Feeding 2 BMSs from one DC input

[gattu marrudu]

Hi there,
I am building a battery-powered circuit with a class D amplifier and a single-board computer serving as a music source.

The amp takes anywhere from 12-24V and the SBC is a Raspberry Pi Zero with a 5V input.

I have a 6x18650 battery pack with a 6S BMS attached, fed by a 22V switching transformer, and a buck/boost module to regulate the input to 5V for the SBC.

Now, I found the hard way that connecting both the amp and the SBC to the same DC input results in terrible noise from the SBC current draw, as well as power-cycling the SBC when I power up the amp.

I have thought about a few solutions:

1. Using some combination of capacitors as noise filters. I tried a 10nF ceramic cap across the SBC input but that didn't change anything
2. Add a decoupling LC filter along with a bypass cap. I'd like to understand better how this works and how to calculate the component values. Any suggestions?
3. Using two power sources. I built a separate 3.7V battery pack with BMS for the SBC, using the same switching power supply to recharge both packs (otherwise my setup would be much less portable). But I am not sure how the layout would look like. I can't put the BMS after the DC-DC converter as it would make the converter fail (because it's a power supply as well as a load? Would a diode work?)

I have only basic knowledge of electronics and I'm missing some key concepts, but I feel like this should work one way or another. Any hints would be highly appreciated.

Thanks.
gm

[gattu marrudu]

Update: adding a diode between the DC-DC converter and the BMS (in the solution with a separate battery pack) worked and got rid of the SBC losing power and rebooting when I turn on the amp, but not of the noise problem.

Next I'm trying the setup in the attached image.



This uses a 7.4V battery pack instead of a 3.7V one, and two DC-DC converters (one to get from 22 to 7.4 V to charge the batteries, the other one to get to 5V to power the SBC). I ordered a 2S BMS. Any hints?

Thanks.
gm