S14K300 Metal Oxide Varistor for Bitmain APW9 PSU

S14K300 Metal Oxide Varistor (MOV) | 300VAC / 470V Clamp Surge Suppressor for Bitmain APW9 PSU

The S14K300 is a metal-oxide varistor (MOV) rated for 300V AC continuous with a 470V clamping voltage and 4500A peak surge current — the AC-line surge suppressor used on the Bitmain APW9 power supply unit input. Sits across the AC mains lines after the fuse and clamps transient overvoltages before they reach the bridge rectifier and primary-side switching circuitry.

ф14mm through-hole disc in the standard MOV form factor — drop-in replacement when the original sacrifices itself absorbing a surge (its job) or degrades from years of mains transients. A fresh S14K300 restores the PSU's first line of input protection.

When to Replace the S14K300

• PSU dead after a known voltage event — surge, lightning, utility transient — varistor often sacrifices itself and shorts to protect downstream circuitry.
• Input fuse blown with no other visible damage — varistor shorted, took out the fuse on the next surge.
• Visible cracking, blackening, or charring on the disc body or epoxy coating.
• Burn marks on the PCB around the varistor footprint after a fault event.
• Preventive replacement on PSUs returning from areas with poor mains quality / frequent transients.

S14K300 Varistor Specifications

FAQ — S14K300 Varistor

Q: Why does the varistor short when it absorbs a surge?
A: That's its design behaviour — a MOV clamps overvoltage by conducting the surge to neutral. Big surges fuse the internal granular structure into a low-impedance path, sacrificing the part to save the rest of the PSU. Always replace a sacrificed varistor along with the input fuse.

Q: Can I substitute a different MOV size or voltage?
A: No — substitute exact part number. Smaller disc = lower energy capacity = won't survive the next surge. Different clamp voltage = wrong protection threshold (too low = constant nuisance clamping in normal operation, too high = surge passes through and damages the bridge / caps).

Q: How do I test if the existing varistor is still healthy?
A: Power off and isolated, measure resistance across the leads with a high-range DMM. Healthy MOV reads "OL" (megohms+). Shorted or partially-conducting reading = degraded varistor, replace.

Q: Bulk pricing for APW9 repair benches?
A: Yes — email contact@lys-sz.com for volume pricing on S14K300 plus matched input fuses for APW9 repair kits.

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APW9 repair benches stocking S14K300 varistors by the strip? Email contact@lys-sz.com for bulk pricing. Worldwide shipping from our Shenzhen warehouse.