2PAC Mafia said:
I already checked that we would have so much heat at the transistor but this IRFZ44R I already checked it supports at least 100W and I found some more which supports more than 100W. The cost of installing a MOSFET there should be cheap, it´s around 2 or 3 euros and the vacuum I have I got from fuel station BP card points, so it´s like free. I also do it to learn I little bit more.
The IRFZ44R can dissipate 100W as a maximum IF the back is kept very, very cool. If you dipped it in cool oil for example the back might be kept at 25C but the internal junction will still melt. If the backing is hotter, the maximum power rating goes down.
Keeping a TO220 this cool under 100W isn't going to happen, not for 3 euros. A cheapo folded aluminum clip-on heatsink can allow a TO220 to dissipate something in the 5W range or so. The modest sized heat sinks with milled fins that fit within a few cubic inches can allow a TO220 to go into the tens of watts. 100W requires a HUGE heatsink, lots of fins, skillful thermal mounting, and a fan.
You can keep the heat in the temp-sensitive MOSFET low by adding a resistor. For example if you put a 1.2 ohm resistor in series with the 12v supply it would burn up 8.4v, thus 58.8 watts of the heat. 5-20W resistors are relatively cheap and building a network of them will bring the MOSFET heat down to a realistic level.
Still, off the shelf, I'd say this project can easily run 30-40euro or more, and the results will be less than "satisfactory" due to the size and heat generated. It will also run down your battery pretty fast! That's why I suggest getting a 12v vacuum which is quite common.
I take it you want a learning experience here. First thing to learn is nobody will
ever design a linear regulator like this, it's impractical. When we have to step down voltages like this we use a DC/DC converter- a switching reg- which will do the job cleanly. Cool, efficient, and cheaper than huge FETs and heatsinks. It would be difficult for us to communicate how to do this to you because it doesn't sound like you're ready for advanced circuits like this.