Picture of terminal postSetup illustrated hereI'm new here so I hope all goes well!

I have used an ATX PSU to create a power bench tester for testing automotive headlights. HID in particular which draw around 8-10amps on startup. I have noticed that whenever I start the bench with such a draw, the USB ports on my PC, connected to the same wall socket, disconnect and reconnect immediately. When tested with a standard 55W halogen bulb, the problem doesn't occur.

I don't recall doing that before therefore what could've gone wrong in my circuit to cause perhaps a jump in amps or what can I do to prevent troubles to my PC's USB devices?

I have used a 12V wire connected to a binding post by squishing the wire between the two nuts - afterward a binding connector which is crimped to a wire which has a female connector to which the HID bulb connects to. I have jumped the green/ground wires in order to start the PSU.

Everything is properly insulated with electrical tape.

  • \$\begingroup\$ Just to clarify, the PC is on a different power supply, just plugged into the same circuit in the building? \$\endgroup\$
    – C_Elegans
    Aug 29, 2018 at 21:37
  • \$\begingroup\$ Yes, sorry, I didn't make this clear enough. The PC is running idle using a Seasonic 650 80+ Gold. The bench supply is some cheapo. \$\endgroup\$
    – Tisho
    Aug 29, 2018 at 21:40
  • 1
    \$\begingroup\$ I've got 2 theories then. 1. The USB ports flickering is caused by a drop in line voltage from the other power supply drawing a large inrush current. If you have lights on the same circuit, do they dim slightly when you connect the headlamp? 2. The power supply is injecting high frequency noise onto the line which is interfering with your computer. Can you try it with a higher quality power supply? \$\endgroup\$
    – C_Elegans
    Aug 29, 2018 at 21:45
  • \$\begingroup\$ I'm afraid I can't try on a different power supply as I don't have access nor means to play with a new one. The lights in the room aren't flickering. As per what's wrong in the PSU, do you know and if something is indeed wrong? I had only one mishap with it - I had connected the 12V and ground on the terminal posts not between the nuts but on top of them - upon starting up it just shut off and then ran fine after fixing it. \$\endgroup\$
    – Tisho
    Aug 29, 2018 at 21:52
  • \$\begingroup\$ Well, regarding theory 1, you could also test it by hooking up something like a vacuum cleaner to the same outlet as your PC and seeing if that triggers the issue as well. Regarding theory 2, you could try putting a clamp on ferrite to the cord on the power supply, but I don't think that'll do much. A nicer power supply will likely have more filtering between it and the mains which will reduce the noise if it's injecting it in the first place \$\endgroup\$
    – C_Elegans
    Aug 29, 2018 at 21:54

1 Answer 1


Lamp ignition on a HID lamp is electrically very noisy, being as it involves very high voltage pulses for arc ignition.

I would expect the problem here to be RF pickup by the USB leads during lamp ignition (You may also see HDMI dropping out), cure is probably some ferrites as common mode chokes on the ballast DC connections (And maybe also on the USB leads).

I see something similar with the workshop PC when welding for much the same reason.


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