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

[Cactus Charlie]

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?

The current that flows through a wire is controlled primarily by the source voltage and the load impedance. The resistance of the wire may limit the current but it will then get hot and may catch fire.

The wire must be sized so it can pass the expected maximum current. It is never intended to be a current limiter.

Circuit breakers and fuses should be chosen to limit current to less than the maximum value that can be safely passed by the wire.

First determine the expected maximum current either from source voltage and load impedance or from the load specifications. Then select the wire size so it has adequate current margin. Then select a CB or fuse with a lower current rating than the wire can safely pass.

If your EarthX "load" can draw 15 A from a 14 V supply then the CB, fuse, or diode may trip/blow. The circuit was not designed to pass 15 A. If you increase the CB and fuse ratings the diode may blow. I have not mentioned the switch rating before since I don't know what it is.

There are tables than can be used to find appropriate wire size in AC 43.13-1B.

 

[Cactus Charlie]

Found it. I don't have a large enough charger.

You don't want a charger for this test as it will have internal current and voltage control. You need a fixed voltage power supply with no currrent limiting.

 

[Cactus Charlie]

You need a fixed voltage power supply with no currrent limiting.

The battery of a running car may be a suitable alternative. Safer than trying to test with a running aircraft engine.

 

[Neal]

My test plan / goal is to discharge the backup battery. I can do this by powering my Starlink Mini using an adapter I have for the Starlink to connect to a 12V battery. Then I'll do a ground run and monitor the amps the plane will supply a discharged battery. What I'm trying to determine is what is the max amps the aircraft is going to try pushing to this battery. This is the worst case scenario I'm testing for in this installation.

The scenario that is of concern is aircraft charging the battery by the aircraft alternator. There is no concern of battery supplying power when called for.

I will also have alerts programmed in the G3X so I am aware if the ignition b/u battery goes offline which already should be programmed to alert below a certain voltage which indicates the ign b/u battery is unusable. I will verify this when I program the LiFePO4 numbers.

I would love to see a MOD thread on using the TCW IBBS 3AH battery in a E/FX-3 and how it would be wired. It's my next go to. I looked at the specs for the EarthX EBBS which is quite large and seems to be competing with the TCW IBBS 3AH product. I'd prefer TCW but don't understand the wiring needed so that's for another thread if someone wants to start that discussion. The TCW IBBS 3AH + Wiring harness seems to be around $500.

 

[Cactus Charlie]

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.

If you are wise you'll test backup ignition at least before the first flight of the day.

Let's say the airplane sat a week and you did not have the ignition battery on charge. You run the ignition test then restore to normal operation. The week sitting and the 10 second ignition test pushed the subsequent re-charge over 10 A and blew the fuse but did not trip the CB.

You now launch on your long cross country flight knowing the emergency ignition is good because you tested it before takeoff. You don't know the fuse or diode blew because there is no cockpit indication. You have no backup ignition.

I think you need to be very sure you cannot induce this scenario.

 

[Neal]

I test the backup ignition at every runup. It's part of the checklist. Correct me if I'm wrong but if the fuse blows the voltage is going to read zero in the G3X? It seems there is a clear indication the ignition backup circuit is offline and will display a red CAS alert or am I missing something?

 

[Cactus Charlie]

Correct me if I'm wrong but if the fuse blows the voltage is going to read zero in the G3X? It seems there is a clear indication the ignition backup circuit is offline and will display a red CAS alert or am I missing something?

No, there will be no cockpit indication. Ignition battery volts will read MAIN bus volts with the fuse blown. It will drop to zero when EMER is selected.

That's based on a study of the schematic. Test it yourself by pulling the fuse.

 

[ve6yeq]

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

Just bite the bullet and replace the cable with a A-790 Vernier Control Cable (I got the 96” one and cut off lots) and you will find it much easier to lean accurately, repeatably and quickly. Now that I have done it, I am not sure why I did not go that way to start with.

 

[Neal]

Just bite the bullet and replace the cable with a A-790 Vernier Control Cable (I got the 96” one and cut off lots) and you will find it much easier to lean accurately, repeatably and quickly. Now that I have done it, I am not sure why I did not go that way to start with.

