Topic: Does MTII charge as fast from USB as it does from the AC PS?

[Breeze]

I got my Microtrack II without the AC PS. So I'm wondering: does MTII charge as fast from USB as it does from the AC PS? Thanks.

[bdasilva]

Yes.. USB ports all have the same po wer output 5V 500ma

[Breeze]

Yes.. USB ports all have the same po wer output 5V 500ma

500ma is maximum: it's typically 100ma unless more is actually negotiated with the host. Some devices, like iPods, will only consume 100ma from a dumb USB charger unless the charger uses resistors offering a certain load to the data pins that tell the iPod that it can consume more; in some cases that can be close to 1 amp. I'm wondering if the same is true of the MT2 charger.

[Breeze]

For the record, this is what I've found:

- If I connect the MT2 to a battery PS supplying 5 volts regulated, it will consume about 117 mA while charging.
- If I connect the MT2 to an AC-powered regulated DC 5-volt supply, it will also consume 117 mA while charging.
- But if I connect the MT2 to a USB 2.0 port, it won't consume more than 77 mA or so while charging.

It doesn't seem to negotiate for any more power from the USB port, and the MT2 appears to the system as a mass storage device. I tried it on two computers.

So in fact, it would seem that the MT2 does charge faster using the AC adapter (by 40mA: that's 34% more than 77), QED.