MOD Upgrading the ignition backup battery in a Carbon Cub E/FX-3 (EarthX ETX104)

[Neal]

A few discussions on the forum about choosing an ignition backup battery but this thread will document the actual mod of switching to a different ignition backup battery from the PowerSonic AGM installed in my FX-3. Anyone else that wants to contribute with their mod to their Carbon Cub of any flavor feel free to use this thread as well.

This evening I decided to pull the right forward panel off and begin the brainstorming process of changing out the PowerSonic battery to another option of higher capacity and likely LiFePO4. I didn't take any pictures but here are my discoveries from the start of this process.

The EarthX almost fits in the hole of the PowerSonic bracket but it does not. I thought about removing the bracket used to hold the PowerSonic but that would be a challenge due to the small nuts behind the bracket that holds the custom built bracket in place. I also would prefer to leave the bracket intact should I ever want or need to go back to the factory setup. So that area is out.

Now where can I put this small EarthX battery? I pulled the GDU and it will not fit behind the GDU so that option is out.

Back to the right forward panel. There is a lot of space below the Light Speed ignition modules and forward at the firewall end. After maneuvering the battery around I think that's the best spot. I need to design a mount that will likely use Adel clamps to secure it in place. It's going to take a few iterations I'm sure and I surely want to make sure I never touch or impact the boot cowl and cause a dent on that thin aluminum so I'll also want to put a piece of foam pad between the battery and the aluminum for safety. Again, there's plenty of room but I don't need any more drama with this plane so I am being extra careful.

An alternative but far less desired location would be possibly mounting it below the pilot seat underneath the aircraft from the access panel on the bottom.

The TCW IBBS battery is an ideal size and it's tempting but it too needs a bracket of some type. I'll see what I can come up with for the EarthX I have first. Time for some CAD work to see what I can design for a PETG bracket.

 

[Neal]

@Cactus Charlie when disconnecting the PowerSonic battery I noticed a blade fuse holder connected to the wire. I didn't open it to check the size of the fuse. If you have your schematic handy can you tell me what size fuse is inline to the ignition backup battery?

If it's less than 10A this may be an issue with putting a pig tail on the EarthX battery to directly charge it with my Optimate charger that pushes 10A if that current can go downstream of the battery and through that fuse? Then again if nothing is energized to pass the current maybe I'm incorrect but I just want to make sure charging the EarthX directly at 10A max won't be a problem with the wires connecting to the battery that go to the backup ignition circuit.

 

[Neal]

I'll ask my question in advance. Let's say the fuse is a 2A or 5A fuse. I have a pigtail connected to my EarthX battery to charge while in the hangar which can push up to 10A with my current charger. I "believe" that current will not flow through that blade fuse as no circuit is open while the aircraft is not in use, correct? So charging the battery at 10A with that wire downstream with a smaller fuse is not at risk?

 

[Cactus Charlie]

The ignition battery blade fuse is 10 A. The fuse will not pass current from an external charger if that charger is connected directly to the battery terminals.

 

[Neal]

I went back to the plane after realizing my plan last night wasn't going to work. While there is space below the Light Speed ignition modules I think fabricating a mount there is going to be more difficult than I care to pursue. So I decided to remove the bracket for the PowerSonic battery and check fit of the EarthX in this location and if it checks good then I'll fabricate something to mount it in that location.

I cannot say enough how painful it was to remove this PowerSonic bracket. Getting a 1/4" socket behind and dealing with the thread marker stuff that's in the way and the soft phillips screws all make for what could be a disaster. It's a good exercise as you're going to need to deal with this if/when the time comes to deal with your IBBS battery. Why CubCrafters didn't go with 2 x IBBS batteries I don't know, why they don't improve things like this later in production, I don't know. But 2 x IBBS is a perfect fit in this area. Anyways, the EarthX will fit fine and now I need to figure out the bracket which will be 3D printed as I don't have a way or skill in forming Aluminum. I probably could bring back my erector set days and figure something out but I'm going to put my Mechanical Engineering degree to use and see what I can do with an ABS or PETG setup via 3D printing which I enjoy as a hobby.

