SL10 2R505 - 2.5Ω 5A Inrush Current Limiter NTC | Ametherm
MPN: SL10 2R505 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.95 | $0.95 |
| 10 | $0.86 | $8.60 |
| 100 | $0.72 | $72.00 |
| 500 | $0.61 | $305.00 |
| 1,000 | $0.52 | $520.00 |
SL10 2R505 Overview
An inrush current limiter is a passive component placed in series with a power input to protect downstream circuitry from the large transient currents drawn when capacitors, transformers, or motors are first energized. The component category hierarchy is: inrush current limiter (ICL) -> NTC thermistor -> thermistor -> passive component -> circuit protection. ICLs exploit the negative temperature coefficient (NTC) of their ceramic semiconductor body: resistance is highest at turn-on and decreases as self-heating raises the body temperature toward steady state. This makes them an ideal one-shot, resettable alternative to fixed resistors or fuses for capacitor-bank inrush protection.
Key specifications include 2.5 Ω cold resistance at 25°C with ±30% tolerance, 5 A maximum steady-state current at ambient up to 65°C, 30 J maximum recommended inrush energy rating, and a dissipation constant typical of 10 mm disc NTC thermistors. The device offers a simple two-terminal construction with no polarity, no control electronics, and no programming required, making it ideal as a bolt-in protection element in AC/DC converters, motor drives, and large capacitor banks.
The internal construction is a dense sintered metal-oxide ceramic pellet with silver-clad electrodes and radial lead wires. The high steady-state beta curve allows the device to handle continuous 5 A operation with minimal derating, while the 30 J energy rating ensures survival of the high-peak pulse that occurs during initial bus capacitor charging.
Typical applications include AC/DC switch-mode power supplies, motor soft-start circuits, audio amplifier power rails, large electrolytic capacitor banks in industrial inverters, and transformer primary protection. The 2.5 Ω cold resistance is appropriate for 24 VAC, 48 VDC, and 120 VAC rails where peak inrush must be limited without unacceptable steady-state loss.
When designing with this device, verify the steady-state current does not exceed 5 A at the maximum ambient temperature and calculate the peak inrush current using the bus capacitance and source impedance to ensure the 30 J energy rating is not exceeded.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for SL10 2R505 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
SL10 2R505-B
✅ Drop-In📋 Reference alternative (not in catalog)
SL10 50005
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
SL10 50004
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
B57236S0259
✅ Drop-In📋 Reference alternative (not in catalog)
B57236S0509
✅ Drop-In📋 Reference alternative (not in catalog)
SL10 2R505 Specifications
| Component Type | Inrush Current Limiter (ICL) NTC Thermistor |
| Cold Resistance @ 25°C | 2.5 Ω ±30% |
| Maximum Steady-State Current (up to 65°C) | 5.00 A |
| Maximum Recommended Inrush Energy | 30 J |
| Body Diameter | 10.00 mm (0.394") |
| Package Type | Radial Lead Disc (Through-Hole) |
| Mounting Type | Through-Hole (radial leads) |
| Resistance Tolerance | ±30% |
| UL Certification | Yes (UL recognized) |
| RoHS Status | Compliant |
| Manufacturer Series | SL10 |
| Body Material | Sintered metal-oxide NTC ceramic |
SL10 2R505 Pin Configuration
| Pin 1 | Lead 1 — Non-polarized terminal - connect to power source side |
| Pin 2 | Lead 2 — Non-polarized terminal - connect to load side |
Typical Applications
SL10 2R505 is suitable for 6 applications: AC/DC Switch-Mode Power Supply Inrush Limiting, Motor Soft-Start Protection, Audio Amplifier Power Rail Protection, Industrial Inverter DC-Link Protection, Transformer Primary Inrush Limiting, LED Driver and Lighting Ballast Protection.
AC/DC Switch-Mode Power Supply Inrush Limiting
The Ametherm SL10 2R505 is placed in series with the AC mains input or the bulk-capacitor charging path of an offline SMPS to limit the high peak current that occurs when the large bulk electrolytic capacitors are first energized. With a cold resistance of 2.5 Ω, the device limits the inrush to a safe value on the first half-cycle, then self-heats within 1-3 seconds and its resistance drops to a fraction of the cold value, minimizing continuous conduction loss. The 5 A steady-state rating covers most sub-500 W SMPS designs, and the 30 J energy rating handles 1000-2000 µF bulk capacitor banks at 120-240 VAC inputs without exceeding the surge limit. Place the ICL upstream of the input fuse and bridge rectifier.
Recommended
Motor Soft-Start Protection
The SL10 2R505 serves as a soft-start element in series with small AC or DC motors up to 5 A steady-state, where the initial locked-rotor current can reach 6-10× the running current. The 2.5 Ω cold resistance limits the first-cycle surge while the motor accelerates and its back-EMF naturally limits further current rise. As the device self-heats within a few hundred milliseconds, resistance drops and steady-state loss is reduced. The 30 J energy rating easily absorbs the inrush of fractional-horsepower motors on 24-120 V rails. Mount the ICL on the supply side of the motor contactor or PWM driver.
Recommended
Audio Amplifier Power Rail Protection
Large power-amplifier capacitor banks in professional audio amplifiers draw substantial inrush current at turn-on, which can trip breakers, stress rectifier diodes, and cause speaker thump. The SL10 2R505's 2.5 Ω cold resistance and 5 A steady-state rating are well-matched to Class-D and Class-AB amplifiers in the 200-500 W range, where bulk capacitance typically runs 10000-47000 µF at ±50-70 V rails. The 30 J energy rating protects against the high initial dV/dt, and once the amplifier is running the ICL's resistance drops to minimize voltage drop across the protection element. This improves damping factor and bass response compared with fixed resistor solutions.
