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+<div id="content" class="container">
+<div class="row"><div class="col-md-9"><h1 class="title">Battery charger and dual power supply unit</h1>
+
+<div id="outline-container-sec-1" class="outline-2">
+<h2 id="sec-1"><span class="section-number-2">1</span> General</h2>
+<div class="outline-text-2" id="text-1">
+<ul class="org-ul">
+<li>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.
+</li>
+
+<li>This design is released under Creative Commons Zero (CC0) license.
+</li>
+
+<li>Authors:
+<ul class="org-ul">
+<li>Svjatoslav Agejenko
+<ul class="org-ul">
+<li>Homepage: <a href="https://svjatoslav.eu">https://svjatoslav.eu</a>
+</li>
+<li>Email: <a href="mailto://svjatoslav@svjatoslav.eu">svjatoslav@svjatoslav.eu</a>
+</li>
+</ul>
+</li>
+
+<li>Valeria Agejenko
+</li>
+</ul>
+</li>
+
+<li>See also:
+<ul class="org-ul">
+<li><a href="../../index.html">Other physical projects in this repository</a>
+</li>
+<li><a href="https://www.svjatoslav.eu/projects/">Other projects hosted at svjatoslav.eu</a>
+</li>
+</ul>
+</li>
+</ul>
+</div>
+</div>
+
+<div id="outline-container-sec-2" class="outline-2">
+<h2 id="sec-2"><span class="section-number-2">2</span> Project description</h2>
+<div class="outline-text-2" id="text-2">
+<p>
+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.
+</p>
+
+
+<figure>
+<p><img src="make.png" class="img-responsive" alt="make.png">
+</p>
+</figure>
+
+<p>
+Power supply provides about 13 Volts and 5 Volts simultaneously.
+</p>
+
+<p>
+!!!WARNING!!! I use USB-A connectors for power output, but IT IS NOT
+COMPATIBLE WITH USB DEVICES AND POSSIBLY WITH EXISTING USB CABLES.
+</p>
+
+<p>
+Normal USB devices and cables should not be plugged in! It would
+damage device/cable and likely power supply.
+</p>
+
+<p>
+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.
+</p>
+
+
+<figure>
+<p><img src="connector%20terminal/USB%20hack.png" class="img-responsive" alt="USB%20hack.png">
+</p>
+</figure>
+
+<p>
+As seen, it has dual voltage output. Additionally one wire is
+dedicated to data transmission and can be used with <a href="https://en.wikipedia.org/wiki/1-Wire">1-wire</a>
+protocol. Power supply simply passively links all data wires together
+but does not participate in communication.
+</p>
+
+<p>
+Power supply uses 3D printed body with lots of holes, for fanless
+cooling.
+</p>
+
+
+<figure>
+<p><img src="body%20and%20covers/body,%201.png" class="img-responsive" alt="body,%201.png">
+</p>
+</figure>
+
+<p>
+Various modules are realized on top of prototype PCBs that slide into
+dedicated rails within the body.
+</p>
+
+
+<figure>
+<p><img src="body%20and%20covers/body,%202.png" class="img-responsive" alt="body,%202.png">
+</p>
+</figure>
+
+<p>
+Like this:
+</p>
+
+
+<figure>
+<p><img src="make,%202.png" class="img-responsive" alt="make,%202.png">
+</p>
+</figure>
+
+<p>
+When cover is closed, it blocks PCB movement:
+</p>
+
+
+<figure>
+<p><img src="body%20and%20covers/cover.png" class="img-responsive" alt="cover.png">
+</p>
+</figure>
+
+<p>
+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 :)
+</p>
+
+
+<figure>
+<p><img src="body%20and%20covers/cover%20cover.png" class="img-responsive" alt="cover%20cover.png">
+</p>
+</figure>
+
+<p>
+Download:
+</p>
+<ul class="org-ul">
+<li><a href="body%20and%20covers/body.stl">Body STL file</a>
+</li>
+<li><a href="body%20and%20covers/cover.stl">Big cover STL file</a>
+</li>
+<li><a href="body%20and%20covers/cover%20cover.stl">Small dummy cover on top, STL file</a>
+</li>
+<li><a href="body%20and%20covers/body%20and%20covers.FCStd">Body and covers FreeCAD project</a>
+</li>
+</ul>
+</div>
+</div>
+
+<div id="outline-container-sec-3" class="outline-2">
+<h2 id="sec-3"><span class="section-number-2">3</span> Transformer and AC to DC converter</h2>
+<div class="outline-text-2" id="text-3">
+<p>
+This is where high voltage from mains electricity enters the system.
