Transistor get's really hot and doesn't seem to work.

I'm trying to turn on and off a 12V dc motor/pump (it's one of the motors that squirts the water on your windshield to clean it). Just hooked directly up to the power supply it draws about 1.5A. When I turn on the switch, my transistor gets super hot, to the point I can smell it burning, and the motor does NOT turn on. It's an IRF510 transistor. I copied this circuit from a YouTube video ( and this guy seems to have gotten his version to work fine. I cannot figure out what's going on here.

The wires in my picture that go off the table are connected to a 13V power supply on the ground. The diode attached to the motor is a 6A rectifier to handle the emf surge from turning the motor off.

Let me know if you have any questions for me!

IRF510 Datasheet:

Picture of Transistor get's really hot and doesn't seem to work.
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Zamperweenie (author) 2 years ago

Anyone else running into this issue check out this reddit post:

/u/bal00 does an awesome job at explaining why I was having this issue and offered a solution (that worked!). The short answer is that everything was hooked up correctly, just the transistor wasn't the right kind for this project.

iceng2 years ago

The IRF 510 does not turn on the 1.5A with a 5v Vgs signal !

In fact, the IRF 510 needs over 5V Vgs to turn ON 1.5A ..... and since a dc motor pulls 5 times the motor starting current 7.5A the IRF 510 a peak of 5.6A transistor is underpowered and under gate driven !

Zamperweenie (author)  iceng2 years ago

That makes sense! After looking around I think I'm going to replace it with an NTE2395 MOSFET. It seems it'll dissipate way less heat and everything else seems to be rated alright.

Can't Hurt ! :P

Still feel I should point out that the Vid you linked to uses a Tip120. I rarely have problems with the tip-12X Chipset

seandogue iceng2 years ago


Partial turn-on makes the FET into a resistor, and resistors dissipate energy in the form of heat. For full turn-on at spec'd on resistance values, most N channel devices want the gate at com, and for P channel FETS, gate at rail

Wired_Mist2 years ago

Flip the Fly-back diode over.

That little line represents the negitive side. The line has to face VCC (Positive End)

Zamperweenie (author)  Wired_Mist2 years ago

Yep, I did have that backwards! The 6A diode was overkill I learned. I simple 1A or so diode is fine (I switched to an IN4007), because all that matters is what *current surge* the diode can handle, not the *continuous current*.

A 1A diode can handle a pretty hefty current surge, way more than what I get here. Also the 1A fits on the breadboard so I could place it in parallel with the motor on there instead of clamping it to the motor. Less tacky and easier to see the circuit that way.

Awesome glad it worked !

Oh .... I see what you mean that diode is a short from the plus side.

If the mosfet does not melt first, the diode which looks like a hefty 6A unit might burn out ! ...... Then the motor might run.

It would be better to remove the diode or switch the green and yellow motor clip leads if the motor turns correct.

DC current flows in the direction of the line but not back.

Oh and get a Decent sized heatsink on it too !

kmossman2 years ago
Power MOSFET Motor Control

Because of the extremely high input or gate resistance that the
MOSFET has, its very fast switching speeds and the ease at which they
can be driven makes them ideal to interface with op-amps or standard
logic gates. However, care must be taken to ensure that the gate-source
input voltage is correctly chosen because when using the MOSFET as a switch the device must obtain a low RDS(on) channel resistance in proportion to this input gate voltage.

Low threshold type power MOSFETs may not switch “ON” until a least 3V
or 4V has been applied to its gate and if the output from the logic
gate is only +5V logic it may be insufficient to fully drive the MOSFET
into saturation.
Using lower threshold MOSFETs designed for interfacing
with TTL and CMOS logic gates that have thresholds as low as 1.5V to
2.0V are available.