Brushless motor generator

Discussion in 'General Electronics Chat' started by jeka616, Dec 25, 2012.

  1. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Good day all

    Planning to use brushless RC motor as a simple generator to charge my onboard batteries (which die after heavy flights, as one could expect..) during the flight.

    So will drive the brushless motor on the same axis from the petrol engine. I just purchased a simple sensorless brushless motor. It has 3 wires, and I'm not sure if it is Delta or Y winded. But regardless, I'm planning to connect 3 phase rectifier and capasitor, then voltage regulator, 7805

    Will this simple set up work ? Or do I need to modify and custom wire the brushless motor (not sure how easy this will be , considering the size of the motor....)?
     
  2. JingleJoe

    Member

    Jul 23, 2011
    185
    10
    sounds like you have the basic concept down :) but what voltage does the generator/motor provide? one must be certain it is not more than the L7805 can handle, which I think is 36 volts if memory serves me correctly.
     
  3. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,131
    267
    Using a linear regulator will waste lot's of precious power, why not use one of those integrated three terminal switching regulators instead?

    They operate over a wide range of input voltages and are small and light.
     
  4. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Xmm, interesting :). I'm happy to use any regulator, thanks for suggestion. This is first time I'm hearing about this regulators. So will plan to purchase one and test.
     
  5. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Thanks :) at least theory is correct. So will go back to building board. You are right, I need to check how much voltage the motor will give. I will test the output at mid and full power. If it will exceed >18-19V (just to be on safe side), I will adjust the pulley head on motor, to mechanically reduce the RPM on generator.

    I need only max 1 amp in worst case, as my flight battery pack will be attached to the system anyways, to provide main power.

    The next step will be to built some little relay, to cut the charging power once the battery is full. I did play with automotive regulators, and I had a post here, where my sport bikes regulator was burnt, and I used alternator regulator from the car which was BOSCH made. Guys in forum did really help on that
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Regulators (normal linear ones) just rob you of generated power.

    For small wind generators you can just connect the DC output after the rectifier directly to the battery. That will give max power into the battery.

    Only if the battery gets overcharged will you need to "regulate" which is easily done with a relay etc to disconnect the windmill from the battery. In that case you might also need to brake or feather the windmill to stop it spinning too fast, and some of those systems could also be used for battery-full regulation. :)
     
  7. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    I'm planning to use it in my RC airplane and RC helicopter. The engine rpm for plane will vary 2000-9000, and for heli 2000-12,000. So I need a robust regulator.

    I'm thinking to do same as in cars, just cut off the power when battery voltage goes over 5.5V. and resume when below 4V.

    I need 2 things: schematic for simple automatic relay, which will operate 4<ops range<5.5V

    another question is, 78sr105 is only rated to 1.5A (as per the datasheet that I downloaded). Is there any regulators at higher rating? So if I connect paralel 3 x 7805, what will happen?

    I know I can get answer by reading and calculatin, just don't have spare time for that. I know you guys over here are more experienced and "play" with this topics oftern if not daily, so please post links here
     
  8. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Here is the part that I'm not sure, and not really satisfied: The motor specs mention 4850KV, which means 4850rpm per volt....so to get 7-8volts output I will need to spin it at > 33,00orpm??......xmm, thats not what I expected. ...will have to have pig pulley system....
     
  9. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Just curious, I did have some trouble with my bike alternator, and user DEBE helped out with regulator.

    Wonder if I can modify this circuit to have simple relay, which will cut off power to battery when it exceeds 5v? Just need to adjust some parts and zener diode maybe?

    http://forum.allaboutcircuits.com/showthread.php?t=58592
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Whoops! Sorry I must have been looking at a few threads at once, for some reason I thought it was for a wind powered generator.

    To be driven my a small combustion engine I would pick a generator with very low drag. BLDC motors like the 3 phase aeroplane motor your are discussing have very strong "detent torque" because of the permanent magnets so they will drag a lot even when not generating.

    Some BLDC motor types will work fine with very little drag but are not as common.

    Since you only need about 5v at 1A max, you could use a small DC brushed motor, many of those will give 5v out at 5000 RPM or less and they are also fairly low drag when not generating.
     
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