regulator 12v, 25amps for power supply.

[rc technics]

I hope some one can help me. I have a non-regulated 25-30Amp 14v DC power supply, for use on a lipo charger, which requires a regulated at 12 volts at 25amps. Currently my voltage is going up and down 13.6v to 16.3v

Please can some one show me a diagram and the parts I need to build my own regulator?

Volts: 12
Amps: 25