Hello, l have a circuit that is using mosfets to switch power for an inductive load. The issue is that whenever I power on the Arduino and my cheap ass button decides to open the the gates or l actually press it, the mosfets open and they wont close until I manually short the gate to the ground.
As you can see in the sketch I'm using a pulldown resistor already.
I have replaced the mosfets multiple times
And 1 have checked all the components and wires. The multimeter shows roughly 9,8 kohms from the gate to just before the Arduino ground.
If I'm not mistaken, the gate should be
Internally connected to ground (source) in the MOSFET itself and to the Arduino ground via a 10k resistor.
You can see a yellow wire connecting the grounds in the sketch, although I do not currently have this wire in place. I was told about a "common" ground but not if it was solely a sketch semantic, or if there was actual importance or sense behind it. I did not build it because I'm worried I could fry the Arduino. And its quiet some overhead too.
This circuit is driving me crazy, send help please!
Without a common ground to complete the path, you do not have a circuit, neither in the literal sense of the word, nor in its specific electrical usage.
You are apparently trying to use an N channel MOSFET as a high side switch. That will not end well.
Oh, I do currently have the MOSFET after the load. Ist different in the Sketch because I was preparing another curcuit… well circuits. I’ll can add that sketch in case someone has advice
As to the common ground I have tried to find info on google but I found no insightful results. Is there perhaps a certain terminology for that? And besides the fact that those are 2 connected circuits, is there any harm/ disadvantage?
I note that I will need another MOSFET for that circuit:
Thanks for this reply. The post you linked, contained exactly the information neccessary and was able to solve my confusion:
" It is fundamental to the way electricity works that current has to circulate, it has to start from some source, such as a battery, go around and come back to where it started. This need to circulate is why they are called circuits. Forget the term ground, I think it is confusing you. What matters is the electrons can go back to where they started from."
I was indeed confused by the concepts of grounding as i wrongfully thought, that current can flow from any source to any ground. The circulation part was missing for me.
I´ve now resoldered everything and tested it, its working now
Of course the next problem occurred haha.
I will mark your post as the result because it contained a complete explanation of the issue and solution, thank you.
I wanted to mark your answer as the solution first, as it is indeed the solution, but another one here made a very detailed exlpaination of the issue and solution and I thought that was quite helpful.
It really was that "little" detail of the common ground
Oh and thanks for the note of changin the order of the resistors! Ive now wired it like you noted.
As of right now, it is wired like that. The sketch shows it different as im preparing to expand the circuit as its shown in post #3. Thanks for the note, and in fact I was able to find useful and good information after googling the term "source follower". It led me to similar concepts as in post #3 although its quite confusing at some points...
thank you for the reply!
As of now, ive not selected a specific part as for the step-up converter and for the capacitors, although Im eying some parts.
I used 2 capactiros to display how i would wire any 'n' number of similar capacitors in parallel to increase the capacitance.
This coil is quite literally a coil serving as electromagnet to move a mechanical bolt type thingy, that has quite some mechanical resistance(weight) for the scale. That cannot be done with motors unfortunately.
The reason why Im looking forward to expand the circuit as I´ve shown is to increase the strength of the "impuls" of the EM.
The idea really is that, the mosfet switches up to 24V to the step-up converter, which then converts them to lets say 50V and with that "charges" a row of capacitors which then release a stronger impuls to the coils as the MOSFET opens.
But as Im writing this, I realized that this could only work if the switch was after the capacitors, which would expose them to the stronger impuls and probably kill them....
The issue really is, that the impuls is not strong enough at 24V. Note please that the circuit shown is somewhat simplified of course.
