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Topic: Can a Pi be powered from the 5v pin ? (Read 798 times) previous topic - next topic

Apache14

Hello,

This is my first post here, i am working on a project that involves a Pi and a ardunio UNO (the Pi communicates with UNO via the serial over USB connection). The final device has to run off of a 7.6v battery, i have tested this and the ardunio + servos + speed controllers can all operate together well while running on the battery. However I am having issues determining the best way of powering the Pi. I know that the UNO has a 5v pin that (from some reading) should be able to supply a maximum of between 500-700mA, I am unsure of any damage that can happen when powering the Pi from the UNO and then connecting the Pi to the UNO via USB.

Any advice would be greatly appreciated


p.s. I hope this is the correct forum for this  :smiley-roll-blue:

pYro_65

If you have a large enough power supply, I would run a separate regulator for the pi, I thought the Arduino maxed out at around 300ma. Either way the onboard regulator will become inefficient at a high load.

JimboZA

Quote
run off of a 7.6v battery


I'm interested to know, Apache, what battery you use please?
Arduino ethernet server here.... http://jimboza.gotdns.com:8085/

No PMs for help please

Apache14


Quote
run off of a 7.6v battery


I'm interested to know, Apache, what battery you use please?


Sorry that was a typo its a 7.4v Li-Po battery, i think its from an old RC plane.

Sorry for any confusion


If you have a large enough power supply, I would run a separate regulator for the pi, I thought the Arduino maxed out at around 300ma. Either way the onboard regulator will become inefficient at a high load.


Yeah any recommendations for a good regulator ? i was looking at the TS7805 (1A 5V) as its available from maplin :P

JimboZA

Quote
Sorry that was a typo its a 7.4v Li-Po battery, i think its from an old RC plane.

Sorry for any confusion


Haha no I wasn't confused! It was a genuine question because I'm looking for a sensible source of energy for a robot arm. 7.6V made just as much sense to me as 8.5 or 6.3 or any other random pair of digits!
Arduino ethernet server here.... http://jimboza.gotdns.com:8085/

No PMs for help please

Apache14


Quote
Sorry that was a typo its a 7.4v Li-Po battery, i think its from an old RC plane.

Sorry for any confusion


Haha no I wasn't confused! It was a genuine question because I'm looking for a sensible source of energy for a robot arm. 7.6V made just as much sense to me as 8.5 or 6.3 or any other random pair of digits!


Specifically the battery is a PKZ1032  :)

Grumpy_Mike

Quote
I know that the UNO has a 5v pin that (from some reading) should be able to supply a maximum of between 500-700mA,

No it can't. It is limited by the power dissipation of the regulator:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

MichaelMeissner

#7
Jan 02, 2013, 03:10 am Last Edit: Jan 02, 2013, 03:20 am by MichaelMeissner Reason: 1
IIRC, the Pi needs at least 5 volts and 800 maH, and so the Arduino would not be able to drive it directly.  When the Pi's first came out, there was a scramble to find wall warts and USB hubs that provided enough power (the latest generation of smart phones and tablets wanting more than the 500 maH for fast charging has meant it is now easier to find 1 amp and 2.1 amp wall warts, though it would be nice if wall warts with multiple plugs could provide 2.1 amps to each plug, rather than dividing it among the devices).

MichaelMeissner


Haha no I wasn't confused! It was a genuine question because I'm looking for a sensible source of energy for a robot arm. 7.6V made just as much sense to me as 8.5 or 6.3 or any other random pair of digits!

IIRC, the common lithium cell in a lot of batteries delivers 3.7 volts.  So if internally the battery has 2 cells in parallel, it would deliver 7.4 volts (11.1 volts if the battery has 3 cells in parallel).  Nimh batteries like AA rechargeables tend to deliver 1.2 volts, so 3 AA rechargeable batteries would be 3.6 volts, 6 would be 7.2 volts, etc.

Of course batteries often times deliver voltage in a range, rather than being a specific value.

Funky Diver

A very cost effective method for powering a pi is using a UBEC

http://www.hobbyking.com/hobbyking/store/__14310__HobbyKing_UBEC_3A_2_6s_LiPO.html#relprodspan_focus

You can select 5 or 6 volt output up to 3amp draw, so perfect for a pi.
It'll draw power from 2S (7.4 volts) up to 6S (22.2 volts) DC source, so perfect for most hobby style LiPo batteries.  You will need to solder some terminals and possibly reconfigure the it put, the white wire is. Signal wire, btw, so you won't need that.  You can either just chop it out or ignore it.

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