48 volt battery charger circuit diagram pdf11/29/2023 I am glad I did it this way because I had wiring errors that showed up before causing smoke. There is much destructive power here so it is wise to bring the voltage up gradually via an adjustable DC power supply or Variac powering the transformer primary. Kuberkoos, who suggested this project, will be using a number of transformer secondaries (and/or partial secondaries) connected in series to obtain the required voltage-this also is an acceptable technique. Drop-out voltage is 4.3V-if the raw voltage ever drops below this level, the output drops out of regulation. Note: to keep the series regulator from having to dissipate an unreasonable amount of power, the raw DC voltage should be about 10V higher than the maximum output voltage. Both types of rectifiers are indicated on the battery charger schematic. To use the 24V transformer, a voltage doubler rectifier is required to obtain the raw 53V supply. DigiKey does not have an affordable 48V transformer. The BOM indicates an acceptable 24V transformer available at DigiKey. Note that the transformer is by far the most expensive item if actually purchased. While this provided the correct DC voltage, I opted to use a smaller 24V transformer that is more representative of what others may have available. I started with an old multi-tap Stancor rectifier transformer conservatively rated at 100VA. Key to this project is the transformer selection. I accidentally shorted the output and yes, the current remained at 1.1A. ![]() The battery charger circuit has short-circuit protection, but this is momentary at best as the transistor gets very hot. I will let you select your own I did not find an extrusion at DigiKey that was drilled for the TO3 package, so you may have to drill your own heatsink for the 2N3055 transistor. I used a puny 5.8☌/W heatsink and while it worked on the bench OK, I recommend a much larger extruded heatsink. There are two modes of operation-voltage regulation or current regulation-the current regulator (when in operation) takes precedence over the voltage regulator. When the voltage across R5 exceeds about 0.65V, Q5 turns on and shunts base drive from the power Darlington thus causing the output voltage to be reduced. ![]() High voltage (80V) transistors are required for this application and the MPSA06 and A56 are suggested. Working into a current source, Q4 dissipates less power, increases maximum voltage applied to the Darlington and increases voltage regulator gain. Instead of using a pull-up resistor to turn the Darlington on, Q3 is configured as a 1mA current source. ![]() C3 is a compensation capacitor that slows down the regulator in order to prevent potential oscillation. The base of the Darlington is controlled by Q4, the voltage regulator transistor-it compares the feedback voltage coming from the voltage scaling pot with the 6.2V zener reference connected in the emitter circuit. Here VO represents output voltage from regulator IC.Q1 & Q2 make up a power Darlington using the venerable 2N3055 power transistor. It can be modified depends on this circuit design as, LM317 regulator gives variable output voltage and it can be varied by using Adjust pin, We can calculate Vo from IC LM317 as, Here Green LED represents the Charging condition and Red LED indicates the fully charged battery when the battery becomes fully charged then reverse voltage through Zener diode (12V) flows to transistor BD139 base and makes it turn ON due to the conduction in transistor Adjust pin of Voltage regulator connected to ground and cut the output voltage from regulator.Ĭonnect heat sink with voltage regulator LM317 to avoid thermal runaway. Step down (230V to 15V) transformer is used to step down the AC power supply and bridge rectifier (1N4007 X 4) converts AC supply into DC supply, C1 and C2 capacitor performs filter operation then IC1 LM317 regulates the DC power supply, VR1 variable resistor changes the supply to Adjust pin of voltage regulator and it changes the output voltage range. The LM317 is a monolithic Integrated IC comes with three different packages and it is a positive adjustable voltage regulator delivers 1.5A of load current, output voltage can be adjusted from 1.2 to 37 V. This circuit will give adjustable DC supply output and charges battery ranges from 6 volt to 12 Volt. Here Battery charger circuit diagram designed by implementing adjustable voltage regulator LM317 with auto cut off feature.
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