Transformer output

Discussion in 'The Projects Forum' started by boatsman, Oct 31, 2014.

  1. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    I have a heavy duty transformer rated at 22oVAC 500W input and 24V 20amp output. The secondary has no centre tap. I want to use the output to power 12v portable drills and also to be able to use it as a power supply for a 12DC model railway and as a base for a bench power supply. Are all these things possible to do?
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    They're possible, but it may not be the easiest/cheapest solution.
    To get down to 12VDC efficiently would need a switch-mode converter. It may be easier/cheaper to source a 220VAC/12VDC converter than a 24VAC/12VDC one (I haven't checked).
    We don't know your bench supply spec.
  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    Since the 12VDC Model Railway is likely mainly an inductive load, isn't there protection if the switching power supply necessary?
  4. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    Thank you both for the replies. My main concern is to power 12v portable drills as my now very old rechargeable batteries only hold a charge for about a quarter of an hour at most and the battery types I have have been changed by the manufacterers (Bosche) so I am left with several drills in full working order only without a convenient power source
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
    some of the portable drills have variable speed, ac would not work on them, only dc.
  6. MaxHeadRoom


    Jul 18, 2013
    You could look at modifying the secondary, either take the whole secondary off and wind a suitable gauge 12v secondary, or just take turns off, in most cases for motors and relay equip, you do not need a cap smoothed supply, which in that case use 12AC rectified, if you cap smooth it, you need 8.5v AC. it most likely will work out to ~2turns/volt.

    Yes, the AC powered are Universal, the portable/battery operated are P.M. DC brushed.
  7. Johann

    AAC Fanatic!

    Nov 27, 2006
    Agree on the series motor, but doubt if the DC speed regulator behind the trigger would be happy with the AC. If the transformer laminations are bolted together and you have the time, dismantle it one weekend and rewind the secondary or centre-tap it, then use 2-diode rectifier with centre tap as common.