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NoahF
03-25-2010, 05:20 PM
Am I correct in assuming that the internal Li-Ion battery will automatically provide uninterrupted EM service during engine start, when my main bus voltage sags below 8V? That is to say, there is diode "or" functionality between the main power input and the internal battery?

NoahF
03-25-2010, 06:29 PM
A related question: The Li-Ion battery is only a 7.4V battery (manual p. 72). How can this power the Advanced Deck if minimum input power is 10V (manual p. 72)? This leads me to believe that the unit WILL function at BUS voltage below 10V, no? Which begs the question: At what minimum voltage do I REALLY need to be worried about operation being affected? Obviously this answer determines whether alternate power sources (internal battery, aux battery, TCW Intelligent Power Stabilizer, etc) are required to maintain functionality during engine start bus voltage sag event.

flickroll
03-26-2010, 08:01 AM
And related to Noah's question, is it OK to have the EE and EF units in the main master switch, or should they be on the avionics bus? I'd prefer them on the master, but I wonder if starting voltage drops will muck things up. As Noah asks, will the battery backup keep power going to all AFS devices (EFIS, magnetometer, etc) so that the starting voltage drop does not affect them?

Also, is it preferable to have the autopilot on the master or on the avionics bus?

Thanks

Trevor Conroy
03-26-2010, 08:46 AM
The AFS units will run on their internal battery which is indeed a 7.4V Li-Ion. They will not, however, run on a 7.4V main buss. The units are internally designed to run on a main buss voltage of 10V DC. Any lower and the units will go into battery backup mode.

To answer the first question: You don't need to worry about a voltage drop (8V) during start-up. The unit will go into battery backup mode, but unless you run your starter for 30 seconds straight, the EFIS will not shut off. Once the engine is online the screens switch right back to main buss power.

The second question: You may wire the EF/EM to your main battery buss rather than your avionics buss (so you can see your engine instrumentation during start-up). However, you MUST have the protection diodes. Van's sells them for pretty cheap.

NoahF
03-26-2010, 09:26 AM
The units are internally designed to run on a main buss voltage of 10V DC. Any lower and the units will go into battery backup mode... You don't need to worry about a voltage drop (8V) during start-up. The unit will go into battery backup mode.

Thanks for the response Trevor. What if you DON'T have the internal battery? At what voltage do things stop working? I believe that this is usually a DIFFERENT answer than the "design" voltage minimum of 10V.

Flickroll, I am concluding that an avionics bus is not necessary. I have contacted Garmin and voltage sag / brownout will not damage their hardware. I don't believe that AFS' hardware could be damaged from low bus voltage either, even in the case of no internal battery (Trevor?) Take a look at Nuckolls article about avionics busses on his website. Without risk of hardware damage, the remaining issue is preventing reboot at engine start so that you can enter flightplans prior to and monitor engine parameters during startup. Sounds like the internal battery takes care of this problem, in addition to providing an hour (max) of operation after the bus falls below 10V(?). That sound about right, Trevor?

Trevor Conroy
03-26-2010, 10:02 AM
What if you DON'T have the internal battery?
They will turn on with about 7.4V, but will automatically turn off after 30 seconds if the voltage is not at or above 10V.


I don't believe that AFS' hardware could be damaged from low bus voltage either, even in the case of no internal battery
Operating at very low voltages is actually very damaging to circuitry. However, for the short amount of time you are starting your engine, it is not a problem. This is especially true when their is an internal battery installed. The unit never operates at very low power settings in that case.


Sounds like the internal battery takes care of this problem, in addition to providing an hour (max) of operation after the bus falls below 10V(?)
Duration depends on the type of unit (EE/EF/EM/MFD). An MFD will last the longest (Well over 1hr) with the EE lasting the shortest (1hr).

Hope this helps guys!

Bernard VDS
04-08-2010, 10:04 AM
Hi Trevor
My intention is to place the EE and EM on an avionic bus (should ever the diodes work fault). Before the starting of the engine I wanted to start the EM on the internal battery just to have the engine information and after starting switch on the avionic bus.
Am I wrong ?

Trevor Conroy
04-08-2010, 04:15 PM
That configuration will work just fine. However, you can certainly place your EM unit on the battery buss as long as the protection diodes are in place.