Relay Board Schematic Design

flux

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
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10-Channel AC Power Sequencer thumbnail
Low-voltage control and power-control electronics for a 10-channel 220 V AC power sequencer using ESP32, shift registers, OLED display, and isolated/high-current AC sections to be added later.

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