I bought a startech ST4200SUBM USB hub for my QA403. I put 7 V on the external power source pins and confirmed it converts it to 5V on the USB port. Opening it I see it uses a DC-DC switching converter chip (MT3905), which supposedly can output 4A, which surprises me a bit, since it’s a little SMD guy, but I’m pretty sure it’s good for the current the device needs.
I hadn’t thought about it being a USB 2.0 device. Spec sheet says so and it has a USB 2.0 hub chip in it sure enough.
Is USB 2.0 OK bandwidth-wise? I see mention of USB 3.0 but that seems more related to the power requirements.
I have found voltage at the unit is closer to 5V when using a USB C to B cable from a USB C port. Every USB C port supports at least 1.5A. Even if the hub supports high currents, individual USB A ports may not go over the 0.5A minimum for USB A 2.0 or 0.9A for USB A 3.0. USB C supports the USB 2.0 speeds with no issues. I’ve tried this with a few hubs and direct with a couple different computers.
That’s a good thought about what the hub will provide per connection. I made a breakout out of an old cable to test it. It had 24 ga wire for the power leads and I made it about 12 in long. I found that one port will provide 1.5 A (didn’t go past that). What I don’t like is that the voltage is dropping to 4.6 V at around 900 mA. The manual says the QA403 can draw 800 to 900 mA or more depending on the measurement, so I don’t like the idea of hitting the orange level if I’m doing a test that is drawing more current. I don’t know if it’s dropping purely through the 24 ga wire or the regulation is just not that good. Maybe they put a series resistor at the power output to protect from shorts. Anyway thanks for the response, good info
Contact resistance in the USB connector can dominate sometimes - the springiness in old connectors can reduce, and surface tarnish (oxide) will only increase with time. Manufacturer’s insertion-cycle ratings are only for a new connector in a dry atmosphere, not real-world use with finger-grease, humidity and long periods between uses. So suspect any old lead to be problematic if not visually inspected and perhaps cleaned / burnished.
Cheap unbranded connectors (and thus cables) are unlikely to have any datasheet and are pot-luck. They can also have CCA wire which is even worse (brittle, doesn’t crimp well, less current handling).