#+TITLE: Battery charger and dual power supply unit
#+AUTHOR: Svjatoslav Agejenko
#+LANGUAGE: en
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* 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: [[mailto://svjatoslav@svjatoslav.eu][svjatoslav@svjatoslav.eu]]
- Valeria Agejenko
+ See also:
- [[../../index.html][Other physical projects in this repository]]
- [[https://www.svjatoslav.eu/projects/][Other projects hosted at svjatoslav.eu]]
* Project description
I needed dual voltage power supply for my lab that runs on mains
electricity (wall power) and slowly charges (use-changing) 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.
[[file:make.png]]
Power supply provides about 13 Volts and 5 Volts simultaneously.
*!!!WARNING!!!* [[../alternative%20USB%20layout/][Alternative and incompatible USB wiring/layout]] is
being used here.
*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.
[[file:../alternative%20USB%20layout/schematic.png]]
As seen, it has dual voltage output. Additionally one wire is
dedicated to data transmission and can be used with [[https://en.wikipedia.org/wiki/1-Wire][1-Wire]] protocol
1-Wire data router/hub is really simple. Power supply simply passively
links all data wires together.
Power supply uses 3D printed body with lots of holes, for fanless
cooling.
[[file:body%20and%20covers/body,%201.png]]
Various modules are realized on top of prototype PCBs that slide into
dedicated rails within the body.
[[file:body%20and%20covers/body,%202.png]]
Like this:
[[file:make,%202.png]]
When cover is closed, it blocks PCB movement:
[[file:body%20and%20covers/cover.png]]
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 :)
[[file:body%20and%20covers/cover%20cover.png]]
Download:
+ [[file:body%20and%20covers/body.stl][Body STL file]]
+ [[file:body%20and%20covers/cover.stl][Big cover STL file]]
+ [[file:body%20and%20covers/cover%20cover.stl][Small dummy cover on top, STL file]]
+ [[file:body%20and%20covers/body%20and%20covers.FCStd][Body and covers FreeCAD project]]
* Transformer and AC to DC converter
This is where high voltage from mains electricity enters the system.
Schematic:
[[file:transformer%20and%20AC%20DC%20converter%20board/schematic.png]]
For safety I kept high voltage section as minimal as possible. That
is, wall plug runs straight into transformer. Also I used [[https://www.amazon.de/gp/product/B07VGQKM3G/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1][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 [[id:c9a69490-f920-4a31-b32e-b101bfc3d01b][indicator panel]].
[[file:transformer%20and%20AC%20DC%20converter%20board/make,%201.png]]
DC current of about 30 volts is then routed to [[id:65d68227-4bf2-4c4f-b4d3-c390bc6a9c34][Main board]].
[[file:transformer%20and%20AC%20DC%20converter%20board/make,%202.png]]
[[https://www.amazon.de/gp/product/B07RLQH5TR/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1][Single sided prototype PCB is used]].
* Main board
:PROPERTIES:
:ID: 65d68227-4bf2-4c4f-b4d3-c390bc6a9c34
:END:
This is logically main board because it appears to be central hub that
connects all components. It also houses 2 [[https://www.amazon.de/gp/product/B072MQYJ93/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1][adjustable DC-DC Step Down
voltage converters]].
[[file:main%20board/main%20board,%201.png]]
High-level schematic of entire device:
[[file:main%20board/schematic.png]]
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 [[id:afc22d23-9bc4-421c-9cac-e0ce34bd36bc][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 [[id:e33940bd-652f-4ec0-b53b-1c03e16941c8][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 [[id:e33940bd-652f-4ec0-b53b-1c03e16941c8][connector
terminal]].
Both 13V and 5V lines are also routed to [[id:c9a69490-f920-4a31-b32e-b101bfc3d01b][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.
[[file:main%20board/main%20board,%202.png]]
* Current limiter
:PROPERTIES:
:ID: afc22d23-9bc4-421c-9cac-e0ce34bd36bc
:END:
Schematic:
[[file:current%20limiter/schematic.png]]
Simple LM317 based current limiter is used. I used 4.7 ohm
resistor. It provides about 265 milliamps of current. See [[http://www.reuk.co.uk/wordpress/electric-circuit/lm317-current-calculator/][calculator]].
[[file:current%20limiter/current%20limiter,%201.png]]
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.
[[file:current%20limiter/current%20limiter,%202.png]]
Note: resistor gets hot too.
* Indicator panel
:PROPERTIES:
:ID: c9a69490-f920-4a31-b32e-b101bfc3d01b
:END:
[[file:indicator%20panel/indicator%20panel,%201.png]]
Basically 2 digital DC voltmeters and main on/off switch.
[[file:indicator%20panel/indicator%20panel,%202.png]]
Download:
[[file:indicator%20panel/indicator%20panel.png]]
+ [[file:indicator%20panel/indicator%20panel.stl][STL file]]
+ [[file:indicator%20panel/indicator%20panel.FCStd][FreeCAD project]]
* Connector terminal
:PROPERTIES:
:ID: e33940bd-652f-4ec0-b53b-1c03e16941c8
:END:
Schematic:
[[file:connector%20terminal/schematic.png]]
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.
[[file:connector%20terminal/make,%201.png]]
Those PCBs are wired to central small PCB that acts as a hub:
[[file:connector%20terminal/make,%202.png]]
PCBs are held together by being sandwiched between front panel:
[[file:connector%20terminal/front%20panel.png]]
and smaller back-end plate:
[[file:connector%20terminal/back%20panel.png]]
Result:
[[file:connector%20terminal/make,%203.png]]
Download:
+ [[file:connector%20terminal/front%20panel.stl][front panel STL]]
+ [[file:connector%20terminal/back%20panel.stl][back panel STL]]
+ [[file:connector%20terminal/connector%20terminal.FCStd][FreeCAD project]]
* 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! :)