If You Build It

A project log for 100W MPPT Prototype Charger

Prototype of a MPPT charger for 12V PV systems.

brian-cornellBrian Cornell 10/31/2019 at 18:360 Comments

If you really want to build this as documented you'll need to go thru some hoops.  Keep in mind that it is a prototype and doesn't contain the refinements and circuit protection features of a finished design.

  1. Go to the 125vbuck project to get the clean PCB and have it manufactured.  But if you're willing to go thru that effort I'd suggest that you modify the board following the mods in this project to make assembly much easier & cleaner.  Otherwise you will need to hack your shiny new board according to the board PDF in this project.
  2. Reconcile the BOM.  The design workbook has the BOM from 125vbuck project.  Reconcile with the schematic and only install what the schematic lists.  There are additional parts on the schematic, specific to this design.  Most of those contain a Digikey part number; a few don't and their specs / tolerances aren't critical.
  3. Wind the inductors.  The design workbook should provide what's needed (core #s, wire gauge, # turns, etc.) for the buck & current transformer.  The core part # for the SSR flyback is in the BOM.  The primary is 6 turns and the secondary is 17.  Use 28 AWG magnet wire.  Be sure the polarities are opposite one another when installed; it should output ~ 12-17V across the MOSFET G-S.
  4. Consider adding fuses, particularly on the battery side.
  5. Connect to the battery first (then the PV).  Otherwise it's possible that the PIC will be damaged (pin protection diodes will forward bias since Vdd isn't applied).  A short could also develop between the high & low side MOSFETs since the gate driver isn't energized: the gates might float and turn on.
  6. Exercise care when working on an energized unit.  While the working voltages are less than 30V, the reset voltage on the current transformer can reach 100V at high loads.  Be careful when probing.