Hi community, nice to meet you,
I would need advices to control intensity (between 0 and 2 amps) in a home-made electromagnet for a small ferrofluid sculpture.
I’ve already built the sculpture but I can only switch it ‘on’ (2amps), or ‘off’ (0amps).
Now I’m planning to use an Arduino Uno to control intensity level.
Details of current project: 12V DC + a switch + my electromagnet (1ohm, non-laminated core, unknown inductance) + a resistance (5ohm).
Current is around 2amps. The resistance gets hot but not too hot, no need cool it down.
As said, my goal is to control the current from 0 to 2 amps with the Arduino.
I can imagine 2 designs:
1 Use a transistor in its ‘linear’ range to statically control a DC current in 0-2amps.
2 Use PWM and a saturated transistor. In this case current will evolve in time (typical exponential shape due to the inductance of the coil). I hope that current variations in the coil will be fast and small enough to be ‘smoothed out’ by the fluid inertia. I suppose PWM parameters will not be easy to get right.
In both cases I will add a flyback diode to protect the transistor (around coil + resistance in design 2 to keep same time constant in both part of the PWM cycle).
So my questions are:
A – Do you recommend 1, 2 or another design?
B - What transistor would I need (reference?)
C – Should I use an optocoupler or something to protect the Arduino? (reference?)
D – Somewhat unrelated: I have the feeling that my design is wasting energy in the resistance. How could I maintain the 2 amps without having the resistance getting hot? (If I had a 2V power source, I wouldn’t need the resistance at all) how can I get a 2V/2Amps source from my 12V/2amps without a resistance getting hot?
Thanks