Boombox power/charge help

[MechaMatt]

Hi, I'm trying to work out how to power (and charge) my project. It's a portable boombox with a big sound system and lots of lights and is designed to be powered by the batteries for approx 3.5 hours. It requires a 24v supply of up to 15 amps max and 4-8 amps average. I'm quite limited in space so I worked out that I can fit two 6S4P packs (22.2v) of 3,500 mah 18650 cells wired together (with 40 cm wires) to create a 6S8P (28 Ah) battery outputting to a buck/boost converter to regulate it to 24v. I am not sure if I like the idea of that many wires, with that much power, travelling 40 cm and passing within 5 cm of audio amplifiers.

The power requirements are dictated by:
x2 amplifiers @24v and up to 3A each (full volume) - yes I know about %THD.
A 10" 12v monitor @2A
3 metres of 5v LEDs @ 7A (full brightness) - yes I know that's for full white.
5v Raspberry Pie 4 @ 3A

I need to know which way to proceed with the power supply - 24v (after amplifiers) regulated to 12v then down to 5v? Or 24v to 5v (bigger loads first) then up again to 12v?
Should I find a BMS to control a 6S8P pack (40 cm balance wires everywhere)
or else configure it as two 6S4P packs with one BMS each (but how to still get 24v?). The BMS's would be permanently wired to the batteries and the charger plugs into a port on the back.

Then we can get to how to charge the batteries. Ideally the boombox would be able to still be used when plugged in to the wall outlet . This means the mains supply would either power everything directly (bypass the charging system with a relay but requiring a 24v 25 Amp psu) or go through the BMS and charge at the same time (very complicated).

A little guidance on how to configure and charge the battery packs (no I won't just carry two car batteries around with it!) would be much appreciated. Thanks.

 

[gophert]

If you get 15A peak, figure 3A to 5A average current load.
That means you'll need 3.5 hours x 3 Amps = 10.5Ah. So you'll need 3 battery packs for the audio.

Figure 3.5A average for LEDs (so another 3 battery packs) - but get 12V packs instead of step down the voltage).

Add Pi power the same way ( same math).

 

[MechaMatt]

The two packs wired together will

create a 6S8P (28 Ah) battery

I worked this out to be able to provide 8 amps of current for 3.5 hours (x48 3500mah batteries). Considering the lights will probably only be on 50% brightness and be flashing, rather than displaying solid colours, and the speakers will sound horrible at 100% volume anyway, 8 Amps is a more realistic peak.

I like the idea of 11.1v battery packs, I can have x2 3S4P packs in parallel each side (x4 total) then combine the output to 22.2v (I'd have to isolate the batteries so they don't try and charge each other) for the amps but tap off before that for the 12v and 5v circuits. So I'd need four BMS's and a (much cheaper) 12v 5 Amp power supply.

Thanks! That helped change the track of my thinking a bit!