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I must admit, I've yet to see a blazing cell phone and there are a bunch out there. However, I think there could be a possible reason for that. The "energy" available from a 12-16 Volt aircraft electrical system is a bit higher than from a small 3.3 volt battery in a cell phone. So the failure mode would likely tend to be more "explosive" with higher energy source - more energy to feed the "bang!".
I can not say it was the fault of a Tant capacitor for certain, but I recently had two boards fry. One clearly resulted from a short that caused the voltage regulator to overheat and actually char the board around it. I caught the other one before it got to that stage. In any case, I've never had a ceramic capacitor fail and have redesigned my boards to use ceramic. The only down side I could see if that you might need to use two ceramic in parallel if you need over 10-20 uf.
So, while Al's expert viewpoint certainly appears valid to me, since my board will be airborne and I can use ceramic, I will err on the side of caution.
Ed
----- Original Message ----- From: "Al Gietzen" <ALVentures@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, May 13, 2007 2:22 AM
Subject: [FlyRotary] Tantlum capacitors
Here's the opinion of my "expert" who has been designing and breadboarding
custom microprocessors and electronics stuff for 15 years -- Oh, BTW, the
Ta capacitors on my board are rated for 16V and are on a 5V circuit.
Al
Subject: Re: FW: [FlyRotary] Re: EC2 question
A few things to know about tantalum capacitors:
Just about all electronic devices manufactured in the last 25 years
use tantalum capacitors. If the explosion problem was an issue, then
cell phones, laptops, auto engine controllers, medical life support
equipment, satellites, televisions, nuclear power plants would all be
having problems. And believe me, when it comes to consumer
electronics, there is no voltage de-rating because a higher voltage
capacitor costs more.
Although the more I think about it, the idea of exploding cell phones
is appealing, especially when people are talking while driving.:-)
The claim about not using tantalum capacitors in aircraft is
dubious. If this were the case, then nobody would be able to bring
their electronics on-board a commercial aircraft. I would find it
amazing if your EFIS/GPS doesn't have tantalum capacitors in it.
I'm quite certain that Tracy already has tantalum caps on the ECU
board. The primary failure mode of this type of capacitor is a short
circuit. Since it's unlikely to have two fail at once, the short
would be isolated to one controller and you would fly on the other.
In all of the circuits I've designed, I have never had a board come
back from the field with a failed tantalum capacitor. 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).
--
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