[Solved / Archived] Witty Pi (4 mini) - switch to battery 5v when standby, usb 5v when active

If you configure the low-voltage threshold to higher than 4.2V, that means a battery will always be considered as "low voltage" and it will shutdown your Pi when no 5V is provided via the USB-C connector. The shutdown will be graceful because the battery will power the Pi to finish the shutdown.

However, that means the switching between battery and powerbank is actually (manually) controlled by you: the Pi boots up when you connect the powerbank, and it shuts down when you disconnect the power bank.

Witty Pi 4 L3V7 doesn't do the power source switching according to the Pi's state (ON or OFF), it gives USB-C higher priority and switchs to battery if no 5V is provided via USB-C.

Thank you for your explanation. I want to keep the 5V USB-C from the powerbank always plugged in. To be sure, I guess it is not possible to connect a Li-Ion battery (delivering exactly 5V) to the Witty Pi 4 mini's 3-pin headers (5V and GND, P2) while simultaneously having the USB-C connected to get 5V from the powerbank and have some smart way to switch in idle to battery power and in active to USB-C from the powerbank? Or would I need other solutions/additional switching hardware to make this working with the Pi?

@t-abma there is no Li-Ion battery that can directly deliver exactly 5V.

Witty Pi 4 Mini's 3-pin header allows you to connect a DC/DC converter to the board, which can convert the battery voltage to 5V. However that 5V pin in the header directly connects to the USB-C connector, so you should not connect another power source via USB-C at the same time. Otherwise they might fight each other, if the 5V from them are not 100% the same.

Witty Pi 4 and Witty Pi 4 Mini have only one power channel, and you are not suppose to connect two power supplies to them. Someone does that and it may work, but we do not recommend it.

Witty Pi 4 L3V7 has two separated power channels: one for USB-C and one for battery. USB-C has higher priority than the battery.

Zero2Go Omini has three separated power channels. The power channel with higher voltage has the higher priority.

Maybe you should consider using a powerbank with smaller quiescent current.

Thank you for your explanation. I meant using a Li-Ion with a converter that outputs consistent 5V needed. I understand that you don't want them to fight with each other. I was not aware of the Zero2Go Omini.

It is very hard to find a powerbank that won't go into sleep mode after a certain period. I am currently using a UGREEN 25000 mAh powerbank and that seems to be running fine for days, but the Witty consumes about 4% per day in trickle charging mode while the Witty is only in standby mode/sleep mode. That is a lot what I would not expect. So I think the display of the powerbank and its electronics consume the most.

I was thinking of another approach now to not mix up the power:

- Feed battery Li-Ion 5V via USB-C to the Witty Pi 4 mini
- Feed powerbank 5V via micro-USB to the Raspberry Pi Zero 2W
- only connect essential ('communication') pins between them (GPIO17, GPIO14, GPIO4, any more?), not any 5V pins

So the Witty Pi will only draw power from the Li-Ion battery when in idle mode, hopefully much more efficient than the powerbank so it can run for months. And when the Witty Pi becomes active somehow send a signal to the Raspberry Pi that it can turn on. About that last part I am confused if that's feasible. Any idea on that?

@t-abma If you use Witty Pi (any model), you are suppose to connect power supply ONLY to Witty Pi and let Witty Pi to decide when your Raspberry Pi gets powered. If you power your Pi directly, that effectly bypass Witty Pi and there is no way Witty Pi can still manage the power consumption. Powering Raspberry Pi via mciro-USB and via Witty Pi at the same time also has the "power supplies fighting" issue.

If shape-factor is not a problem, and you don't mind using 2S/7.4V battery, the full-sized Witty Pi 4 already has a DC/DC converter on board, and you just need to implement your own battery charging circuit.

For other models of Witty Pi, you may implement your own "power bank", which is bascially battery+DC/DC converter+charging circuit.

Looking back and thinking about the direction I wanted to go I think I should stick back to the original (well thought) concept of the Witty Pi stacked to the Raspberry Pi. I was doing some calculations and I have a 2-way 18650 3450 mAh battery holder with recharger/converter that delivers 5V. If the Witty is running idle it would consume 0.5 mAh. My plan is to run the Raspberry Pi only for say three minutes a day doing its work and repeat that every day. I could theoretically run for about 200 days on the battery. Even if it would be a bit less that's also fine.

And I will then control via the Raspberry Pi my MOSFET to switch the powerbank power supply on to deliver power (12V via USB-C) to another device that I control.

That way it is running as the Witty Pi was meant and I don't mix up anything making it harder.  Sorry for my creative thinking,  but thanks for the feedback. Your help was greatly appreciated.