+</p>
+
+<p>
+Schematic:
+<img src="transformer%20and%20AC%20DC%20converter%20board/schematic.png" class="img-responsive" alt="schematic.png">
+</p>
+
+<p>
+For safety I kept high voltage section as minimal as possible. That
+is, wall plug runs straight into transformer. Also I used <a href="https://www.amazon.de/gp/product/B07VGQKM3G/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1">UV hardening
+glue</a> for extra safety and isolation on PCB.
+</p>
+
+<p>
+Power on/off switch operates on already reduced voltage of about 30
+volts. Power switch is located on <a href="#sec-6">indicator panel</a>.
+</p>
+
+
+<figure>
+<p><img src="transformer%20and%20AC%20DC%20converter%20board/make,%201.png" class="img-responsive" alt="make,%201.png">
+</p>
+</figure>
+
+<p>
+DC current of about 30 volts is then routed to <a href="#sec-4">Main board</a>.
+</p>
+
+
+<figure>
+<p><img src="transformer%20and%20AC%20DC%20converter%20board/make,%202.png" class="img-responsive" alt="make,%202.png">
+</p>
+</figure>
+
+<p>
+<a href="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</a>.
+</p>
+</div>
+</div>
+
+<div id="outline-container-sec-4" class="outline-2">
+<h2 id="sec-4"><a id="ID-65d68227-4bf2-4c4f-b4d3-c390bc6a9c34" name="ID-65d68227-4bf2-4c4f-b4d3-c390bc6a9c34"></a><span class="section-number-2">4</span> Main board</h2>
+<div class="outline-text-2" id="text-4">
+<p>
+This is logically main board because it appears to be central hub that
+connects all components. It also houses 2 <a href="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</a>.
+</p>
+
+
+<figure>
+<p><img src="main%20board/main%20board,%201.png" class="img-responsive" alt="main%20board,%201.png">
+</p>
+</figure>
+
+<p>
+High-level schematic of entire device:
+<img src="main%20board/schematic.png" class="img-responsive" alt="schematic.png">
+</p>
+
+<p>
+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 <a href="#sec-5">Current limiter circuit</a>. 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 <a href="#sec-7">connector terminal</a> to be
+consumed by connected devices.
+</p>
+
+<p>
+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.
+</p>
+
+<p>
+Also about 13V output voltage is approximate and depends on connected
+battery charge level.
+</p>
+
+<p>
+Second Step-Down converter reduces voltage even further to quite
+precisely 5V DC. This resulting voltage is also routed to <a href="#sec-7">connector
+terminal</a>.
+</p>
+
+<p>
+Both 13V and 5V lines are also routed to <a href="#sec-6">indicator panel</a> for
+monitoring.
+</p>
+
+<p>
+There is single on/off switch. In off position, it disconnects battery
+and transformer from the system effectively powering everything down.
+</p>
+
+<p>
+On schematic above, some wires are annotated with numbers from 1
+to 13. This corresponds to output pins on the board.
+</p>
+
+
+<figure>
+<p><img src="main%20board/main%20board,%202.png" class="img-responsive" alt="main%20board,%202.png">
+</p>
+</figure>
+</div>
+</div>
+<div id="outline-container-sec-5" class="outline-2">
+<h2 id="sec-5"><a id="ID-afc22d23-9bc4-421c-9cac-e0ce34bd36bc" name="ID-afc22d23-9bc4-421c-9cac-e0ce34bd36bc"></a><span class="section-number-2">5</span> Current limiter</h2>
+<div class="outline-text-2" id="text-5">
+<p>
+Schematic:
+<img src="current%20limiter/schematic.png" class="img-responsive" alt="schematic.png">
+</p>
+
+<p>
+Simple LM317 based current limiter is used. I used 4.7 ohm
+resistor. It provides about 265 milliamps of current. See <a href="http://www.reuk.co.uk/wordpress/electric-circuit/lm317-current-calculator/">calculator</a>.
+</p>
+
+
+<figure>
+<p><img src="current%20limiter/current%20limiter,%201.png" class="img-responsive" alt="current%20limiter,%201.png">
+</p>
+</figure>
+
+<p>
+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.
+</p>
+
+<p>
+If attached battery is really empty, significant voltage drop can
+occur in LM317. Heatsink is needed to dissipate that power.
+</p>
+
+
+<figure>
+<p><img src="current%20limiter/current%20limiter,%202.png" class="img-responsive" alt="current%20limiter,%202.png">
+</p>
+</figure>
+
+<p>
+Note: resistor gets hot too.
+</p>
+</div>
+</div>
+
+<div id="outline-container-sec-6" class="outline-2">
+<h2 id="sec-6"><a id="ID-c9a69490-f920-4a31-b32e-b101bfc3d01b" name="ID-c9a69490-f920-4a31-b32e-b101bfc3d01b"></a><span class="section-number-2">6</span> Indicator panel</h2>
+<div class="outline-text-2" id="text-6">
+
+<figure>
+<p><img src="indicator%20panel/indicator%20panel,%201.png" class="img-responsive" alt="indicator%20panel,%201.png">
+</p>
+</figure>
+
+<p>
+Basically 2 digital DC voltmeters and main on/off switch.
