Others have commented on the controller aspect.
I'll just comment on rectification.

For low output voltages rectifier voltage drop becomes a significant part of
total system voltage and a significant factor in power loss and efficiency.

Voltage drop for silicon rectifiers at 70A are liable to be 2v or so.
Even Schottky rectifiers are liable to have voltage drops of around 1 volt
at this current.
These are limitations of the technology (y' canna break the laws of physics)

FETs can have as low a forward voltage drop as you want - you just have to
pay more :-)
eg at an Rdson of 0.01 ohm at 70 A the voltage drop will be 0.7 volt.
Very best FETs available are down in the 0.005 ohm range (0.35 volts here)
and you can parallel as many as your bank balance allows. Lead drop,
mounting, bus bars etc are liable to be major features.

If your FETS have Rdson effective (1 or several in parallel) of over about
0.015 ohm you may be better off with Schottky diodes and at about 0.03 ohm
Silicon diodes may be no worse.

If efficiency is not an issue you could just use silicon diodes with
suitable power ratings.
Remember, 70A x 2v = 140 watt !!!!. Drop could be even higher than this.
Schottky is not too dear and will about halve power loss.





      Russell McMahon
_____________________________

>From another world - www.easttimor.com

What can one man* do?
Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/

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-----Original Message-----
From: McMeikan, Andrew <andrew.mcmeikan@MITSWA.COM.AU>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Friday, 22 October 1999 01:43
Subject: 1V to 1.8V 70A PSU Digitally controlled


>Hi all,
>
>Some time ago on the list someone was after an efficient 1V PSU, with the
>resulting discussion on losses in the diodes.
>
>There have also been discussions about using PIC's to PWM DC motors.
>
>Having some interest in switching PSU's I've been looking around and found
a
>chip that provides 1V at 70A, looking at the circuit I noticed that rather
>than use diodes they used FET's to clamp at the correct time.
>
>No I have only used 16C84's so I don't know too much about those PIC's with
>AtoD on them but it would seem that a PIC with a couple of FET's and an
>inductor could make a nice PSU or motor driver?
>
>        Anyone have comments as to why this would not be a good thing to
>build?
>
>        cya,    Andrew...
>
>http://members.xoom.com/andrewmuck/MP3.htm
>