Would an embedded internal wireless 3G modem draw significantly less power from a laptop battery than an external USB wireless 3G modem?

October 12, 2009 4:05 PM

Would an embedded internal wireless 3G modem draw significantly less power from a laptop battery than an external USB wireless 3G modem?

Generally I would assume, an integrated device will draw less power, but these wireless modems just use up a lot of power regardless so the difference may be negligible.

However, some actual facts or links would be useful.

Thanks!

posted by gttommy to technology (5 comments total)

It has been my experience that an internal 3g modem is actually connected through the USB bus. In that case it would draw the same power as a normal USB 3g modem. I'm not sure how you would determine whether it is or is not internally wired to the USB bus by looking on the specifications. Maybe internet reviews would have info like that?
posted by AltReality at 4:26 PM on October 12

AltReality said what I came to say: many internal devices (USB webcams, microphones, etc) are identical to external ones, just connected to the bus internally to save space and a connector. As such they're identical in power draw. I'd have the opposite of your assumption: I assume they're the same unless shown otherwise.

The word "integrated" is pretty loose, so it will depend on the device and manufacturer, but I would not be surprised to hear that "integrated" 3G modems are actually the same USB modems, shaved of their plastic cases and connected to the same bus as external devices.
posted by rokusan at 4:30 PM on October 12

Minipci cards have a max 2W power draw (from Wikipedia) vs 5V/100mA = .5W for USB. Actual device power draw will vary, but in theory an internal modem could draw 4x as much power.

Mini-PCI devices tend to draw 3.3V and Mini-PCI Express can be configured for 1.5V so in theory you should see those devices draw a lot less power give that they don't have to push the voltage up to 5V and then back down for the chips which all tend to run at 3.3V internally.

So... I don't know. Because there's less voltage conversion going on for a minipci device, I would say internal would draw less power. But if the model is simply an internal USB device then it will be the same.
posted by GuyZero at 4:36 PM on October 12

Make that "… vs 5v/500mA = 2.5W for USB", GuyZero, and you'll be right.

100mA is the base default for USB; the device can then request up to 500mA during the negotiation / registration stage.

My experience (admittedly not with laptops per se, but using off-the-shelf embedded hardware) with internal wireless / 3G cards has been slightly different - most are Mini-PCI devices, not USB.

Given that the 3G in all its forms is effectively limited to 1~2W ERP or EIRP, and the power amps used are only ~40% efficient, this suggests that supply power - not transmission power - is the limitation. Both will draw the max available to them, meaning a USB adaptor can use up to the full 2.5W and have slightly more range, but a Mini-PCI card can only use up to 2W and have slightly less range.

So a Mini-PCI card can suck less power than a USB, but it probably only makes a real difference in marginal conditions.
posted by Pinback at 5:35 PM on October 12

So my memory said 500mA but I found something online that said 100mA and your explanation reconciles what happened there.

Regarding range vs power, a built-in modem will probably use an antenna embedded in the laptop's lid while a USB stick will be stuck with a much smaller antenna which is probably a more important factor for reception rather than power draw since they're roughly the same (2W vs 2.5W). If it's an internal USB modem it's the best of both worlds (bigger antenna + higher power draw) but anyway, budget roughly 2W in a laptop's power budget for a 3G connection.
posted by GuyZero at 7:15 PM on October 12