# DeWalt 21V 5S Experimental Charger ## Description Experimental 21V/5S Li-ion DeWalt battery charger with 21V DC input, relay-switched charge path, tap monitoring, ESP32-WROOM external controller interface, test header, and 2-layer prototype PCB intent. ## Project Details - **Owner:** 19002041 - **Created:** 3/28/2026 - **Last Updated:** 3/28/2026 - **Visibility:** Public - **System Architecture:** ```mermaid flowchart TD J1[21V DC Input] --> F1[PTC Fuse 3A] F1 --> VINF[VIN_21V_FUSED] VINF --> D1[TVS Protection] VINF --> K1C[Relay Contact COM] K1C -->|when enabled| K1N[Relay NO] K1N --> CHG[CHG_21V_OUT] CHG --> J2BP[Battery Bplus] J1G[GND Input] --> GND[GND Common] GND --> J2BM[Battery Bminus] J2C1[Battery C1] --> DIV1[Divider C1] J2C2[Battery C2] --> DIV2[Divider C2] J2C3[Battery C3] --> DIV3[Divider C3] J2C4[Battery C4] --> DIV4[Divider C4] J2BP --> DIV5[Divider Bplus] J2TH[Battery TH] --> TH[TH Pullup and Filter] J2ID[Battery ID] --> ID[ID Pullup and Filter] DIV1 --> ADC1[ADC_C1] DIV2 --> ADC2[ADC_C2] DIV3 --> ADC3[ADC_C3] DIV4 --> ADC4[ADC_C4] DIV5 --> ADC5[ADC_BP] TH --> ADCTH[ADC_TH] ID --> ADCID[ADC_ID] J3[ESP32 Interface Header] --> EN[CHARGE_EN] EN --> R13[Base Resistor] R13 --> Q1[NPN Driver] Q1 --> K1COIL[Relay Coil] K1COIL --> P5[5V Rail] K1COIL --> D2[Flyback Diode] VINF --> LED1[Power LED] EN --> LED2[Charge LED Signal] J4[Test Header] --> TP[Test Access Nets] ``` ## Key Components ### D1 — [SMBJ24A R5G](https://www.flux.ai/lcsc/smbj24a-r5g.md) - Role: TVS Protection - Manufacturer Part Number: SMBJ24A R5G - Package or Case Code: DO-214AA_L4.4-W3.6-LS5.3-RD - Package: DO-214AA - Manufacturer Name: Taiwan Semiconductor(台湾半导体) - Role Details: TVS between VIN_21V_FUSED and GND - Part Type: TVS - LCSC Part Number: C484012 **Pins:** - 1 [pin 1] - 2 [pin 2] ### D2 — [1N4007RLG](https://www.flux.ai/jecstronic/1n4007rlg.md) - Role: Flyback Protection - Manufacturer Name: onsemi - Role Details: Reverse-biased diode across K1 coil - License: https://creativecommons.org/licenses/by/4.0/ - Package: DO-41 - Manufacturer Part Number: 1N4007RLG - Part Type: Diode - Datasheet URL: https://www.onsemi.com/pdf/datasheet/1n4001-d.pdf **Pins:** - anode [pin 2] - cathode [pin 1] ### F1 — RGEF300 - Package: Through Hole - Package or Case Code: FUSE-TH_L6.6-W3.0-P5.10-D0.8-S1.20 - Manufacturer Name: Littelfuse(美国力特) - Role: Input Protection - Manufacturer Part Number: RGEF300 - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2304140030_Littelfuse-RGEF300_C315965.pdf - Role Details: 3A resettable PTC fuse on VIN_21V input - LCSC Part Number: C315965 - Product Info Url: https://lcsc.com/product-detail/PTC-Resettable-Fuses_Littelfuse-RGEF300_C315965.html - Part Type: Resettable Fuses - JLCPCB Part Class: Extended Part **Pins:** - 1 [pin 1] - 2 [pin 2] ### J1 — [KF128-5.08-2P-AA](https://www.flux.ai/lcsc/kf128-5p08-2p-aa.md) - LCSC Part Number: C474952 - Pin Number: 1=VIN_21V,2=GND - Connector Pitch: 5.08mm - Package or Case Code: CONN-TH_P5.08_KF128-5.08-2P - Product Info Url: https://lcsc.com/product-detail/New-Quadratic-Unclassified-Data_Cixi-Kefa-Elec-KF128-5-08-2P_C474952.html - Package: THT - Implementation Details: Silk: 21V IN, GND - Connector Rows: 1 - Part Type: Screw terminal - Connector Gender: Female - Role: Power Input Connector - Manufacturer Part Number: KF128-5.08-2P-AA - Connector Type: Screw terminal - Operating Temperature: -40℃~+105℃ - Current Rating: 24A - Manufacturer Name: KEFA(科发) - JLCPCB Part Class: Extended Part - Role Details: 21V DC input, 2-pin 5.08mm screw terminal, board edge entry - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2408211511_Cixi-Kefa-Elec-KF128-5-08-2P-AA_C474952.pdf - Connector Positions: 2 **Pins:** - 1 [pin 1] - 2 [pin 2] ### J2 — [4304-50812](https://www.flux.ai/cherepanyadima/4304-50812.md) - Part Type: Connectors - Datasheet URL: https://tools.molex.com/pdm_docs/ps/PS-43045.pdf - Manufacturer Part Number: 0430450812 - Manufacturer Name: Molex - Symbol Style: Parametric - Mount: Solder - Pin Number: 1=BAT_B-,2=BAT_C1,3=BAT_C2,4=BAT_C3,5=BAT_C4,6=BAT_B+,7=BAT_TH,8=BAT_ID - Package or Case Code: TO - Role Details: DeWalt battery interface carrying charge path and sense taps - Role: Battery Connector - Package: Through Hole - Implementation Details: Silk: B-, C1, C2, C3, C4, B+, TH, ID **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] - 5 [pin 5] - 6 [pin 6] - 7 [pin 7] - 8 [pin 8] ### J3 — [Pin Header 01x14 2.54mm Vertical](https://www.flux.ai/adrian95/pin-header-01x14-254mm-vertical.md) - Pin Number: 1=+5V,2=3V3,3=GND,4=ADC_C1,5=ADC_C2,6=ADC_C3,7=ADC_C4,8=ADC_BP,9=ADC_TH,10=ADC_ID,11=CHARGE_EN,12=LED_CHARGE,13=LED_FAULT,14=NC - Role Details: ESP32 external controller header with ADC, power, and charge control signals - Part Type: Connector - Role: Controller Interface - License: https://creativecommons.org/licenses/by/4.0/ - Package: Through Hole - Implementation Details: Suggested ESP32 mapping: VP, VN, GPIO34, GPIO35, GPIO32, GPIO33, GPIO25, GPIO26, GPIO27, GPIO14 **Pins:** - Pin_1 [pin 1] - Pin_10 [pin 10] - Pin_11 [pin 11] - Pin_12 [pin 12] - Pin_13 [pin 13] - Pin_14 [pin 14] - Pin_2 [pin 2] - Pin_3 [pin 3] - Pin_4 [pin 4] - Pin_5 [pin 5] - Pin_6 [pin 6] - Pin_7 [pin 7] - Pin_8 [pin 8] - Pin_9 [pin 9] ### J4 — [Pin Header 01x10 2.54mm Vertical](https://www.flux.ai/vasy_skral/pin-header-01x10-254mm-vertical.md) - Role Details: 1x10 debug and measurement header - Part Type: Connector - Implementation Details: Test access header with silk pin labels - Role: Test Header - Package: Through Hole - Pin Number: 1=VIN_21V,2=CHG_21V_OUT,3=BAT_B-,4=BAT_C1,5=BAT_C2,6=BAT_C3,7=BAT_C4,8=BAT_B+,9=BAT_TH,10=BAT_ID **Pins:** - Pin_1 [pin 1] - Pin_10 [pin 10] - Pin_2 [pin 2] - Pin_3 [pin 3] - Pin_4 [pin 4] - Pin_5 [pin 5] - Pin_6 [pin 6] - Pin_7 [pin 7] - Pin_8 [pin 8] - Pin_9 [pin 9] ### K1 — [SRD-05VDC-SL-C](https://www.flux.ai/vasy_skral/srd-05vdc-sl-c.md) - Role Details: 5V coil relay, NO contact used to switch charger output - Manufacturer Name: Ningbo Songle Relay - Role: Charge Relay - Package: THT - Manufacturer Part Number: SRD-05VDC-SL-C - Part Type: Relay - Datasheet URL: https://www.circuitbasics.com/wp-content/uploads/2015/11/SRD-05VDC-SL-C-Datasheet.pdf **Pins:** - A1 [pin A1] - A2 [pin A2] - COM [pin COM] - NC [pin NC] - NO [pin NO] ### LED1 — [SM0805HCL](https://www.flux.ai/adrian95/sm0805hcl.md) - Part Type: LED - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.bivar.com/parts_content/Datasheets/SM0805HCL.pdf - Manufacturer Name: Bivar Inc. - Role: Status LED - Role Details: Power present indicator on fused input rail - Package: 0805 - Manufacturer Part Number: SM0805HCL **Pins:** - A [pin 2] - K [pin 1] ### LED2 — [SM0805HCL](https://www.flux.ai/adrian95/sm0805hcl.md) - Role: Status LED - Manufacturer Part Number: SM0805HCL - Manufacturer Name: Bivar Inc. - Package: 0805 - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.bivar.com/parts_content/Datasheets/SM0805HCL.pdf - Part Type: LED - Role Details: Charge enabled indicator **Pins:** - A [pin 2] - K [pin 1] ### LED3 — [SM0805HCL](https://www.flux.ai/adrian95/sm0805hcl.md) - Package: 0805 - Role Details: Optional MCU-driven fault indication - Part Type: LED - Role: Fault LED - Datasheet URL: https://www.bivar.com/parts_content/Datasheets/SM0805HCL.pdf - License: https://creativecommons.org/licenses/by/4.0/ - Manufacturer Name: Bivar Inc. - Manufacturer Part Number: SM0805HCL **Pins:** - A [pin 2] - K [pin 1] ### Q1 — [2N2222A](https://www.flux.ai/lcsc/2n2222a.md) - Manufacturer Part Number: 2N2222A - Package: TO-92 - LCSC Part Number: C118536 - Role: Relay Driver - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/1809200018_ST-Semtech-2N2222A_C118536.pdf - Package or Case Code: TO-92-3_L4.9-W3.7-P1.27-L - Product Info Url: https://lcsc.com/product-detail/Transistors-NPN-PNP_2N2222_C118536.html - Compliance: RoHS - Role Details: NPN transistor driven by CHARGE_EN through base resistor - Manufacturer Name: ST(先科) - Frequency: 250MHz - JLCPCB Part Class: Extended Part - Part Type: Transistors/Thyristors/Bipolar (BJT) - Transistor Type: NPN **Pins:** - B [pin 2] - C [pin 3] - E [pin 1] ### Q2 — [QM6015D](https://www.flux.ai/kicad-part-library/qm6015d.md) - Package or Case Code: TO-252-2 - Role Details: P-MOSFET high-side for reverse polarity protection on 21V input - Package: TO-252 - Manufacturer Part Number: QM6015D - Role: Reverse Polarity Protection - Datasheet URL: http://www.jaolen.com/images/pdf/QM6015D.pdf **Pins:** - D [pin 2] - G [pin 1] - S [pin 3] ### RLED1 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor.md) - Package: SMD_0805_2012Metric - Resistance: 4.7kΩ - Part Type: Resistor - Role Details: Current limit for VIN present LED - Role: LED Current Limit **Pins:** - P1 [pin 1] - P2 [pin 2] ### RLED2 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor.md) - Package: SMD_0805_2012Metric - Role Details: Current limit for charge enabled LED - Resistance: 1kΩ - Role: LED Current Limit - Part Type: Resistor **Pins:** - P1 [pin 1] - P2 [pin 2] ### RLED3 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor.md) - Role: LED Current Limit - Resistance: 1kΩ - Package: SMD_0805_2012Metric - Part Type: Resistor - Role Details: Current limit for optional fault LED **Pins:** - P1 [pin 1] - P2 [pin 2] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/19002041/dewalt-21v-5s-experimental-charger](https://www.flux.ai/19002041/dewalt-21v-5s-experimental-charger).* --- *Generated from [https://www.flux.ai/19002041/dewalt-21v-5s-experimental-charger](https://www.flux.ai/19002041/dewalt-21v-5s-experimental-charger)*