Relay Board Schematic Design

Thought for 4 sec

Here’s the schematic plan I’d use for the separate 10-channel 220 VAC relay board.

High-level architecture

Text
Control board harness
10x coil drive signals
        │
        ▼
Relay coil interface / flyback protection
        │
        ▼
10x 24 VDC relay coils

AC mains input
L / N / PE
        │
        ▼
Main protection ~50 A
        │
        ▼
AC live bus
        │
        ├── CH1 fuse 15 A ─ relay contact ─ output terminal CH1
        ├── CH2 fuse 15 A ─ relay contact ─ output terminal CH2
        ├── ...
        └── CH10 fuse 15 A ─ relay contact ─ output terminal CH10

Neutral and protective earth distributed to all output terminals

Schematic blocks to create 1. AC mains input

Use a high-current terminal block for:

AC_L_IN
AC_N_IN
PE_IN

For 220 VAC and high current, I would keep this as a physically separated high-voltage section with clear labeling and wide spacing.

2. Main input protection

Add one main protection device before the per-channel distribution.

Recommended options:

Panel-mount / chassis-mount breaker or fuse, not PCB-only, for ~50 A mains input.
If represented on the PCB schematic, use a connector or symbol for an external 50 A breaker/fuse.
Do not rely on a small PCB fuse holder for 50 A mains protection.

Suggested net flow:

Text
AC_L_IN → MAIN_FUSE_OR_BREAKER → AC_L_PROTECTED
AC_N_IN → AC_N_BUS
PE_IN   → PE_BUS

3. Ten relay output channels

Each channel should have:

HANKUK HR85AKS-DC24 relay
Replaceable 15 A fuse on the live output path
AC output terminal, preferably 3-pin:
- switched live
- neutral
- protective earth

Recommended per-channel topology:

Text
AC_L_PROTECTED → CHx_FUSE_15A → relay COM
relay NO → CHx_L_OUT
AC_N_BUS → CHx_N_OUT
PE_BUS   → CHx_PE_OUT

I’d use the relay in normally-open mode unless you explicitly need fail-on behavior.

4. 24 V relay coil power input

Add a low-voltage power connector:

Text
+24V_COIL_IN
0V_COIL_IN

Then distribute:

Text
+24V_COIL → one side of all relay coils
coil low side → harness drive signal / transistor driver return path

Important question: are the 10 incoming control signals already low-side coil drivers, or are they just ESP32/logic-level signals?

If they are already ULN2803/open-drain low-side outputs from the control board, this relay board only needs coil connections and flyback handling.
If they are logic-level signals, this relay board needs transistor/MOSFET/ULN2803 drivers.

5. Harness connector from control board

Use a harness connector with at least:

COIL_DRV_1
COIL_DRV_2
…
COIL_DRV_10
0V_COIL
optional +24V_COIL if coil power is also delivered through the harness
optional spare / key / detect pin

For reliability, I’d prefer the 24 V coil supply on a separate higher-current connector, not the signal harness, unless the harness is sized for relay coil current.

6. Coil flyback protection

Each 24 V relay coil needs suppression.

Options:

Diode across each coil: simple, low-cost, slower relay release.
TVS or diode + Zener: faster release, better for relay contact timing.
If the control board already has ULN2803A, note that ULN2803 includes clamp diodes, but the relay board still needs the correct COM clamp connection to +24V.

For a separate relay board, I’d put local flyback diodes or TVS protection on the relay board so protection stays close to the coils.

Safety/layout constraints to carry into the schematic

Keep low-voltage harness/24 V coil section physically isolated from 220 VAC contact/output section.
Use large creepage/clearance between:
- AC live/neutral/PE and low-voltage control
- relay contact pins and coil pins
- adjacent high-current channels
Use wide copper or copper pours for 15 A paths.
Consider using slots/cutouts between relay coil/control pins and contact pins.
Label all high-voltage nets clearly.
Prefer external/chassis wiring for the full 50 A main feed if PCB copper thickness/width cannot safely support it.

Open design decisions before schematic capture

Are the incoming 10 control signals logic-level inputs or already coil-driver low-side outputs?
Should each output socket switch live only, or live and neutral?
Should the board include current sensing or status feedback per channel?
What connector style/current rating do you want for the AC input and outputs?
Will the 50 A main protection be on-board, panel-mounted, or external?

My recommended starting schematic is: external/main 50 A breaker → live bus → 10× 15 A fused normally-open relay channels, with neutral and PE distributed directly to each output, and local flyback suppression for all 24 V relay coils.

Use low-side drivers

Add relay drivers

Switch live only

Specify connectors

Create schematic plan

Files

Schematic

Layout

3D View

Generic Passive MPN and Footprint Assignment

Date: 2026-06-15

Scope

Assigned exact manufacturer part numbers, manufacturers, ratings, and Flux package properties for all generic resistors R1–R39 and capacitors C1–C14.

Resistors

All resistors use YAGEO 0603 chip resistors, Flux package SMD_0603_1608Metric, 0.1 W rating.

Table

Designators	Value	Tolerance	MPN	Role
R1–R10	470Ω	5%	RC0603JR-07470RL	Channel LED current limiting
R11–R12	4.7kΩ	1%	RC0603FR-074K7L	I2C pull-ups
R13–R26, R39	10kΩ	1%	RC0603FR-0710KL	74HC165 input pull-ups and ADC series resistor
R27–R36	1kΩ	1%	RC0603FR-071KL	Manual override 2N2222 base resistors
R37	100kΩ	1%	RC0603FR-07100KL	PT voltage-sense divider high side
R38	33kΩ	1%	RC0603FR-0733KL	PT voltage-sense divider low side

Capacitors

Table

Designator	Value	Voltage	MPN	Manufacturer	Flux package	Role
C1	220µF	35 V	EEH-ZA1V221P	Panasonic	CP_Elec_10x10	24 V input bulk capacitor
C2	220µF	16 V	EEH-ZA1C221P	Panasonic	CP_Elec_8x10	5 V buck output bulk capacitor
C3	470µF	10 V	EEH-ZA1A471P	Panasonic	CP_Elec_8x10	3.3 V ESP32 Wi-Fi peak-current reservoir
C4–C9, C14	100nF	25 V	GRM188R71E104KA01D	Murata	SMD_0603_1608Metric	IC decoupling / ADC filtering
C10–C11	10µF	10 V	GRM188R61A106KE69D	Murata	SMD_0603_1608Metric	AMS1117 input/output capacitors
C12	100nF	10 V	GRM188R71A104KA61D	Murata	SMD_0603_1608Metric	OLED/local display decoupling
C13	10µF	25 V	GRM21BR61E106KA73L	Murata	SMD_0805_2012Metric	Rectified PT voltage smoothing

Verification Notes

BOM query now reports MPN/manufacturer metadata for the generic resistor and capacitor groups, but Flux groups generic passives by generic part type, so the grouped BOM display shows only one representative MPN per group. The individual schematic component properties were assigned by designator.
The bulk capacitors were corrected from impossible 0603 footprints to large electrolytic/polymer-style Flux packages.

Remaining Cautions

Confirm the Panasonic hybrid/polymer capacitor mechanical land pattern against the exact datasheet before final fabrication; if the library footprint does not match the manufacturer recommended land pattern, replace the generic capacitors with exact library parts.
C10/C11 10µF 0603 MLCCs will lose capacitance under DC bias; acceptable for local regulator stability only if the AMS1117 variant remains stable with the effective capacitance and ESR. Consider larger 0805/1206 MLCC or tantalum/polymer if regulator stability is uncertain.

Scope
Resistors
Capacitors
Verification Notes
Remaining Cautions