I don't know that I'll use these same ridiculous screws to put this back together. The phillips are probably done and needs to be replaced with something new or better.

The task continues.

 

[Cactus Charlie]

Put some tape on those battery terminals before doing trial fits in close proximity to metal structure.

It was easy for CubCrafters to fit all this stuff before the boot cowl was added. I doubt they gave a minute of thought to maintainability.

 

[Neal]

Progress update: Iteration 3 of the EarthX battery mount fits perfect. I had to make some adjustments as there isn't much space on the front and back side so the position has to be accurate as I certainly don't want to be hitting the boot cowl. I modified the design to have rounded edges as well keeping this concern in mind. I have rubber pads so I put one on the boot cowl but there is at least 1/4 inch separation from the mount and the boot cowl. I just want to play it safe.

I have to wire it up next, today was just a quick check of the fit and I screwed it in place, far easier than disassembly so it's ready to wire up and test.

This design has a 15% infill, meaning it's not solid, but it's a 13 hour print. Strength is fine but I'd prefer a solid version which is printing now which will be a 20 hour print.

When ready for final install the battery will be secured with double-sided foam tape to provide some shock absorption and also secure the battery in place.

Click the 3D model images for a better view.

 

[Cactus Charlie]

Looks nice. I'll be very interested to see data on the performance and longevity of this battery

 

[Neal]

My main concern and potential deal breaker is what charge rate will this battery pull. LiFePO4 can take a high charge rate as we see with our EathX starter batteries with amps over 20 after start not unusual. If this battery causes more than a 10A charge rate the inline fuse will blow. I’m not sure if there is anything to limit the charge rate inline now. So this is my top concern. I won’t be putting the right panel back on for a few flights until I see this is going to be okay.

 

[ve6yeq]

I would only worry about the charging current if the backup battery is discharged significantly. If the backup battery is fully charged, then the voltages will be very close so the current will be minimal. If you want to be safe, charge the backup battery completely with an external charger before powering on the main bus for the first time.

 

[Neal]

I am installing a pigtail to be able to do that but I also think I need to see if this is going to be an issue such as when away on a trip and sitting for weather. I wish there was a way to limit charge current.

Edit: I don't know how max charge amps are handled in these batteries. I don't know if the BMS is programmed for this as well and what limits it sets. I know my RV (motorhome) LiFePO4's can pull 300A. I don't know the max my ETX-900 can pull or this backup battery. I'll see if I can find any info in the EarthX manual to calm my fears.

 

[Neal]

I did a little RTFM and found the info. 15A max charge for the backup battery. 80A for the starter battery I have.

The 10A fuse may be a problem. Not sure if it's safe to upsize that to 15A? I probably should match it to the battery specs. Opinions?

 

[Cactus Charlie]

Charge current with the standard wiring passes through the 10 A CB, the 10 A fuse, and the blocking diode. I agree that charge current for a fully charged LiFEPO4 will likely not be a problem. However, if you ever use the emergency ignition battery in flight, the CB may trip when you stop using the battery and it goes back on charge.

I'd suggest some ground tests with a multimeter with at least 10 A capability in series with the new ignition battery. Do the 10 sec runup test and observe charge current when test terminated. Then increase emergency time in steps to see how charge current changes.

If you feel bold run a 30 minute in flight emergency test and observe charge current.

I have emergency ignition battery current displayed and recorded so I know how the AGM behaves for that test.

You could run the same discharge/charge test on the bench. You need a load that pulls about 1.3 A and a power supply (not the LiFePO4 charger) capable of at least 15 A set to 14.2 V.

 

[Neal]

I have spare CB's for all sizes up to around 20A so I may change out the CB and fuse to 15A but will test. Good info! Thanks @Cactus Charlie.

