Common Issues/Questions

  • What is Coil Whine?

    • Cause: When current through the inductor changes, the magnetic field does as well. This causes a small attraction/repulsion action in the coils of the inductor, which manifests itself as a vibration/sound.

      Toroidial inductor
      Picture of a toroidial inductor


  • What is this white greasy stuff in my PSU?

    • PSUs use white thermal compound between components like MOSFETs and diodes and the heat sinks they mount to.

      Thermal grease on heatsink Thermal grease on heatsink
      Picture of thermal grease on heat sink inside (left) and outside (right) of the PSU


  • What are these black markings on my connectors?

    • Cables are often tested to make sure they are pinned correctly. When the cable passes the test, it is marked with a Sharpie marker to show that it has been tested and passed.

      Black marks on PSU connectors
      Picture of black marks on PSU connectors

  • What is this goo in my PSU?

    • This is RTV (room temperature vulcanizing) silicone. It’s a glue-like substance used to keep heavier parts in place on the PCB during transit. It is also sometimes used in magnetic components to help reduce coil whine. The color of the RTV can be white, black or gray.

      RTV in a PSU
      Picture of RTV in a PSU

  • Why does my PSU smell like it’s burning?

    • It`s normal for new Transformers to release some harmless odors from the varnish impregnation used in the coils for a week or two after energization. Older Transformers can also release some odor if loaded to a higher level than they have experienced previously in their history.


      Varnishing transformer
      Picture of a transformer getting varnished

  • Why does my PC shock me?

    • If your mains are not grounded, there will be 3.5mA of power looking for a ground. When you touch a metal part of the PC, you become that ground. It’s perfectly safe, and normal, but you really should use a grounded outlet.

      Power supplies use “Y” capacitors connected from the neutral to ground as part of their integral EMI filter.  These specially rated capacitors provide a low impedance path to the ground for high frequency noise to reduce EMI. 

      Y-capacitor
      Picture of a Y Capacitor

  • Should I use PCIe pigtails for my graphics card?

    • The advice to not use pigtails is based on the assumption of worst-case scenario and should not be a blanket recommendation.

      The “weak link” in a cable is the terminal and not the wire gauge. The most commonly used 18g Mini-Fit terminals support 9A each. Some better PSUs use 16g HCS (High Current System) which supports 13A each terminal.

      This results in a 432W limitation for typical 8-pin Mini-Fit connector 18g terminals if all eight terminals on the PSU are populated, and 624W for 8-pin connectors with 16g HCS terminals if all eight terminals are populated. If only three terminals of either row are populated, then your limitation is 324W and 468W respectively. Therefore, PSUs that use standard mini-fit terminals with 18g wire for their PCIe pigtail cables are not recommended for 450W+ cards.

      Most reviews by Aris Bitziopoulos have wire gauge reported in them. If you can find your PSU in a review, check the wire gauge table in the review. If not, when in doubt, opt for not using pig-tails.

  • Why does my PSU "click" when I shut down and after I power up?

    • When a power supply is initially turned on, there is a high rush of current entering the circuit in order to charge the bulk capacitors. This rush of power could potentially cause damage if not kept into check. We call this rush of current "in rush current" and the act of limiting the amount of current delivered is called "inrush current limiting".

      Typically, the act of limiting this inrush uses an NTC (negative temperature coefficient) thermistor. The thermistor's high resistance slows the inrush current. As the current goes up the thermistor's temperature increases and resistance decreases and eventually, once the bulk cap is fully charged, only the amount of current required by the load is flowing through the circuit. The problem with this is that the NTC is never "removed" from the circuit and always adds some resistance to the circuit.

      Lately, the strive to make electronics more and more efficient has become paramount. Removing something that adds resistance to a circuit while literally doing nothing is a good place to start.

      This is where your "click" noise comes into play. By using a relay, the NTC can be bypassed once the bulk cap is charged and the NTC's function is no longer required.

      Inrush current limiter relay
      Picture of an actual relay used in a PSU