N190YX wrote:You never, ever want to have any avionics on when starting the engine.
Yikes, I guess starting my aircraft nearly a thousand times in the last 10 years with the avionics and strobes on must have cost me thousands of dollars in repairs.
The voltage spikes and issues revolving around starting our aircraft engines have been well understood for a long time. The simple snubber diode on our contactors/relays have long been used to protect them. The resulting spikes and voltage drops are not mysterious things. I know of no current avionics products that aren't compliant with DO-160 which describe in detail what our current avionics are supposed to be able to handle without damage, and that includes starter voltage spikes.
I can't state that older products like the KX-155 or non solid state devices might not be damaged, but all our current devices shouldn't even blink at the voltage spikes.
The biggest problem with most devices now is simply not getting enough juice during start, causing them to reboot. It is silly to put in a modern EFIS with built in engine monitoring and not have it available during startup. I also consider a strobe light to be an important safety item to be on during engine startup.
The reboot issue can be solved several ways. In my Sonex with an Enigma, I had a very small 2ah battery installed that provided BU power for any voltage drops, either at start or a complete loss of the main bus. It only required about $30 in parts to hook this up to the dedicated alternate power connection built into the Enigma. I had an avionics switch in the Sonex, it's only purpose was to be able to separate the avionics from the higher power devices during an inflight loss of power which never happened in my 400 hours on the plane.
In my current aircraft, one of the devices Garmin sells along with their G3X Touch system will provide 2A of stable 12v of power to supply whatever devices you need during a voltage drop. In my case it provides power to itself, the PFD and the ADAHRS. Since I have a dual buss/battery system, all my avionics have an alternate power feed to each of them (most of the Garmin equipment has two diode isolated power inputs). I have eliminated the avionics switch in my current airplane and anything I want up at power on can be on with no drop in voltage during startup.
You don't need to get as elaborate as I have in my new aircraft. Simple backup power systems are available off the shelf that can provide power to a single device during a loss of power emergency or low voltage situation. Even simpler brown out devices are also available.
While my current avionics are beyond what you could even install in a Sonex legacy model, my Sonex equipment was very common. Next generation equipment from MGL, Dynon etc. that has been installed at modest cost are even more common and very robust. With the B model, even more avionics can now fit (I could probably squeeze in my current panel). There is no reason to fear the starter voltage transients with any of these systems as long as you build yourself a solid aircraft electrical system. The AeroElectric is a great resource for learning how to do just that, and there are many other good references out there as well.
Posted: Mon Mar 26, 2018 2:21 am