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I can only offer that logic led me to investigate every contact between the battery (serving that buss) and the alternator, and then to the buss solenoid served by the two devices. The thought is that there is a very brief interruption of battery connection to the alternator, resulting in a millisecond of voltage and current output surge that fies the electronics.
I was lucky that I found a LOOSE connection, but some connections may seem tight but have some corrosion that is undetectable but nevertheless creates the intermittent problem. I would think that a total removal, cleaning and repositioning of all the contacts serving this alternator-battery arrangement would be a thorough investigation of the recurring problem.
Headsets are poorly protected (except for Bose) against this type of voltage spike. The PS Engineering is poorly protected. The Garmen GPS units are not very good at protection, but the old Apollo (UPSAT) units are very good about protecting their internal circuits.
Your implication of the low boost pump, not an impressive load, may have some causative relation to this problem is interesting, and requires some understanding of how it's wired to the buss. The high boost is the same pump with added power delivered, so I'm unsure why it would be with one (low boost side) terminal and not both terminals (high boost) on the pump.
Mine was an investigative challenge, but might be helpful in solving your problem.
Jeff L
Jeffrey Liegner, MD wrote:
Alternator Load Dumping and Voltage Spike
I recently experienced a sudden failure of my PS Engineering intercom during the take off roll,
Very interesting and timely post. I have been having a similar experience.
My LIV-P has been eating avionics. In 100 hours I've lost the PS Engineering audio panel, AOA computer, encoding altimeter, one headset, and my electronic trim controller board (Precise Flight)...The loss of trim was particularly troublesome, it went out during decent and just before I needed to shoot an ILS...fortunately to a high ceiling.
I have also discovered a nasty power surge that occurs only when I shut off the low boost pump and then only on some occasions. My first impression was that I might have a big back EMF surge. There's no obvious surge when I have the high boost on, though, but I've only attempted that on the ground at idle or slightly above.
I have a couple TranZorb devices on their way from Digi-Key. I'm concerned that they may not be nearly beefy enough to withstand the surges that seem to be going through my avionics. And exactly where do I put them? Across the leads to the fuel pump?
Any thoughts about how the chase down this intermittent gremlin?
LIV-P, Conti TSIO-550, 24V 100 Amp alternator with full size battery, reserved and isolated backup 24V 100 Amp alternator and full size battery.
Barry Knotts
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