Power issues.

After a power cut power does not restore to the Kiwi's.

However, if I have the PSU powered up , unplug the Kiwi's and plug them back in again they power up no problem but not while the PSU is attached.

It's a linear supply.

Any ideas ?


  • can you describe linear supply or upload a picture of it?
  • That is a sure sign of the power supply not meeting the 50 millisecond "ramp up" requirement of the Beagle. That is, if you were to look at the time it takes the 5V waveform to go from 0V to 5V it would be too slow. This can happen if it is taking too long to charge the power supply output capacitor which will will look like a dead short for a period of time (especially if it is a large cap).

    But when you plug the power supply into the Kiwi the cap is already charged and the waveform appears to ramp up quickly.
  • Thanks for the reply JKS, yeah I was thinking it was more of a PSU issue but the linear is too clean to change it, pity.

    Would it be possible a clean UPS exists ? this would be even better if it were cheap enough although I could probably live with it if it were not so clean for some hrs of backup.
  • The things that may help may be minimising the length of any DC leads and improving or removing mating connectors.
    The Kiwi takes very little power but light wiring or poor connectors could exacerbate any momentary current issues.

    Imagine this the PSU may be just capable of getting the 5V up in the time the Beaglebone requires, but the wiring/connectors drop just enough in resistance to delay the full voltage. It's a long shot but worth experimenting with before looking for other supplies.

    The issue is also not specifically the supply being not clean it's just the time taken for the voltage at the Beaglebone (through wiring and Kiwi DC filtering) to get where it needs to. From other posts and personal experience increasing the voltage by about 0.3V can sometimes help. The ideal solution would be have some way to remotely switch the DC side once the PSU is powered.
    There are quite a few IOT switches, networked relay boards or add ons for say Raspberry PI.
  • you can delay the load from being applied to the PSU with a simple relay.
  • A delay sounds good , thanks for all the replies everyone !
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