Front panel USB 3.0 power shenanigans

Hardware Cases / Chassis
1

So I noticed something interesting on my work PC which has two front USB 3.0 ports.

I had my wireless mouse plugged in one of the front panel ports. It worked just fine like that. But then, when I plugged a USB 3.0 drive in the other front port, the signal was intermittently being lost. It only seemed to work with the mouse nearby.

It seems the power is somehow being split between the two devices.

2

That’s because the power is being split between the two devices, and the HDD is either 1) inputting too much noise into the 5V line or nearby usb 3.0 power line, and/or 2) The HDD is causing too much of a voltage drop, affecting the wireless mouse.

The 5V rails of the USB 3.0 connector is likely split for both USB ports.

1 Like
3

This PC has an 1 TB HDD and an m.2 nvme ssd.

So this noise (if that’s the cause) is being generated by the HDD and is affecting the 5V rail that’s connected to the MOBO?

I’ve connected the wireless antenna to the back of the PC and it seems to have solved the problem. I think this suggests that the problem is in the splitting of the USB 3.0 connector.

I do wonder, is this a universal problem with all cases?

4

The electric motor from the harddrive spindel introduces a very slight ripple into the 5V rail. On bigger devices, there are options to put supression and conditioning circuits to take care of the problem.
But with super small USB dongles, they hope the power is clean.

2 Likes
5

And to further from maze’s addition. Front panel stuff is usually not as shielded or reliable. Front panel is only for light duty stuff.

2 Likes
6

Huh… interesting. Where the hell does one learn such information?

7

Facts of electricity. That’s all. I dont understand it though just know it happens

2 Likes
8

Well, while you’re here…

I had connected my electric piano with an audio jack to my PC (back panel) and there was this humming and crackling in the sound.

I was listening with my USB headphones connected to the same PC.

How can I reduce this noise? Shorter cable? A sound card?

9

Either by reading or by troubleshooting electronic, probing about with a scope and multimeter.

The humming is probably a ground loop (can look for videos showing it). Easy way to fix that is to use a common ground point (the screw terminals on audio equipment are for that).
Alternatively you can buy a “ground loop isolator” (Behringer HD400, most DI-units have “GND lift” functions too).

2 Likes
10

Thanks, I’ll have to check that it’s actually a ground loop.

1 Like
11

Yup, is a ground loop. There are a few ways to solve it, but the main (and safest) is to just use a isolated transformer (a transformer with equal turns on the primary and secondary). They can be bought for quite cheap.

Here is a video by BigClive talking about ground loops and tearing down the isolator. It’s quite interesting!

1 Like
12

ftfy

1 Like
13

@Zibob,@SapereAude1490
mazes information is correct
the ripple effect on a split power rail causes a temporary brownout situation and the wireless mouse dongle cannot cope with it as it requires a set amount of power to operate.
for instance using an external sata or ide dock can be powered thru the usb but you may run into excessive current draw when spinning up or performing a read/write function that the usb port may not be able to satisfy
(its one of the reasons many come with their own wall wart and separate power jack)
this phenomenon is electrically known as inrush current
It is the initial amount of current needed to initiate movement in an electromagnetic device.
inrush current can often exceed 10 to 100 times the amount required to move something already in motion (IE increasing / changing the speed of a motor)

many years as an electrician and instructor!

3 Likes