Solid-State Power Controllers (SSPC) vs Fuses and Relays
A solid-state power controller (SSPC), also called a solid-state circuit breaker, is a semiconductor switch with current sensing and control logic. It switches a load, trips on overcurrent, can be reset remotely and reports status over a bus. In many DC systems it replaces a fuse or thermal breaker plus a relay or contactor.
What is an SSPC?
The power stage is a semiconductor switch, typically a MOSFET. A current sense element feeds control logic, which decides when to turn the switch off. One device switches the load and protects the wire, so it does the work of two parts: the fuse or breaker and the relay or contactor.
Trip thresholds and timing are set in firmware instead of being fixed by a fuse element or bimetal strip. After a trip, the controller can be reset by command, without a visit to the vehicle or cabinet, and measurements can be sent to a system controller over CAN or RS-485.
“SSPC” is the term used in aerospace and defense power distribution. “Solid-state circuit breaker” and “electronic circuit breaker” describe the same class of device in vehicle, industrial and telecom work.
SSPC vs fuse, circuit breaker and relay
The four devices answer different questions. A fuse and a breaker protect; a relay switches; an SSPC does both and adds feedback.
| Attribute | Fuse | Thermal or magnetic circuit breaker | Relay or contactor | SSPC |
|---|---|---|---|---|
| Switching | None | Manual | Remote (coil) | Remote (command or bus) |
| Protection | One-time | Resettable | None | Resettable, programmable trip |
| Response time | Depends on I²t; milliseconds to seconds | Thermal element depends on I²t and can take seconds; magnetic element is faster | Not applicable (no protection) | Microseconds to milliseconds, set by the design |
| Reset | Replace the fuse | Manual | Not applicable | Remote, by command or bus |
| Diagnostics | None | Trip indicator | None | Load current, voltage and temperature measurements and event logging, over a bus (product-dependent) |
| Wear | Single use | Mechanical and contact wear | Contacts erode and arc when switching under load; finite cycle life | No moving parts, no contact arcing |
| Size and weight | Small | Larger than a fuse of the same rating | Two parts (relay plus fuse or breaker) | One device; may need a thermal path at high current |
General engineering comparison; actual values depend on the specific part, the rating and the fault current.
Where SSPCs fit
SSPCs suit DC systems where remote control, repeatable protection and monitoring matter more than the lowest part cost.
Military and tactical vehicles
Vehicle systems are typically 28 V DC; MIL-STD-1275 describes their characteristics, including surges and spikes.
Defense solutionsUGVs and robots
Battery-powered platforms commonly run 24 V to 48 V buses. One controller per channel gives remote on/off, protection and load current feedback.
Robotics solutionsEV and battery systems
Higher-voltage DC packs need a switch that interrupts faults without contact arcing and reports to the battery or vehicle controller.
Automotive solutionsTelecom and data centers
Telecom plants distribute -48 V DC. Per-channel switching and metering allow remote reset and load monitoring.
Telecom solutionsDesign considerations
Points to check when replacing a fuse and relay with an SSPC. Confirm the details against the datasheet of the part you select.
- Trip curve and I²t
- Match the trip curve to the wire, not only the load. An I²t characteristic rides through short harmless overloads but trips a sustained one before the cable overheats. Check that the minimum fault current at the end of the harness is high enough to trip.
- Inrush and capacitive loads
- Motor drives, DC/DC converters and lamps draw well above steady-state current at turn-on. Confirm the trip settings allow the inrush, or use soft start or current-limited turn-on, to avoid nuisance trips.
- Voltage class and transients
- Select for the maximum bus voltage including transients, not the nominal voltage. Check the absolute maximum rating against surges and inductive spikes.
- Thermal derating
- The switch dissipates I²R in its on-resistance. Continuous ratings assume a stated ambient and mounting; derate for high ambient temperature and poor heat sinking.
- Bus integration
- Decide how each channel is commanded and read, for example CAN (including J1939) or RS-485. Define timeouts, message rates and the system response to a reported trip.
- Fail-safe state
- Define each channel's state on loss of control power or communication: on, off or last state. Choose per load; a drive motor and a payload camera may need different answers.
