Kiwi doesn't power up after power loss
Hello,
I have been running my Kiwi (model May 2016) for many years and I've always had the problem I am about to describe.
I run the Kiwi behind a linear 5V power supply, which in turn is behind a 1000VA UPS. My problem is that when power is out long enough to drain the UPS battery, the Beaglebone will not power itself back up when power is eventually restored.
When that happens, the only way to restart the Kiwi is physically disconnecting the power connector and then reconnecting it. It is worth noticing that the on/off button on the power supply itself also doesn't restart the Kiwi.
I suppose that the reason for this issue is the power supply. Its output capacity must be large enough to slow down the ramp-up time to a point where the beagle doesn't recognize it as such anymore.
Is anyone having the same issue? Any solutions out there?
Thanks
Alain
Comments
Assuming the supply can provide 3A on peaks, then Increase the supply voltage to 5.4v measured at the Kiwi input power connector.
There is a slight voltage drop under load within the KiWi and Beaglebone circuit, and increasing the supply voltage slightly solves the problem.
It took me a while to discover this, and all my KiWi power supplies are now set to between 5.4v to 5.5v and I have not had any further problems.
Regards,
Martin
There's this module which switches on the power with a configurable delay:
I suppose that the reason for this issue is the power supply. Its output capacity must be large enough to slow down the ramp-up time to a point where the beagle doesn't recognize it as such anymore.
Maybe. Another part of the problem could be that some inverters and also UPS' have a "soft start feature" which causes an extra slow voltage rise. (A "feature" which may cause more problems than benefits, I think.) I would also suggest a solution like HB9TMC's.
The Beagle has a very strict 50 millisecond maximum "ramp up" time required on the 5V input. If your power supply takes longer than that the power management IC (PMIC) on the Beagle will refuse to power up.
This is because the sequencing of the multi-voltage power rails to the various chips on the board cannot be guaranteed under those conditions. It might occur when a power supply has a large output capacitor or something else effecting the ramp behavior. This is why a subsequent manual application of 5V, where the ramp is fast, works.
I don't know why this would be in your case, but the only way to really understand what's happening is to look at the power up waveform with a scope and see what the exact behavior is.
Thanks for the very useful feedback. I suspected the "ramp up" time since the beginning and now my suspicions are even higher. Unfortunately I don't have a scope at this location, but I already ordered a delayed relay.