Need advice on battery system redo

[kaa]

Hi all,

I'd appreciate your thoughts on the following situation.

My airplane has dual battery & dual alternator setup. The problem is that the batteries sketch me out (they are some sort of motorcycle batteries without BMS). The current power architecture is like this:



I'd like to replace the batteries with EarthX. The problem is that I don't really have enough space to install two ETX-900s. Then again, I'm not sure if I need two? What if I just remove everything in the red area and install a single ETX-900? I usually operate with Bus Tie turned on anyway (it's easier operationally, because the backup alternator doesn't charge the battery on the ground). What would be the downsides of this? This is what it would look like:



Of course this removes the redundancy of having a second battery, but do they really fail in flight? Would appreciate your thoughts on this.

The plane is glass (G3X + G5). I do fly a certain amount of IFR. It's usually not very hardcode, but losing the radios in case of an electrical failure would definitely suck.

Thanks!

 

[Carl Froehlich]

Single battery, dual (or more) alternators falls short of the redundancy offered by a thoughtful two battery design. If you really must use an EarthX, why not two of the smaller ETX 680?

I note that you are feeding your Essential buss directly from the battery (as in between the battery and the master solenoid). This is a key feature that many overlook. I do not know the function of the diodes however. If you do go with two batteries I suggest making two essential busses, one from each battery. Split your avionics between the two batteries, such as EFIS #1 on one, EFIS #2 on the other, Comm #1 and Comm #2 and so forth. Now have a three way toggle switch to be able to select which battery if feeding which Essential buss (an in Normal and Backup modes).

Consolidate your main and aux busses into one as these are secondary to your vital buss. You should be able to continue IFR flight on just the essential buss until battery(s) exhaustion. The main buss has all the stuff you don’t need on the panel (e.g. Pitot Heat, Boost pump, landing and nav lights, seat heaters, etc.). This supports the pilot’s immediate action of opening the master solenoid(s) for a major electrical fault.

Side note - this approach eliminates the function of the Cross Tie as the batteries are in parallel for normal operations and split out for backup modes. It also eliminates the need for avionic backup batteries.

Carl

 

[Mike S]

I note that you are feeding your Essential buss directly from the battery (as in between the battery and the master solenoid). T

Carl

Good way to drain the battery/s-----depending on what is on your essential buss.

I suggest you consider taping the battery feed after the master solenoid for the essential buss. That is unless you are trying to eliminate the master as a point of failure?

Lightspeed ignition is the only thing I can think of at the moment that specifically tells you to take the wiring directly to the battery.

 

[KMMUflyer]

Some things to consider.
Is the Engine ignition or fuel supply electrically dependent?
What is on the essential bus?

 

[Carl Froehlich]

I suggest you consider taping the battery feed after the master solenoid for the essential buss. That is unless you are trying to eliminate the master as a point of failure?

This is one of several reasons to do as I suggest.

Carl

 

[kaa]

Thanks everyone for the opinions! To clarify some points:

• I'm on a 24V system, so ETX680-24 and ETX900-24 are the same size for me. I also have a 100amp alternator which rules out ETX680-24
• The engine is stock with magnetos. The panel is fully electrically dependent (except G5, which has a built-in battery).
• I'm looking for the simplest solution to get rid of the ATV/motorcycle batteries and get back in the air.

Good way to drain the battery/s-----depending on what is on your essential buss.

I didn't show it but there is a separate essential bus switch after the diodes, so it seems pretty safe? Both G3Xs and ADHRS are on the essential bus I think.

Single battery, dual (or more) alternators falls short of the redundancy offered by a thoughtful two battery design

Could you clarify on this? I already have dual alternators and I'm unlikely to change that. I'm trying to come up with a realistic failure scenario where single battery/dual alternators will be a problem, but dual battery / dual alternators won't.

 

[dmattmul]

Thanks everyone for the opinions! To clarify some points:

• I'm on a 24V system, so ETX680-24 and ETX900-24 are the same size for me. I also have a 100amp alternator which rules out ETX680-24
• The engine is stock with magnetos. The panel is fully electrically dependent (except G5, which has a built-in battery).
• I'm looking for the simplest solution to get rid of the ATV/motorcycle batteries and get back in the air.

I didn't show it but there is a separate essential bus switch after the diodes, so it seems pretty safe? Both G3Xs and ADHRS are on the essential bus I think.


Could you clarify on this? I already have dual alternators and I'm unlikely to change that. I'm trying to come up with a realistic failure scenario where single battery/dual alternators will be a problem, but dual battery / dual alternators won't.

In the -12 world the ETX680, ETX900 and ETX1200 all have the same case size just different weights and amp-hours. Dual alternators single battery a very common layout for non-energy dependent engines. See Z-12 drawing.

 

[gkochers]

My architecture is similar to what you propose except my main and aux buses are not split. It is similar to Aeroelectric Z-13 Dual alternator single battery. I have a non-electrically dependent ignition but very dependent avionics suite. My only addition to what you show is an IBBS backup for the PFD and EIS mostly to serve as brown-out protection which you likely don’t need on a 24V system. I didn’t plan on it for emergency use, but it’s there if the main battery were to fail. I have not yet committed to earth-x but leaning towards it. My thought on dual batteries is that an event that takes out one is likely to take out both.

And I too pulled my e-buss alternated feed off before the master contactor with a separate guarded switch on the panel specifically to address master contactor failure or a situation where I needed to quickly turn off everything non-essential for max endurance.

24V with 100Amps? That’s a lot of juice.

 

[Ben Ellis]

My thought on dual batteries is that an event that takes out one is likely to take out both.

If you go with two separate buses like Z-14 then both batteries couldn’t be taken out unless you have the cross feed contactor closed. An added benefit of Z-14 is that the second battery is more useful than a IBBS backup battery and possibly cheaper.