misc/12V Lead-Acid battery changer and terminal/index.org

   1 #+TITLE: Battery charger and dual power supply unit
   2 #+AUTHOR: Svjatoslav Agejenko
   3 #+LANGUAGE: en
   4
   5 * (document settings) :noexport:
   6 ** use dark style for TWBS-HTML exporter
   7 #+HTML_HEAD: <link href="https://bootswatch.com/3/darkly/bootstrap.min.css" rel="stylesheet">
   8 #+HTML_HEAD: <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
   9 #+HTML_HEAD: <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.5/js/bootstrap.min.js"></script>
  10 #+HTML_HEAD: <style type="text/css">
  11 #+HTML_HEAD:   footer {background-color: #111 !important;}
  12 #+HTML_HEAD:   pre {background-color: #111; color: #ccc;}
  13 #+HTML_HEAD: </style>
  14
  15 * General
  16 + DISCLAIMER: I DO ELECTRONICS AND 3D DESIGN SOLELY AS A HOBBY. THERE
  17   COULD BE ERRORS THAT CAN RESULT IN ALL KINDS OF DAMAGE. USE THESE
  18   DESIGNS AT YOUR OWN RISK.
  19
  20 + This design is released under Creative Commons Zero (CC0) license.
  21
  22 + Authors:
  23   - Svjatoslav Agejenko
  24     - Homepage: https://svjatoslav.eu
  25     - Email: [[mailto://svjatoslav@svjatoslav.eu][svjatoslav@svjatoslav.eu]]
  26
  27   - Valeria Agejenko
  28
  29 + See also:
  30   - [[../../index.html][Other physical projects in this repository]]
  31   - [[https://www.svjatoslav.eu/projects/][Other projects hosted at svjatoslav.eu]]
  32
  33 * Project description
  34 I needed dual voltage power supply for my lab that runs on mains
  35 electricity (wall power) and slowly charges (use-changing) attached
  36 12V Lead-Acid battery. Lead-acid battery in turn provides high current
  37 when needed as well as power in portable situations or when mains
  38 electricity is not available.
  39
  40 [[file:make.png]]
  41
  42 Power supply provides about 13 Volts and 5 Volts simultaneously.
  43
  44 *!!!WARNING!!!* [[../alternative%20USB%20layout/][Alternative and incompatible USB wiring/layout]] is
  45 being used here.
  46
  47 *Normal USB devices and cables should not be plugged in! It would
  48 damage device/cable and likely power supply.*
  49
  50 I found USB-A connectors to be easily available, cheap, reliable and
  51 functional, so I re-purposed connector for my own needs but I'm using
  52 totally incompatible electrical wiring.
  53
  54 [[file:../alternative%20USB%20layout/schematic.png]]
  55
  56 As seen, it has dual voltage output. Additionally one wire is
  57 dedicated to data transmission and can be used with [[https://en.wikipedia.org/wiki/1-Wire][1-Wire]] protocol
  58
  59 1-Wire data router/hub is really simple. Power supply simply passively
  60 links all data wires together.
  61
  62 Power supply uses 3D printed body with lots of holes, for fanless
  63 cooling.
  64
  65 [[file:body%20and%20covers/body,%201.png]]
  66
  67 Various modules are realized on top of prototype PCBs that slide into
  68 dedicated rails within the body.
  69
  70 [[file:body%20and%20covers/body,%202.png]]
  71
  72 Like this:
  73
  74 [[file:make,%202.png]]
  75
  76 When cover is closed, it blocks PCB movement:
  77
  78 [[file:body%20and%20covers/cover.png]]
  79
  80 There is still some empty space inside, so why not add dummy cover on
  81 top that can be replaced later with add-on functionality/expansion
  82 board/terminal :)
  83
  84 [[file:body%20and%20covers/cover%20cover.png]]
  85
  86 Download:
  87 + [[file:body%20and%20covers/body.stl][Body STL file]]
  88 + [[file:body%20and%20covers/cover.stl][Big cover STL file]]
  89 + [[file:body%20and%20covers/cover%20cover.stl][Small dummy cover on top, STL file]]
  90 + [[file:body%20and%20covers/body%20and%20covers.FCStd][Body and covers FreeCAD project]]
  91
  92 * Transformer and AC to DC converter
  93
  94 This is where high voltage from mains electricity enters the system.
  95
  96 Schematic:
  97 [[file:transformer%20and%20AC%20DC%20converter%20board/schematic.png]]
  98
  99 For safety I kept high voltage section as minimal as possible. That
 100 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
 101 glue]] for extra safety and isolation on PCB.
 102
 103 Power on/off switch operates on already reduced voltage of about 30
 104 volts. Power switch is located on [[id:c9a69490-f920-4a31-b32e-b101bfc3d01b][indicator panel]].
 105
 106 [[file:transformer%20and%20AC%20DC%20converter%20board/make,%201.png]]
 107
 108 DC current of about 30 volts is then routed to [[id:65d68227-4bf2-4c4f-b4d3-c390bc6a9c34][Main board]].
 109
 110 [[file:transformer%20and%20AC%20DC%20converter%20board/make,%202.png]]
 111
 112 [[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]].
 113
 114 * Main board
 115 :PROPERTIES:
 116 :ID:       65d68227-4bf2-4c4f-b4d3-c390bc6a9c34
 117 :END:
 118
 119 This is logically main board because it appears to be central hub that
 120 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
 121 voltage converters]].
