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Topic: Controlling a magnetic shock (Read 689 times) previous topic - next topic

Microcontrol

Mar 22, 2020, 03:57 pm Last Edit: Mar 27, 2020, 02:37 pm by Microcontrol
Hey guys,

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.

Speed and accuracy are important.


what hardware should i be using?

Paul_KD7HB

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.

Get a bigger PSU.

Paul

Microcontrol

The shock range is .1-1.1 amps

the shock uses 2 coils moving through ferrofluid, that is a motor? I should be using an h bridge to drive the shock?

Paul_KD7HB

The shock range is .1-1.1 amps

the shock uses 2 coils moving through ferrofluid, that is a motor? I should be using an h bridge to drive the shock?
What does your documentation say?

Paul

Microcontrol

What does your documentation say?

Paul
I wish I had documentation, ford doesnt share the specs of the shocks.

Everything I know has been gleaned from trouble shooting documents

There is a company that builds a standalone controller for these shocks, which how I know the range for the shocks.

Paul_KD7HB

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.

Paul

Microcontrol

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

Microcontrol

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.

Wawa

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..

MarkT

IRRF520 isn't logic level at all, they need 10V or more gate drive to work properly.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Wawa

#11
Mar 26, 2020, 11:17 pm Last Edit: Mar 26, 2020, 11:19 pm by Wawa
Can't find a datasheet for the IRRF520 either.

The IRF520 (guess) is useless for 3.3volt logic, and not even right for 5volt Arduinos.
Leo..

Microcontrol


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