From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [LML] Shielding
To: lml
Date: Sun, 16 Apr 2006 11:02:37 -0400
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In-Reply-To: <001a01c6611b$13d698c0$650610ac@jacky0da39824a>
References: <list-1069796@logan.com>
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  "Tom Gourley" <tom.gourley@verizon.net>:

  Paul,
  
  Good comments about "ground".  Ground is simply a concept; a reference point
for measurements.  The utimate "ground" point on our airplanes is the negative
terminal of the battery.
  
  Some comments about using capacitors.  The voltage value you called out, 
35V,
is fine for 14V systems.  For 28V systems use capacitors rated at 50V or
higher.  Ceramic disk capacitors also have voltage ratings.  Most are 50V or
100V but some are rated as low as 16V so you need to pay attention to this
voltage rating as well.  Ceramic disks are non-polar so you can connect either
lead to power or ground.  A 4700uF capacitor will undoubtedly be polar so be
sure to pay attention to the plus and minus markings on the capacitor, i.e.
plus goes to the main bus (14V or 28V) and minus goes to ground.  Getting
these leads reversed can result in some interesting displays of smoke and
sound; maybe even a little flame.  Depending on the type of electrolytic used
in the capacitor it may erupt within seconds of applying power, or it may fail
after hours of use.  If a capacitor blows it was either connected wrong or its
voltage rating was too low.  The 1uF may or may not be polar so check its
specs carefully.  Try to mount the capacitors where it's relatively cool (not
in front of the firewall) as their effective capacitance, and in some cases
life expectancy, decreases with increasing temperature.
  
  I would not start off using the ferrites you mentioned.  They are generally 
a
last resort for dealing with some forms of interference.
  
  Tom Gourley