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

[Cactus Charlie]

For reference for the thread here is Figure 1 from Light Speed:

Just to be sure there is no misunderstanding - The FX-3 and EX-3 emergency ignition battery is not wired like this.

In the EX-3 and FX-3 switching to emergency disconnects MAIN bus from the ignition battery, and disconnects MAIN bus from the right ignition module, and connects the ignition battery to the right ignition module.

There is no configuration in which MAIN bus and the ignition battery can power the right ignition module at the same time.

 

[Neal]

The relevant information per Figure 1 was to point out the battery size. It's also technically irrelevant. Size it to what you want. Light Speed tells me the plasma III at cruise draws 1.2A.

Use the battery you trust. Size it to the duration you want.

 

[Neal]

It was brought to my attention from a friend via email that the EarthX ETX104 4AH backup battery is being phased out and replaced with a new offering coming in January. It's larger, heavier and 8AH but at 2 lbs not bad. If you want the ETX104 I suggest ordering ASAP.

EBBS Backup Battery: COMING SOON

EBBS is a backup battery for avionics and critical electronics controls for your aircraft. Delivering uncompromising reliability when it matters most.

earthxbatteries.com

 

[Neal]

I emailed TCW and inquired about their IBBS battery which we have for our G3X to see if it's a viable option. It seems two of these mounted back to back would be an ideal setup. One for G3X, the other for Light Speed.

Integrated Battery Back-up System (IBBS) - TCW Technologies

 

[Neal]

I put the EarthX battery on my Optimate charger so when it's time to install I know it's fully charged. I will keep tabs on the voltages to see if it gets to full charge from routine aircraft charging. I am considering also adding the same optimate pig tail I have on my starter battery and see if I can route it over the top under the panel so I can plug my optimate charger into it to let it maintain the battery a few times a year.

You can get the dimensions from the EarthX website but it fits in my hand, here is a picture of it on the floor of the hangar charging. It's tiny. But I don't know about fitment yet behind the panel.

 

[Neal]

Here is the pigtail for the Optimate 10A charger. I ordered this and will consider installing this on the battery.

Amazon.com: OptiMATE Cable O-11, Weatherproof Battery Lead, Heavy Duty/Auto/Marine : Everything Else

Amazon.com: OptiMATE Cable O-11, Weatherproof Battery Lead, Heavy Duty/Auto/Marine : Everything Else

www.amazon.com

This is the Optimate charger I use on my EarthX starter battery:

Amazon.com

 

[Neal]

TCW responded to my inquiry about using their IBBS battery like we use for our G3X as a backup for the Light Speed electronic ignition:

Neal, yes one of TCW Technologies IBBS Battery Back Up would be a suitable replacement.
TCW Support

As CubCrafters has a mount already designed for this, and possibly a dual mount I hear may be used in XCubs? This seems like an ideal solution to have two of these back to back in the right forward panel area, one for the G3X and one for the Light Speed.

 

[Neal]

I think an advantage of the TCW such as the 3AH model is that you could wire this into the GEA 24 to view voltage readings on the G3X. Although our current ignition backup also does this so it's probably moot. But form factor wise this seems like something to consider.

Product:

Integrated Battery Back-up System (IBBS) - TCW Technologies

The Integrated Battery Back-up System (IBBS) provides an engineered solution to enable an endurance bus for critical loads found in aircraft. The IBBS system provides back-up power to critical electronic loads such as EFIS, GPS, Autopilots and engine monitoring systems.

www.tcwtech.com

I didn't look at dimensions to compare the 3AH to the 6AH model. Curious so I'll look those up later.

Documentation:

https://www.tcwtech.com/wp-content/uploads/2020/03/725.0022-Install-Instr-1.8-IBBS-12v-3ah.pdf

 

[Neal]

If/when I install my EarthX backup battery I want to perform a test on the removed (recently installed) PowerSonic battery. I'd like to put a simulated load on it such as 1.2A and chart the voltage drop. The question also is when is this battery considered unusable and needs to be replaced. Typically AGM/Lead Acid batteries below 50% are potentially damaged. People performing tests such as ground runs until engine running rough need to be aware of an excessive discharge on this battery.

I welcome any tips for testing the removed PowerSonic battery so we can see how long it will take to run it down and monitor/measure the test.

 

[Cactus Charlie]

I welcome any tips for testing the removed PowerSonic battery so we can see how long it will take to run it down and monitor/measure the test.

The simplest test setup is to connect a load and a voltmeter across the battery terminals and start a stopwatch. Log the voltage before load connection and then periodically, say every 10 minutes. Terminate the test at about 10 V to avoid deep discharge damage.

I use high power wire wound resistors but a tungsten filament car brake light bulb can be used. (Brake light will change resistance with current and skew the discharge curve but it will still provide a baseline for comparison.)

First enhancement to that test method is to add a second meter to measure and log the current.

Fully charge the battery before testing but let it rest for at least an hour before running the test.

 

[Neal]

I need to figure out how to get a simulated load matching the Plasma III ignition module, i.e. find something that's a 1.1A continuous load. I also need to determine the 50% voltage point on the PowerSonic battery. Some batteries use 11.9 in the RV (motorhome world of golf cart batteries) and some use 12.1. Just need to do some research when that time comes for testing.

 

[Cactus Charlie]

The Yuasa data sheet shows typical discharge plots for their AGM batteries. If an ignition module draws 1.2 A from an NP2-12 battery (2AH) then the plot of interest is the 0.6CA curve. That curve stops at about 9.5 V after 60 minutes.

The Genesis manual has a similar plot:

PowerSonic does not give a 0.6CA curve but they appear to claim significantly greater capacity but at a lower temperature than the others:

And here is a discharge plot for the first battery I removed from my FX-3:

I don't think this data tells us anything new and I don't think the test you plan will either. Any of these batteries will keep the engine running for over 30 minutes when in good condition. A discharge plot of a new battery tells you nothing about how it will perform after 6 or 9 months in the aircraft. Only on aircraft testing, or removal for test, will do that.

 

[Neal]

What catches my attention from your discharge plot, bottom most chart, is your starting voltage. The battery was either not charged or damaged to only have a starting voltage of 11.4V.

 

[Cactus Charlie]

What catches my attention from your discharge plot, bottom most chart, is your starting voltage. The battery was either not charged or damaged to only have a starting voltage of 11.4V.

The test was run several years ago but I have no doubt the battery was changed before testing. It was removed from the aircraft because it was no good.

 

[Neal]

How long was the battery in use? I assume you followed the guidance of annual replacement. That's what concerns me about these cheap batteries. If this is the state at the end of a year, or your plane was not sufficiently charging it?