Choosing an ignition backup battery for an electronic ignition piston aircraft engine

[Cactus Charlie]

Wouldn’t it be nice if the backup ignition switch was just an arming feature? In fact how about removing it and the ignition fails over to the backup battery when voltage drops below a level? Sense alternator and starter battery voltage. When insufficient then engage backup ignition. Make the switch an override only. It should never need to be touched.

When I was designing my TCW IBBS installation that will, one day, replace my 2 AH AGM I considered 3 switch options:

OFF ARM
OFF ARM ON
OFF ON

I decided on OFF ON keeping the switch functionality the same as the CubCrafters design.

There were several reasons for this choice -

It keeps the existing switch and placard
It works the same as any other FX-3
It can be tested without needing a breaker pull
It keeps the same LED warning lamp and it is functional with Master off

An auto ARM function must be designed so there is no drain on the ignition power source when Master is off when not in flight. That pretty much forces a switch with an OFF position and a light to warn when On.

 

[lrobichaux]

Please don't enable me. I want to upgrade to the 1200 but don't see that it's necessary haha.

OK, let's clear up any misunderstanding ... since when does something need to be "necessary" before we spend money on an airplane?

I'm waiting for my 900 to show even the slightest degradation so I can break out the credit card

Now this is the correct mindset.

Wouldn’t it be nice if the backup ignition switch was just an arming feature?

This is the way the CCX-2300 is designed. The (R) backup battery switch is a 3-position switch - off, auto and on. Auto is "armed" where so long as main bus voltage is normal, then it's my understanding that it "passes through" the (R) back-up IBBS unless and until main bus voltage drops below normal level. If that happens when the switch is in "auto," the (R) back-up IBBS automatically begins powering the (R) ignition and (L) ignition continues to be powered by the main bus / battery. Not sure if this can be designed into the FX-3 panel / system, but should be a simple question to investigate.

 

[Cactus Charlie]

Not sure if this can be designed into the FX-3 panel / system, but should be a simple question to investigate.

I did investigate this option and decided against it. That does not mean it could not be done.

 

[Cactus Charlie]

Another one bites the dust. This one, which was not PowerSonic, was useless after 9 months.

 

[Neal]

Now imagine how many out there don't know that their ignition backup battery is bad. And how many aren't changing them annually? Yeah...scary. I need to get that forward right panel open and start working on my mod.

 

[Neal]

Going to be a warm(er) weekend here in VA. May be time to get the right forward panel off and look into my EarthX backup battery mod. Sitting on the shelf isn't doing much

 

[lrobichaux]

Let us know how that goes. If you can get it to work, I will definitely consider it for my EX-3.

@Neal I'm sure you saw Pete's answer to my battery question posted on FB. I'm going to call EarthX to inquire if they plan to offer a vented version of the ETX1200.

 

[Neal]

I'm sure you saw Pete's answer to my battery question posted on FB. I'm going to call EarthX to inquire if they plan to offer a vented version of the ETX1200.

I did and I know they push the vented version and rightfully so, why not? It's up to each to consider the risk involved. I'm not concerned about my non vented 900. I also run LiFePO4 in my RV (motorhome) with no issues to date (2 years) and you also have LiFePO4 non vented for your IBBS battery and ignition backup battery (by TCW). Ensuring proper care and installation is key to success.

As to the comment about breathing the thermal runaway smoke/fumes whatever, I wonder how our breathing 100LL each time we fly compares. I imagine it's toxic yet we never think about that. Food for thought

 

[lrobichaux]

Just spoke to technical support at EarthX and received a very interesting recommendation. Evidently, EarthX then looked at my FB post and responded. It's worth you taking a read. Bottom line is that the tech support represented said that they DO NOT recommend the ETX1200 unless its a last resort to solve a persistent hard starting problem. He went so far as to say that "the 1200 has too much starting power in many applications." He said that if additional starting power and amp-hour capacity is desired, that a second ETX900 in parallel is a much preferred option. Parallel installation of two batteries may work in the NX/XCub, but will presumably not work on the FX-3 based on where the battery is installed. From a cost / benefit perspective, as @Neal suggested it may be best to focus on bolstering the right ignition back-up battery and live with the reliability of one EarthX LiFePO4 main battery. THe tech rep I spoke to was not high on the ETX1200.

