REFLECTOR: egt and cht problems

[dean fitzbag]

I'll give this a try.   Using a charger sounds like a good idea.
  ----- Original Message ----- 
  From: michalk<mailto:michalk at awpi.com> 
  To: Velocity Aircraft Owners and Builders list<mailto:reflector at tvbf.org> 
  Sent: Monday, May 02, 2005 8:26 AM
  Subject: Re: REFLECTOR: egt and cht problems


  This sounds like a ground problem.

  The higher the current, the larger the voltage differential.

  First have you always had this problem?  If so, your ground wire to the 
  battery may be a bit small.

  Now, if this is a recent development, it's probably a corroded 
  connection or wire that is broken/breaking.  A broken ground wire is a 
  dangerous thing.  It causes fires to jump out of the strangest places, 
  like throttle cables, expensive engine monitors, etc.

  You can't ohm it out in most cases.  The best is to clean all the 
  connections.  Maybe get a hefty battery charger and connect it to the 
  alternator battery post, and the ground lead to the alternator case.
  Turn on all your loads, simulating the problem condition.  If you see 
  the problem.  Take your voltmeter, using the ground lead of the charger 
  as your ground reference, turn your meter to the 1 or three volt range, 
  and poke around on various places that should be grounded until you find 
  your voltage differential.

  Where is your ground wire attached?  I would suggest as close to the 
  alternator as possible to eliminate the normal operating problems.  What 
  I did was run my starter ground cable to the starter case, with a 10 
  gauge pigtail over to the alternator case.

  dean fitzbag wrote:
  > I have JPI slim line instruments.  They are a egt, cht, outside air, oil 
  > pressure, oil temp, tach, ameter-voltmeter, and fuel pressure.  All are 
  > connected to my master panel for the plus side.  All except the egt and 
  > cht are grounded to the master panel ground.  The egt and cht are 
  > grounded directly to the engine.  All is fine on the ground and in the 
  > air provided that no large current is flowing out of the alternator.  If 
  > I turn on the gear pump, nav lights, strobe lights, landing lights, 
  > electric fuel pump or if the battery needs recharging, then the 
  > temperature read outs of the egt and cht will read low.  The more 
  > current, the lower the reading.  There is no problem on the ground since 
  > my engine isn't running fast enough to drive the alternator output high 
  > enough.
  >  
  > The JPI folks insist that I must have the ground on these two 
  > instruments somewhere other than the engine.  I have a direct wire 
  > connection.  The voltmeter reads 13 to 14 volts.  The ameter reads 2 to 
  > 3 amp on the ground, normal 8-9 in the air without the additional load 
  > of the above devices, and up to 15 and above with them.
  >  
  > I have the factory wiring system.  The engine ground and panel ground 
  > meet at the battery.
  >  
  > The cht will drop about 50 degrees with the nav lights, and another 100 
  > degrees with the landing lights.  The drop seems to be proportional to 
  > the extra current.
  >  
  > Any ideas?
  > 
  > 
  > ------------------------------------------------------------------------
  > 
  > _______________________________________________
  > To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector<http://www.tvbf.org/mailman/listinfo/reflector>
  > 
  > Visit the gallery!  www.tvbf.org/gallery<http://www.tvbf.org/gallery>
  > user:pw = tvbf:jamaicangoose
  > Check new archives: www.tvbf.org/pipermail<http://www.tvbf.org/pipermail>
  > Check old archives: http://www.tvbf.org/archives/velocity/maillist.html<http://www.tvbf.org/archives/velocity/maillist.html>

  _______________________________________________
  To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector<http://www.tvbf.org/mailman/listinfo/reflector>

  Visit the gallery!  www.tvbf.org/gallery<http://www.tvbf.org/gallery>
  user:pw = tvbf:jamaicangoose
  Check new archives: www.tvbf.org/pipermail<http://www.tvbf.org/pipermail>
  Check old archives: http://www.tvbf.org/archives/velocity/maillist.html<http://www.tvbf.org/archives/velocity/maillist.html>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20050502/a7bb8943/attachment.html