Off topic for this thread but I'll add, if my mixture cable goes that I am replacing it with the vernier as well. Let's create a new thread on that topic if any further discussion is needed.

 

[lrobichaux]

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.

Thx! We’re standing by!

 

[Neal]

While I started a new thread to get educated on the option of using a TCW IBBS 3AH LiFePO4 battery I have not abandoned the EarthX option. I still have testing to do. I realize the one edge case and biggest concern is if/when the battery could demand 15A for charge current and pop the breaker, blow the fuse, etc. and potentially have the failure go undetected until a R ign test is done. In my opinion this is an unlikely scenario as the battery will remain charged until discharged from actual use or a charge failure which will be observed by low voltage. I installed a pigtail to be able to charge and maintain this battery for extended non use such as my RV travels. I can't maintain the factory installed AGM as there is no provision to charge it other than aircraft power so extended non use puts you at risk in this scenario until the battery is recharged.

With all of this said, 99% of us will never need or use the ignition backup battery as it's a 3rd stage failure. In the case of N40DT the planets were completely out of alignment with both starter and ignition backup batteries weak or defective from what we assume from the preliminary, which could be wrong. I use an EarthX ETX-900 for my starter battery which is significantly better than the SBS-J16 I wouldn't trust after a week of non use unless on a charger. And then pair that with an older PowerSonic AGM (i.e. 9-12 months) and it's a degraded scenario for sure.

Proper alerts for loss of alternator as discussed in another thread which seems to be not configured properly from CubCrafters is your first priority and first indication for immediate air abort. A good starter battery is your next priority. The ignition backup should never come into play but if it does, we know the options as currently being discussed.

 

[ve6yeq]

When charging a flat battery without a charger that controls current and voltage, the initial current draw is always an issue.

For example, the EarthX ETX-900 in my EX-3, which serves as the main starter battery, is connected to the main bus and a 40 A alternator via a 40 A fuse and a 50 A breaker. As the battery's internal "BMS" is rated at a maximum 80 A charging current, and there is no current limiting that I know of in the alternator other than resistive heating, the same issue of blowing a fuse / tripping a breaker exists if the battery is too flat and the alternator turns on.

Given the low self-discharge rate of an EarthX lithium battery, I would not worry about using an EarthX ETX104 as a backup battery, as it will remain nearly fully charged. My biggest concern of using the ETX104 over an EBBS (or IBBS) is that switching rt ignition backup on is a manual troubleshooting step that I have to perform in my emergency flow: A (airspeed), B (best field), C (cause check), D (declare), E (evacuation plan), F (fuel shutoff) which has to be completed really fast if I am only at 1000 ft AGL.

 

[Cactus Charlie]

For example, the EarthX ETX-900 in my EX-3, which serves as the main starter battery, is connected to the main bus and a 40 A alternator via a 40 A fuse and a 50 A breaker.

I thought EX-3 used (almost) the same electrical system as FX-3. Where is that 40 A fuse in your EX-3 (physical position and schematic reference)?

I'm was very surprised to see the XCub has an alternator fuse but I'm not aware of one in the EX-3 or FX-3.

 

[ve6yeq]

My EX-3, which I had the kit built at the factory, is effectively an FX-3.

It has a 40 A "Maxi Fuse" under the seat between the output of the master contactor and the battery current shunt, before connecting to the main bus (See the second page of diagram SK75101 Rev NC in the kit dropbox).

My EX-3 currently has a Denso 021080-0760 Alternator - 12V, 40A, 1 Pulley Groove, Internal Fan and Regulator. The "B" lead of the alternator is connected to the main bus (See page 4 of diagram SK75101 Rev NC in the kit dropbox) via an overvoltage protection circuit and a 50 A breaker.

As the XCub appears to use an alternator without an internal regulator, it has an external aircraft regulator with an internal overvoltage trip that trips the field breaker. Also, the battery is wired differently, as there is a fusable link between the battery and the master contactor input, and the alternator is directly connected to the master contactor output. There is a 40 A fuse between the master contactor output and the main bus. Not a conventional design as far as I know.

 

[Cactus Charlie]

It has a 40 A "Maxi Fuse" under the seat between the output of the master contactor and the battery current shunt, before connecting to the main bus

I found it before I saw your reply. I had forgotten that was there.

