A20 Lime not always boot when power is plugged

[zeallin]

Hello my friends,

Thanks you for the outstanding A20 board. I love it so much!
Currently we are testing for a A20 Lime based product. We found that the A20 Lime board is not always boot when power is plugged. We tried several type of adapters with a automatic power switch, which have a 15min interval of power on and off :

1. 5V 1.8A 9W: Powered on 174 times, not boot: 21 times, 17% failure rate 
2. 5V 2A 10W: Powered on 46 times, not boot: 2 times, 4% failure rate
2. 5V 3A 15W: Powered on 132 times, not boot: 15 times, 11% failure rate

When the A20 is not boot, the power indicator red LED is on, screen is blank, and USB have no power.

Operating system: Debian Jessie, latest image
A20 board: A20 LIME rev. I
 
Do you guys have any suggestion on how to prepare the power supply for A20 Lime to have 100% boot rate?

Thanks you!

Best regards,
Zeal

[LubOlimex]

How much time you leave between power down and power up? If you do it in quick succession the board would probably not boot, since some passive components like capacitors still have charge and when you apply the power supply again several components would be left at inappropriate state. You need to wait at least 5 seconds between power down and power up.

Consider that some peripherals might parasitically power insufficiently the boards leading to similar problem as the first mention. I've seen HDMI monitors and USB serial cables affecting the voltage levels of the board.

For better reliability consider using a Li-Po battery. The Li-Po battery would keep the whole board alive and when the main supply comes back the powering would be switched to it automatically and seamlessly. Also when you detect that the main power supply is missing you can track battery charge and issue a software shutdown if battery goes too low.

[zeallin]

Thanks you very much for the quick reply!
HDMI and USB cable is connected to the board. I will try to remove them and and test again.

Best regards,
Zeal