 

[Neal]

I will be keeping the right panel off for a few flights while testing and monitoring the area (smoke, etc.). I may velcro or strap my multimeter in place and monitor it real time as well as suggested.

 

[Cactus Charlie]

CB and fuses should be sized to protect the wiring not the equipment at the end of the wire. You can't increase the CB and fuse rating without considering whether the wire is rated for the increased current.

I don't know what blocking diode CubCrafters uses but the 90SQ030 diode shown in the LSE ignition schematic is rated at 9 A.

 

[Neal]

I may put a 15A fuse in place of the 10A as that's behind the panel and not something I can reset in flight. I believe that limit is only affected by charging and not discharging of the battery for demands such as Light Speed. It's really just to protect the incoming current (charge). The breaker I can reset but again should not be affected by charging but only in use activities?

Am I thinking this through correctly as my only concern of going over 10A is during charge.

 

[Cactus Charlie]

The 10 A fuse is in circuit for charging and discharging. The 10 A CB and the blocking diode only pass current when charging.

When I was concerned about the charge rate of the AGM I devised and tested a simple current limiter but I never fitted it to the aircraft. I stopped doing in flight testing as I found the 10 second run-up test was a good indicator of battery condition.

The limiter was based on the characteristics of tungsten filaments. They have low resistance when cold and high resistance when hot. In series between source and load they act as a current limiting device. More current, filament gets hotter, resistance goes up, voltage drop increases, current goes down.

My limiter used a car tungsten brake light bulb. I do not know if such a limiter would be compatible with the LiFePO4 BMS but it could easily be tested on the bench and I doubt it could harm the battery.

 

[Neal]

Has anyone checked the specs for max charge rate of the IBBS 3AH battery or the EBBS? Good info to know before diving into this mod. I hope to test mine today with a ground run.

@Cactus Charlie can you post the electrical schematic of the ignition backup circuit showing the charge path so I can see what you mention about going through the breaker, Light Speed, etc.? Just want to have it here in this discussion for educational purposes of anyone considering changing the factory setup.

Thanks!

 

[Cactus Charlie]

Has anyone checked the specs for max charge rate of the IBBS 3AH battery

Yes, I did as part of the research of my plan to replace the AGM with a 3 AH IBBS.

"Pin 5 provides charging and bus voltage sensing for the IBBS unit and must be connected to an aircraft power bus. When the voltage on pin 5 falls below about 11 volts the system automatically transfers the load current on the output pins to the internal back-up battery source. Pin 5 maximum current draw is 2.5 amps during charging."

 

[Neal]

I hate electrical, it's that one thing that can insidiously bite you and takes careful planning and design. It bit me two years ago when upgrading my landing lights and blowing out the flaky wig-wag controller and took me months to get confidence I wasn't going to be Haley's comet cub edition. I'm happy to report that didn't happen and so far so good with the ground run post install completion of the EarthX backup battery in use for my ignition backup.

My plan today was to use male spades to connect to CubCrafters female spades used to connect to the PowerSonic battery to make reverting as easy as possible. As we all know that use the PowerSonic, the spades are narrow so sure enough I didn't have a compatible mate. I realized the wires coming in are coming down from the top and there is plenty of wire to reach the terminals on the EarthX without having to add wire. I cut the zip ties in the loom and pulled out the wire for the ignition backup battery which is interesting, the core is positive, the shield is the negative. I cut off the spades and installed ring terminals and heat shrunk the connection for additional security. I mistakenly loosened the wrong part on the EarthX which is the part the bolt goes into but I was lucky to get that resecured as I thought the day was done and I'd have to send the battery back for repair. I installed the pig tail, normal wires, and used a washer as the pig tail has quite a large hole in its terminal. I was surprised the pig tail I bought was shorter than the one for the starter battery but it will work out fine as it tucks under the panel near the 12V adapter and USB ports. I added electrical tape over the terminals as I don't like exposed terminals on the battery. Getting the battery in with wires connected was a tight fit but it worked. I used 3M dual lock (stronger than velcro) to secure the battery, it will be interesting trying to remove it someday as this stuff is strong.

