voltage drop

Discussion in 'The Projects Forum' started by levs, Jun 17, 2009.

  1. levs

    Thread Starter New Member

    Jun 17, 2009
    2
    0
    hi, i dont know if anyone can help me out with this, i have a rc boat and the motor seems to work only on and off ( one speed for forwards) it is far to fast for what i need it for. is it possible to to slow it down by adding l.e.d's bulbs or anything to the +/- black/red wires on the motoers? it runs on 7.2v nicad , dropping the out put to the motor to drop it down, making it run slower?

    thanks
    levs
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    For an "easy fix", you could add some diodes in series with the motor.
    1N5400 diodes are rated for 3 Amperes.

    Each diode you put in series with the motor will drop the voltage by somewhere between 0.7v and 1v, depending on the load.

    A more elegant solution would be to use PWM. Check out Bill Marsden's circuits, here:
    http://forum.allaboutcircuits.com/showthread.php?t=24028

    Note that you don't HAVE to have D1/D2/R1/R2 in the circuit, but they'll give you a rough visual indication of what the output duty cycle is - and whether it's working or not.
     
    Last edited: Jun 17, 2009
  3. mauro.laurenti

    Active Member

    May 8, 2009
    68
    0
    ...I'm assuming that you are talking about a standard DC motor.
    If you connect a resistor in serie with the motor you will get what you want.
    ...by the way some power will be dissipated on the resistor and the battery will not last more...

    If you want to reduce the speed and increase the battery life, you should use a PWM technique.

    Ciao,

    Mauro
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    What you suggest will work, but will waste power. A more efficient method is to use a thing called "PWM" or "Pulse width modulation." Enter either term with the search function to learn more.
     
  5. levs

    Thread Starter New Member

    Jun 17, 2009
    2
    0
    thanks alot for those replys, very quick! you know what your on about! i will try these options out.

    thanks again
    levs

    great forum
     
  6. mauro.laurenti

    Active Member

    May 8, 2009
    68
    0
    ...now three people has suggested to use the PWM...

    you should be convinced of using it...

    I would suggest to use an NE555 (LM555) and a power mos for making the PWM generator you need.
    It's simple and cheep.

    You should easily find schematics on line.

    Ciao,

    Mauro
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    905
    Here's a non-PWM method, assuming you do not need variable speed.

    7.2V is 6 cells. Will it run on just 3 cells or 4 cells? If it runs on 3 cells, then your 6-cell pack can be reconfigured to two, 3-cell packs. Connect those in parallel for longer running time.

    John
     
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