Output pin on low is opening MOSFET gate

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1

Hi,

First of all Im completely new to electronics and this forum, so Im on the lower level of understanding.

I have some very strange scenario where I use an Arduino R4 Wifi to control an MOSFET directly over pin 9, defined as OUTPUT. It is a programmed sequence that starts with a button signal on pin 8, defined as INPUT.
In the code pin 9 is set to LOW on startup and then to HIGH for 1500ms, followed by LOW on an input signal from pin 8.

I purchased N-Channel MOSFETS (IRLZ44N) from "ALLECIN" on Amazon and they started working as expected. However now they dont. I read a lot and changed the wires, added resistors and so on until I concluded, that i destroyed them due to not adding a flyback diode to the inductive 12V load. Now added. I then ordered more MOSFETS. Accidentally IRFZ44N instead of the logic gate equivalent.

All of the MOSFETS are open and allow current, wihtout any gate voltage applied. To make sure the pins are on LOW, i added leds to the curcuit and they indeed only turn on as supposed within the sequence. However the inductive load is charged as soon as i physically connect the power source.

I tried 11000 and 1001000 ohm resistors between gate and ground. The odd numbers are due to the fact 2 resistors are in series. The 1000 ohm resistor is between the pin and gate as i dont need high frequency PWM signals to control the MOSFET.

I have made sure the diodes are connected the right way.

Also i had to add a diode between gate and ground as i noticed that the ground pin was charging the gate. I did this by disconnecting all other power sources and pins until the ground pin of the Arduino was the last thing connected with the gate and the breadboard.

I probably forgot a lot of details and i tried quite some configurations. I also read about fake MOSFETS being sold. Im clueless right now why the MOSFETS are not working as expected and i wonder if the Arduino output pins are perhaps leaking a little bit of power, not enough for the leds but enough for the gate. Weirdly it also turns on the IRFZ gates, which are supposed to need a much higher voltage. Also its worth to note that the inductive load started to "flatter".. like i would have used a PWM signal instead of a continuos one. Very strange. I have also tried different pins: 5, 6, 7.

I do be sorry for the messy setup. It was orignally more complicated so I reduced it to the problem.

Greetings :slight_smile:

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I was only allowed to add 3 pictures. Ill to choose the most important.

2

You need a logic level N channel MOSFET. The IRF is not of that type.
Please post schematics. Pen and paperm a camera and posting that picture is fine. The fotos You posted are of no use.

3

  • Images are nice and clear, but very busy.

  • Suggest the leads on the resistors be cut down so the resistor lays flush on the solderless breadboard.

Always show us a good schematic of your proposed circuit.
Show us good images of your ‘actual’ wiring.
Give links to components.

4

Sounds like they are all bad.
Were they in an anti-static bag or were the leads pushed into anti-static foam when you received them?
The bags are silver looking and the foam is either pink or black

5

Thank you all for your quick replies!

So i drew a schematic on paper:

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Since the explaination came in the first post and the schematic now, I will describe it here again:

  • The switch S1 is used to physically signal the Arduino to power the Mosfets gate for 1500ms. The program takes the signal from the digital pin 8 as pulldown input and starts the sequence.
  • I added the led to physically see wether or not the program and arduino are working as intended. Judging from the led, its fine. However the MOSFET allows full current flow even as the gate is not powered, and the led is dark.
  • Note:: i disconnected the grounds from each other as I got afraid to damage the Arduino.
  • The diode D1 above the inductive load is a flyback diode.
  • The diode leading to ground on the gate wire is to remove stray charges as i first assumed this was the cause. The diode was necessary because the ground pin was charging the gate.
  • Both is wired over the plug and not by a battery as the schematic shows.

I have also tried variations with similar results:

  • connecting the gate to the ground of the inductive load power source
  • connecting the gate to both the grounds. Putting different resistances around the gate.

I forgot to note that R1 has a resistance of 1000 ohm, while R2 has a resistance of 1 million ohm and i also tried 10000.

The IRLZ44N came in violet colored half translucent plastic bags, while the IRFZ44N came in a hardplastic cover. Both cases without foam. I will add the links as asked:

Greetings again

6

Where is the common ground?

7

"Where is the common ground?"
I tried it with both grounds connected aswell. Is this recommended practise? I later undid it because i got scared the 12 or more volts could fry the Arduino over the ground pin.
I did already melt 2 ground wires, figuring out the mosfet is open without signal.

In fact both, the arduino aswell as the inductive load are powered by the plug, so I assume that they are both connected to the buildings ground wire.

8

Melted wires sound bad, I don't know what you are doing, I cant see from incomplete schematic, What's R2, diode, LED and switch for?
When you draw schematic, you must have a dot when wires are crossing if they are connected.
Learn the basic things first and try it without Arduino, I hope you didn't burned it.

9

Thank you for your reply. I added notes under the schematic to clarify those points.
The melted wires happen due to the fact, that the load was not supposed to be constant but in programmed short intervals. For that purpose the wires are sufficient, although better would be better.

10

Your assumption is wrong.

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Thank you. I have tested your exact setup and 9 out of 10 IRLZ44N mosfets showed the known, faultry result. Howeber one of them actually worked as intended! I have not tried all the IRF ones, but of the 2 i tried 1 worked and one not- I will need the logic variant anyways as the IRF was an accident.

I couldnt confirm wheter its 5 volts or not because my multimeter just broke today- I will see if i can fix it or just send it back into the Amazon.

Qiestion: Why dont i need to be worried to damage the Arduino as the ground wires heat up under stonger loads?

Does by the way anyboder know the producer of those IRLZs I have linked to amazon? Is it worth paying double to a knows electronics reseller or will i get the same results?

13

“ Why dont i need to be worried to damage the Arduino as the ground wires heat up under stonger loads?”

  • The GND wire from the battery negative to the Arduino GND carries almost zero current.
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  • There is the possibility you damaged the ones that don’t work.
    :wink:
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"The GND wire from the battery negative to the Arduino GND carries almost zero current." But it seems that its possible for the power coming from the source pin of the posfet to run to the Arduino ground pin right? In case that for some reason the reistance of the wire leading from the intersection of those 3 wires to the arduino pin is lower than the resistance from the intersection to the battery ground. Or am i confusing it here?

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"There is the possibility you damaged the ones that don’t work.
:wink:"
That feels more like certainty haha

17

  • The positive side of the battery is not connected to the Arduino so current from positive battery cannot hurt the Arduino (i.e. as long as you don’t physically short it to the Arduino pins).

  • Suppose if you wanted to feel more safe, change R1 to 470R.

BTW

  • High current loads with batteries should be fused properly.
18
  • It happens.
  • The more equipment you destroy the more experience you have.
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"The positive side of the battery is not connected to the Arduino so current from positive battery cannot hurt the Arduino (i.e. as long as you don’t physically short it to the Arduino pins)."
Im confused here as someone said there should be a common ground, hence they should be connected. But also that would imply that the battery (in reality a lab power supply) positive would have physicall access to the arduino ground. Is the common ground just a schematic thing, and i am supposed to keep the battery positive with the battery negative isolated from the Arduino 5V out and GND?

I have market where i believe to see a connection. passing through the MOSFET:

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Sorry to bother you with these beginner questions, but Im somehow confusing things here. And to be honest they are pretty confusing by nature.

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