pruggia
Posts: 3
Joined: Wed Dec 26, 2018 6:46 pm

Wi-Fi issue powering Pi from gpio

Fri Dec 28, 2018 6:17 pm

Hi!
I have a pi model 3b. When I power it through usb the onboard Wi-Fi works great. But when I power it through the 5V gpio pins with batteries the Wi-Fi doesn't seem to work at all. I measured the voltage with a multimeter and it is properly getting a steady 5V and drawing about 0.4A.
Is what I'm trying to do even possible or there is some kind of limitation on what can be powered through gpio and the wifi will never work that way? If it is possible, any tips on how can I debug this issue? (I read that power saving mode is turned off by default now so it is probably not related to that. I'm on raspbian totally updated/upgraded).
Thanks!

drgeoff
Posts: 9761
Joined: Wed Jan 25, 2012 6:39 pm

Re: Wi-Fi issue powering Pi from gpio

Fri Dec 28, 2018 7:12 pm

There is no limitation of the sort you are imagining.

Can you be more specific about the "batteries" you are connecting to the GPIO header?

pruggia
Posts: 3
Joined: Wed Dec 26, 2018 6:46 pm

Re: Wi-Fi issue powering Pi from gpio

Sat Dec 29, 2018 5:08 pm

Thanks for answering!
I'm powering the Pi with 8 rechargeable NiMH batteries, 1.2V each in series that go through a 5V LD1085V50 voltage regulator (the reason for that many batteries is that they are also used to power some motors, but that part of the circuit I don't have connected and still wifi is not working).

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mooblie
Posts: 125
Joined: Fri Oct 14, 2016 2:07 pm
Location: The Scottish Highlands

Re: Wi-Fi issue powering Pi from gpio

Sat Dec 29, 2018 5:35 pm

If you fully recharge the NiMH batteries and try again, does it work then?

EXACTLY what DC voltage are you feeding to the Pi when the Wifi isn't working?

Rather than a fixed IC regulator, you might have more success with a DC-DC "buck" converter module, because they have an adjustable output, and you may find the Pi works better with about 5.1VDC (or more) input. They're not expensive, see here:

https://www.ebay.co.uk/itm/262868515931
Last edited by mooblie on Sat Dec 29, 2018 5:43 pm, edited 2 times in total.

drgeoff
Posts: 9761
Joined: Wed Jan 25, 2012 6:39 pm

Re: Wi-Fi issue powering Pi from gpio

Sat Dec 29, 2018 5:38 pm

Unless you have that voltage regulator on a reasonably large heatsink the power it needs to dissipate will very quickly make it reach a temperature where, in order to protect itself, it limits the power available to the RPi.

If you insist on powering that way, use a DC-DC converter not a linear voltage regulator.

pruggia
Posts: 3
Joined: Wed Dec 26, 2018 6:46 pm

Re: Wi-Fi issue powering Pi from gpio

Sat Dec 29, 2018 6:46 pm

Thank you so much for the tips!
The voltage reading was 4.95V (or close to that, definitely on the high 90s). With batteries fully charge I still have the same issue.
I won't insist on powering it like that =) This was a bot that I built with a beaglebone black (for this MOOC https://www.coursera.org/learn/mobile-robot) and was trying to make it work with a pi this time. Looking around for similar bots built with pis, a lot of them chose to have a dedicated usb power bank, so I'll probably go with that for the pi, and keep the batteries just for the sensors/actuators.

rhubarbdog
Posts: 64
Joined: Mon Dec 11, 2017 9:58 pm

Re: Wi-Fi issue powering Pi from gpio

Sun Dec 30, 2018 12:17 am

I have no problems running a pi zero w. Off a lithium ion remote control car battery via a regulator like yours . I have a 1.1 amp poly fuse in series between the regulator and raspberry pi

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