​

I'm so paranoid with this stuff, even with all switches off I thought I smelled smoke, I thought I saw smoke, I'm checking everything with a flashlight, haha...just paranoid as can be!! That's okay, I respect this electrical stuff and am being extra cautious obviously concerned with the potential 15A input with 10A CB/Fuses. Oh...I did pull the inline fuse while connecting the battery leads, and yes, it's 10A.

I turned on MASTER and the voltage showed and matched my voltmeter test of 13.3V. I wanted to use the multimeter during the engine run but it has a 10A max so I didn't connect for fear of blowing its fuse which I did years ago when testing solar in my RV and learned this lesson.

Time for the ground run, all checks good, so far.

Engine cranked fine and AMPS only got up to around +20 but immediately came down to around 14, then 11, etc. Charge voltage showed 13.7 on the ignition backup (14.0 on the starter) and with ignition backup on the voltage dropped to around 13.4. No breakers or fuses popped, engine ran fine as you can see in the video if desired. I'll also attach the G3X log file if anyone wants to review it.

What is of interest and I'll be paying attention to this is the max charge voltage of the ignition backup circuit. I did charge my EarthX backup battery after receiving it to ensure it is charged when put into use but that was a month or so ago, if not more. But nothing has been connected to it. What I'm curious is what voltage is actually the charge voltage on the ignition backup circuit. If 13.7 is the max then this could be the reason the PowerSonic's never proved to be a good battery. An AGM battery needs to bulk charge in the mid 14's for voltage. As someone pointed out that it appears it's just getting a constant float voltage, this is the reason the ignition backup battery is never healthy. This is also why I installed a pigtail on my EarthX so I can charge and maintain it properly. I'm curious what others see as max charge voltage on their ignition backup circuit.

The last thing I need to do is update the ignition backup battery params in the G3X config which I'll match my EarthX starter battery numbers. I need to review those anyways, I want to make some adjustments to alerts.

A few pics showing the install and the pigtail which tucks up under the panel.

I'll fly with the right forward panel removed for a while and make sure all is good before reinstalling that panel. I'll do a ground charge as well to make sure that works as expected. Overall, it's going to be nice having a strong battery with 4 AH capacity and 6 year life. It was not an easy mod nor one I'd recommend to all as you need to have a good understanding of the ramifications. I think if there was a way to improve the charging profile of the PowerSonic it would be a viable solution but something is just wrong in the electrical design it seems for charging that battery. But I'm on expert so I defer to those that know more.

I welcome any feedback, opinions, suggestions for improvement, or if I need an intervention

 

[mechTBM]

Neil - Following this topic with interest. I know the builder of 40DT (also my builder) and he's been working on a more robust backup solution as well.

Jim

ps - Installed a whelen taxi light via your CNC'd mount the other day. Fantastic!

 

[Cactus Charlie]

What I'm curious is what voltage is actually the charge voltage on the ignition backup circuit. If 13.7 is the max then this could be the reason the PowerSonic's never proved to be a good battery. An AGM battery needs to bulk charge in the mid 14's for voltage. As someone pointed out that it appears it's just getting a constant float voltage, this is the reason the ignition backup battery is never healthy.

The AGM charge voltage is MAIN bus volts less the diode drop. On my aircraft that's about 14.1 V which is enough to ensure full charge. I do not believe the short life of the AGM batteries is caused by the available charging voltage.

I turned on MASTER and the voltage showed and matched my voltmeter test of 13.3V. I wanted to use the multimeter during the engine run but it has a 10A max so I didn't connect for fear of blowing its fuse which I did years ago when testing solar in my RV and learned this lesson.

You'd rather risk blowing the blocking diode than the meter fuse?