 122
 123 [[file:main%20board/main%20board,%201.png]]
 124
 125 High-level schematic of entire device:
 126 [[file:main%20board/schematic.png]]
 127
 128 As seen from schematic, ~30 volts DC from transformer board is routed
 129 into first step-down converter that reduces it to about 15V. Reduced
 130 voltage is then directed to [[id:afc22d23-9bc4-421c-9cac-e0ce34bd36bc][Current limiter circuit]]. Current limiter
 131 loses about 2 volts. Now we have current and voltage limited power at
 132 about 13 volts. This power is used to charge connected 12V Lead-Acid
 133 battery. Also the same power is routed to [[id:e33940bd-652f-4ec0-b53b-1c03e16941c8][connector terminal]] to be
 134 consumed by connected devices.
 135
 136 As seen from this schematic, device is not meant to provide high
 137 current for long periods of time. Instead it gets comparatively
 138 limited current to charge the battery and feed devices with low
 139 current requirements. Occasional current spikes are backed up by
 140 battery that stays in use-changing mode.
 141
 142 Also about 13V output voltage is approximate and depends on connected
 143 battery charge level.
 144
 145 Second Step-Down converter reduces voltage even further to quite
 146 precisely 5V DC. This resulting voltage is also routed to [[id:e33940bd-652f-4ec0-b53b-1c03e16941c8][connector
 147 terminal]].
 148
 149 Both 13V and 5V lines are also routed to [[id:c9a69490-f920-4a31-b32e-b101bfc3d01b][indicator panel]] for
 150 monitoring.
 151
 152 There is single on/off switch. In off position, it disconnects battery
 153 and transformer from the system effectively powering everything down.
 154
 155 On schematic above, some wires are annotated with numbers from 1
 156 to 13. This corresponds to output pins on the board.
 157
 158 [[file:main%20board/main%20board,%202.png]]
 159 * Current limiter
 160 :PROPERTIES:
 161 :ID:       afc22d23-9bc4-421c-9cac-e0ce34bd36bc
 162 :END:
 163
 164 Schematic:
 165 [[file:current%20limiter/schematic.png]]
 166
 167 Simple LM317 based current limiter is used. I used 4.7 ohm
 168 resistor. It provides about 265 milliamps of current. See [[http://www.reuk.co.uk/wordpress/electric-circuit/lm317-current-calculator/][calculator]].
 169
 170 [[file:current%20limiter/current%20limiter,%201.png]]
 171
 172 Thermal paste below and UV hardening glue on top is used to attach
 173 LM317 to the heatsink. There is also jumper-like solution on top
 174 right. This is handy to attach multimeter tap to verify/monitor
 175 current during initial device calibration.
 176
 177 If attached battery is really empty, significant voltage drop can
 178 occur in LM317. Heatsink is needed to dissipate that power.
 179
 180 [[file:current%20limiter/current%20limiter,%202.png]]
 181
 182 Note: resistor gets hot too.
 183
 184 * Indicator panel
 185 :PROPERTIES:
 186 :ID:       c9a69490-f920-4a31-b32e-b101bfc3d01b
 187 :END:
 188
 189 [[file:indicator%20panel/indicator%20panel,%201.png]]
 190
 191 Basically 2 digital DC voltmeters and main on/off switch.
 192
 193 [[file:indicator%20panel/indicator%20panel,%202.png]]
 194
 195 Download:
 196
 197 [[file:indicator%20panel/indicator%20panel.png]]
 198
 199 + [[file:indicator%20panel/indicator%20panel.stl][STL file]]
 200 + [[file:indicator%20panel/indicator%20panel.FCStd][FreeCAD project]]
 201
 202 * Connector terminal
 203 :PROPERTIES:
 204 :ID:       e33940bd-652f-4ec0-b53b-1c03e16941c8
 205 :END:
 206
 207 Schematic:
 208 [[file:connector%20terminal/schematic.png]]
 209
 210 As seen above, most of the USB connectors are used to deliver dual
 211 power output and 1-wire data connectivity, except one on the bottom
 212 right. This is used to attach 12V battery. Some capacitors are thrown
 213 in as well to stabilize against smaller current spikes.
 214
 215 Electrically schematic is realized using smaller prototype PCBs.
 216
 217 [[file:connector%20terminal/make,%201.png]]
 218
 219
 220 Those PCBs are wired to central small PCB that acts as a hub:
 221
 222 [[file:connector%20terminal/make,%202.png]]
 223
 224 PCBs are held together by being sandwiched between front panel:
 225
 226 [[file:connector%20terminal/front%20panel.png]]
 227
 228 and smaller back-end plate:
 229
 230 [[file:connector%20terminal/back%20panel.png]]
 231
 232 Result:
 233
 234 [[file:connector%20terminal/make,%203.png]]
 235
 236
 237 Download:
 238 + [[file:connector%20terminal/front%20panel.stl][front panel STL]]
 239 + [[file:connector%20terminal/back%20panel.stl][back panel STL]]
 240 + [[file:connector%20terminal/connector%20terminal.FCStd][FreeCAD project]]
 241
 242 * Calibration
 243
 244 Since device uses adjustable step-down modules, these need to be
 245 calibrated to provide correct output voltage. It is important that
 246 battery receives proper charging voltage otherwise either no charging
 247 occurs or battery starts gassing out and gets destroyed.
 248
 249 See here for more details: https://www.powerstream.com/SLA.htm
 250
 251 -----
 252
 253 Happy building! :)