Ignition backup battery failure on run up - FX3

[Cactus Charlie]

That isn't a PS-1221S so, no, wrong form factor.

 

[lrobichaux]

this battery right ? dims 151 x 20 x 89h, 1.2Ah@1C discharge

1. have capacity greater than '3 amp hour'... 4ah
at a1.5A discharge rate, must use a LFP chemistry , no bms, just a balancer
2, have a loaded terminal voltage of at least 10 V after 1 hour discharge at 1.5A,ok
3. match the dimensions and terminal type of the Panasonic PS -1221S confirm this .. I think you can change the terminals from spade to another quick connect
4. draw no more than 5 A from a 14.2 V supply at any state of discharge. most likely
5. last at least 5 years including long periods of storage with no charging, probably
NOW,... how much would this be priced at ????? what would people be willing to pay ? certainly not even close to the $30 a ps1221 costs...

I think @Cactus Charlie 's point is that there would be demand (at least from the folks on this forum) for a safe, proven drop-in replacement for the PowerSonic battery, with minimal required alterations. While I wouldn't go so far as to say that cost would be "no issue," IMO it's fair to say that we understand that a robust, improved solution is gonna cost more (at least I do).

 

[aerolithium]

' The solution to this was to replace the PS122S battery with a ......."
no ???

 

[Neal]

This conversation quite frankly is quite odd and not the most professional if you are representing a business. First you need to understand the problem and what the limitations are that a replacement battery must meet in charge current limitations, and other limitations due to the Light Speed ignition used in our aircraft. You can read my thread on the ETX-104 I linked and do some study. You are focused on price before you seem to have a solution to offer. This is not presenting well for you, in my opinion.

Do your research, identify the problem, identify the requirements, come up with a solution. You're the vendor, you price it as you see fit. We are the potential customer and will decide if it meets our needs and the price represents the value.

I suggest starting over when you're ready bringing something to the table after you've done your homework, in a new thread.

 

[Neal]

@newstuff I'm not going to respond to your other thread, just a little feedback here for you. I know anyone can build their own LiFePO4 batteries, I'm not aware of other chemistries, ordering cells, components, etc. and build your own. This is not something I'm going to put in my aircraft or behind a system like my electronic ignition or in a use that is now a 3rd level failure and I have to rely on this to keep my engine running.

You haven't instilled confidence in us here, to be honest. I suggest working on your brand, show us your web site, prove to us you offer reliable and reputable aircraft solutions. It's okay if you're new and a startup or not even launched yet, be honest about it. I'm being honest that none of us here are looking for home brew batteries for any use in our aircraft. You don't use your business name in your username, you don't show a link to a web site. So let this be a nudge to help you launch your new business if that's the case. Build your brand, build your reputation, show us a catalog of your offerings, not offer custom builds.

I wish you the best but I think most of us that are in this conversation are probably not your customer right now. You've lost us in the handling of this so far. It's time for a professional start wherever that may be and then bring it here when you're ready to earn our trust.

 

[aerolithium]

My website is in my profile, but here it is aerolithium.com.
Building batteries since 2010. But, I understand now, your looking for a large corporate entity that produces a certified battery.
Best of luck

 

[Neal]

I suggest build up your signature and if you want your username changed you can submit that in the profile area too, up to you.

Yes, a company that produces certified solutions certainly adds confidence but most of us here discussing this are Experimental. But we need to trust the solutions and we just haven't seen your business, website, etc. I haven't at least.

https://flightinfo.com/account/signature

 

[Cactus Charlie]

I did recently purchase an EarthX ETZ5G and intend to run some tests with it as a substitute for the AGM battery.

After a 2 hour 40 minute discharge at about 0.9 A the terminal voltage had dropped to 13.1 V.

The initial charge current after this discharge test was over 9 A. Charge current was still over 6 A after 13 minutes but was close to zero after 30 minutes.

This battery will need charge current limiting to protect the isolation diode and battery fuse.

 

[Neal]

The initial charge current after this discharge test was over 9 A. Charge current was still over 6 A after 13 minutes but was close to zero after 30 minutes.

That is from what charge source? An optimate? I'm curious if you put this in your plane, discharged, and tested the current the plane supplies over its charge path what the amps would read. In my case it never exceeded 1.4A if I recall. Granted, it wasn't discharged but I don't know the current setup is going to supply what you're seeing from a dedicated charger such as a 10A Optimate like mine.

 

[Cactus Charlie]

Charge source was a 30 amp bench power supply set to 14.2 VDC. This emulates aircraft Main bus with alternator working.

I would not run the test you suggest because there is some risk the isolation diode will be blown.

Next step will be to test with a charge current limiter.

 

[lrobichaux]

@Cactus Charlie I think you're getting close to a really good solution? 2 hours 40 min is a very long time to find a suitable landing spot. What solution are you considering to limit the charge current? Just curious, as I'm still learning all this aviation electrical / avionics stuff.

 

[Cactus Charlie]

2 hours 40 min is a very long time to find a suitable landing spot.

That was the test time at about 0.86 A. The ignition pulls about 1.3 A. Still should be good for well over an hour. The proof will be a flight test using emergency ignition. Several years ago I demonstrated 30 minutes with an AGM (PS-1221S or equivalent) in good condition.

I plan to experiment with a current limiter that uses a tungsten filament lamp - old style car brake light lamp. Any tungsten filament lamp has high resistance when hot but low resistance when cold. The more current it passes the hotter it gets which tends to limit the current.

I ran the current limiting test several years ago with the PS-1221S and it worked as expected. Need to run it again with the EarthX as that has very different charge characteristics.

I didn't invent the idea but I used about 45 years ago in a charger for a kit built air band portable transceiver.

 

[TailwindsJJ]

Earlier this summer while performing a engine run up prior to a flight I had the Right Mag emergency backup battery fail.

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View attachment 871
Video taken after aborting the flight and returning to the hangar


The PS-1221S battery had been replaced in October of 2025 during my conditional inspection. Normally I fly my FX3 about 120 hrs a year, but I am down to about 50 hrs a year due to work, weather and an elderly mom who has needed a lot of care recently. Prior to this attempted flight on June 6th, the plane had not flown for 3 weeks and had less than 15 hrs since January. Whether this is a factor or not, it’s worth noting. Also note the battery had a date sticker of 06/20/25 and this failure occurred on 06/06/2026.

View attachment 870

During the run up the voltage dropped to 5.9 before I shut off the RT IGN Battery. I considered this a failed runup and returned to the hangar for diagnostics.View attachment 869

The solution to this was to replace the PS122S battery with a new one. My new SOP will be to replace that battery one year after the battery manufacturing date and not during the conditional inspection time. I have also changed my engine run up check list to include a 10 sec run on the emergency battery.

if you haven't already changed the alerting on for Alternator/Amp to give you a red and audio alert I strongly recommend doing so. This is aligned with what Cactus Charlie recommended in some earlier threads (see the N40DT accident threads and the ignition battery threads).

I’m posting the videos and pictures as most people have never seen (and hopefully never will) this failure before. Hopefully this thread and the other discussions on the ignition system will educate folks and prevent another N40DT situation where the emergency backup system failed when it was needed the most.

I could not help but notice your panel layout is very different from mine - If you look at my attached pic can u tell me how to match your layout
Thanks