Powering from USB


#1

Hi All,

Hopefully someone may be able to provide some much needed knowledge on this.

I noticed when plugging in another device to the spare USB port that the PI immediately rebooted. Presumably the device requested a charge which overloaded the power supply, with only 5V available this now seems fairly obvious.

Ideally I wanted to be able to occasionally charge a small tablet from the HestiaPI without having to run from an additional outlet. It wouldn’t even need to draw much power logically, but unfortunately I can’t really control that. Presumably I would need to replace the power supply with something more capable, but would that be likely to solve the problem and would other precautions need to be made in regulating the power?

Thanks


#2

Hello,
The power supply is chosen as a safe option for the needs of the Pi and the LCD. Adding something extra is an unknown parameter.
If it draws a bit too much or may cause reboots or overheating.
Replacing with a stronger power supply (5A ?) will cover you on this but you cannot use the internal USB connector of the pi as you would be asking the pi to produce the power needed by the external device and it will not work. This was probably the reason it caused the reboot you got.
What will work though is to install a micro USB connector in parallel to the new power supply. This way the power supply will produce 5V directly to the Pi and to the tablet. Make sure you choose a stabilised one that will not alter the 5V according to the current drawn.


#3

Thanks for the quick response.

The tablet seems to receive a charge (Though I haven’t measured how much it is getting), so it is currently working. It just appears to be the initial connection which causes the pi to reboot. But you’re saying it cannot be done that way even if a better power supply covers the initial current?

I’m not sure what is involved in adding a new micro USB connection directly to the power supply but I imagine it would be quite complicated to fit that in the case even if I could work it out.


#4

Getting power through RasPi involves a component on the board (voltage regulator) that is designed to withstand powering RasPi and 1 typical usb device. The spike on the current needed of the connection of the tablet causes that component to shut down and restart to protect the pi.
Supplying the pi with a larger power supply will not affect that component’s limitation :slight_smile:
The extra connector I suggested involves soldering a usb cable on the +5V and GND (or - depending on the board you have) labels of your PCB and placing it outside the case. Is that something you can do yourself or with the help of a friend or a local hackerspace?