Hello, I am new to this forum and am working on upgrading my Anet A8 printer as much as I can to make it safe enough to leave overnight without worrying about it catching fire in the middle of the night. I have ordered a mosfet for my printer that I will be installing for my heat bed( a second mosfet for the extruder and larger power supply to come later) but I am a bit confused as to how the mosfet actually works.
Now, this may be a dumb question but I have been searching around with no answers. I know the signal wires plug into the controller board but how does the controller board know not to send the full 12V down the smaller wire. Does the mosfet have a resister or something to drop down the voltage so the controller does not burn out the thin cable or do you have to change a setting on the printer to tell the controller board not to send the full 12V down the signal wire. Does the signal wire take the full voltage but with reduced amperage.
There is a lot of information on how a mosfet works in theory but little on how a mosfet works when retrofitting one onto a currently running system and how the mosfet manages the different power levels.
I know just enough about electrical system to get myself into trouble.
dugly66
2
I have the anet A8 also and a mofset
On the mofset there will be four larger connections (usally screws) 2 of them will come from the power supply(12v) the other 2 go to the bed.
The signal wire hooks on the motherboard where the
heatbed went.
Mavyre
3
Actually, there is a big resistance on the control signal, so the signal intensity is very low, and won’t burn the Anet A8 motherboard’s connectors. I ran the this printer with PLA without mosfets overnight, for 100+ hours without problems. I’m currently running it with two mosfets at once, with the default 12V power supply!
Urubo
4
How a mosfet works?
Well, it takes a small power signal on the input (from the board to the mosfet), then the mosfet “transform” the low power signal in a high power signal (from the mosfet to the heated bed for example).
Why should Iuse a mosfet?
Basically using a mosfet you’re unloading your main board (because now it only need a 0.1W signal (for example) to drive the load and the mosfet care about the “dirt job”). Less power through your board -> less heat ->less connector problems and longer board lifespan.
Level shifting and small signal wiring: between the board and the mosfet you have a full 12V signal, no voltage reduction, only the current changes (from 12A for a direct load of the heated bed to maybe 0.01 average current to drive the mosfet). Of course the 12A for the bed will be feed through the mosfet thanks to a direct connection mosfet/power supply. If the mosfet board is correcly designed there isn’t the “level shifting” problem, I designed/builded my own mosfet board and the mosfet that I choosed can handle without any problems 20V on both sides.
Hope this will explain all 
Sorry for my crude english, I need to practice more about it.
