Dc motor/battery combo

Discussion in 'General Electronics Chat' started by lecron, Nov 15, 2010.

  1. lecron

    Thread Starter New Member

    Nov 13, 2010
    Hi to all, I've just joined this forum and know nothing about electronics but hopefully I can learn something from you guys and gals
    I'm just dabbling with the very basics so please forgive me when (not if) I ask dumb questions... here goes..

    Ok, I've got this small 'can' type brushed dc motor to play with and there is no information stamped on the barrel, at all, ie voltage required or current rating. I have used a 6v 6ah lead acid to power it up and it seems ok, but I don't know if a 4v 9v or 12v would be a better power plant for it, Is there a way of determining the ideal voltage for this motor without buying several batteries and trying them all.
    I have put a multimeter on the set up which is showing 1.57 ah draw.
    Any advice would be much appreciated but please be aware that if you make it too technical for me I'll pester you for more advice!!
    Many Thanks Lecron
  2. mik3

    Senior Member

    Feb 4, 2008
    6V volts should be fine, you might burn it with 9V.
  3. lecron

    Thread Starter New Member

    Nov 13, 2010
    Thanks for the reply but I'm still in the dark about whether its possible to determine the ideal battery size for this dc motor, and if so, how would I do it please?
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Check the RPM, they are typically around 3000 RPM, if you are getting 5000 out of it, the bearings may not last long. They Run QUIET. If you hear it "humming", you may have too much voltage going to it. Reduce voltage until it doesn't buzz or hum.

    RPM can be measured a few ways, easiest is to put a small stick on the output shaft and use a R/C airplane contactless tachometer on the stick (it counts pulses of light, divides by 2).

    Another option is hall effect sensor + manget, but I'm unsure what size output shaft you are using.

    If the motor is around 1" around, and about a 1/16" output shaft, grey colored, those are most often 3-5VDC motors and are extremely common in the hobby area.

    Is there a flat spot on the shaft, or threads so that you can use gears or pulleys to lower the RPM and increase torque to make it useful?
  5. lecron

    Thread Starter New Member

    Nov 13, 2010
    Thanks for that.. I have a tachometer so will check it out. Could I also check the resistance through the terminals then divide by the amps to get the voltage: or am I talking cobblers?
  6. Audioguru

    New Member

    Dec 20, 2007
    A DC motor with no load generates a "back EMF-voltage" which decreases its current (so its effective resistance is much higher than you measure). When the motor is fully loaded then it draws almost as much current than can be calculated from its resistance.