[Introduction] 　The reason I started making this charger was because I made a supplementary charging device for batteries (12V) for electric fences. I had charged 12V batteries in the past, but I had forced the current from a constant voltage power source instead of using a regular charging device. This would result in overcharging or undercharging, making stable charging impossible. This time, I charged a spare battery at 2A from a constant voltage power source, and when I checked it 14 hours later (the next morning), the 6A ammeter had gone off the scale. When I checked the battery, two of the six cells were shorted, making it an 8V battery. To avoid this kind of problem, it is necessary to charge the battery using the regular flow chart, and I tried to design a way to do it using parts I had on hand. 【Generation of original DC voltage】 　I used a power transformer to generate the power, but there were quite a few restrictions with the parts I had on hand, and it depended heavily on what the maximum charging current was set to. Therefore, I had three 24V-3.3A switching power supplies on hand, which I had previously gathered while making an intermediate amplifier, and it looked like I could use them this time. When using this power supply, set the maximum charging current to 2.5A. When setting it to 5A, use a 24V-10A product, and when setting it to 10A, use a 24V-20A product. It is sold online for around 2K-3K yen. 　　　　　　　　　　 【Voltage Control Element】 　I use NJM723 for voltage control, and NPN Darlington transistor 2SD2081 or 2SD2083 for current control. I used NJM723 often for FET bias control when I made power MOS-FET power amplifier in the past, and it has a current control function, so I will use it. I have control transistor 2SD2081 (10A-30W) on hand, which can be used for charging current = 2.5A products, but I purchased 2SD2083 (25A-120W) from Akitsuki, which can be used for 5A and 10A products. 　　　　　　　　 【Diode used as reverse current blocking】 　I will use 20A or 30A products. I will use two FMQG5G 10A products that I got a lot of at a meeting before. 　　　　　　　　 【relay】 　The 1-circuit 2-contact relays, 2-circuit 2-contact relays, and RL3 are 2A 1-circuit 2-contact relays, all of which are sold by Akizuki, and the output circuit RL1 is a 16A relay used in linear amplifiers, sold by Sengoku. All relays are 12V powered. 　　　　　　　　 【Device for controlling voltage】 　In manual mode, the output voltage is adjusted by a VR mounted on the panel, but in auto mode, the voltage needs to be controlled automatically. There are many types of electronic control devices that can be used for this, such as +5V single power supply or ±5V drive devices, but there are only a few high-voltage control devices, so we will use Analog Devices' AD5290. This was used when designing a flexible LPF for a homemade machine in the past. However, this has one drawback: the device shape is only MSOP (MSOP10 pin). Therefore, we will use a board that converts MSOP10 pin to DIP10 pin, which is sold at Akizuki. 　　　　　　 【Heat sink】 　The heat sink for mounting the control transistor (2SD2083) and diode is 　　　　　　　　　Charging current = 2.5A specification → Pd = 20W heat sink required 　　　　　　　　　Charging current = 5A specification → Pd = 40W heat sink required 　　　　　　　　　Charging current = 10A specification → Pd = 80W heat sink required 　　　　　　　　　  To fit both specifications, I cut an aluminum heat sink I had collected in the past to 20cm x 11cm with a W cutter. In reality, half of this size would be fine. 　　　　　　　　　　　 The other parts are general-purpose items, and the director, who always makes his own parts, has plenty of them lying around. 【Circuit Operation】 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Circuit Diagram 　The DC24V power supply is adjusted to +20.0V using the output voltage adjustment. The voltage control is made variable from 3.2V to 17.2V using the NJM723, and the current is amplified using a Darlington NPN transistor 2SD2083 (25A, 120W). The NJM723 can set the current limit by detecting between ② and ③. For the 2.5A model, R2 = 0.47Ω (10W), for the 5A model, 0.47Ω/10W is connected in parallel with two wires, and for the 10A model, 0.22Ω/10W is connected in parallel with two wires. The power supply for the control circuit is +15V, and +5V is supplied to the display unit. 　①　Relay circuit 　　　RL1 switches between supplying the charger output to the output terminal or disconnecting it from the battery. 　　　