No subject

The same AWG you use between the wall wart transformer and the XO in an AC 
setup should suffice between the bus and the XO... 14-16 at most.

I use #14 to power the thin clients and displays on runs of greater than 
50 feet without issue.  At one point, I was using the unused pairs in CAT6
for this purpose... 1,2,3 and 6 were my network signal, as normal, and 
4,5,7 and 8 carried the current.  I never had a problem with this 
arrangement.


> Since the 70A load will only show up near the
> top of the distribution chain can you get away with 8 or even 10 guage
> for most of the system and only have 4 guage where its really needed?
> Its non-trivial for the non-technical to design that system though.

Correct, and once again, already done on the design;)

>
> To wire up a area of 50 kids how much wire do you need?

No more than if you are using mains, or a generator, or any other power 
method.

> Whats the I2R
> losses associated with distribution?  At some cable length even with the
> conversion losses AC becomes more efficient than DC unless you have
> _really_ thick cable. [1]

In this case, you have to go a very long way on a very small cable to lose 
half your energy.


>
>> One could always correct the power factor to the load with a
>> tuned capacitor bank.
>
> With an SMPS the input draw is non-linear so you can't correct it with a
> simple capacitor bank.

There are circuits run by a microcontroller that monitor power factor 
on load and parallel different cap values in or out as necessary... real 
time PF correction.

>
> http://en.wikipedia.org/wiki/Switched-mode_power_supply#Power_factor
>
> [1] Interestingly enough at super high voltage DC distribution now seems
> to be winning due to our ability to deal with it via high voltage
> semi-conductors.
>

Personally, I would prefer to use impulse currents, or Pulsed DC as it is 
also known, but that type of thing is a bit esoteric at this point. 
Doable on a bench, but needs more work for the field.


Cheers,
Scott

> http://en.wikipedia.org/wiki/High-voltage_direct_current
>
> -- 
> Richard A. Smith  <richard at laptop.org>
> One Laptop per Child
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