My question is now: Can I use the PWM signal comming from the arduino and put that into the motor controller and by writing an analogvalue of lets say 200, get below the 2 amps, that each bridge of the motor controller can pull through or would that damage the motor controller?
I intended to use only 2 of these motor controllers, if the above is possible, but I have read somewhere, that you can use both bridges to the same DC motor and that lets you run 4 amp DC motors. Could that be a solution and how would I physically do that (wiring it up)?
When you say 2.5A at full speed, is that under load or free-running? If free-running then you can expect the load current to be a lot more (and stall current even higher). I'll assume full load current for now:
I wouldn't put more than 1A through a L298 - for two reasons.
Firstly the power dissipation is very high. At 2A you can expect 7.5W to 10W being dissipated in the L298, requiring a fan to cool the heatsink.
Secondly the voltage loss to the motor will be around 4 to 5V - your 12V supply will end up looking like 7 or 8V and the motor will run slow.
With a 1A motor the losses would be more reasonable at 2.5W to 3W, 2.5 to 3V (still rather high, but that's the problem with darlington output stages).
For a 2.5A motor I'd recommend a MOSFET bridge with R(on) values at or below 0.25ohms. Someone here recently built a motor driver using the TLE5206 (see the Motors, Mechanics and Power subforum) - this is much more suitable and there is a board design called the HexMotor that uses it. Also the LMD18200 is suitable (though will run a bit hotter) and ebay has some little boards with it. And also look around the Pololu site, they will have several suitable driver boards I am sure.
An alternative strategy is to parallel L298's to reduce the current in each, but requires twice the number of driver chips.
Okay I see. So the only way I can use these 3 boards with the L298 chip on them is to run them in parallel and still this isnt the best way to do it. How would I do that with these boards? What connections do I have to make?