Hello ,i am going to show now and dummy load around 15 ampere maximum
Original circuit is from here in Greek language
We are using here the 555 as unstable multi vibrator opening and close the gate of the IRFP250. With the pot. 470 Kho we can adjust the duty cycle at the output of the 555. The measured voltage can be from 1-30 volts. The maximum measured current is 15 ampere for a short time and 10 ampere for a longer.This mosfet can handle around 200w, so for a measured voltage 30v ,current should be lower than 6 amper with a good heat shink.
The case is from an old power supply ,mounted with 2 fan side by side