General > General Technical Chat
Measuring max output current of a USB port.
balnazzar:
--- Quote from: pcprogrammer on October 21, 2022, 02:06:08 pm ---Ah a modern laptop. Yes USB-C can handle a bit more. There are cables that on one end have USB-C and on the other end the USB connector needed to plug into the scope. Just a google search away 8)
Have you searched this site for threads about your scope?
Here is one: https://www.eevblog.com/forum/testgear/owon-vds-1022i-review/
--- End quote ---
Ordered the cable right now :)
Also reading through the thread, thanks! You know, that little Owon thing is good for its price (119 eur with two probes) and has a good software, after all. Not good as Digilent Waveforms, but good nonetheless.
I'm considering the 12/14 bit, 4 channels, 100 MHz, 1 GSa/s, 10M depth, VDS6104A. 375 bucks plus VAT. It's waaay less than a Pico 2000 with similar specs. Like 3X less. And the Pico is just 8 bit...
Can't do Bodes, but I got the AD2 for that.
pcprogrammer:
You can use it to check things while building your own scope :)
I have two proper scopes and five simple ones to play with. Used the proper ones to measure on the simple ones while doing reverse engineering.
hans:
Concerning the short..
If the port is protected, it should switch off power. But how are you certain you can catch the correct max current in time? If a port has some output caps, you'll measure their short circuit current spike. If the port protection is anything 'fast' (which you force it into because of the a dead short), then the DMM won't respond in time.
Likewise, a gross overload for various durations can also kill power. Many ports are protected with polyfuses. E.g. these might burst in 0,1s with 5A load, but take 1min to burst at 1A load, or 15min at 800mA. If the rating is 500mA indefinite then 800mA or 1A is still too much.
Trial and error tests, in particular short test IMO is bad advice borderline malicious, as it is not going to give any valuable information besides anecdotal evidence, but has high risks damaging poorly protected ports. I would expect a modern Asus MB to have proper protection, but anyone finding this thread through google to test on their 15 year old system is going to blow it up.
That Owon scope looks very weird. Why is it using an USB A plug for a downstream port? It should be USB B or C.. and if they need more power then either A) use a second USB A plug upstream or B) use a DC barrel jack of some sort.
Those PSU to USB A, or USB A to USB A cables also look downright dangerous..
wraper:
You don't need any scope or other nonsense. Peak currents will tell nothing about current capability of the port. To figure out at what current protection will trip, you need to gradually increase the current until protection acts. Easiest to do with electronic load. But just using a multimeter and adding resistors in parallel will work too. Also current at which protection will act is not the same as current capability of the port, actual capability is somewhat lower.
SiliconWizard:
The question doesn't make much sense if you know USB. ???
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