Recommended
Industrial Inverter DC-Link Protection
Industrial motor inverters and variable-frequency drives use large DC-link capacitors (often 1000-5000 µF at 400-800 VDC) that draw damaging inrush currents when the rectifier first energizes. The SL10 2R505 can be used on the low-voltage aux rail or pre-charge circuit where the 2.5 Ω cold resistance limits inrush to a safe level. The 30 J energy rating handles pre-charge events on capacitor banks up to several hundred watt-seconds. For higher-voltage inverter applications, two or more SL10 2R505 devices can be paralleled to share the energy and steady-state current. UL certification simplifies agency approval for industrial equipment.
Recommended
Transformer Primary Inrush Limiting
Large toroidal or EI transformers exhibit severe inrush on energization due to core saturation, with peak currents reaching 10-30× the rated primary current for the first few cycles. The SL10 2R505 placed in series with the transformer primary limits this magnetizing inrush while remaining compatible with continuous 5 A primary operation. The 30 J rating absorbs the saturation surge that occurs when the transformer is energized at the worst-case flux mains-core point. This is especially useful for medical and audio isolation transformers where mechanical stress and fuse fatigue from repeated inrush events are reliability concerns.
Recommended
LED Driver and Lighting Ballast Protection
High-power LED drivers and HID lighting ballasts use large bulk capacitors that draw significant inrush on turn-on, often exceeding the rating of the upstream fuse or circuit breaker. The SL10 2R505's 2.5 Ω cold resistance limits inrush to within fuse limits while the 5 A steady-state rating covers most commercial LED drivers up to 200 W. The 30 J energy rating protects against the inrush of PFC capacitor banks at 400 VDC rails. The radial through-hole package is easy to hand-solder or wave-solder on driver PCBs and the UL recognition simplifies lighting-equipment safety certification.
Recommended
Recommended Products Summary
Engineering reference data for SL10 2R505 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | SL10 2R505-B | SL10 50005 | SL10 50004 | B57236S0259 | B57236S0509 |
|---|---|---|---|---|---|---|
| Package | Radial Lead Disc 10 mm | Radial Lead Disc 10 mm - same | Radial Lead Disc 10 mm - same | Radial Lead Disc 10 mm - same | Radial Lead Disc 10-11 mm - same class | Radial Lead Disc 10-11 mm - same class |
| Brand | Ametherm | Ametherm | Ametherm | Ametherm | TDK | TDK |
| Cold Resistance @ 25°C | 2.5 Ω ±30% | 2.5 Ω ±30% | 50 Ω ±25% | 50 Ω ±25% | 2.5 Ω ±15% | 5 Ω ±15% |
| Max Steady-State Current | 5.0 A | 5.0 A | 5.0 A | 4.0 A | 5.0 A | 5.0 A |
| Body Diameter | 10 mm | 10 mm | 10 mm | 10 mm | 10-11 mm | 10-11 mm |
| Resistance Tolerance | ±30% | ±30% | ±25% | ±25% | ±15% | ±15% |
| UL Recognized | Yes | Yes | Yes | Yes | Yes | Yes |
| Mounting Type | Through-Hole (radial) | Through-Hole (radial) | Through-Hole (radial) | Through-Hole (radial) | Through-Hole (radial) | Through-Hole (radial) |
Key Differentiators
- Tighter cold resistance tolerance vs TDK equivalent (vs B57236S0259)
- Higher maximum inrush energy rating vs SL10 50005 (vs SL10 50005)
- Same Ametherm SL10 mechanical family - drop-in compatible (vs SL10 2R505-B)
Design Notes
Estimated: At maximum rated steady-state current of 5 A and assuming a hot resistance of approximately 0.1 Ω (after self-heating drops from the cold 2.5 Ω), the SL10 2R505 dissipates roughly P = 5² × 0.1 = 2.5 W in steady state. Mount the device in still air with at least 10 mm clearance to adjacent components and provide lead-length heat conduction to the PCB copper. For continuous operation at 5 A above 85°C ambient, consult the Ametherm derating curve and consider forced-air cooling or a higher-rated SL22 series device. Input values used: I=5 A, R_hot≈0.1 Ω (typical for 2.5 Ω cold NTC at steady state); this is an engineering estimate, not a datasheet specification.
Do not place the SL10 2R505 on the load side of a large hold-up capacitor without considering the inrush energy: peak energy = 0.5 × C × V² must stay below 30 J. For a 120 VAC rectified input (peak ~170 V) charging 1000 µF, the per-half-cycle energy is ~14 J - within spec but limits cumulative cycles during the cooling window. Also, do not rely on the NTC as a safety disconnect - it is not a fuse. Always include a proper upstream fuse or circuit breaker. The NTC resistance decreases with temperature, so a sustained overload can cause thermal runaway, not fusing.
For through-hole mounting of the SL10 2R505, drill holes sized for the lead diameter plus 0.2 mm clearance and provide a land pattern that supports the body weight and lead bending stresses. Wave-solder the device from the lead side; the disc body should not contact the solder wave. Maintain at least 5 mm spacing between the disc body and adjacent heat-sensitive components. If hand-wiring, use crimp-on quick-disconnect terminals or solder the leads with strain relief to prevent mechanical stress on the disc.
Compliance Information
RoHS and REACH compliant per Ametherm product page. UL recognized per the manufacturer datasheet (UL file available from Ametherm). Not AEC-Q100 qualified - this is a passive component not intended for automotive qualification.
