I am powering a motor with a 12 V battery. When I power on the motor I am using 12 amps of current. As a result the motor uses 144 Watts.
Before I used to have this diagram:
(Powering the left relay would have the motor spin in one direction and powering the other relay in the opposite direction)
And now I want to achieve the same goal using a MOSFETs. So now I have this diagram:
- All MOSFETs in diagram have the Gate, Drain and Source in order from left to right.
- Green lines represent 22K Ohm resistor. There are only 2. They act as pullup resistors.
- MOSFET Q2 and Q4 are P channel MOSFETs. Specifically BOJACK IRF4905
- MOSFET Q1 and Q3 are N channel MOSFETs. Specifically BOJACK IRFZ44N
If none of the buttons are pressed then Q2 and Q4 MOSFETs are left closed so no electricity can flow. As you can see the gate is attached to a pullup resistor of 22k Ohms. So the gate is by default with a positive voltage. Because it is a P-Channel MOSFET that will make the MOSFET be left open. Because the MOSFETs on the bottom are N-Channel that means by default they are open.
If I press button 1 then the Gate of Q2 and Q1 will become negative instead of positive. As a result electricity will flow this way:
Why are the P-Channel MOSFETs (ones on top) getting really hot? When spinning the motor by pressing the button on the left, the top MOSFET Q2 gets really hot. When I press button 2 instead of button 1 then the top right MOSFET Q4 gets really hot. I gets so hot to the point that smoke comes out.
Why are the P-Channel MOSFETs the only ones getting so hot and not the N-Channel MOSFETs?
These are the specs of the IRF4905 MOSFET:
- Voltage Vgs highest: ±20V
- Number of stitches: 3
- Operating Temperature:-55 °C to +175 °C
- Thermal resistance junction to case A: 1.3°C/W
- Voltage Vds Typical: 55V
- Current Id continuous: 74A
- Current Idm pulse: 260A
- Surface Mount Device: Through Hole Mounting
Is my diagram incorrect? It works great when using a 9 V battery. But when I use the 12 V battery the p-channel MOSFETs get too hot. Should I buy a different p-channel MOSFET instead? If so what p-channel MOSFET do I have to buy?
This are the reviews of the P-Channel MOSFET that I purchased:
I guess that is my problem and that explains why only the p-channel MOSFET overheats.