I have a battery pack with lithium ion cells. The battery pack has a maximal voltage of 84V (it goes from 84V to ~50V -> depending about the current state of charge).
I use this battery pack to power all sort of things (lights, horns, MCU(BMS), inverter – that then gives power to the eletrical motor…). The inverter draws about 60A of current continuously from a battery pack when the motor is rotating.
For my concept to work I must have different DC voltages on a single PCB:
- 12 VDC (for lights and horns)
- 5 VDC (for some sensors…)
- 3.3 VDC (for MCU, operational amplifiers…)
The idea is to use some sort of step-down converters on the PCB to convert from 84V to 12VDC and to convert from 84V to 5VDC. And then to use a LDO to give me 3.3V from 5V.
The 12VDC must have a power of ~40W, and the 5VDC must have a power of ~10W.
The question is regarding if the step-down converter should have galvanic isolation (like a flyback) so that I can have different grounds for high voltage and low voltage? Or is OK to use a "normal" buck regulator?
I think that for 12VDC that supplies the horns and lights is not so necessary to have different grounds as for 5VDC that supplies most of the electronic ?
Any suggestion?
Best Answer
Not a small amount of current and, if you don't get your grounding sorted out correctly you might find tens of amps trying to flow through the wrong ground return wires and hurting your MCU.
Therefore there is a case for providing galvanic isolation to your sensors (5V) and MCU (3V3) supplies because, although your MCU may need to connect to ground at the motor controller, having isolation in a potential ground return path could save you lots of heartache and dollars.