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secondary power input and auto startup/shutdown

Posted: Tue Sep 15, 2020 10:30 pm
by rv7charlie
Hi,

I've got a new-to-me HX in my RV6 (along with a Mini GA), and while the Mini seems immune to voltage sag during engine start, the HX is not. Occasionally it will continue its boot process through engine cranking, but typically hangs during boot, so I'm forced to cycle power to the electrical buses to get the HX to boot.

Does the HX have the 'smarts' to auto-powerdown after an optional timer runs, when voltage is removed from the primary input? edit:Should have specified in the powerdown question: 'with a secondary battery tied to the secondary power input'. Newer EFISs with internal battery backup will do this, but I don't see anything in the docs showing that the HX has this capability. Is this a 'catch 22', where I'll have to install a separate switch on the 2nd supply to turn off the HX?

Also, the manual mentions '10 seconds' for initial boot, but since the manual includes later models, I don't know if that applies to the HX. My HX takes roughly 2 minutes, based on the on-screen countdown timer, to fully boot. Is this normal behavior for the HX, and do I need to keep the plane stationary until I get the EFIS display?

Thanks for help with this older model,

Charlie

Re: secondary power input and auto startup/shutdown

Posted: Wed Sep 16, 2020 2:45 am
by Bobturner
The Hx has multiple power inputs but they are all equal - no primary or secondary. So yes, they all need to be switched off to turn off the unit. OTOH if one power source fails, you don’t have to do anything to keep the second supply on. The Hx takes a couple of minutes to fully boot up. It’s important to keep the airplane stationary for the first 10 seconds or so, as the initial attitude software boots up. It will still boot if you start taxiing right away, but will take longer.

Re: secondary power input and auto startup/shutdown

Posted: Wed Sep 16, 2020 4:56 am
by jnewsum1
To prevent the Hx from hanging up or rebooting due to voltage sag during engine start up GRT recommends using an external backup battery on one of the power inputs.

TCW Technologies makes several different ones of varying capacities. I initially installed the 3 amp BU battery version with my GRT EFIS units but replaced it with a TCW Power Stabilizer. The TCW backup battery needs to be enabled on before engine start and turned off after shutdown and needs to be periodically tested for capacity. The Power stabilizer requires no pilot interaction, it just works in the background. Even if your alternator were to fail, the Power stabilizer will extend operation as the primary ships battery discharges for the units that get backup power from the stabilizer.

For VFR operation the stabilizer is a good option. If your doing IFR flying a BU battery might be a better choice.

https://www.tcwtech.com

Re: secondary power input and auto startup/shutdown

Posted: Wed Sep 16, 2020 4:32 pm
by rv7charlie
Thank you both for the info. After reading your answers, I re-read 6.2, 'power connections' & finally picked up the 'isolated' term in the description; that simplifies the brownout/sag cure. It's also good to know that I don't have to wait the entire 2 minutes to move the plane. 30 seconds isn't even noticed, but 2 minutes feels like an eternity, for a quick VFR flight from an uncontrolled field. :-)

Charlie

Re: secondary power input and auto startup/shutdown

Posted: Wed Sep 16, 2020 9:22 pm
by Bobturner
As an old electronics guy, I would recommend not running avionics during engine start, unless you have backup power. Modern electronics are usually very tolerant of over-voltage events, but not necessarily under-voltage events.