Mailing List lml@lancaironline.net Message #53181
From: Robert Pastusek <rpastusek@htii.com>
Sender: <marv@lancaironline.net>
Subject: RE: [LML] Diodes vs. Bi-Directional Zeners (SnapJacks) on Contactor Coils
Date: Mon, 12 Oct 2009 19:22:38 -0400
To: <lml@lancaironline.net>

Mike Easley wrote: I came across some literature from Tyco on what they call "back EMF suppression", basically the reason everybody installs diodes on their contactor coils.  After reading a bunch of literature, it appears that the diodes protect the switches on panel, but severely degrade the speed that the high amperage contacts separate.  That's bad, since it increases the wear on the contacts significantly.  I remembered that Eric at Perihelion Design sold Snapjacks that are supposed to be superior to diodes.  They're Bi-Directional Zener Transient Voltage Suppressors, what a mouthfull.  That is exactly what the Tyco literature explained.

 

Eric only lists a SnapJack kit for 12V airplanes.  I need 24V and I only need a few SnapJacks.  So I decided to track down what Eric is using in his SnapJacks.  By tracking Eric's part #P6KE18CA, they also manufacture a P6KE36CA that increases the voltage to what I need for my customer.  I figured Eric had a 50% headroom 12-18V for his Snapjacks, so I should go with 36V.

 

Mike,

 

I ordered a 24v “kit” from Eric and installed these on my IV-P. As far as I can tell, they are at least as good as elephant repellant…no electrical problems/failures of any components in 350+ hours/18 months of flying. I say “elephant repellant” because this is probably pretty early in the life of my electrical system to be making rash claims, but so far, they have been worth the investment. Easy to install as well..

 

Bob

 

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