+</p>
+
+
+<figure>
+<p><img src="indicator%20panel/indicator%20panel,%202.png" class="img-responsive" alt="indicator%20panel,%202.png">
+</p>
+</figure>
+
+<p>
+Download:
+</p>
+
+
+<figure>
+<p><img src="indicator%20panel/indicator%20panel.png" class="img-responsive" alt="indicator%20panel.png">
+</p>
+</figure>
+
+<ul class="org-ul">
+<li><a href="indicator%20panel/indicator%20panel.stl">STL file</a>
+</li>
+<li><a href="indicator%20panel/indicator%20panel.FCStd">FreeCAD project</a>
+</li>
+</ul>
+</div>
+</div>
+
+<div id="outline-container-sec-7" class="outline-2">
+<h2 id="sec-7"><a id="ID-e33940bd-652f-4ec0-b53b-1c03e16941c8" name="ID-e33940bd-652f-4ec0-b53b-1c03e16941c8"></a><span class="section-number-2">7</span> Connector terminal</h2>
+<div class="outline-text-2" id="text-7">
+<p>
+Schematic:
+<img src="connector%20terminal/schematic.png" class="img-responsive" alt="schematic.png">
+</p>
+
+<p>
+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.
+</p>
+
+<p>
+Electrically schematic is realized using smaller prototype PCBs.
+</p>
+
+
+<figure>
+<p><img src="connector%20terminal/make,%201.png" class="img-responsive" alt="make,%201.png">
+</p>
+</figure>
+
+
+<p>
+Those PCBs are wired to central small PCB that acts as a hub:
+</p>
+
+
+<figure>
+<p><img src="connector%20terminal/make,%202.png" class="img-responsive" alt="make,%202.png">
+</p>
+</figure>
+
+<p>
+PCBs are held together by being sandwiched between front panel:
+</p>
+
+
+<figure>
+<p><img src="connector%20terminal/front%20panel.png" class="img-responsive" alt="front%20panel.png">
+</p>
+</figure>
+
+<p>
+and smaller back-end plate:
+</p>
+
+
+<figure>
+<p><img src="connector%20terminal/back%20panel.png" class="img-responsive" alt="back%20panel.png">
+</p>
+</figure>
+
+<p>
+Result:
+</p>
+
+
+<figure>
+<p><img src="connector%20terminal/make,%203.png" class="img-responsive" alt="make,%203.png">
+</p>
+</figure>
+
+
+<p>
+Download:
+</p>
+<ul class="org-ul">
+<li><a href="connector%20terminal/front%20panel.stl">front panel STL</a>
+</li>
+<li><a href="connector%20terminal/back%20panel.stl">back panel STL</a>
+</li>
+<li><a href="connector%20terminal/connector%20terminal.FCStd">FreeCAD project</a>
+</li>
+</ul>
+</div>
+</div>
+
+<div id="outline-container-sec-8" class="outline-2">
+<h2 id="sec-8"><span class="section-number-2">8</span> Calibration</h2>
+<div class="outline-text-2" id="text-8">
+<p>
+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.
+</p>
+
+<p>
+See here for more details: <a href="https://www.powerstream.com/SLA.htm">https://www.powerstream.com/SLA.htm</a>
+</p>
+
+<hr >
+
+<p>
+Happy building! :)
+</p>
+</div>
+</div>
+</div><div class="col-md-3"><nav id="table-of-contents">
+<div id="text-table-of-contents" class="bs-docs-sidebar">
+<ul class="nav">
+<li><a href="#sec-1">1. General</a></li>
+<li><a href="#sec-2">2. Project description</a></li>
+<li><a href="#sec-3">3. Transformer and AC to DC converter</a></li>
+<li><a href="#sec-4">4. Main board</a></li>
+<li><a href="#sec-5">5. Current limiter</a></li>
+<li><a href="#sec-6">6. Indicator panel</a></li>
+<li><a href="#sec-7">7. Connector terminal</a></li>
+<li><a href="#sec-8">8. Calibration</a></li>
+</ul>
+</div>
+</nav>
+</div></div></div>
+<footer id="postamble" class="">
+<div><p class="author">Author: Svjatoslav Agejenko</p>
+<p class="date">Created: 2020-07-12 Sun 02:52</p>
+<p class="creator"><a href="http://www.gnu.org/software/emacs/">Emacs</a> 26.1 (<a href="http://orgmode.org">Org-mode</a> 9.1.9)</p>
+</div>
+</footer>
+</body>
+</html>
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