USB fax modem makes kernel crush

[riaqn]

(sorry for my poor English)I Bought a USB fax modem, to run a fax server on Pi.The model is conexant.USB ID 0572-1329)
I plug it on my Laptop(Lenovo F31,Intel Pentium T2330,ArchLinux,Linux3.8.8-1),when I run dmesg it print:

[ 7332.892751] usb 5-2: new full-speed USB device number 2 using uhci_hcd
[ 7335.639659] cdc_acm 5-2:1.0: ttyACM0: USB ACM device
[ 7335.642262] usbcore: registered new interface driver cdc_acm
[ 7335.642268] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters

It seems that kernel detect it and work fine without the native driver.
And a new device /dev/ttyACM0 appeared.So it's behave properly on my laptop.

However, When I plug it on my pi,all of a sudden, the ssh out of control,I can't input anything, and it didn't print anything.When I use ping command, it shows "unreachable".and the only thing I can do is cut the power.
Even though I do a "shutdown -t 120 -h" before the pluging, Pi cannot shutdown itself two minutes later.So it's aparent that the kernel crush.
Anyone know why?

[riaqn]

I tried again and I found when I plug in the modem, the four lights turn black except PWR.one second later they lit again.
Will it relate to the electricity problem like overload?But my AC Adapter is 800mA at max, and the modem use 70mA at max.What's the problem?

[remsnet]

I tried again and I found when I plug in the modem, the four lights turn black except PWR.one second later they lit again.
Will it relate to the electricity problem like overload?

Yes that behavior provide that you overload the crappy and unsupported Power .
At such overload that USB Power can become an Bomb either... when permanent in use.

800ma are too less for Model B . Requirement are allmost :
1000-1200mA at precise 5,0 V for the PI
250mA Max for your Modem , usb keybord , usb mouse.

Assume you need an extra Powered USB HUB to get it stable.

Be shure that your next USB Power deliver stable 5,0 Volt at 2000mA without getting HOT