I am trying popped a transistor while trying to power my raspberry pi from a bread board. I have a 12v battery pack that I am going to use to power my raspberry pi and some servo's. Yesterday I checked the voltage coming out of the output voltage from one of the power rails on the breadboard and it was 5 volts. When I attached my raspberry pi it popped one of the transistors on the board that I used to convert the 12volt to 5 volt. BTW the odd thing is that after frying the transistor it was outputting 10 volts to the rails. Luckily it did not cook my pi :) . I am using a B+ and connected the first 5v pin and the 3rd pin which is ground on my pi. Counting pins only on the outside of of the header and not the board layout. Should I have used the second 5v (pin 2 on the outside of the header). BTW what is the second 5v pin for? I only have one 5v on my model B.

Any ideas would help as I am new to electronics and don't want to fry another board. I apologize if this is not the right forum maybe there is a better stackexchange site but I figured I would start here.

Here is the breadboard power supply that I was using. http://www.amazon.com/gp/product/B00GWIL0MQ/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Here is the power supply I was using. http://www.amazon.com/gp/product/B007RQW5WG/ref=oh_aui_detailpage_o04_s01?ie=UTF8&psc=1


Found another option on amazon and it appears the mb102 max output is 700ma and the pi can pull 1.5A current so this is probably what happened.


2 Answers 2


Why not connect the 12V supply to a 5V UBEC? A UBEC converts anything within a wide range of voltages (typically 5.5V-26V) to 5V and they are generally rated for 3-4 amps.

Search on eBay, a UBEC costs a couple of UK pounds.

You are lucky the Pi wasn't damaged.

Anything over 6V is likely to damage the Pi.

Anything over 5.25V could potentially damage anything connected to the Pi (like a USB device).

The Pi has always had two 5V pins. See http://elinux.org/RPi_Low-level_peripherals#General_Purpose_Input.2FOutput_.28GPIO.29

On early revisions they were marked Do Not Connect (DNC) but in fact were always 5V.

I feed 5V from a UBEC into a 5V pin and a ground pin (my UBEC is powered from a 12V laptop power transformer). I use the other 5V pin to feed power into a breadboard. Similarly I use a 3V3 pin to feed power into a breadboard if I'm using a component which needs 3V3.

  • Appreciate the advice but I want to power other devices too and the breadboard power supply seems like the perfect option. I need to power a couple of servo's and a relay. The looked and the pi only pulls 1500ma at max and my battery pack supplies 3800ma so I don't know if it was pulling too much current. Oct 1, 2014 at 17:42
  • What amperage is that breadboard supply rated for? I doubt it could power a Pi and a decent servo.
    – joan
    Oct 1, 2014 at 18:10
  • Looking online it seems like the 7-12 amps. Didn't even think about the max amperage for the breadboard. I did also have a 5v relay connected yesterday to the opposite site of the breadboard on the opposite rails. I think my problem may have been that the adapter may not have been connected securely to the bread board and this could have caused it to pop. I definitely checked the voltage before connecting the pi and it was a perfect 5v on the pi rails. I ordered two more just in case I messed something up. Hoping it was a fluke because it seems like a cool little connector. Oct 1, 2014 at 18:33
  • I might use the usb connection on the adapter referenced above. This should be safer for my pi also. Oct 1, 2014 at 18:34
  • There is no way that zitrades unit could supply 7-12 amps. At maximum rating it might supply 2 amps but I doubt it would last long at that current. As I say I doubt it will power a Pi and a servo.
    – joan
    Oct 1, 2014 at 18:54

The exploding part you called "transistor" is most likely the integrated regulator itself. From the description given it is highly likely that that was caused by overcurrent/short circuit. To be honest I'd consider it a bad design that the regulator has no current limiter. But I doubt the current rating of 1500 mA for the RPi for any typical application given the reportet power consumption of less than 1.5 W (see How much energy does the raspberry pi consume in a day?). The 10 V output after the failure is also reported at amazon reviews for the product used.

Using a linear regulator for a portable solution however is not a good idea. If the input voltage is 12 V and output voltage is 5 V you're wasting more than half your energy used for the RPi just to heat your regulator (which seems to have little to none heatsink attached). So if you want to safe batteries you should really investigate Step-Down Converters. But maybe https://electronics.stackexchange.com/ would be more helpful concerning such issues.

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