Making own simple controller

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Ampy
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Joined: 03/27/2014
Points: 52

I've ordered a IRF3205 75amp MOSFET to try and experiment if I can make a simple DC speed controller, using an arduino I have to give a PWM signal to it.
I posted on another forum asking if I can just use the single MOSFET on its own, and I was told I would need also at least a diode to stop voltage spikes back from the motor.
Does anyone know which component diode I can use for this?
Do DC motors generally have a diode already built in to stop these back spikes?
I'm a bit clueless on all this so very grateful if someone can point me where to start

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Spaceangel
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Joined: 07/15/2009
Points: 491
Re: Making own simple controller

Making a controller is more of an art. Pulse width modulation controllers are very efficient and the work by chopping up the DC supply to the coil or field or armature therefore reducing voltage to the load. So when the voltage is removed from load the magnetic field collapses and a counter EMF or voltage appears and can pop a MOSFET or transistor so most engineers use a flyback or a high speed switching diode to recover voltage for the load. Free Wheel effect. Maybe practice taking a coil / solenoid and apply voltage to coil and quickly as possible make and break connection to coil. The coil will drop in and out. Now put a diode across the could and make and break connection as fast as possible. Wow, the coil remains energised. Nifty , hey that neat oh! Free wheeling.
So use quality high voltage break down components and for recovery diode use fast switching diodes for this isn't 50/60 Hz stuff. Also different PWM frequencies are needed for different motors. Also lower frequencies are needed for lower RPM's usually and you can experiment with the Chinese PWM controllers that are variable frequency. You will be surpassed how little current is needed to hold in a could or spin a motor. I know I didn't answer your question but maybe should get you started on a known path. There are a lot of kits imported and domestic for you to compare part numbers of components. Some times you can interchange transistor or MOSFETS with each other without too much redesigning.
You will also notice that if you place an ammeter in series with input and another one on motor circuit and set PWM to 10 - 50 % lets say, then the current will be greater on motor side proving PWM is working to some extent.
After you do all of that then you can use larger capacitors to sustain energy to motor also. So they all work together. A good start is look at some of the Block Diagrams of controllers.
Building them is a learning experience and can be fun.

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Ampy
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Joined: 03/27/2014
Points: 52
Re: Making own simple controller

Thank you for your help, all i need now is to know where to order such a diode.
Do Diodes have different powers, which one could work with 200amps?

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