RL2 switches between measuring the charger output voltage or the battery voltage alone. 　　　RL3 is the battery dummy resistance (10Ω/10W) and switches the dummy current ON/OFF. 　　　RL4 switches between controlling the panel VR with voltage control of NJM723 or controlling it with AD5290. 　②　Voltage Detection Circuit 　　　The voltage from the voltage divider resistors R7, VR2, and R11 is supplied to the A/D converter from CNP7 no. ④, and the voltage is displayed on the LCD. 　③　Current Detection Circuit 　　　The voltage across R2 is detected and amplified by the op-amp U4, then supplied to the A/D converter from CNP7 no. ③ to display the current. To improve the accuracy of the current detection, a negative power supply for the op-amp was required, and initially a DC/DC converter (MAU108) with a +5V input and ±12V output was purchased from Akizuki and used, but midway through, it stopped outputting -12V and the MAU108 broke. As a result, we stopped using the DC/DC and generated additional -12V with a small transformer. (Only drives two bipolar op-amps) 　　　　　　　　　　　　 　④　Battery checker drive circuit 　　　The RL3 relay is used to pass a battery dummy current of 1.3A, and the battery voltage is detected to drive U5 (op-amp). Normally, the accuracy would be improved by passing a dummy current of several tens of amps, but this is a simplified format. A 100uA current meter is used to divide the zones into green, yellow, and red. The JPG image at the bottom left is printed out onto a sticker and attached to the meter. 　　　　　　　　　　　　　　 　⑤　Automatic Voltage Control Circuit 　　　In automatic charging mode, the RL4 relay is switched to U6 (AD5290) and the CPU controls the NJM723 via the AD5290, constantly controlling the voltage. 【Production】 　I was able to gather the main components to make the kit, but I asked the local station chief to etch the printed circuit board according to the circuit diagram. There were SSOP components, so I was worried whether it would turn out well, but it turned out perfectly. 　　　　　　　　　　Pattern 1x size 　Silk printing 1x size Components were attached to the completed printed circuit board to complete the assembly, and it was then stored in the case. 　 The case I chose was inexpensive and easy to process the panel. 　　　 【Adjustment】 　Set the main power supply (24V) to 20.0V. Turn on the power while pressing the 'MODE' and 'START' keys. 　①　Voltage detection adjustment 　　　1）Connect a multimeter (tester) to the output terminal and adjust the panel VR so that it is 15.5Vdc. 　　　2）Adjust VR2 so that the LCD display voltage is 15.5V. 　　　　　　　　　　　　　　　　 　②　Current Sense Adjustment 　　　1）Maximum charging current adjustment 　　　　Set VR1 all the way to the right, then connect a multimeter (in 10A mode) between the positive (+) and negative (-) output terminals. In other words, set it so that you can measure the output short-circuit current. In this state, gradually turn VR1 to the left and adjust VR1 so that the multimeter display reads 2.50A. Remove the multimeter when adjustment is complete. 　　　　　　　　　　　　　　　　 　　　2）Current display adjustment 　　　　Set the panel VR all the way to the left, then use the multi-tester's DC voltmeter to adjust VR4 so that CNP7 pin ③ reads ±0V. Next, the panel VR can be positioned anywhere, but short out the output terminals. At this time, adjust VR3 so that the LCD current display is 2.50A. After adjustment, quickly release the short. 　　　　　　　　　　　　　　　　 　③　Battery-Check meter adjustment 　　　Adjust the panel VR so that the voltage display on the LCD is 12.7V. Next, press the 'START' key. The meter needle will fluctuate, so adjust VR5 and adjust it so that it is 100% (full scale). After adjustment, press the 'START' key again to return it to the original state. 　　　　　　　　　　　　　　　　 Now all adjustments are complete, you can turn the power off and use the unit normally. 【Finished state】 　To be foolproof, the battery reverse connection protection is not a hardware protection but a software protection. In NORMAL-MODE, you can force the charging current to the battery, but if the battery is reversed, or if it is reversed at any point, the display will say "NOT-BATTERY" and the power will be turned off. In AUTO-MODE, if the battery is reversed at any stage, the display will also say "NOT-BATTERY". In B-CHECK mode, there is no problem, just the meter will not swing.