I'm concerned that you did not do the bench tests that I suggested. If this battery does pull more than 10 A when charging after use it could completely disable your emergency ignition system by blowing the battery fuse.

 

[Neal]

I'm concerned that you did not do the bench tests that I suggested. If this battery does pull more than 10 A when charging after use it could completely disable your emergency ignition system by blowing the battery fuse.

Please provide the tests you suggest that I missed. Yes, I agree, if the 10A fuse blows the b/u ignition is offline. Air abort and investigate. I am stocking my spares kit with extra fuses both 10A and 15A. Obviously this scenario is an overcharge condition and not a loss of ignition, alternator, or starter battery sources for the ignition. Exceeding 10A is my main concern, I did not see it in this test i.e. no breaker pop or fuse blown. I believe your test is an extended use of the b/u ignition battery to try and demand a higher charge rate?

 

[lrobichaux]

I welcome any feedback, opinions, suggestions for improvement, or if I need an intervention

Great post, @Neal!

I know the builder of 40DT (also my builder) and he's been working on a more robust backup solution as well.

I'm interested in a more robust backup system as well. Something more similar to that in the X/NXCub electrical system which uses a TCW IBBS. @Cactus Charlie may also be pondering a more robust set-up, but he points out that his ability to procrastinate is unusually high (HA!). Any chance you could get your builder to join the forum and share his thinking? We'd all be very appreciative.

 

[Cactus Charlie]

Please provide the tests you suggest that I missed.

Perhaps I composed then deleted. Can't scroll up through the thread to check.

A bench test would require a load than pulls about 1.3 A and a 14 V power supply capable of sourcing a least 15 A.

You would discharge the battery using the load for multiple tests of increasing duration. After each of those tests you would charge the battery and record the charging current.

That would give some data on what charge current you would expect after in flight usage. You could then use the data to decide whether there needed to be changes to wire size, CB rating, diode current rating, or battery fuse.

 

[Neal]

That would give some data on what charge current you would expect after in flight usage.

If I used it in flight I would not be terminating use. I would be landing with it on. After that obviously there will be a investigation as to why I needed b/u ignition power and I'd also likely use my pigtail connection and charger to ensure a full charge of the battery for next use. The only "risk" scenario I see is a long term of non use just like the starter battery drawing a high charge rate. I will see what I can do to discharge the battery for a higher demand charge rate. I'm not convinced the ignition backup circuit pushes current the same as the starter battery.

I will test what I can, use the voltmeter, and report back any results.

 

[Cactus Charlie]

Any chance you could get your builder to join the forum and share his thinking?

If that was directed at me - I don't have a builder.

I have the design/schematic for using a 3 AH IBBS for emergency ignition but there is still a lot to work out in the installation details. I need the trial installation to be completely reversible.

My immediate priority for FX-3 work is to fix the mixture cable which has either shed, or broken, the detent spring.

 

[Neal]

He's talking about another member that knows the owner of N40DT (EX-3).

So here's another thought @Cactus Charlie. An electrical circuit, I would imagine, is designed to limit the current that "can" flow based on wire size, length, etc. As we know, this circuit is fused and breakered at 10A. It shouldn't matter if the "receiver" (battery) can take a charge at 2A or 100A. The circuit should be designed to not push current beyond the design. Correct?

It's the same concept as the charger I use to charge my starter battery, and now ign b/u battery. I bought the charger that is sized based on the circuit, i.e. 10A max (by Optimate). I don't put a 50A charger on the line just because my EarthX ETX-900 can take 80A. The same situation actually applies with the starter battery. As we learned in researching max charge rates, the ETX-900 can take 80A. But the circuit is not sized for that. Isn't it the same exact scenario? (Edit: The alternator is limited to 40A I believe, so that solves that)

 

[Neal]

Perhaps I composed then deleted. Can't scroll up through the thread to check.

It's in this post. Found it. I don't have a large enough charger.