Crappy USB Hub
This is another grind my gears, this little issue caused a lot of headache before it was found.
2 Weeks ago at work we needed a couple of powered USB hubs. We found the following hubs on Conrad webshop:
We used these before with usb sticks, so we figured these where fine. However, plugin in a small 2.5 inch hard drive, caused it to reset randomly. It did this even while it was powered via a heavy external power supply. (Our use case was within the specified value). So what is going on?
Opening up the hub showed a horrible PCB, full of bad soldering connections (we retouched), flux remainder and tiny tracks.
Doing a quick measurement on the PCB, shows that there is a 1.3 Ohm resistance between the power-supply positive pin, and the USB VCC pin. This means on 500mA load (max according to spec) we loose around 0.35V in this trace. Confirming this with a dummy load showed a drop of 0.65V (see below). Enough for the hard drive to drop out and reset.
Adding a little wire from the power supply connector to the USB connector resolved the issue.
If you look at the PCB, you can see that one of the Power line PCB tracks goes around most of the PCB. It goes from the connector to the switch that is above the connector. Making it a 13cm track ( to cover a 1.5 cm distance). Assuming 3.5mil copper thickness this already results in a 0.56 Ohm resistance (measurements confirm this). It then goes via the switch and continues to the power connector.
It is likely that the hard drive drawn current on spin-up peaks above it specification, this will drop the voltage even lower. While this is probably out of thespecifications, but users expect things to just work and it does with most USB hubs. The problem would not exist if they have done a better job on the design of the PCB, giving it shorter and thicker VCC tracks. Then it would have worked.
Long story short, this powered hub is not up to the task and not worth it money.comments powered by Disqus