MOSFET not giving sufficient power

[microwavedbread]

Hello everyone,

I am trying to use a MOSFET module I bought off of Amazon to control a 12 V DC motor (car door actuator) with an arduino.

when I hook the motor directly up to the power supply, I get a nice snappy motion. However, when I wire everything together, the motor barely twitches when in the on position. It is worth noting that the MOSFET does get hot, which would imply that a lot of current is passing through. I do have a fly back diode installed as well, so I don’t think that is an issue. Does anyone have any idea what might be going on?

For some reason the site is is giving me errors when I try to upload pictures, but I will try again to upload photos later.

 

[Harald Kapp]

We need more details:
- type of module (ideally link to a datasheet)
- type of motor (power requirements)

For some reason the site is is giving me errors when I try to upload pictures

Resize to < 300 kB, that'll work.

 

[microwavedbread]

We need more details:
- type of module (ideally link to a datasheet)
- type of motor (power requirements)

There is no power rating for the motor, but it is running on 12 volts and the current current consumption according to the supplier is .25-2.25 Amps, so it could take up to 27 watts. The power supply is a 12V, 3.25A power supply. I plan on only actuating this motor for very short periods of time. It is going to work as a pop bumper for a small pinball machine.

The MOSFET is an IRF520.
Here is the amazon link: https://www.amazon.com/IRF520-MOSFE...pd_rd_i=B07F7SV84V&psc=1&ref_=pd_bap_d_rp_1_t
Attached below is a picture of the circuit diagram and my wiring to the DC motor.

 

[crutschow]

The IRF520 requires a Vgs of 10V to fully turn on (below).
What is the control signal level you are applying?

 

[Alec_t]

You have no Vcc connection (3.3V, 5V?) from the micro to the module.

 

[crutschow]

You have no Vcc connection (3.3V, 5V?) from the micro to the module.

It appears the Vcc is not connected on the module, only signal and ground.

 

[bertus]

Hello,

The Mosfet module will work much better when you replace the IRF520 by an IRL520.
The IRL520 has a much lower threshold voltage.



Bertus

 

[microwavedbread]

update: I tried wiring everything up to a different mosfet module and I actually got a much better response! However, I do think it’s a little more powerful when connected directly to the source.

The IRF520 requires a Vgs of 10V to fully turn on (below).
What is the control signal level you are applying?

The signal wire is directly connected to the arduino, so def not 10 V. Does this mean I can’t get the full power of my motor without using a different mosfet? If so, that’s really misleading that the supplier says it’s made to work with an arduino :/

 

[crutschow]

The signal wire is directly connected to the arduino, so def not 10 V

So does the Arduino put out 5V or 3.3V?

Does this mean I can’t get the full power of my motor without using a different mosfet?

Yes, you may need a different MOSFET as bertus suggested.

 

[microwavedbread]

The Mosfet module will work much better when you replace the IRF520 by an IRL520.
The IRL520 has a much lower threshold voltage.

Thanks for the tip! I may end up doing that if I can’t get enough power to bounce the ball around with what I already have at my disposal.
Some thing else I have noticed is that whenever I connect my motor directly to the power source and then disconnect, it seems that the electrical surge (that I am protecting my circuit from with the fly back diode) causes the motor to retract a little. this is actually good for me because it allows the pop bumper to kind of naturally reset at the top position and have more distance to accelerate down and hit the ball. However, when I wire it to the breadboard it no longer does this. Does this also have to do with the motor not getting enough current from the mosfet?

 

[microwavedbread]

So does the Arduino put out 5V or 3.3V?

5 volts!

 

[Harald Kapp]

What is the control signal level you are applying?

Likely only 5 V as it comes from

The IRF520 requires a Vgs of 10V to fully turn on (below).

V_GSth(max) is only 4 V:


Therefore a 5 V gate drive signal will turn on the MOSFET, good for a drain current of ~2 A. Although that is not an ideal operating condition, it should suffice for your motor.

and



The vendor of the MOSFET module states that for currents above 1 A you need to use a heatsink. I do not see this heatsink in your photos. The MOSFET may easily overheat.

Here's a discussion on using power MOSFETs with an Arduino that explicitly mentions the IRF520. I also found the circuit diagram of your cheap module. The level shifter / driver transistor that is used in the discussion is not present here. The Arduino directly drives the MOSFET's gate. Arguably not the best circuit.

 

[crutschow]

Therefore a 5 V gate drive signal will turn on the MOSFET, good for a drain current of ~2 A

Those curves show a "typical" characteristic (likely for a Vgs(th) of 3V).
(You should never design a circuit using typical characteristics).
The particular MOSFET you have would have a current less than 2A at a 5V Vgs if its Vgs(th) was the 4V max value.

 

[bertus]

Hello,

Have a look at these output characteristics:

Bertus

 

[Harald Kapp]

Of course typical, you are fully right there.
See this post for a simple level shifter using a transistor and 2 resistors. Replace as follows:
V1 = 12 V (from 12 V power supply)
V2 = output of Arduino
V3 = 5 V (from Arduino)
That will give a clean 12 V gate drive to the IRF.


Or replace the IRF by an IRL which has a much lower gate drive requirement, see the characteristics posted by @bertus ,

 

[crutschow]

Below is the LTspice simulation of the circuit Harald suggested:

 

[crutschow]

R2 should be 10kΩ, not 5k.

 

[Harald Kapp]

R2 should be 10kΩ, not 5k.

R2 needs to be much less. The circuit diagram I linked in post #12 shows input resistors of 1 kΩ from the gate to ground (1 direct, one via an LED). These resistors form a voltage divider with R2. Therefore R2 should be around 100 Ω.

 

[Audioguru]

The graphs on most datasheets show only a device with "typical" specs. Where on earth can you buy one that has typical or better specs? The Mosfet manufacturer might have sold all the very sensitive ones to a product manufacturer who paid more for them.

 

[crutschow]

The circuit diagram I linked in post #12 shows input resistors of 1 kΩ from the gate to ground (1 direct, one via an LED). These resistors form a voltage divider with R2. Therefore R2 should be around 100 Ω.

Yes, I missed that.
But changing R2 to 100Ω means the Arduino output must sink 120mA, which it can't.
My suggestion is to remove the 1kΩ resistor from gate to ground or increase it's value to about 100kΩ.
That will still be sufficient to pull the gate low with a floating input.