Raspberry Pi B+ wiith USB 3g/4g dongle

Question

Hi,

I am trying to set up my rpi with its own internet usig a 4g USB Dongle: (ZTE Australia > Products > MF823). I have read many articles about it but haven't found anything current so not sure if they apply to the B+.

Setting up the 4g dongle was very simple, I installed usb-modeswitch, switched form USB to ethernet, added some basic config to the interfaces file, rebooted and it worked....It was a nice surprise.

Here are the questions I have,:

1) Will the B+ have power issues with the 4g Dongle, specs say it draws 700mA, im using 2.1A power supply? (do I still need a powered hub)

2) I read in many places that ppp and wvdial although I believe my dingle has a built in dialer. How do I confirm this?

3) If I send the device to a location that has 3g only, will everything still work the same ?

Thanks in advance.

rew · Answer

1) There is a 1.2A "fuse" on the 'pi. This may lead to problems: if say you perform a remote update and you require a constant download of data for several minutes/hours, the fuse might overheat and you'll "lose" your pi. (it won't recover unless you unplug it by hand). Theory says you're too close to the limits for comfort. In practise the 'pi will usually not consume its full power, but for the dongle, the conditions where it might do so might be out of your control. If you're on 4G now, the power requirements might be lower than when you're on the edge of a 3G cell, and the module has to use "full transmit power" to make itself heard by the cell-tower.

I have a powered-hub that powers up the 'pi when I connect it to the 'pi as a HUB. (i.e. nothing in the power connector of the 'pi). Such a construction would be ideal. Aim for at least 1.5A of REAL deliverable power. (A chinese 2A power adapter might run short of have short lifetime if loaded like this).

2) Yeah, If it works like this, don't touch it. wvdialer would normally need a virtual com port to talk to so if you now just use the dongle as an ethernet adapter, then wvdial has no business talking to that thing. (it cant).

3) I think so.

rew · Answer

The raspberry has a fuse at the power-connector. Your total consumption is too much for that fuse. Even though your tests seem to indicate that right now it works, you cannot depend on it. It might fail at any inconvenient moment.

A powered hub with a sufficient powersupply will work. (If backfeeding as described above works: fine, otherwise you need to run a micro-usb-cord-for-power to the power port of the 'pi)

I saw a nice 7-port powered hub at a friend's place one day. As required: a 3.5A powersupply. So I got one too. THEN he tells me that he replaced the powersupply with a better one: it comes from the shop with a lowsy powersupply. So: Be careful: Get a proper powersupply even if on first look you think it should be enough.