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lightning bolt and rPI 3 power requirements

Posted: Wed Aug 23, 2017 10:28 pm
by tadd
What are the conditions which cause the lightning bolt to show up on the Raspberry PI HDMI display, upper right? Does it do this during normal operation? Does it do it while booting with text scrolling on the display?

I have a dozen field deployed systems built out of a 12v to USB switcher supply providing 4.95 to 5.1 volts and successfully running Raspberry PI B+, 2 B and 3 B boards. Some of these show an intermittent color square in the upper right at some points during booting but all seem to run ok. Some of them have been up 24/7 for years. All are presently running Raspbian 8-jessie. Does the intermittent color square do the same thing the lightning bolt does?

Should I be worried about using Raspberry PI 3 running Raspbian 9-stretch with those power sources? I need to run the systems from battery power some of the time and all of the sites have gel-cel and 13.8v AC-DC power supplies so using conversion from 12v to USB voltage is reasonable.

Can you recommend a power supply for the Raspberry PI that draws power from 12V DC?

Thanks!
Tadd

Re: lightning bolt and rPI 3 power requirements

Posted: Wed Aug 23, 2017 10:52 pm
by drgeoff
If you are confident that the switching PSUs are performing as you expect, look to the wiring between them and the RPis. If you are using USB to micro-USB cables, some of those drop too much voltage because they are too long or too thin or use wet string instead of real copper conductors.

Re: lightning bolt and rPI 3 power requirements

Posted: Thu Aug 24, 2017 8:56 am
by davidcoton
tadd wrote:
Wed Aug 23, 2017 10:28 pm
What are the conditions which cause the lightning bolt to show up on the Raspberry PI HDMI display, upper right? Does it do this during normal operation? Does it do it while booting with text scrolling on the display?
The 5V bus on the Pi falls below 4.65V. Can happen under heavy load, like at start-up.
Caused either by a supply which cannot maintain 5V at the required current, or by a USB power cable that is too long and/or thin, thus giving a voltage drop under load.
For reference the "official" power supply maintains 5.1V at 2.5A.
tadd wrote:
Wed Aug 23, 2017 10:28 pm
Does the intermittent color square do the same thing the lightning bolt does?
A square of a solid colour indicates that the SOC is getting hot. IIRC, Yellow at 80C and Red at 85C, red also means the Pi is throttled (slowed) to prevent damage.
The cure is better ventilation, a heat sink on the SOC, or in extreme cases a fan. Cases will keep heat in, especially plastic ones.
tadd wrote:
Wed Aug 23, 2017 10:28 pm
Should I be worried about using Raspberry PI 3 running Raspbian 9-stretch with those power sources?
It will not permanently harm your Pi in the short term, but it may become unreliable and the SDCard could be corrupted, which could prevent proper operation.
Attached USB or HDMI devices may malfunction.
Ignore either warning in the long term at your own risk.

Re: lightning bolt and rPI 3 power requirements

Posted: Thu Aug 24, 2017 9:34 am
by jamesh
All firmware warning icons described here...

https://www.raspberrypi.org/documentati ... g-icons.md


If you are getting a square, your firmware is a bit out of date.

Re: lightning bolt and rPI 3 power requirements

Posted: Thu Aug 24, 2017 9:56 am
by Burngate
... and a thread about the various icons: viewtopic.php?t=82373

The original icons (July 2014) were a four-colour square for low voltage, and a yellow / red square for high temperature.
They were replaced in September 2016

Re: lightning bolt and rPI 3 power requirements

Posted: Thu Aug 24, 2017 2:15 pm
by tadd
Thanks for the information. It appears that 4.65v, even for transient periods, gets a lightning bolt for a short time.

According to a little USB voltage widget, the KIS3R33S power source I'm using never went below 5.02v and is 5.06v at idle. When using some fancy colored 1 meter USB cable plugged into the power source, and measuring at the USB hub output on the Raspberry PI (where a keyboard would plug in) the socket was at 4.69v during boot and 4.8 when idle. I imagine that the little USB voltage widget doesn't see fast transients to lower voltages. I also haven't verified it's accuracy. Using a 15cm cable of unknown parentage the voltage was better, 4.96 at the Raspberry PI's hub output at idle and no less than 4.9v when booting. No lightning bolt this time.

Perhaps the trick is to keep the cable lengths short. Is there a recommended A to micro-B cable at > 15cm?

Re: lightning bolt and rPI 3 power requirements

Posted: Thu Aug 24, 2017 6:54 pm
by HawaiianPi
tadd wrote:
Thu Aug 24, 2017 2:15 pm
Perhaps the trick is to keep the cable lengths short. Is there a recommended A to micro-B cable at > 15cm?
Short cable with fat wires are best. You'll want something with at least 24 AWG power wires, but lower gauge would be even better (lower gauge = thicker wires). I posted about several micro USB cables I have experience with. Check out that thread for more info.

viewtopic.php?f=63&t=165393

I'm currently using a 1.5 foot Monoprice Premium micro-USB cable to power my Pi3 from a 5.3V/2.4A supply. No power problems here.

Re: lightning bolt and rPI 3 power requirements

Posted: Thu Aug 24, 2017 6:56 pm
by tadd
Fantastic! Thanks.