I'm kinda green to this and looking for a general direction to move in.
the hardware:
Arduino Due
IRLZ34N Mosfets
Ford GT350 Shocks
12v 2 amp power supply
the Specs:
Due is running 20khz on channels 6,7,8,9
the Mosfets are getting car VDC @13-14.7V
The shocks have 1.5 ohms of resistance at rest. with a Max of 1.1 Amps
So here is the issue i have.
i need to be able to control current to the magnetic field. I find using the mosfets@20k i have a huge dead zone where the shock doesn't react till about 75% duty cycle.
I cant seem to get an accurate voltage reading or they don't make sense.
for example I'll read the voltage at 12v and Ill divide that by 1.5 ohms and get 8 amps... which the power supply cant even do.
The 8 amps are for a pulse rating. Same as a motor's stall current. And you do realize you are dealing with a motor? The lower rating is for continuous powering.
After reading about ferrofluid, I guess you cannot approach your project as a motor. Neither does AC seem to be involved. And it looks like applying a polarizing magnetic field will make the shock central shaft move easier.
Do you have the mechanism in place to analyze the shock resistance to movement in relation to the applied magnetizing current?
You seem to be pretty much into personal research at this point.
It's definitely a DC Current, i've had to experiment quite abit I know anything below 16khz the coils whine when moving the shock through its travel.
I found that at 480hz the shock responded linearly to the PWM Duty cycle
At 20khz i've found that it does not respond Linearly to the PWM signal until about 75% duty cycle.
I do know it'll accept a PWM or DC analog signal, PWM uses less hardware.
what I'm trying to wrap my head around is how can I measure the current of a PWM Signal so i'm not for the lack of a better work over saturating the coil.
Should I be using a 12v battery to power this?
I have a plug in wall adaptor that is supplying 12V 2A, is there a variable I am not aware of when using a plug in wall adaptor?
Paul_KD7HB:
You have apparently reached the limit of investigation "on the cheap". Time to get a suitable power supply and a suitable oscilloscope.
Paul
I do have an oscilloscope
Figured it out, was feeding the mosfet too much voltage.
Had a 12v supply and trying to limit the voltage to 1.3 volts with duty cycle.
Used a lm7805 to power the shock brought the duty cycle to about 30%.
Going to try a 2v 5a linear regulator and it should get me to where I need to be. Eventually move to a buck converter when I have 4 shocks to power.
I didnt realize I could do that solely through a single mosfet and that I needed to step down the voltage close to the range that I'll actually be working in.
Can't find the IRFZ520 datasheet.
Are you sure it's a 3.3volt logic type.
Highly unlikely you can drive a power mosfet at 20kHz from a weak 3.3volt pin.
You most certainly need a mosfet driver in between.
Leo..