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From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2043445@logan.com>
Subject: Re: [FlyRotary] Re: Tantlum capacitors
Date: Mon, 14 May 2007 10:04:22 -0400
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 >> ----- Original Message ----- From: "Al Gietzen" <ALVentures@cox.net>
>>>  All of the
>>> failures I've seen (2) occurred in the first few seconds of testing
>>> (1) or because the electronic assembler installed the capacitor
>>> backwards (reverse polarity) (1).
>
> This may be the most important point, Ed.  My experience was on a test 
> fixture at the end of the assembly line.  It was the first time the caps 
> had seen a biasing voltage.  Think of it as dramatic crib death.  It was 
> stated at the time that the insulating oxide formed on the tantalums when 
> the voltage was applied.  Don't know if it was true, but the solution is 
> to bring the voltage up rather slowly to give the chemistry a chance to 
> work.
>


No doubt, Ernest, properly designed/tested etc, Tant Capacitors are viable, 
however, given I've never had a board chrisp before and now I have had three 
go into failure mode since the first of the year, something is happening. 
In any case, I've reworked the PC board design to use ceramics - now, if the 
failure mode continues then clearly, the cause will be something other than 
the TanT capacitor usage.  Since I am dealing with Pulsed inputs from the 
injection circuit  that may have some influence even though I have no Tants 
in those circuits.

In looking at my circuit, it appears that the TanT capacitor I have on the 
+5V lead feeding the PIC Chip is a likely culprit for shorting and causing 
the current to run-a-way.  I am going to check that out later today.

Ed


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