Raspberry Pi Forums

Hi all,

I run a few gadgets on my RPi B+. I have:

- USB 3G modem
- USB Creative Webcam
- Motor controller board (L298)
- USB GPS (BU 353)

And of course, I have to run this on batteries as well... (remote battleship).

It has work well a few times (probably by accident) but now I cannot get all gadgets to run at once any more. If all is connected, the 3G modem is struggling and needs maybe 7-8 retry attempts/reboots before connecting. If I remove the webcam, the modem connects immediately after a reboot.

In the past, I've used a usb batterypack to run it all (http://forum.xda-developers.com/showthr ... ?t=1921093) but now it cant provide enough amps (i'm guessing). If I connect both ports from the USB-battery to the regular mini-usb connection, it's about 3.1A (according to specs).

So, I added powered usb hub connected to a second battery (lead) via a UBEC 5V, 3A and connected some devices to it, but still no success (still struggling with the 3G connection). I noticed as well that I could disconnect the USB battery without the RPi complaining/halting.

My theory is... Could it be that the USB battery powers down since the RPi gets power from two sources? I'm guessing that the RPi gets it's juice from the USB hub as well? In total I'm using up to 6A, so it cant be that that's the issue.

In this case, I cannot connect anything to the GPIO since thats blocked by the motor controller board connections.

Any suggestions?

Have you changed the config.txt file to allow maximum power (1.2A) to the USB ports? (If not changed then the default is 600mA)

boot/config.txt
max_usb_current=1

After boot is completed the B+ and 2B will allow 'backfeeding' power into the USB ports from the powered HUB.
It is not good to have 2 power sources connected together. If the voltage on one is a bit lower than the other then the weaker one may stop outputting properly.
HUBs are not supposed to 'backfeed' by specification, but many cheap HUBs do anyway. I would either get a HUB that does not 'backfeed' or modify your existing HUB. HUBs are modified either by opening the HUB and disconnecting the USB power wire or slicing into the USB feed cable and cutting the power wire. Note the Ground wire must remain connected. Use Google to search. There are many threads here and elsewhere on HUB modifications to prevent 'backfeeding'

klricks wrote:Have you changed the config.txt file to allow maximum power (1.2A) to the USB ports? (If not changed then the default is 600mA)

boot/config.txt
max_usb_current=1

After boot is completed the B+ and 2B will allow 'backfeeding' power into the USB ports from the powered HUB.
It is not good to have 2 power sources connected together. If the voltage on one is a bit lower than the other then the weaker one may stop outputting properly.
HUBs are not supposed to 'backfeed' by specification, but many cheap HUBs do anyway. I would either get a HUB that does not 'backfeed' or modify your existing HUB. HUBs are modified either by opening the HUB and disconnecting the USB power wire or slicing into the USB feed cable and cutting the power wire. Note the Ground wire must remain connected. Use Google to search. There are many treads here and elsewhere on HUB modifications to prevent 'backfeeding'

Hi,

Thanks for your input. I'll take the config file into consideration.

As you're suggested, the hub is probably 'backfeeding' power to the Pi. I'll try and see if a newer not so cheap hub will work better.

Thanks for your input!