-#+TITLE: 12V Lead-Acid battery changer and terminal
+#+TITLE: Battery charger and dual power supply unit
#+AUTHOR: Svjatoslav Agejenko
#+LANGUAGE: en
+ This design is released under Creative Commons Zero (CC0) license.
-+ Author:
++ Authors:
- Svjatoslav Agejenko
- - Homepage: https://svjatoslav.eu
- - Email: [[mailto://svjatoslav@svjatoslav.eu][svjatoslav@svjatoslav.eu]]
+ - 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 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!!! 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.
+
+[[file:connector%20terminal/USB%20hack.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. 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.
+
+[[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]]
-Simple charger and terminal (front-end) for 12V lead-acid battery.
+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 to.
+
+* 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]]
+
-Idea is to distribute power from rechargeable 12V battery to various
-appliances (soldering iron, radio transmitters, etc..) while also
-providing use-charging in the background.
+Those PCBs are wired to central small PCB that acts as a hub:
-Single on/off button disconnects battery and up-step voltage source
-from front panel terminal connectors.
+[[file:connector%20terminal/make,%202.png]]
-[[https://www.amazon.de/gp/product/B07G4KWV6S/ref=ppx_yo_dt_b_asin_title_o08_s01?ie=UTF8&psc=1][Tecnoiot MT3608]] voltage up-step is used. 3V DC external power supply
-is used to feed voltage up-step. Up-step is tuned to ~14.4 V.
+PCBs are held together by being sandwiched between front panel:
-[[file:schematic.png]]
+[[file:connector%20terminal/front%20panel.png]]
-Current design is rather of blog (experience sharing) value. It has
-quite some drawbacks:
+and smaller back-end plate:
-- Warning: Circuit has dangerous instability. Requires low voltage
- ~3V but relatively high current external power supply. Using
- higher voltage but low current power supply could easily lead to
- situation where step-up generated load pushes power supply output
- voltage down too much. This leads to too much power being lost
- within power supply and easily leads to power supply overheating!
+[[file:connector%20terminal/back%20panel.png]]
-- There is no dedicated current limiter. 3V external power supply
- and up-step are acting as current limiters.
+Result:
-- While RCA connectors do work as DC power connectors, but are not
- intended to be used this way and are not very reliable.
+[[file:connector%20terminal/make,%203.png]]
-- Voltage up-step provided output is not very clean. Extra capacitors
- and induction coils could be added to remove high frequency noise in
- the voltage.
-- Metallic and shielded body would be helpful to reduce
- electromagnetic/radio noise generated by step-up.
+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]]
-* Body
+* Calibration
-[[file:body.png]]
+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.
-[[file:cover.png]]
+See here for more details: https://www.powerstream.com/SLA.htm
+-----
-+ Download:
- + [[file:body%20and%20cover.FCStd][body and cover FreeCAD file]]
- + [[file:body.stl][body in STL format]]
- + [[file:cover.stl][cover in STL format]]
+Happy building! :)
projects / physical.git / blobdiff