Issues with MOSFET module

Question

This first MOSFET switch burn out if I run the pump more than 10 seconds.
The output of MOSFET connected to 1100gph bilge pump. The power source of MOSFET connected to battery 7 Ah. Anyone who has experience with this MOSFET module, kindly help me why its happen.

Link of the product: 5-36V Switch Drive High-Power MOSFET Trigger Module

Issue with another F5305S power FET MOSFET is analog write not working. I can't control speed of the pump.

Product link: MOSFET Electronic Switch DC Controlling Board

Schematic:

Pump product link: DC12V 1100GPH Bilge Pump

Answer 1

The module uses D4184 Alpha&Omega MOSFETs (at least according to the ad photo, they may have a different brand, perhaps less famous one, on the actual part). They only have guaranteed Rds(on) at 4.5V or greater, and you are driving them with 3.3V. Hence they will tend to overheat.

As others have noted you should also have a diode (such as a 3A to 5A Schottky diode) across the pump terminals with reverse bias. With either circuit.

I don't know why the second one is not working- and your description is not very helpful- the optoisolator circuit should level shift the input- but if you're trying to do PWM, the optisolator circuit gate drive may be too slow.

If you're going to use these hobby type modules, you should not use them at the highest or lowest limits they claim, they're often not all that well designed.

Answer 2

Place suitable capacitor or flyback diode in pump end or MOSFET end to avoid voltage spike. The MOSFET module doesn't have a diode built-in. Add diode or capacitor to protect your MOSFET from burning out.

Answer 3

You need a flyback diode across the inductive element, and skimming through you question, I could not find the power or current your pump needs. As expected, things burn when overloaded so make sure your transistor can handle it. You can see the effect caused by not having a diode in this simulation. On the right you have an unclamped circuit, and on the left you have a one with a diode across the inductive load. In this case the pump is represented as the LR series circuit at the top.