Voltage fall down when connecting a device in MOSFET IRF520

Hi all, I'm facing a weird behaviour on this circuit when connectig a device at the output of the mofets. i'm pretty noob with electronics and probably I'm missing something obvious... The thing is, if I take a measure of the mosfet output with the tester, the voltage is correct (12V aprox) but if I Attach the motor (is a 12v water pump actually) the voltage falls instantly to zero.

Any clues? I bet the problem is related with having two mosfets in parallel, but no idea why or how to solve it.

Thank you very much in advance for your support.

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What is the output voltage of the controller? 3.3V? IRF520 MOSFET is not a logic level device. It needs on the order of 10V to turn on. You need a MOSFET that will turn on with the output voltage from your controller and handle the stall current of the motor.

Is this your module?
RV mineirin

Thanks for the quick response; the controller output is indeed 3.3V but is working fine with a single mosfet schema. This is the evolution of another project that I had working for some months with a single mosfet (same model) and that's why I think dual mosfet in parallel behavior is not the same.


The output of the MOSFET should be at 0V with nothing connected to the output, and rise to 12V with the motor connected (MOSFET off), but then fall down to a low voltage if the MOSFET is turned on. You definitely need a logic-level MOSFET if driving from 5V Arduino, not the 520.

Thanks! something like IRL540 or IRLZ44? could you recommed me any model with good performance based on your experience?

... Nevertheless, I can't still wonder why it does work with a single mosfet...

There are literally 1000's of logic level MOSFETs - what performance are you looking for?

Something to activate two 12v water pumps (max 5A) with a Wemos D1 Mini

I've found this quite cheap and available at Amazon (ES), would do the job?


Thanx! but is for 5v or 3.3v?

Adequate for 5 A.


Thank you all for your support

If you look at the datasheet, (google "IRL540 datasheet"), it will tell you, there's a spec for Rds(on) which gives the value(s) of Vgs needed. For the IRL540 its given for both 5V and 4V. Alas the on-resistance is fairly high, there are much better MOSFETs out there. Don't pick a 100V MOSFET for a 12V load, the higher the voltage the higher the on-resistance (as a rule of thumb).

I bought some IRL540 today and can't make them work either, is it normal sorce and drain pins to be closed (transmit power) by default despite no Gate voltage is applied?

No, power MOSFETs are enhancement mode, so non-conducting with Vgs=0

You devices are fried? Or counterfeit? (these days all semiconductors bought from eBay or randoms on amazon are very likely to be junk - only buy from genuine electronics stockists)

You know to observe precautions to avoid static discharge when handling any MOS devices?

They were bought in a specialized electronics shop, i'll contact them then...

Were they packaged in anti-static bags?