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I'm a noob so please have patience with me. I have a 12V power supply to charge a motor driver, that I also want to power my Raspberry Pi-4B. I bought these mini buck converters on Amazon:

https://www.amazon.com/gp/product/B01MQGMOKI/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

I adjusted the power supply to 12V and connected the +/- to the converter's IN. I then adjusted the out voltage of the converter down to 5.09v (closest I could get with the POT). Then I connected the converter's OUT to the Pi, + to pin 2 (5v) and - pin 6 (gnd).

When I turned on the power, the Pi started smoking and of course didn't power on. The converter has a max 3A, which is what I need for the Pi, right? So why would this setup fry my Pi?

Prior to running this test, I adjusted my power supply to 5.2V and hooked it up to those same pins, and when I powered it up it worked beautifully.

Anybody have an idea on what I'm doing wrong? This is my first time using these buck converters.

Thanks!

  • Thanks for replying. I am thinking it must have been the wrong polarity, even though I checked it. I'm about ready to try it again, but quadruple checking everything this time. :D – Kevin Sep 7 at 0:12
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The converter you have found is tiny and there is no way it could provide 3A. From the looks it could continuously deliver 0.3..0.5A, not more.

enter image description here

For comparison, this is how an actual 4.5A buck converter looks like:

enter image description here

When you connected it to the Pi, the converter got overloaded, and, having no overload protection (also not surprising for $1/piece module) it simply let 12V right though. This is what have killed your Pi.

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    Thanks for the great response. I'm sure you're right. I hooked up another one and it didn't fry it this time, but it didn't seem to give it sufficient power to even boot up. I'll go ahead and get a real buck converter for the job. Thank you! – Kevin Sep 11 at 1:58
  • @Kevin Yeah, actually the MP1584 is advertised to have overload protection, but in my experience such cheap-brand parts still have failure modes the protection is supposed to prevent. – Dmitry Grigoryev Sep 11 at 13:35
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I don't see any reason for what you describe to have killed the Pi. I regularly use UBECs to power the Pi and that is pretty much the same (apart from the output voltage being preset).

As to what happened in your case. Either the wrong polarity of the input voltage was quite a lot more than 5V.

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You should also check carefully those cheap converters before connecting them to the pi. Some people has observed voltage changes that blown their devices.

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