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I am trying to power two Raspberry Pi Picos with one breadboard power supply (found here.) When I connect a 9V battery to the supply (and have ensured correct wiring, correct rail polarity, etc.,) the Picos turn on and execute the correct code, but the power supply gets super hot (specifically the two voltage regulators in the middle) within about two minutes of the system being turned on. I connected a 2.1mm wall-plug power supply next to try and debug and it gets even hotter.

Is there something I am missing here, maybe in terms of the current? Is the current draw/intake too much? This also happens with a second breadboard power supply, so I am at a loss.

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  • \$\begingroup\$ Is anything (i.e. peripherals) connected to the Picos? You can safely draw up to 300 mA from one Pico, and the breadboard supply (according to your link) can supply a maximum of 700 mA. Without any peripherals one Pico consumes about 91mA during the popcorn test (VGA video, SD card and I2S audio) with power-saving disabled \$\endgroup\$
    – Greenonline
    Commented Jun 30, 2023 at 17:12
  • \$\begingroup\$ Only thing that is connected is one LED to each Pico. They all light up correctly when one Pico is powered via USB through my laptop. They are also brand new Picos \$\endgroup\$
    – harryt
    Commented Jun 30, 2023 at 17:16
  • \$\begingroup\$ Check for shorts (or low resistance) using multimeter on the breadboards supply rails (not the breadboard power supply input, but rather the output pins), with the power/battery disconnected of course. \$\endgroup\$
    – Greenonline
    Commented Jun 30, 2023 at 17:18
  • \$\begingroup\$ 12 V down to 3.3 V via linear regulator will be very hot. Do you need 12 V? \$\endgroup\$
    – winny
    Commented Jun 30, 2023 at 19:36
  • 2
    \$\begingroup\$ what temperature is super hot? \$\endgroup\$
    – jsotola
    Commented Jun 30, 2023 at 21:46

2 Answers 2

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Sounds normal.

Your breadboard supply has linear regulators, that must waste excess power as heat.

Supplying input with 9V, and using 5V output at e.g. 100mA, the 5V regulator must drop 4V at 100mA, wasting 0.4W as heat.

So basically, either the current consumed by load is too high and regulators heat up, or input voltage to regulator is too high and they heat up, or both.

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This is not "normal." The circuit board you have purchased is far overrated.

The linear regulators used drop voltage by converting power to heat. To work properly, they need to be attached to a large surface to radiate away the heat.

There are two AMS1117 regulators on that PCB.

According to the datasheet, it takes a 5x5 centimeter PCB area to keep one regulator below 55°C while dissipating one watt.

If you are using 3.3V for the Pi Pico, then at 700mA, the regulator has to waste ((9-3.3)x.7)= 4 watts of power. Even with the mentioned 5x5 cm PCB area, that would be heating the regulator to 4x55°C= 220°C. That far exceeds the rated 125°C. The regulator will shutdown to prevent damage.

The little PCB you have is nowhere near large enough to keep the regulators properly cooled at the rated current. It would need to be much larger if using only the PCB surface for cooling, or else it would need to have additional heat sinking added to it.

Linear regulators should not run hot. They must be kept cool by radiating away the excess heat. The PCB you have is simply not designed to fulfill the promised specifications.

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