Brushed DC motor

Discussion in 'The Projects Forum' started by amilton542, Jun 30, 2011.

  1. amilton542

    Thread Starter Active Member

    Nov 13, 2010
    I want to build a brushed DC motor but there are a few things that have confused me. I took apart a drill to get the motor out and the armature had a pair of drill holes on the face of a slot and another pair in the vicinity of the other two about 3 or 4 slots away, the assumption would be to self start in any position?

    Also, the conductors driving the armature were wound round a small core about 6 turns per conductor, why have they done this?

    For excitation I was thinking of seperately excited. Car battery for the armature, car battery for the field windings. I want my motor to be "beefy".
  2. SgtWookie


    Jul 17, 2007
    Those drilled holes were to balance the armature assembly. When it was wound, it was not in perfect balance. If you somehow filled those holes back in with core steel, the motor would vibrate due to the imbalance.

    That is to reduce the transient spikes that would otherwise enter/exit the motor housing.

    A car battery can supply hundreds of Amperes. for short periods of time; enough to turn an automotive engine over for a minute or more.
    But then, you need to charge them back up right away, or they will quickly fall apart.
  3. amilton542

    Thread Starter Active Member

    Nov 13, 2010
    Are the drill holes and iron core necessary for a first time build? As long as there is rotation im happy :)

    Are car batterys dangerous to use? Cheap pillow-block bearings can be quite "stiff", the amperage should furnish the torque required to overcome the friction. The brush assembly will be mounted on brackets that petrude from underneath the bearings but If I have to get rid of the car battery as excitation many other things go down the "pan" with it.
  4. Adjuster

    Late Member

    Dec 26, 2010
    Yes, car batteries can be dangerous: the large short-term current capacity which permits engine starting also makes it quite easy for things connected to them to overheat or even catch fire if they develop a fault. A short-circuited battery will itself overheat, with the potential to release corrosive and toxic material, perhaps explosively.

    At the very least, you should have a suitably rated fuse in the line to your battery, to protect it and whatever is being tested.
    amilton542 likes this.