On Mar 31, 5:59 pm, MikeMl wrote:
Lancair IV-P Flyer wrote:
On Mar 29, 4:45 am, "

Steve,

I do not have any specific Lancair experience, however, I know about
Cessnas. The new glass-panel Cessnas have an alternator controller which
includes an overvoltage detector which incorporates an electronic
"crowbar" circuit. It purposely overloads and trips the Alternator Field
Breaker if a momentary bus voltage transient is detected. Could your
Lancair have a similar system?

On the radios unsquelching, is it possible that the radios are just
overly voltage sensitive? With the alternator on-line, the bus voltage
should be nominally 28.5V. With the alternator off-line, the bus voltage
will quickly sag to about 24V. Some radios do better than others at not
having their squelch threshold change when the input power changes that
much.

MikeM

Mike,

The solid state voltage regulators used in many experimental category
aircraft do in fact have "crowbar" type protection as well as over
voltage protection. As I understand the operation of the crowbar trip
from a simple over voltage trip is if the crowbar opens the circuit,
it can only be reset by turning off the alternator switch. Once that
occurs, you can reset the breaker, turn the alternator switch back on
and the alternator will be back in business. My breaker trips are
always resettable without resetting requirement of the alternator
switch. So, I think something is shorting to ground that shouldn't
be. I am thinking the main alternator may still be the culprit or
possibly the battery, which is an AGM type, may be shorting as it
heats up. I am going to try pulling the field breaker and sense
breaker of the backup alternator to see if the problems occur during
the isolation. If so, then running from the backup system and pulling
the breakers of the main system. If the failures only occur on the
main system I am going to replace the alternator with a completely
different unit. If both tests show voltage excursions, I am going to
replace the battery and see if that isn't the culprit. There is
really not much left to try.

Thanks for your help.
Steve