I tried to build a simple circuit that would send current through a resistor...

Discussion in 'The Projects Forum' started by eyik66, Feb 11, 2016.

  1. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
    I tried to build a simple circuit that would send current through a resistor if it was no longer being drawn by the load.

    I thought I could do it with a PNP transistor with the charger on the Base, the resistor on the collector, and the voltage source on the emitter. That didn't work.

    Any simple circuits that you guys know about that will do what I need. I've attached a block diagram. This idea is that a stepper motor will create a 5V power source, but if the battery is charged, the 5v power source will bleed off through the resistor. View attachment 100490

    [​IMG]
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    Are you wanting to make a wind turbine or generator from a stepper motor?
     
  3. Veracohr

    Well-Known Member

    Jan 3, 2011
    552
    76
    Why waste power by diverting it to ground? Why not just cut off the connection to the circuit?

    I don't know anything about motors, maybe there's a factor I'm not aware of.
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    That wasted power might make a wind turbine take just a little energy out of a weather system that could turn destructive.

    If everyone did that, there might be slightly less - or less destructive tornados.

    An unloaded generator could over-rev in strong winds.
     
  5. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
    The motor is being used as a generator and will always be rotating. So if the circuit isn't drawing current, the AC gets too high on the rectifier circuit and ruins it.

    I've been messing with PNP transistors all day, I must be on the wrong path. This can't be that hard though, any ideas please???
     
  6. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
    Yes, it is a stepper motor generator. The stepper motor will always be driven and I have no control over that. So I need to have a way send the power somewhere before the AC gets too high on the rectifier circuit.

    I was under the impression that a PNP transistor would connect the emmiter and collector if no current was being drawn from the base. So I was hoping to connect the battery charger circuit to the base, so that when it stops drawing current, the current is diverted through the collector and a resistor. Unfortunately, it isn't working.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    While the current direction changes between NPN and PNP transistors, they function identically. With no base current, both are "open" from collector to emitter.

    Is it the Inverter/Regulator that is failing in the unloaded condition? If so, what is the normal voltage range under load, and what is the open circuit voltage range that is "ruining" the rectifiers?

    And of course, a schematic of the inverter would be very helpful. Without it, everything is just guessing. Maybe high-quality guessing, but still...

    ak
     
  8. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    Would it be possible for you to measure the ac input voltage to the regulator? Any idea how much current the motor can supply?
     
  10. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    That is a complete AC-to-DC power supply (minus the AC source),. It is a straight 7805 regulator with a full wave diode bridge input, so the input must not exceed 17 Vac RMS or 24 Vdc. There are other regulator assemblies with a higher input voltage tolerance, but without a measurement of your unloaded generator voltage there is no way of knowing if they will survive.

    What you are trying to do is a version of what is called a shunt regulator. A less complex approach is to figure out what your actual input voltage range is, and find a module or combination of modules that can handle it.

    ak
     
  11. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
    I can try and figure out how high the DC voltage will get. Won't the voltage just keep increasing at the regulator input if there is nothing drawing from the regulator output?

    I'll do some google searches on a shunt regulator. Hopefully there is a simple circuit example somewhere.
     
    Last edited: Feb 12, 2016
  12. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745

    Can you measure the ac from your stepper motor going into the bridge rectifier with no load, to see what its giving out, then we can see what the peak dc would be, also which stepper motor are you using, 4wire or 6 wire,? mosfets would be best for shunting the dc.
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    No. There is a maximum value for the unloaded output, based on the strength of the magnets, rotating speed, wire gauge and lengths, magnetic coupling, eddy currents, and on and on. A real motor expert probably could tell us which ones matter in the real world.

    ak
     
  14. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
    ok great. I will try to get the measurement today. Thanks for the help so far.
     
  15. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
  16. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    Its a four pole 8 wires, how are you wiring it up, can you post your circuit.
     
  17. eyik66

    Thread Starter Member

    Dec 15, 2012
    30
    0
    I added some more detail. Thanks again,

    Eric Screen Shot 2016-02-12 at 10.50.52 AM.png
     
  18. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    So does the stepper motor charge the battery and feed the Arduino, and when the battery is full, dump the stepper voltage into a resistor?
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    You can add the PNP transistor to a TL431 programmable-Zener in the manner of a Szicklai pair.

    You set the shunt voltage with a pair of resistors, make sure the added emitter follower PNP is enclosed in the nfb loop and the whole thing is as precise and sharp knee as the TL431.
     
  20. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    So you have 4 of those little regulators in parallel?
     
Loading...