Alternator feeds MAIN bus via 50 A CB but MAIN bus to battery connection is via the 40 A fuse.

 

[Neal]

I have two spare fuses once I learned of that as well and keep it in my spares kit.

Okay, I returned to the plane today for more ground run testing.

1) Pulling the emerg ignition breaker drops the voltage to 0 in the GDU

2) Pulling the inline fuse at the battery positive does nothing to the GDU

I need my clamp meter to measure amps for the charge, I looked at buying a mini meter with a display or a bluetooth option which would require a shunt install like in my RV but decided not to.

AMPS today during the ground run did not exceed 11. I will never be in a condition where the starter and/or ignition backup are not in a nearly full state of charge. With pigtails on both, they will be maintained and charged after any period of non use.

I've decided to call this MOD done. I'm staying with the EarthX ETX104. I will fly with the right forward panel off a few flights to monitor for my own comfort, both the electrical but also my mount solution.

 

[Cactus Charlie]

1) Pulling the emerg ignition breaker drops the voltage to 0 in the GDU

That is unexpected and seems to be in conflict with the published schematic.

IGN VOLTS is sensed at ignition switch terminal 5 by wire A11A20O which feeds the GEA 24.

With ignition switch Off terminal 5 is connected to the battery via switch jumper 5-3. Terminal 5 should see battery voltage when the ignition CB is pulled.

2) Pulling the inline fuse at the battery positive does nothing to the GDU

As expected since, with switch Off, switch terminal 5 is connected to switch terminal 4 and reads MAIN bus volts when the fuse is missing.

 

[ve6yeq]

As part of other design work, I calculated the book endurance of different backup batteries. The load I considered is a single Lightspeed Plasma III configured for an IO-360, with a rated power consumption of 1.3 A at 13.8 V. Since power consumption should be approximately constant with voltage, I assume it is 13.8 V * 1.3 A = 18W.

For Lithium batteries, the discharge voltage curve is very flat at about 13.0 V so 18 W / 13.0 V = 1.4 A.

So looking at the EarthX ETX 104, we have 4 Ah rated capacity: 4 Ah / 1.4 A * 60 min/h = 171 min. Batteries are normally considered EOL when the actual capacity is 80% of the rated capacity: 171 min * 0.8 = 136 min. Looking at the EarthX Technical docs, they suggest that capacity is reduced by 10% at -10 degC (winter flying inside the side panel): 136 min * 0.9 = 122 min. The book suggests we should see a practical endurance of 2 hours, which easily meets the 30 min IFR requirement.

If I repeat this for the TCW IBBS 3 Ah powering only the right ignition, I get an endurance of 91 min. Once again, 1.5 hours is clearly enough.

However, if I repeat this for the PowerSonic PS-1221 AGM battery, the calculations become slightly more complex because of the faster voltage drop during discharge. The 18 W constant-power load is 3 W per cell (6 cells in a 12 V AGM battery). According to the PS-1221 documentation, the constant power table indicates a 45 min endurance for a fully charged battery. Using 80% rated capacity as end of life reduces this to 36 min, and a -20% for -10 deg C (AGM batteries are much worse in cold temperatures than Lithium) results in just 28 min. Just less than the 30 min IFR requirement.

Given that I have always assumed book values are best-case numbers, and that, in my experience, with flying only a couple of hours a week, the PowerSonic battery is never fully charged, given its self-discharge rate and the time required to charge to 100% (28+ hours). I will be upgrading the AGM battery before I go too far from a precautionary landing site.

 

[Neal]

That is unexpected and seems to be in conflict with the published schematic.

IGN VOLTS is sensed at ignition switch terminal 5 by wire A11A20O which feeds the GEA 24.

With ignition switch Off terminal 5 is connected to the battery via switch jumper 5-3. Terminal 5 should see battery voltage when the ignition CB is pulled.

Give it a try on your plane and see if the results are the same with the breaker (no sense in testing the fuse)

Given that I have always assumed book values are best-case numbers, and that, in my experience, with flying only a couple of hours a week, the PowerSonic battery is never fully charged, given its self-discharge rate and the time required to charge to 100% (28+ hours). I will be upgrading the AGM battery before I go too far from a precautionary landing site.

