Help needed,transformer voltage

Discussion in 'The Projects Forum' started by speedster, May 15, 2013.

  1. speedster

    Thread Starter New Member

    May 14, 2013
    Hello all, first post on the forums.
    I tried searching other posts but didn't find anything similar so here goes.

    I need help and advice with a small 20va chassis mount transformer i found.

    The secondary output voltage is dependent on the fluctuating input voltage.

    The mains voltage varies from 220-250v.a.c and regardless of input voltage i need to work out how to achieve a constant secondary loaded voltage of 5.5v.a.c at 3.4A.

    The secondary is used to constantly power a NiChrome wire length and cant deviate more than +/- 5°C if possible, the wire isn't in free air.
    Sorry i haven't got any photos of what i'm trying to do as of yet.

    Do not really want to use a switch mode power supply because of the expense, not sure how to do it and need a poke in the right direction :confused:

    Thanks a lot

  2. MrChips


    Oct 2, 2009
    You could use a constant voltage transformer but it isn't cheap.

    Presumably the nichrome wire can be heated with DC current. Use a regulated DC supply.
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Aren't heating elements usually controlled by a thermostat type circuit? Relying on strictly voltage level won't account for changes in the surrounding environment. Especially if you need to hold a specific temperature range.
  4. speedster

    Thread Starter New Member

    May 14, 2013
    Mr Chips, thank you, Using regulated DC supply would solve a lot of issues. but not as cheap as a transformer or as small.

    shortbus, thank you, i guess some elements are controlled by t'stat, i've been experimenting today with the wire temp,with steady volts and amps and the resistance wire load at 1.4ohms, as long as the air is still the wire temp is quite steady.

    will keep on trying tonight
  5. wayneh


    Sep 9, 2010
    That comparison is valid if you can find the perfect transformer, meaning that's all you need, but if you need to use a regulated AC supply, the DC choice will look better.

    You could consider winding your own transformer, or removing windings from an existing "close" transformer.

    A dummy load in series with your wire is another option. A 0.1Ω resistor, 5W (for safety) resistor for instance would drop 0.34V. You could drop a whole volt using 3 0.1Ω, 1W resistors in a row.