SS301 vs SS501: Which Bolec Speed Switch Should You Choose?
Choosing the right Bolec Speed Switch is essential for reliable engine protection and performance monitoring.
Whether you’re managing an irrigation pump, industrial engine, or mobile equipment, the right speed sensing solution
helps prevent costly downtime. Here we compare the classic SS301
and the advanced SS501
to help you decide which model best fits your application.
Overview: From SS301 to SS501
The SS301 is a long-serving single-channel analog speed switch with epoxy-filled construction,
designed for vibration resistance in harsh environments.
The newer SS501 brings digital precision, dual-channel monitoring, and a weatherproof housing—ideal for
modern engine panels and outdoor installations.
Feature Comparison
| Feature | SS301 | SS501 |
|---|---|---|
| Control Type | Analog (DIP switch + trimmer) | Digital microprocessor control |
| Channels | Single-channel | Dual-channel (independent) |
| Input Type | Magnetic pickup / ignition / ECU signal | Magnetic or Hall-effect (10kΩ pull-up built-in) |
| Frequency Range | 10 – 12,000 Hz | 2 – 9,990 Hz |
| Voltage Range | 12V / 24V selectable | 12V / 24V selectable |
| Output | Open collector (3A @12V) | Relay outputs x2 (5A, N.O/N.C/Pulse modes) |
| Hysteresis | Analog trimmer adjustment | Digital high/low threshold adjustment |
| Display | LED indicator only | 7-segment display + buttons |
| Enclosure Type | Epoxy-filled (vibration resistant) | Weather-proof housing (dust & moisture resistant) |
| Environment Strength | Excellent vibration & humidity resistance | Excellent outdoor weather protection |
| Typical Applications | Engine overspeed alarm, shutdown relay | Dual alarm (warning + stop), RPM limiter, vehicle speed logic |
| Status | Discontinued (service use) | Current model |
Environmental Durability
The SS301 is epoxy-sealed internally, making it highly resistant to vibration and moisture ingress.
However, its external switches and trimmers are exposed, so it’s best suited for enclosed control panels.
The SS501 features a sealed Weather Proof enclosure suitable for outdoor environments such as
irrigation engines or pump stations. Mounted with terminals facing down, it prevents dust and water ingress
while maintaining serviceability.
Functionality: Analog vs Digital
SS301 – Simple and Reliable
Using a coarse and fine trimmer to set switching frequency, the SS301 offers dependable analog performance.
It’s ideal for legacy systems such as BEM301 or simple overspeed alarms where fine calibration is not critical.
SS501 – Precision and Flexibility
The SS501 allows independent setup for two channels, with each capable of Normally Open, Normally Closed, or Pulse output.
It supports advanced use cases such as:
- Two-stage alarms (pre-warning + engine stop)
- Dual input logic (RPM and vehicle speed)
- Programmable hysteresis and latching modes
The built-in display provides real-time frequency readings, simplifying field setup and diagnostics.
Replacement and Compatibility
The SS301 and SS501 share the same input principle and 12/24V operation.
While not pin-compatible, the SS501 can replace the SS301 with simple wiring changes (5-pin → 8-pin conversion).
This upgrade adds precision, flexibility, and long-term serviceability to existing panels.
Which One Should You Choose?
- Choose SS301 for simple single-threshold analog systems, where vibration resistance and cost-efficiency are key.
- Choose SS501 for dual-channel monitoring, programmable alarms, outdoor use, and integration with modern BEM/EM panels.
In short, SS301 is the classic analog workhorse, while SS501 is the smart, weatherproof successor built for today’s demanding applications.
© Bolec Electronics – Australian Made Speed Switches, Engine Protection & Control Solutions.