12V Lead-Acid battery changer and terminal
+Battery charger and dual power supply unit
1 General
@@ -206,10 +206,13 @@ COULD BE ERRORS THAT CAN RESULT IN ALL KINDS OF DAMAGE. USE THESE DESIGNS AT YOUR OWN RISK. -- Svjatoslav Agejenko - +
- Homepage: https://svjatoslav.eu
- Email: svjatoslav@svjatoslav.eu @@ -217,6 +220,11 @@ DESIGNS AT YOUR OWN RISK.
- Other physical projects in this repository
@@ -232,121 +240,443 @@ DESIGNS AT YOUR OWN RISK.
2 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. +
+ ++Power supply provides about 13 Volts and 5 Volts simultaneously. +
+ ++!!!WARNING!!! 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. +
+-Simple charger and terminal (front-end) for 12V lead-acid battery. +As seen, it has dual voltage output. Additionally one wire is +dedicated to data transmission and can be used with 1-Wire protocol
-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. +1-Wire data router/hub is really simple. Power supply simply passively +links all data wires together.
-Single on/off button disconnects battery and up-step voltage source -from front panel terminal connectors. +Power supply uses 3D printed body with lots of holes, for fanless +cooling.
+ + +-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. +Various modules are realized on top of prototype PCBs that slide into +dedicated rails within the body.
-Current design is rather of blog (experience sharing) value. It has -quite some drawbacks: +Like this:
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-
- 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! - -
- There is no dedicated current limiter. 3V external power supply -and up-step are acting as current limiters. - + -
- While RCA connectors do work as DC power connectors, but are not -intended to be used this way and are not very reliable. - +
- 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.
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+
+
+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: +
+
+When cover is closed, it blocks PCB movement: +
--+ +3 Body
+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: +
+ + +-
-
- Download: - +
++ +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: +
++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! :) +
+