Greetings All

Im building a fixed regulated 12v dc power supply using standard bridge rectifier and smoothing capacitor. Problem is i have a 400VA 24v 230V step down transformer. That said this transformer can safely give about 16amps at 24v, however i need it to be 12v. I know its easier to buy a dedicated 230 to 12v transformer, but i got this one for free and would like to use it if possible. Normally i would use a 7812 voltage regulator and use 3 or 4 2n3055 power transistors on that to boost current, however 24v is far above the 12v required hence it will generate way too much heat.

The logical approach would be a buck converter but finding one for the high current would be expensive and kind of defeats the budget build, for the money spend on such a high current buck converter i can just as well buy a new smps for the project. I only need about 15amps of current at 12vcd.

Any suggestions for this budget build would be appreciated.

 

How about a stack of there in parallel?
Just connect all the outputs together via a 0R047 resistor in each line to help equalize the current. The resistors can be equal lengths of hookup wire. And make sure they are all set to the same voltage.
It may not be the best way, but it is cheap.

 

i have a 400VA 24v 230V step down transformer.

You should be careful about units. You mean that the secondary is 24VAC (not 24v). Volts as a unit is a capital V, never lowercase. That's going to give you around 32V at the filter cap.

I only need about 15amps of current at 12vcd.

The only realistic option for 12V @ 15A is a buck regulator. If cost is that big of a factor, use an old computer power supply.

 

DC DC 20A Try this. It will take your 24V unregulated down to 12 regulated.
With display This one will give a very professional look.