 

[Neal]

Credit card saved

I'm fine with a single 900. It's worked great to date. A better battery to support the backup ignition should be the objective. I'm going with the EarthX I bought but with the TCW / IBBS on the radar. Both are similar (LiFePO4) with different form factors.

 

[Neal]

Just spoke to technical support at EarthX and received a very interesting recommendation. Evidently, EarthX then looked at my FB post and responded. It's worth you taking a read. Bottom line is that the tech support represented said that they DO NOT recommend the ETX1200 unless its a last resort to solve a persistent hard starting problem. He went so far as to say that "the 1200 has too much starting power in many applications." He said that if additional starting power and amp-hour capacity is desired, that a second ETX900 in parallel is a much preferred option. Parallel installation of two batteries may work in the NX/XCub, but will presumably not work on the FX-3 based on where the battery is installed. From a cost / benefit perspective, as @Neal suggested it may be best to focus on bolstering the right ignition back-up battery and live with the reliability of one EarthX LiFePO4 main battery. THe tech rep I spoke to was not high on the ETX1200.

I read the post and had to find the jump pack that they carry which I was not aware of.

12V-24V Jump Pack (all-in-one)

One of the most powerful jump packs available and can jump either a 12V or 24V battery! Jump your truck or certified aircraft and much more!

earthxbatteries.com

I carry a NOCO GB40 which I'll stick with. Compact and has a pigtail. Hope to never need it for my 900.

 

[lrobichaux]

I carry a NOCO GB40 which I'll stick with. Compact and has a pigtail. Hope to never need it for my 900.

Their jump pack is too large and too expensive. I carry a very powerful Likithor LiFePO4 jump pack which I too hope to never need. I've had an avionics shop wire in a dedicated pigtail to facilitate easy access.

 

[Cactus Charlie]

. I'm going with the EarthX I bought but with the TCW / IBBS on the radar. Both are similar (LiFePO4) with different form factors.

There is a big difference between the EarthX battery you have purchased and the TCW IBBS.

The TCW IBBS will keep the engine running when the voltage drops below 8 V. The EarthX will cut off at a much higher voltage (about 10.5 V). I do not know how much difference that is in terms of engine run time but I'd rather destructively discharge an IBBS battery pack ($150 ish) than have the engine stop and break the airplane ($100,000- $300,000).

Either will likely be far better than the existing 2 AH AGM but I have a strong preference for the 3 AH IBBS. The EarthX does have the advantage of much simpler installation. That may make it an attractive interim improvement.

Since we are also talking about the main battery in this thread - I'm pleased with the performance of my ETX680C and have no reason to change to a larger battery.

 

[Neal]

What's involved in making a TCW IBBS work? I have no problem converting my EarthX to a Starlink Mini power source as I already bought the 12V to SL Mini converter as I knew it may end up this way. Not a big deal.

I may need to run a discharge test on the EarthX and validate that number. Seems odd. I believe I read the BMS will let it run down to about 10% state of charge remaining. That's closer to 10.0 V in a LiFePO4 battery, In fact I'm not sure a LiFePO4 battery goes below 10V. You may want to verify that 8V number.

I did a quick google search and it appears my info is accurate, 10.0V is the floor for LiFePO4.

 

[Cactus Charlie]

You may want to verify that 8V number.

I did a quick google search and it appears my info is accurate, 10.0V is the floor for LiFePO4.

I have the full discharge plot for when I accidentally deep discharged my G3X IBBS. I don't need to verify anything.

G3X shutdown at 8.2 V but the ignition system would have continued to drain the IBBS. The time between 10.5 V and 8.2 V is 177 seconds or close to 3 minutes.

Faced with an imminent forced landing what would 3 minutes more engine run time be worth to you?