jk3k+@andrew.cmu.edu (Joe Keane) (08/03/89)
Can someone help me solve this problem? We have a line carrying a large DC current (say 100 amperes), and we want a device that we can insert to put in or take out a small amount of power (say 10 watts). Assume any reasonable power supply. Now the load on the wire is highly inductive, so the first priority is to keep the current flowing (or deal with a few megawatts...). This is all DC, so a transformer won't work. How the heck do you do this?
rob@wiley.UUCP (Robert Heiss) (08/09/89)
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!robpiner@pur-phy (Richard Piner) (08/10/89)
To get power from a DC magnetic field, use a rotating coil. "flip coils" are used to measure magnetic fields. A big one in a strong field should be able to deliver 10 watts. Never mind that it may take more power than that to turn the coil :-) Richard Piner