Core voltage is 1.2V, not 120V.
Right but I did not state the core voltage was 120V. The stated power consumption of an Avalon is 620w @ 120v which is what I used in my estimate. If each chip does indeed use 1.5A each then an Avalon would use more than 43kW so that can't be right. If the core voltage is 1.2V then each chip uses ~24mW by my estimates.
Power consumption = amps * volts. Avalon's power consumption at the wall, through the PSU, is ~620w @ 120v, so 5.16 amps @ 120v. The PSU converts that down to +12vdc to feed each of the three modules, figuring ~80% efficiency let's just call that 500w of +12vdc. This is 41.6 amps of +12vdc. Now each module has groups of chips fed by a +12vdc to +1.2vdc converter to feed the cores. ~500w @ +12vdc divided by 240 chips = ~2w per chip BEFORE the losses of the +12vdc to +1.2vdc converter. Those are usually incredibly efficient, let's call it 95%, so 475w of +1.2vdc, 395 amps.
I'm sure I'm butchering all the math here with calculating PSU efficiencies and such but this shows 1.979 watts @ +1.2vdc or 1.64 amps per chip.
I hope this makes sense to you. With these numbers, 3 of their chips, which provides (63,000/240)*3=786MH/s could be powered by a USB port providing 0.5 amps @ +12vdc. Call it 2 chips to give a nice buffer under the 0.5 amp limit and you have a neat little device. It won't generate crap for BTC though.. better off targeting something in the 5-10 GH/s range.
The information i found stated 450W for 3 modules not including PSU. USB is 5VDC nominal +/- 5% limiting the device to 2.5W total. We'd need around 300 - 500mW for micro and clock generation. The rest of your math looks spot on.
So far I'm up to to around US$7 in parts, not including the Avalon chip, with a few technical assumptions. Assuming we'd get the avalon for $2 - $5, a unit price for a usb miner under $15 is realistic. For the next generation, hopefully they include a PLL on die!
Sam.