max current limit for USB port

[Davadoo]

Hi there!

I'm trying to connect to an USB device (it is a RFID reader) that needs to receive up to 500 mA of current. I am using a Raspberry B+ model with (up-to-date) Raspbian. When the USB device is idle, it is happy with just 100mA and I can interact with it, but when it has to do some RF operation it requires more current and it simply disconnects. I think the problem is that the device, when attaching to the USB port, "negotiates" a maximum current of 100 mA. I've checked this with "lsusb -v" command. I have also tried connecting the device through an externally powered USB Hub and it simply works, but I need to connect the device directly to the raspberry and get rid of the external hub. Considering the B+ model can provide that current without problems (am I correct?), how can I override the max current limit for the device and provide up to 500 mA? Any ideas?

Just in case it is relevant, when attached, the device uses ACMx ports (as if it were a modem).

Thanks!

[fruitoftheloom]

Hi there!

I'm trying to connect to an USB device (it is a RFID reader) that needs to receive up to 500 mA of current. I am using a Raspberry B+ model with (up-to-date) Raspbian. When the USB device is idle, it is happy with just 100mA and I can interact with it, but when it has to do some RF operation it requires more current and it simply disconnects. I think the problem is that the device, when attaching to the USB port, "negotiates" a maximum current of 100 mA. I've checked this with "lsusb -v" command. I have also tried connecting the device through an externally powered USB Hub and it simply works, but I need to connect the device directly to the raspberry and get rid of the external hub. Considering the B+ model can provide that current without problems (am I correct?), how can I override the max current limit for the device and provide up to 500 mA? Any ideas?

Just in case it is relevant, when attached, the device uses ACMx ports (as if it were a modem).

Thanks!

https://projects.drogon.net/testing-set ... berry-pi-b

[rpdom]

The B+ doesn't (AFAIAA) negotiate current limits. It just supplies up to 600mA (1200mA with the high-current mode) to the four ports regardless of what the devices ask for. If your device isn't getting the current it needs then you may have a power supply issue. Try measuring the voltage on the 5V pin of the GPIO with the device disconnected and connected. See if you get a large drop.

[Davadoo]

Thanks! I just followed the link and it worked.