Path: utzoo!attcan!utgpu!watmath!att!dptg!rutgers!cs.utexas.edu!uunet!wiley!rob
From: rob@wiley.UUCP (Robert Heiss)
Newsgroups: sci.electronics
Subject: Re: high current
Summary: how to extract 10 watts at 5 volts
Message-ID: <5251@wiley.UUCP>
Date: 9 Aug 89 05:25:36 GMT
References: <4Ypvw2600WAHE0VzYL@andrew.cmu.edu>
Reply-To: rob@wiley.UUCP (Robert Heiss)
Organization: TRW Inc., Redondo Beach, CA
Lines: 26

Changing the subject a little, how to extract 10 Watts of electricity at
a decent voltage (say 5 volts DC) from a source of 100 amps DC at some
unknown high voltage.  Some possibilities:

1.  Direct Voltage Drop

Put enough resistance in series that you can tap off the desired voltage
directly.  For 5 volts that would be .05 ohms.  You can can use the 500 watts
of heat to brown your toast and perk your coffee.

2.  Current --> Heat --> Voltage

Building a little steam engine might be fun.  If you would prefer no moving
parts, get some Peltier devices from a thermoelectric refrigerator and run
them in reverse.  Bond them to an iron bar with 100 amps running through.

3.  Inverter --> Transformer --> Rectifier

The inverter has to efficiently switch a few tenths of a volt, so it's
either relays or a few dozen MOSFETs in parallel.  And a big capacitor on
the input, which will promptly explode when the inverter fails.  The
transformer primaries (two for full wave inverter) are just one turn each, 
like a 100 amp bus bar through the hole in the toroid.  Ordinary rectifier.
Battery backup for the control circuits which require high voltage to start.
---
Robert Heiss   {uunet,cit-vax,trwrb}!wiley!rob