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Topic: Mosfet suddenly doesn't work as intended (Read 227 times) previous topic - next topic

uRThow

Aug 14, 2018, 01:46 am Last Edit: Aug 14, 2018, 01:57 am by uRThow
So I use this mosfet to power my 12v fan: http://www.onsemi.com/pub/Collateral/MTP3055VL-D.PDF and I use this circuit: https://imgur.com/a/Vqi60fY
Before, when I wrote this in the IDE: pinMode(9, OUTPUT); digitalWrite(9, HIGH); the fan started to rotate really fast as intended and this worked for a couple of days but the mosfet did get hot. But now a few days later when I tried to use it again, the fan only spins a little bit. This issue started appearing after I plugged in a second fan.
Does anyone know why?

JohnRob

What board are you using?  Is it a 5V or 3.3 volt board?

If 3.3v, the Mosfet may not be fully turned on.  They symptoms are getting hot.



Please do not PM me with thread based messages.  If your thoughts are worth responding,  the group should benefit from your insight.

larryd

#2
Aug 14, 2018, 03:02 am Last Edit: Aug 14, 2018, 03:03 am by larryd


That MOSFET is .1 - .18 Ω @5v,    this is a poor choice.

What current does your fan use.

If you didn't change the wiring, you may have damaged the transistor.

What is the HIGH level on the output pin?

What is the drain voltage when the HIGH is on the gate?

Show us a good image of the wiring.

No technical PMs.
The last thing you did is where you should start looking.

DrAzzy

Either loose wire or you damaged the mosfet.
ATtiny core for 841+1634+828 and x313/x4/x5/x61/x7/x8 series Board Manager:
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ATtiny breakouts (some assembled), mosfets and awesome prototyping board in my store http://tindie.com/stores/DrAzzy

uRThow

What board are you using?  Is it a 5V or 3.3 volt board?
I am using a 5v board.

What current does your fan use.
In the final setup I want three fans that use 12v and 0.2A.

If you didn't change the wiring, you may have damaged the transistor.
I have not changed the wiring and I tested everything and every wire and component works fine exept for the mosfet.
What is the HIGH level on the output pin?
What do you mean with this?
What is the drain voltage when the HIGH is on the gate?
That should be 12v.
Show us a good image of the wiring.
https://imgur.com/a/rCfSvlN
So currently I am using a simple test setup. The 2 white wires coming from the bottom right of the screen are coming from my 12v adapter. The yellow wire is my gate wire which I use to test my mosfet.

Either loose wire or you damaged the mosfet.
I definitely don't have any loose wires, especially not now that I am using a small test setup.

Do you guys know what mosfet I'd need in order for me to run three 12v 0.2A fans? Thanks in advance.

MarkT

You have no freewheel diode across the load.  Its an inductive load so requires one to prevent
high voltage spikes damaging the MOSFET, which may be what happened.

Another possibility is that you didn't take full static electricity handling precautions with the MOSFET,
which are extremely delicate until in-circuit (power MOSFETs don't normally have any in-built
static protection circuitry, unless they have a built-in zener (fairly rare)).

And the other possibility is an eBay purchase - counterfeit device.

0.2A at 0.12 ohms on resistance should not be getting remotely warm, let alone hot,
so something was definitely wrong.

0.18 ohms on-resistance is perfectly fine choice for a 0.2A or 0.6A load, BTW, it would be
good upto 1.5 or 2A, then a heatsink or a better device would be needed.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

larryd

No technical PMs.
The last thing you did is where you should start looking.

larryd

That looks like a 3 wire fan.
Make sure you are using the correct two wires.

What happens when you connect the fan to 12v directly.

The drain to source voltage should be very low (ideally zero) when the Arduino output is HIGH.

You sould measure nearly 5v on the Arduino output when the pin is HIGH.

Cannot see the resistors in you image.


No technical PMs.
The last thing you did is where you should start looking.

Paul__B

Minor point and not the reason for your trouble, but the 10k resistor is shown on that diagram in the wrong position.

It should be between the Arduino pin and ground, not across the FET gate and ground.





JohnRob

Power MosFET's are pretty tough,  hard to damage them.   If you did manage to damage the MosFET it would most likely fail ON (i.e nearly a short) which would leave your fan on full.  Although obviously I can't be sure but I doubt the MosFET is the root cause.  If I had to guess I would first check the battery voltage.  if you don't have a voltmeter I suggest you purchase one, even if it is a cheapo one from someplace like Harbor Freight.


I would perform the following tests:

  • Connect the fan directly across the batteries and see if it works as you expect (I believe this was suggested previously)
  • If the fan is working fine on the batteries, I would remove the gate connection from the arduino and connect it to the battery Plus.  The fan should go on as strong as in 1 above.


Please do not PM me with thread based messages.  If your thoughts are worth responding,  the group should benefit from your insight.

noweare

What's the 220 Ohm resistor for ?  I was thinking the battery also.

larryd

#11
Today at 04:37 am Last Edit: Today at 04:39 am by larryd
The gate of the MOSFET looks like a capacitor connected to GND.
This capacitor looks like an instantaneous short when the gate goes from LOW to HIGH, vv.
The 220 Ω resistors limits the Arduino output current when the output goes from LOW to GND, vv.





No technical PMs.
The last thing you did is where you should start looking.

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