Hello.
I'm trying to make an motor controller to control a 24 VDC motor, this is just a test circuit to test my idea..
How much is wrong with my circuit? 
The mosfet is going to be a FQP50N06.
The diode is also just one that eagle had in the library.. any suggestions?
Thank you.
How much is wrong with my circuit?
Quite wrong.
Well the 7812T is a 12 volt regulator and you want to drive a 24V motor.
I am assuming the motor is placed across the diode.
Next the FET, is operating in the source follower mode so you will not get much voltage across it when it is switched on.
Finally have you looked to see the gate turn on voltage of the IRF510? How are you going to develop that.
Ohh.. sorry, I've posted the wrong schematics.
I'll post the correct one when I come home tonight!
please look back in a few hours
Here is the correct one..
The motor is Connected to the 24v from the battery, and gets GND from the mosfet.
The 7812 is supplied from the 24v connection, and provides the Mosfet (FQP50N06) with 12v to the gate.
What kind of diode do you guys suggest? The motors is 24VDC 20A
Thank you
I don't see a need for the 7812 regulator - Do you need this for other purposes?. Rather I would connect 24V directly to the opto collector (pin 5) and then use R4/R3 as a voltage divider to control the MOSFET gate voltage (above 4V, less than 25V).
You don't specify what type of opto coupler you use. If Vce at 24V is too high, you should move R4 to between +24V and opto pin 5.
The optocoupler is a 4N37.
The mosfet-datasheet says GS-voltage of max 25v, and fully charged the batteries will have over that voltage.
So what youre saying is that I should just use a simple voltage-divider to obtain the correct voltage( <5v & >24v)?
Just throwing in my 2 cents here, on the power supply side:
Depending on what you are doing, you might want to separate the power supply portion from your circuit; if, for instance, you are driving multiple motors, or you have other circuitry to power that requires other voltage levels...
So - build a power supply module that takes the 24V input from the batteries, and has connections to output "raw 24V", "regulated 24V", "regulated 12V", regulated "5V", etc. Then run jumper wires or traces from that module to the motor module and anything else.
If you want to go with using a voltage divider, that will be your choice based on what the circuit does and what is powering it; just note that a voltage divider's output will shift depending on the input (as the battery runs low). If you input comes from a wall-wart or some other more dependable source, it will probably be ok (well, until that first electrical spike in voltage comes through, I suppose). But if you are using batteries (like for a robot or something), keep in mind that the output can drift with a voltage divider (the same can happen with a regulator, but the voltage generally has to be beyond the extremes of the range of the regulator before this becomes a problem, IIRC).