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I am attaching my Pi 3 to two delicate sensors via USB. My question is, if i was to take the power cords from the sensors and attach them to a male USB cord. The problem is, anything more than 5.5V will fry the sensors permanently and each one costs around $2000.00.

I've looked at different Data sheets for the Pi-3 and have not found the information I am looking for.

Any help would be greatly appreciated.

Jens Carter
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2 Answers2

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~6W — You can draw 1.2A

The voltage is derived from the power you connect to the Pi, which should be 5±0.25V. The Pi does have a diode to limit over voltage, but this is only intended to limit transients.

So the answer to your question depends on what you supply to the Pi.

See Raspberry Pi Power Limitations for further detail and description of the Pi circuitry.

Milliways
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  • Between the zener and the fuse the raspberry pi will likely be adequately sacrificial in case of overvoltage, which may suffice for OP's purposes. However I would test first by burning a few raspberry pi's... $100 for test is less than $2000 – crasic Sep 30 '17 at 06:34
  • @crasic What "zener"? If you are referring to the transient voltage suppressor this has a breakdown voltage of 6.4V - 7.23V – Milliways Sep 30 '17 at 07:18
  • Oh... it is a TVS. Certainly poorer than a rail zener diode clamp. In principle it will start to conduct at `V_R` hence the `5.0` rating, but breakdown for these is always about 15% more than `V_R` – crasic Sep 30 '17 at 17:07
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I believe the Raspberry Pi does not regulate the voltage fed to the USB. If your Pi is receiving 5.5V from its power supply then that voltage will be output to your USB will be 5.5v, you could test this using a multimeter.

Dr.Rabbit
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  • It is not regulated, but is conditioned. There is ["Power Switch IC"](http://www.richtek.com/assets/product_file/RT9741/DS9741-01.pdf) (mosfet) with some additional current limiting and undervoltage dedicated to the host ports, but no regulation. – crasic Sep 30 '17 at 06:32