Electrical – Wrong way usb connexion to MCP73831 lipo charger

No! Your diode scheme won't work. It's not clear how exactly you propose to connect the diodes, but either you will short one or more batteries or you will end up with the full 48V minus two diode drops on the output.

As Leon said, what you need is a 48V to 12V converter. The most likely form of this is a switching power supply called a "buck converter". You can look up that term for details on how exactly they work. At your current (almost 300A at 12V out), this will not be a trivial design and it will dissipate significant heat no matter what you do. Unless you're skilled in switching power supply design (and if you were, you wouldn't be here asking), you're better off buying something off the shelf if you can find it. This is not a beginner project. Do something else first if you want to learn. At this power level and current, you'll need every possible trick including multiple phases and synchronous rectification.

Consider the cooling requirements. Even if you can make the converter 95% efficient (that would be impressive), it will still dissipate 150 W of heat when operating at 3 kW. That is not a trivial amount of heat to get rid of, and will require careful attention to cooling. In other words, this isn't just a expert level electronic design problem, but will also require more than casual mechanical engineering for the thermal management.

Your circuit looks OK.

The 73831 comes in -2 -3 4 & -5 versions. What version do you have?

Original (not your circuit) is a mess - one should never have a diode AFTER a regulator - quite apart from the too low Vout and non swap-over.

The following addresses charge LED issue if there is a problem BUT I think that lack of battery is an illegal condition - see next paragraph. Does any of the following change the charge indication. What is voltage at BATT output in each case?

• Diode leakage SHOULD be very low at room temperature.

• Remove battery AND D2 and see what happens.

• Then remove C5

HOWEVER:

A LiIon battery stops charging when the voltage is held at some fixed threshold (usually ~= 4.2V) and charge current falls to below a preset % of initial current at this voltage. Battery chemistry causes this current to decrease with time. A capacitor does not behave like a battery does. I'd expect it to show end of charge almost immediately, but as you are doing something that the design does not specify as legal, anything MIGHT happen.

Does it stop charging a battery when battery is installed?
What is the end battery voltage?
What is the battery mAh capacity?