12 volt to 24

Discussion in 'General Electronics Chat' started by robinm, Nov 14, 2005.

  1. robinm

    Thread Starter New Member

    Nov 14, 2005
    hi I am new to this forum so can anyone please help me?

    I am TRYING to fix an electrical scooter for a friend

    its got two 12 volt car batteries an switch(toggle) to change from 12 volts to 24 (two speeds)
    and another switch to change the polarity(forward and reverse)

    and a dc motor

    problem is that allthe wires have been disconnected

    I can make it go with 12 volts in series forward and reverse

    and 24 volts in parrallel forward and reverse

    but I cant switch between 12 and 24 volts

    simple I know but its a bit beyond me

    can anyone please help me

    thanks robin
  2. Brandon

    Senior Member

    Dec 14, 2004
    When the 2 batteries are connected in series, you get more voltage 24 in this case, in parallel you will have 12.

    To get it to switch between 12 and 24 you need to change the point of referance OR the point of voltage.

    0v (-B1)+ 12v (-B2+) 24v

    Between the - and a + on each battery you have 12v. So if you use -B1 and +B2 you got your 24v. The switch should either change the -B1 to -B2 OR change the +B2 to +B1 and then you get a change from 24v to 12v.

    Sorry can't really help more than this, but without seeing the switches, no way to really tell you how to connect it.

    For an experiment so you don't hurt yourself, you can use the switches and just a 2 1.5V batteries, or 2 9v. Where the motor would be, put a little flashlight bulb or something. If you got the wires connected corretly when you switch the speed controller, you should see th brightness of the bulb change.

    Just stick with the same concept, 0v (-B1+) 9v (-B2+) 18v
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    I think the 12 / 24V switching is probably supposed to switch between series and parallel, if it only used a single battery in 12V operation it could mess up the charging.

    Try this:
    Battery 1, positive permanently to output +
    Battery 2, negative permanently to output -

    The other two battery terminals go to the Common terminals of a two-pole changeover switch.

    With the switch in the 12V position, the connected terminals (e.g. the normally closed) of each go to the *same* polarity terminal on the *opposite* battery; e.g. the normally closed of the switch pole that has it's common connected to the negative of battery 1 connects to the negative of battery 2.

    The other two terminals of the switch (both normally opens) are connected together.

    In the 12V position, both batteries are used in parallel, in 24V they are both used in series & they should keep a reasonably balanced state of charge.
  4. robinm

    Thread Starter New Member

    Nov 14, 2005

    hi thanks a million you are right on the money

    worked a treat
    nice to know that there are people out there willing to help
    thanks again