Msg: 522 *Conference*

09-19-91 22:50:43

From: TRACY ALLEN

To : RICHARD HANSON

Subj: REPLY TO MSG #482 (POWER PILLOW)


  10 CLS:SOUND1000,10 
  20 PRINT"How come _I_ got stuck at Ft. Mamouth, NJ?" 
  30 INPUT"La Jolla!";STORY$
-------------------------------
  The theory has to do with anything electronic where two gadgets share the
same wiring. The problem comes when one gadget draws a heavy current while the
other is sensitive to power supply voltage changes.
  a                 b             c
  -------->--------------->--------
  |                 |             |
  +                 |             |
 battery         sensitive      heavy
  -                 |             |
  |                 |             |
  -------<----------------<---------
  f                 e             d

  Heavy current flows from the battery around the loop abcdef.  The wires ab
and ef have electrical resistance. So (ohm's law!) the voltage at c is less
than at b is less than at a.  E.g.  Think of how a light bulb in your house or
car goes dim when heavy current is drawn by a washing machine or a starter
motor on the same circuit. Don't put your brake lights on the same circuit as
the headlights!
 
  The model 100 is very sensitive to sudden drops in its power supply voltage.
Sudden drops can trigger the low-battery detection circuit.  Thus when you hook
up a disk drive to the same battery the computer might turn off.  It is better
to wire it as follows:

  a                               c
  -------->--------------->--------
  ----------->------ b            |
  |                 |             |
  +                 |             |
 battery         sensitive      heavy
  -                 |             |
  |                 |             |
  --------------<--- e            |
  -------<----------------<---------
  f                               d

Each device has its own direct connection to the battery, so there is no
voltage drop due to shared wiring.  Still, the battery has to be a good one, so
the battery voltage itself doesn't drop when the heavy load comes on.
 -- Tracy