- Isolation and leakage
- An off semiconductor is not an air gap and has some leakage. Where a requirement calls for galvanic isolation or a service disconnect, keep a mechanical one.
Redler Power Rider products
Power Rider is Redler's family of solid-state circuit breakers and smart power distribution units (PDUs). Values below come from each product's published data; “On request” means the product data does not list that value.
Solid-state circuit breakers
| Product | Current | Voltage | Interfaces | From the product data |
|---|---|---|---|---|
| Power Rider 25A | Up to 25 A continuous | 9–48 VDC (absolute max 55 VDC) | CAN, RS-485 | — |
| Power Rider 80A | Up to 80 A continuous | 9–48 VDC (absolute max 55 VDC) | CAN, RS-485 | — |
| Power Rider 150A | 150 A continuous | 9–48 VDC (absolute max 55 VDC) | CAN, RS-485 | Breaker, relay and contactor in one device; Sub-millisecond fault response; CAN 50 kbps to 1 Mbps |
| Power Rider High Voltage | On request | Up to 400 V DC | CAN, RS-485 | — |
All Power Rider solid-state circuit breakers
Smart PDUs
| Product | Channels and current | Voltage | Interfaces | From the product data |
|---|---|---|---|---|
| Power Rider 12 Channel PDU | 12 channels, up to 25 A each | 9–48 VDC | CAN (J1939), RS-422, RS-485, Ethernet | 1 µs hardware cutoff |
| Power Rider 12 Channel -48V PDU | 12 channels, up to 25 A each; up to 240 A total | -48 V systems | CAN (J1939), RS-422, Ethernet | 1 µs hardware cutoff |
| Power Rider 12 Channel Military Grade PDU | 12 channels, up to 25 A each; up to 240 A total | 9–48 VDC | CAN (J1939), RS-422, RS-485, Ethernet (optional) | CAN 50 kbps to 1 Mbps |
| Power Rider 16 Channel PDU | 16 channels, up to 25 A each; up to 240 A total | 9–48 VDC | CAN (J1939), RS-422 (optional), RS-485 (optional), Ethernet | 1 µs hardware cutoff |
| Power Rider 16 Channel PDU Military Grade | 16 channels, up to 25 A each; up to 240 A total | 9–48 VDC | CAN (J1939), RS-422, RS-485, Ethernet | — |
Frequently asked questions
What is an SSPC?
A solid-state power controller (SSPC) is a semiconductor switch, typically MOSFET-based, with current sensing and control logic. It switches a load, trips on overcurrent, can be reset by command and typically reports status over a bus such as CAN or RS-485, replacing a fuse or breaker plus a relay or contactor.
Can an SSPC replace a fuse?
In many DC designs, yes: it gives resettable overcurrent protection with a programmable trip level. Check that the trip curve protects the wire, that the fault current is within the device rating and that off-state leakage is acceptable. An SSPC gives no air gap or galvanic isolation; where a requirement calls for one, keep a mechanical disconnect.
How fast does a solid-state circuit breaker trip?
It depends on the design and the fault. A hardware short-circuit trip can act in microseconds; an I²t trip for moderate overloads acts over milliseconds to seconds, by design, so normal inrush does not trip it. Redler product data lists a 1 µs hardware cutoff for Power Rider 12 Channel PDU, Power Rider 12 Channel -48V PDU and Power Rider 16 Channel PDU. It lists sub-millisecond fault response for Power Rider 150A.
What voltage do Power Rider breakers support?
Power Rider 25A, Power Rider 80A and Power Rider 150A list an operating range of 9–48 VDC (absolute max 55 VDC). Power Rider High Voltage is listed for DC systems up to 400 V DC. Confirm the rating on the product page or datasheet.
What status information can an SSPC report?
It varies by product. The Power Rider 150A data lists input voltage, output voltage, load current and temperature measurements with event logging, over CAN bus (50 kbps to 1 Mbps) and RS485. The other Power Rider breakers list CAN bus and RS485 interfaces.
Replacing fuses and relays in your design?
Tell us the bus voltage, channel count, load currents and interface, and an engineer will suggest a Power Rider configuration or discuss a custom one.