| General > General Technical Chat |
| Measuring max output current of a USB port. |
| << < (9/9) |
| Nominal Animal:
--- Quote from: magic on October 22, 2022, 06:55:49 pm ---Other possibility is to modify the cable or the device (and void warranty in the latter case :P) so that 5V is completely disconnected from USB and taken from a 5V/2A wall wart. The output negative of the wall wart of course must be connected to USB ground... --- End quote --- That's a better idea than mine above. I can easily find a suitable ready-made USB power injector here: shared ground, but VUSB connected only to the scope and to the 5V/2A regulated power source; data lines only to the host computer (male data connector on the splitter). For example, on Delock 82769, the red male USB connector is for the 5V 2A USB power wall wart, the female is connected to the scope, and the black male to the computer. Here in Finland, Verkkokauppa.com sells Deltaco USB2-16 for 8€, where the female connector is connected to the scope, the primary black male to the computer, and the secondary male connector to the USB 2A+ wall wart. The wall wart should still be isolated, to avoid a ground loop with the computer USB port ground – hereabouts, any legitimate ones sold at computer stores are –, and 2.1A per port ones are easy to find. |
| balnazzar:
--- Quote from: pcprogrammer on October 22, 2022, 07:26:05 pm ---It is a bit strange that balnazzar mentioned that the specs are 5V@2A and the supplied cable, from what I understood of his reply, only has a splice to two connectors. At 500mA per port this only yields 1A. As for the USB isolation a lot of the cheap devices that can be found on Aliexpress are only for full speed (12Mbps) and I guess the scope needs high speed (480Mbps), when it not already has it build in. The prices run up quick on these devices. Especially when one wants USB 3 performance. I recall someone did a review of these USB scopes and that the PCB between the two versions are the same. But not sure if it was for the Owon's --- End quote --- Afaik, the scope is just USB 2.0 And, they explicitly wrote 5V - 2A upon the scope's USB port. I crossed my fingers and just connected ONE usb plug. It works. I operated it with both channels connected and tried to load it with maximum acquisition rate & stuff like that. |
| David Hess:
--- Quote from: ledtester on October 21, 2022, 01:02:07 pm ---See this table: https://en.wikipedia.org/wiki/USB#Power and this comment: --- Quote ---Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices when starting out as unconfigured. 1 unit load is 100 mA for USB devices up to USB 2.0, while USB 3.0 defines a unit load as 150 mA. --- End quote --- So you must perform some USB negotiation in order to draw more than 1 unit load. --- End quote --- Many devices now draw 0.5 or even 0.9 amps without negotiation, and most systems will provide it. |
| Nominal Animal:
Many USB wall warts here provide 2.1A on a single USB port. It seems to me the Owon has been designed to be powered by one of those. |
| David Hess:
--- Quote from: Nominal Animal on October 23, 2022, 03:03:08 pm ---Many USB wall warts here provide 2.1A on a single USB port. It seems to me the Owon has been designed to be powered by one of those. --- End quote --- A limit of 1 or 2 amps is common. There is a standard for USB chargers where 200 ohms is connected across the data signals. The problem I have seen is that the loads which are suppose to use this standard will also draw high current from a standard USB port. |
| Navigation |
| Message Index |
| Previous page |