> http://www.circuitprotection.com/techpapers/1394Firewire.pdf
> 1) A primary power provider must deliver between 20 and 33 V 
> under full load conditions.
> 2) A primary power provider shall implement current limit 
> circuitry to comply with all appropriate regulatory agency 
> specifications.
> 3) Current draw through any single port shall not exceed 1.5 A.
> 
> I would suggest hefty crowbar 5.1V zeners to force the power 
> source to go into limiting mode if the connector is reversed. 
> (How the HECK do they manage that? 4pin FW has no power).
> I had no idea FW could pump out so much power (1.5A x 
> 33V~=50W). {other specs I found say 40V max, 8V min)


I always thought FW was 5v - 40v.  Upping the voltage is an easy way to get
more power, increasing the amps means thicker wires.  Some Dell laptops have
a double USB port to enable devices to use more than 0.5A.  The 2nd port
just supplies power (no data), I'm not sure how much.

Cars are supposed to be going to 42v for the same reason, there's that much
stuff in the average car now the wiring is getting a bit tricky.

Imagine the desktop coffee warmer you can have when more than 2.5W is
available...

Tony

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