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Power draw spike at startup causing reboot

Posted: Sat Sep 24, 2016 1:47 am
by CostasVav
Hi,

I have a RPi2 powered by an Adafruit Powerboost 1000 Charger and a 6600mAh 3-cell Li-ion battery.

Whenever I start the RPi2 on a normal 2A USB charger, I do notice a current draw spike at about 2-3 seconds after startup, causing the rainbow box to appear for a split second in the top-right corner of the screen. If I am not using the USB charger, but the battery and Powerboost, it causes the Pi to reboot every time it hits this spike. If I unplug the HDMI LCD display (that is also being powered by the same Powerboost) until it passes that spike, it works fine.

What is the cause of this spike?

Furthermore, could I add a capacitor to the power circuit that could provide enough juice for a split second to help get passed this spike?

Thanks!

Re: Power draw spike at startup causing reboot

Posted: Sat Sep 24, 2016 6:47 am
by FM81
CostasVav wrote:I have a RPi2 powered by an Adafruit Powerboost 1000 Charger and a 6600mAh 3-cell Li-ion battery.
It seems, that hardware-setup isn't able to provide enough current all the time!? The current, especially during startup, isn't constant. Even if you would add a (very big) capacitor, it wouldn't work very stable.

Greetings, FM_81

(I'm using a 2.5A-step-up to power an RPi2 & official display from an 6600mAh Li-Po. Loading is done by a separate build-in-circuit.)

Re: Power draw spike at startup causing reboot

Posted: Sat Sep 24, 2016 8:17 pm
by CostasVav
I solved the issue for now with two charging circuits in parallel.

However, there should be a capacitor somewhere that could power 5V ~500mA for ~200ms. I was just wondering what that particular spike was. Has anyone else encountered this spike?

But I guess I will call this issue closed for now.

Re: Power draw spike at startup causing reboot

Posted: Sun Sep 25, 2016 9:11 am
by Burngate
CostasVav wrote:... there should be a capacitor somewhere that could power 5V ~500mA for ~200ms.
Given that for a capacitor, Q=CV=it, and you want the voltage to sag less than 0.5v at i = 0.5A, t = 0.2s, C = 200mF or more.
Found this: http://uk.rs-online.com/web/p/electric- ... s/7637848/
CostasVav wrote:I was just wondering what that particular spike was.
So was I

Re: Power draw spike at startup causing reboot

Posted: Sun Sep 25, 2016 11:31 am
by mahjongg
the "spike" was due to the GPU turning on and doing some real work (stretching/blending four pixels to fill the whole screen). It is the GPU's self test during boot. If your setup resets at that moment it means it won't be able to power the PI while the GPU is working. so its NOT a spike, the moment you do something with the PI that requires GPU activity it will require that amount of current all the time!

p.s. you can try disabling the GPU test by entering/enabling the following line in config.txt.

Code: Select all

disable_splash=1