What capcitor(s) needed for DC motor?

Discussion in 'General Electronics Chat' started by jyjohnhenry, Sep 30, 2016.

  1. jyjohnhenry

    Thread Starter New Member

    Nov 16, 2014
    I have a deadlock on a sliding door, utilizing a 12v vehicle window motor to operate it. At the moment I connect it direct to a vehicle and it works fine but is a bit of a kerfuffle. I tried to use to 9v alkaline batteries in series - there is quite a long lead in so that would cover any voltage drop, and 18v for the short time in use will not damage the motor ( I think/hope?!). Nothing happened - I guess the batteries dont give a sufficient discharge rate to run the motor and that I need some capacitance to start/run it?
    Can anyone give me some idea as to what type/rate of capicitors I would need?
    Thanks in advance, john.
  2. kubeek


    Sep 20, 2005
    How much current does your motor need? The 9V batteries will not work like you saw, as their internal resistance is way too high. You could try using 8 AA batteries in series, especially alkaline should have more then enough power to run that motor.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    A 14 or 16 AWG standard extension cord will work just fine. If you go to home depot/lowes/walmart etc. it can be purchased as lamp wire, or zip cord.
    Putting a 9 volt battery in series with your 12 volt lead acid battery is not wise. It acts more like a resistance and will not boost the current output of the 12 volt battery.
  4. tcmtech

    Distinguished Member

    Nov 4, 2013
    A typical 12 volt window motor draws between 10 - 20 amps which is about 50 - 100 times the current of what a 9 volt battery can put out without having a massive voltage drop in itself. :oops:
    #12 likes this.
  5. #12


    Nov 30, 2010
    You need a few pounds of lead-acid battery, like a lawn mower battery or an Uninterruptible Power Supply battery.
    I keep mine charged with a Wall Wart and a tiny 0.1 amp regulator chip in a container the size of a car fob.
  6. MaxHeadRoom


    Jul 18, 2013
    For this type of app, I picked up some obsolete door exit emergency signs, these have two 6v lead acid batteries and a charger.
    #12 likes this.
  7. jyjohnhenry

    Thread Starter New Member

    Nov 16, 2014
    Hi thanks all for the input. I obv. didnt make clear that I wished to have a small enough power source to comfortably carry or place in my pocket rather than having to bring the vehicle to the door each time.
    I think however I will probably stick with what I have for now, its simple and it works!
    Thanks again