Battery charger and dual power supply unit
+ +1 General
+-
+
- DISCLAIMER: I DO ELECTRONICS AND 3D DESIGN SOLELY AS A HOBBY. THERE +COULD BE ERRORS THAT CAN RESULT IN ALL KINDS OF DAMAGE. USE THESE +DESIGNS AT YOUR OWN RISK. + + +
- This design is released under Creative Commons Zero (CC0) license. + + +
- Authors:
+
-
+
- Svjatoslav Agejenko
+
-
+
- Homepage: https://svjatoslav.eu + +
- Email: svjatoslav@svjatoslav.eu + +
+
+ - Valeria Agejenko + +
+
+ - Svjatoslav Agejenko
+
- See also: + + +
2 Project description
++I needed dual voltage power supply for my lab that runs on mains +electricity (wall power) and slowly charges attached 12V Lead-Acid +battery. Lead-acid battery in turn provides high current when needed +as well as power in portable situations or when mains electricity is +not available. +
+ + +
+
+Power supply provides about 13 Volts and 5 Volts simultaneously. +
+ ++!!!WARNING!!! I use USB-A connectors for power output, but IT IS NOT +COMPATIBLE WITH USB DEVICES AND POSSIBLY WITH EXISTING USB CABLES. +
+ ++Normal USB devices and cables should not be plugged in! It would +damage device/cable and likely power supply. +
+ ++I found USB-A connectors to be easily available, cheap, reliable and +functional, so I re-purposed connector for my own needs but I'm using +totally incompatible electrical wiring. +
+ + +
+
+As seen, it has dual voltage output. Additionally one wire is +dedicated to data transmission and can be used with 1-wire +protocol. Power supply simply passively links all data wires together +but does not participate in communication. +
+ ++Power supply uses 3D printed body with lots of holes, for fanless +cooling. +
+ + +
+
+Various modules are realized on top of prototype PCBs that slide into +dedicated rails within the body. +
+ + +
+
+Like this: +
+ + +
+
+When cover is closed, it blocks PCB movement: +
+ + +
+
+There is still some empty space inside, so why not add dummy cover on +top that can be replaced later with add-on functionality/expansion +board/terminal :) +
+ + +
+
+Download: +
+ +3 Transformer and AC to DC converter
++This is where high voltage from mains electricity enters the system. +
+ +
+Schematic:
+
+
+For safety I kept high voltage section as minimal as possible. That +is, wall plug runs straight into transformer. Also I used UV hardening +glue for extra safety and isolation on PCB. +
+ ++Power on/off switch operates on already reduced voltage of about 30 +volts. Power switch is located on indicator panel. +
+ + +
+
+DC current of about 30 volts is then routed to Main board. +
+ + +
+
4 Main board
++This is logically main board because it appears to be central hub that +connects all components. It also houses 2 adjustable DC-DC Step Down +voltage converters. +
+ + +
+
+High-level schematic of entire device:
+
+
+As seen from schematic, ~30 volts DC from transformer board is routed +into first step-down converter that reduces it to about 15V. Reduced +voltage is then directed to Current limiter circuit. Current limiter +loses about 2 volts. Now we have current and voltage limited power at +about 13 volts. This power is used to charge connected 12V Lead-Acid +battery. Also the same power is routed to connector terminal to be +consumed by connected devices. +
+ ++As seen from this schematic, device is not meant to provide high +current for long periods of time. Instead it gets comparatively +limited current to charge the battery and feed devices with low +current requirements. Occasional current spikes are backed up by +battery that stays in use-changing mode. +
+ ++Also about 13V output voltage is approximate and depends on connected +battery charge level. +
+ ++Second Step-Down converter reduces voltage even further to quite +precisely 5V DC. This resulting voltage is also routed to connector +terminal. +
+ ++Both 13V and 5V lines are also routed to indicator panel for +monitoring. +
+ ++There is single on/off switch. In off position, it disconnects battery +and transformer from the system effectively powering everything down. +
+ ++On schematic above, some wires are annotated with numbers from 1 +to 13. This corresponds to output pins on the board. +
+ + +
+
5 Current limiter
+
+Schematic:
+
+
+Simple LM317 based current limiter is used. I used 4.7 ohm +resistor. It provides about 265 milliamps of current. See calculator. +
+ + +
+
+Thermal paste below and UV hardening glue on top is used to attach +LM317 to the heatsink. There is also jumper-like solution on top +right. This is handy to attach multimeter tap to verify/monitor +current during initial device calibration. +
+ ++If attached battery is really empty, significant voltage drop can +occur in LM317. Heatsink is needed to dissipate that power. +
+ + +
+
+Note: resistor gets hot too. +
+6 Indicator panel
+
+
+Basically 2 digital DC voltmeters and main on/off switch. +
+ + +
+
+Download: +
+ + +
+
-
+
- STL file + +
- FreeCAD project + +
7 Connector terminal
+
+Schematic:
+
+
+As seen above, most of the USB connectors are used to deliver dual +power output and 1-wire data connectivity, except one on the bottom +right. This is used to attach 12V battery. Some capacitors are thrown +in as well to stabilize against smaller current spikes. +
+ ++Electrically schematic is realized using smaller prototype PCBs. +
+ + +
+
+Those PCBs are wired to central small PCB that acts as a hub: +
+ + +
+
+PCBs are held together by being sandwiched between front panel: +
+ + +
+
+and smaller back-end plate: +
+ + +
+
+Result: +
+ + +
+
+Download: +
+-
+
- front panel STL + +
- back panel STL + +
- FreeCAD project + +
8 Calibration
++Since device uses adjustable step-down modules, these need to be +calibrated to provide correct output voltage. It is important that +battery receives proper charging voltage otherwise either no charging +occurs or battery starts gassing out and gets destroyed. +
+ ++See here for more details: https://www.powerstream.com/SLA.htm +
+ ++ +
+Happy building! :) +
+