Something does not seem right?

Other Hardware General Electronics
1

I m trying to create a fuel injector testing bench with an Arduino minima r4.
Running on low frequencies as in the first part of my code everything appears to be good, but in the higher frequencies I believe that the injectors doesn' t close at all. I believe this because except for 50 Hz I don t see any difference in the way injectors work? Can anyone spot a mistake on hardware that can cause that. In the software I m using Arduino built in DAC, it would be better using PWM for this application?

#include <analogWave.h>



analogWave wave(DAC);


void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
}
void loop() {
  // put your main code here, to run repeatedly:
    wave.square(50);
    wave.start();
    delay(15000);
    wave.stop();
    delay(20000);
    wave.freq(300);
    delay(20000);
    wave.start();
    delay(60000);
    wave.stop();
    wave.freq(150);
    delay(20000);
    wave.start();
    delay(60000);
    wave.stop();
    wave.freq(80);
    delay(20000);
    wave.start();
    delay(60000);
    wave.stop();
  }

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2

I expect you will be frying FETs, the gate and wiring capacitance will slow down the turn on/off of the gate signal keeping it in the linear (Ohmic) range to long. They will get hot. You should buffer the gate of each MOSFET and place something in the 50 ohm between the gate and buffer. The 1N4002 diodes are not adequate the injectors will fly back with over an amp of current. What you put in is what you will get out.

3

Thank you first of all for your response!!
I have checked the MOSFET and they don t get hot even after running for about 10 minutes.
So the problem sould be that at higher frequencies the gate always stays off? If the signal needed buffering the gates of the MOSFETs should be closed right? But the problem that it appears is like the injectors are on and they don't turn off. Last could you make a suggestion for fly back diode replacement?

4

I tend to agree with @gilshultz , you should use a MOSFET gate driver to drive the gates; especially considering that you have 4 gates to drive at the same time. Since the gates have a fair amount of capacitance, you need a fair amount of charge to get them ON or OFF quickly. Most gate drivers have a charge pump in them for this very purpose.
I would recommend just checking Digikey for an appropriate gate driver (drive voltage, max current, logic levels, etc), and using your A0 pin to activate the gate driver, which in turn activates your MOSFETs.

5

They are not contacts, they are enhanced (on) or not enhanced (off). What you are describing is the MOSFETS have the source and drain reversed (not a contact) hence the body diode will conduct and turn your injectors on. The MOSFET will appear as a resistor with a resistance of about 2X Rds on.

I think it would be better for you to research and find a diode, and let us know what you found, we will let you know if it will work.

6

The flyback diodes will slow down the injectors' release (closing) time. Bidirectional TVS diodes with standoff voltage about 20V might work better?

7

Good point. The minor delay usually doesn’t matter but when you get down to 50 mS, it does.

8

Yes, use PWM BUT use the ledc library doc at
https://docs.espressif.com/projects/arduino-esp32/en/latest/api/ledc.html