Mosfet / short circuit

Other Hardware General Electronics
1

Hi! I need to turn a plasma cutter on and off for my CNC machine.

The machine turns on when two wires are short circuit.
I tried to hook up a MOSFET IRF520 to use that as a gate:

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How should I use a MOSFET for this purpose. I know how to use it if I want to power a motor with external power supply.

But in this case the machine itself spit out 24 V. When it is shortcut - it turns on.

I saw another guy using a relay and an external 5 V power supply: How to control a plasma cutter using GRBL - YouTube

In my case I do not think it works the same way since my machine already runs at 24 V.

I would appriciate some help since I can not find a solution after many hours spent.

Have a great weekend!
/Joel

2

Use the positive line ONLY not the positive and negative.
There are thousands of diagrams for "mosfet arduino"

Notice also that almost all have resistors in the circuit to help prevent damage to the Arduino !

3

Whhhhaaaa? How many amps is your plasma cutter putting out... I feel sorry for your poor little MOSFET. A properly spec’d relay is a better idea for this... it’s not impossible but it’s not simple as that.

4

If the plasma cutter is earthed and your Arduino is also earthed, your circuit might be shorting out something
and damaging it - there's no way to know from the information you've provided.

Please provide good detail on your plasma cutter, this is essential information, just saying its
a plasma cutter is providing no information of use. These two wires from it are for a control switch?
What voltage are they relative to ground? What amount of current flows?

You may be much better off using an isolated switching technique such as a relay or optoisolator
anyway as there may be EMI/interference issues.

The IRF520 is not a logic-level MOSFET anyway, it needs 10V or more to operate properly.

5

Thanks all for your nice comments.

I found a circuit that works:

more information about the plasma
amount of current flows= 2 AMP
24 V

Is my circuit a good way of doing it? I hope that the attached image is ok.
I should maybe add a diode somwhere to protect the Arduino.

I use GRBL to control my rebuilt CNC machine. I just need to get the plasma cutter to work.

It seems to work fine with my latest cirquit.

/Joel

6

Your MOSFET (or transistor) circuit may work with a "logic level" MOSFET. Worst case, you fry the MOSFET/transistor. Just make sure there is a gate resistor/base resistor so you don't fry the Arduino!

saw another guy using a relay and an external 5 V power supply:

A relay is the "safest" way to replace a switch because a relay is simply an electrically-controlled, electrically-isolated switch.

In my case I do not think it works the same way since my machine already runs at 24 V.]

That can work. The relay coil (which operates the relay) can be 5V and the contacts can be rated for 24V or 240V. There is one small "catch". The Arduino can't put-out enough current to directly drive a relay so you need a driver circuit. But, there are lots of relay board with a driver built-in so you don't have to build the driver yourself.

amount of current flows= 2 AMP

That seems odd to me... It's high for a "control signal" and it seems low for the actual plasma cutting.

7

Ok. Quick update.
I am a noob and should do it the right way.
I will now try my new 5v relay to trigger the plasma cutter instead of a mosfet.
My next problem is high frequency noise that shuts down the Arduino.There are a lot of post on this subject already in the forum.
This post can be closed.
Thanks you.

8

If you wish to close a post just go to the first one and edit/change the title to include "(SOLVED)"
That way people know you were ok with what you did to fix the issue.

Bob.