motor. I am looking at this motor: http://www.omega.com/pptst/OMPM-DC.html

    It is a 180VDC permanent magnet motor with 5.2 Armature Amps and 2.917 ft lbs of torque.
     
  6. iONic

    AAC Fanatic!

    Nov 16, 2007
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    I'm a bit perplexed as to what is going to spin this motor at 2400RMS as stated above??
     
  7. wayneh

    Expert

    Sep 9, 2010
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    And I think the OP will be disappointed at what the output will be at a given rpm as a generator versus what is required to spin it at that rpm as a motor.

    Spinning that sucker at 2400 rpm when it's under load will require godzilla on a bicycle.
     
    SgtWookie likes this.
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Who said bike, I think it is water power. Many SMPs input 100 to 240 V AC so 180V DC could be directly fed into the input via bridge rectifier- providing such a power rating could be found , 30 A @ 15V out.{ viariable would be nice ].
     
  9. msmith719

    Thread Starter New Member

    Mar 29, 2011
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    Thank you all for your input. Since my last post, I have redesigned my project to make it more portable. I am designing it to power a device of 80W or less.

    Turbine > DC generator > Voltage Regulator > 30A fuse > Charge controller > Blocking diode > Battery > Invertor > Device

    Turbine (to be determined)
    DC Generator (http://bit.ly/uAfc3q)
    Voltage regulator (need help selecting)
    30A fuse
    Charge Controller (http://bit.ly/uuH0bB)
    High Blocking Diode (need help selecting)
    Battery (http://bit.ly/soLUku)
    Inverter (http://bit.ly/sx1Sqn)
    Device (draws < 80W continuous)

    I am going to rotate the turbine at ~1500RPM Since I want ~200W output from generator.

    What voltage regualtor would you suggest?

    What diode do I need to work with in the Amperage and voltage output of the generator?

    Please double check each component (links provided to specs of the components). Is there someting that I have missed or need to consider?

    Thanks.
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The generator spec shart shows it puts out about 17amps at 24v at 1500RPM.

    I would use a SMPS buck regulator which is adjustable, so you can adjust duty cycle to maximise the power-point tracking (MPPT) to give max power into the 12v battery.

    If your turbine will be fixed at constant 1500 RPM you can just adjust the pot on the buck SMPS for best efficiency (you don't need a MPPT algorithm unless your turbine RPM is widely variable).
     
  11. msmith719

    Thread Starter New Member

    Mar 29, 2011
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    The voltage regulator that I am looking at is the 461400 Voltage Regulator (http://bit.ly/va1T1Z).

    Input voltage – 80 volts dc maximum
    Output voltage – 13.8 volts nominal at no load
    Output current – 10 amperes dc maximum
    Int. voltage drop – load sensitive, 0.5-3 volts

    It it is sold by the same company that sells the generator that I have chosen.
    Can someone provide feedback on this?
     
  12. msmith719

    Thread Starter New Member

    Mar 29, 2011
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    0
    I am not familiar with SMPS buck regulators. What exactly are they?
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    With all these steps comes individual power losses which add up. Starting out high voltage, then stepping down to low then back up to high, what's the point?
    since your generator puts out 180V, why not feed that straight into a SMPS?
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    SwitchMode Power Supply. The "Buck" type converts high voltage to low voltage at high efficiency, so you put in 100v at 1 amp, and you get out 12v at 8 amps!

    It could be adjusted to give maximum power transfer so you get the most possible power into your 12v battery.

    Another good suggestion (as people have said) is to use a ready made SMPS. However I think your generator puts out too low a voltage at 1500 RPM to really make use of a 120v->12v ready made SMPS?
     
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Good question.

    I'm also interested on how he's going to get 1500RPM from water, unless he has a pretty high dam, or some stout gears to increase the speed to 50 Hz, in which case, he is going to need a pretty high dam to create enough torque.
     
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