Relay Selection Guide: Popular Types, Alternatives, and Selection Tips
Relay Selection Guide
Relays let low-power circuits switch high-voltage/current loads. It is the first thing we ask on a new BOM. This guide covers the most popular relay types and their alternatives.
Mechanical vs Solid-State Relay
| Factor | Mechanical Relay | Solid-State Relay (SSR) |
| Contact life | 100K-1M cycles | >10M cycles |
| Switching speed | 5-15ms | <1ms |
| Contact resistance | <50mΩ | 1-100mΩ |
| Heat generation | Minimal | Generates heat (Vf×I) |
| Cost | Lower | Higher |
| Audio noise | Clicks | Silent |
| Best for | Power on/off, motor control, lighting | High-frequency, silent operation |
Most boards we quote are still mechanical-relay designs — usually the right call, and 100K cycles covers most product lifetimes. We only push SSR when speed or silence matters.
Popular Mechanical Relays
SRD Series (Songle) — Most Common 5V Relay
| Parameter | SRD-05VDC-SL-C |
| Coil voltage | 5VDC |
| Contact form | SPDT (1C) |
| Contact rating | 10A @ 250VAC / 30VDC |
| Coil power | 360mW |
| Life | 100K cycles |
| Price | $0.30-0.60 |
| Best for | Arduino projects, home automation, general on/off |
HF Series (Hongfa) — Higher Quality
| Part Number | Coil | Contact | Rating | Price | Notes |
| HF32F-005 | 5V | SPDT | 10A | $0.40-0.70 | Compact DIP package |
| HF33F-024 | 24V | SPST | 15A | $0.50-0.80 | Higher current |
| HF115F | 5/12/24V | SPDT | 12A | $0.80-1.20 | PCB mount, 8mm creepage |
T73 Series — PCB Power Relay
| Parameter | T73 |
| Coil | 5/12/24V |
| Rating | 10-15A @ 250VAC |
| Package | DIP, through-hole |
| Price | $0.25-0.50 |
Chinese Relay Brands
| Brand | Quality Tier | Compared To |
| Songle (松乐) | Standard | Good for general use |
| HF / Hongfa (宏发) | Premium | Better than Songle, ISO certified |
| Sanyou (三友) | Standard | Similar to Songle |
| Tianbo (天波) | Budget | Lowest cost |
SSR Selection
For AC Loads (Lighting, Motors, Heaters)
| Part | Load Voltage | Max Current | Trigger | Price |
| MOC3063 + Triac | 110-240VAC | Up to 10A | Zero-cross | $0.50+$0.30 |
| Fotek SSR-25DA | 24-380VAC | 25A | 3-32VDC | $5-8 |
| SSR-40DA | 24-440VAC | 40A | 3-32VDC | $8-12 |
For DC Loads
| Part | Load Voltage | Max Current | Notes |
| TLP191B | 30V | 2.5A | Photovoltaic output |
| AO4407A | 30V | 12A | P-MOSFET SSR alternative |
Accessories
| Component | Price | Why You Need It |
| Flyback diode (1N4007) | $0.02 | Required across relay coil |
| ULN2003 driver | $0.15 | 7-channel relay driver IC |
| Relay socket | $0.10-0.30 | Easy replacement |
| SN74HC595 | $0.20 | 8-relay shift register |
Important: Always put a flyback diode across the relay coil (cathode to VCC) or you risk damaging your driver transistor — the most common relay failure we see on returned boards.
Where to Buy
PartsCube Global stocks SRD, HF, T73 relays and SSR modules. [
References
Written by Ling Zhang
BOM & Sourcing Specialist · Guangzhou, China
Ling helps customers turn BOM lists into deliverable quotes, specializing in alternative part matching and cost optimization. She joined from a component trading background in Guangdong.
View all articles by Ling →Need help sourcing these components?
PartsCube Global stocks all alternatives mentioned in this guide. Search our catalog or submit your BOM for a quote.
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