I have a RS485-USB converter attached to my openwrt device, for Modbus-RTU. From time to time, the Modbus connection does not start up after power-up of router+converter, which is powered via USB from router.
To eliminate the possibility of some power supply issues of the router, which also includes a LTE-modem, I looked for externally powered RS485-converter, but practically none to be found. Could usage of an active USB-hub improve situation ? Just the router and the converter connected to the hub.
Have you already measured the current draw of the RS485 converter?
Alternatively, what does lsusb say regarding current draw?
- No. Because not so easy.
- Did not know, that lsusb will tell something about current draw. WIll check on this.
However, will any of these procedures provide reliable info about possible current spike during power up ?
I have no problems, when RS485 (Modbus) running. Looks like some start-up issue. So, my strategy is, simply to eliminate potential issues one by one. And check for positive effects.
Measuring USB current is easy with one of these little helpers:
lsusb -v | grep MaxPower will only delivery you a maximum for the current draw.
If it's 100mA, I wouldn't expect a power issue.
If it's 500mA, maybe.
This little helper looks great. Where/how to buy ?
You get them practically everywhere, aliexpress, Amazon, ...
Search for "USB Power OLED" or similar.