Excellent write up @ve6yeq - great information.

I think anyone that chooses NOT to upgrade the PowerSonic battery should at least consider wiring in a charge setup so that a NOCO or similar AGM battery tender can be connected to ensure the battery is maintained and fully charged when ready to fly. They should already be ensuring the starter battery is charged for any periods of non use, this is your first level alternator failure protection.

Great discussion on this forum and a lot learned by me and others stemming from the N40DT discussion. I personally have improved my G3X alerting and understanding of the systems and what to do in the event of an ALT failure to force loads to the IBBS, etc. Thanks all that participated and helped to educate those watching.

 

[Cactus Charlie]

The load I considered is a single Lightspeed Plasma III configured for an IO-360, with a rated power consumption of 1.3 A at 13.8 V. Since power consumption should be approximately constant with voltage, I assume it is 13.8 V * 1.3 A = 18W.

I would expect the current drawn by each ignition module to depend on engine rpm. The higher the rpm the greater the current.

Ignition battery current is instrumented in my FX-3 but that gives me ignition module current only when emergency ignition is active. The highest value I have recorded is 2.0 A but it is more typically around 1.2 A- 1.3 A at run-up rpm.

 

[Cactus Charlie]

They should already be ensuring the starter battery is charged for any periods of non use, this is your first level alternator failure protection.

I disagree. The first level fall back for alternator failure is proper management of the energy stored in the main battery.

With a main battery in good condition, and immediate alerting to alternator failure, I expect to by able to fly for well over an hour without considering use of emergency ignition.

 

[Cactus Charlie]

Give it a try on your plane and see if the results are the same with the breaker (no sense in testing the fuse)

I will, but not likely to be today. WX is low ceilings and drizzle.

Have you done a run-up emergency ignition test since you observed IGN VOLTS drop to zero with IGN CB pulled?

 

[Neal]

Have you done a run-up emergency ignition test since you observed IGV VOLTS drop to zero with IGN CB pulled?

No, will be at runup when I fly next. Is there a concern post CB pull?

 

[Cactus Charlie]

Is there a concern post CB pull?

Well, if I'm right, the engine will stop.

You could avoid that risk by running another test before engine start -

MASTER On
Observe and report IGN VOLTS
Pull IGN CB - Observe and report IGN VOLTS
Switch IGN to EMER - observe and report IGN VOLTS

 

[Neal]

What I'm asking is after the CB is RESET, is there a concern of not returning to normal operation?

It seems you're asking to pull the CB and then leave it pulled and engage emergency ignition for the test?

Honestly, I have no interest in that. I just want to call this done and return to flying. ETX104 is installed, tests I care to do are complete.

 

[Cactus Charlie]

It seems you're asking to pull the CB and then leave it pulled and engage emergency ignition for the test?

The state of the CB should make no difference to IGN BAT Volts when the EMER ignition switch is On.

It's a 10 second test with zero risk. It's something you should already have done as part of your post-mod testing.

 

[Sntry]

Hi Neal. Could you please share photos of your modification with new battery. Interested to see how you connected and secured the battery. Thanks,

 

[Neal]

Hi Neal. Could you please share photos of your modification with new battery. Interested to see how you connected and secured the battery. Thanks,

Sure, there are pictures in the thread if you care to review all but click here for the first pics.

 

[Cactus Charlie]

I will, but not likely to be today. WX is low ceilings and drizzle.

I had no doubt of the result but I did the test since I was at the hangar today. No surprises. IGN VOLTS was 13.9 with MASTER ON and stayed 13.9 when IGN CB pulled.

Interesting day in AZ today and a nice change from 100 mile visibility and no cloud. Low cloud bases with mountain obscuration.

Getting to my favorite dirt strip to hike required a bit of scud running, a climb through a hole, a search for another opening near the strip, then an easy descent to land. More scud running with mountain obscuration to get home. Fun and much easier with G3X with than map and compass.

 

[Neal]

As outlined in this post. I had the engine running so obviously MASTER was ON, EMERG IGN OFF. My results are different. I pulled the EMERG IGN breaker and my volts went to 0.