CubCrafters Carbon Cub FX-3 Electrical Questions

[Meconiates]

Had some more electrical questions:

1) Does anyone know what the electrical draw is for a full IFR panel on a FX3 (G3X, G5, GNC355, two Comms, etc).

2) What does a heated pitot draw? I assume there is an on / off switch for the heated pitot?

3) In a scenario where you are drawing more than 40amp, can you damage the alternator? Or will it just supply 40amp and then the battery will be discharging?

4) Anyone running a EarthX 1200 battery? I wonder if that’s prudent upgrade to give yourself more margin of safety for a situation where you are temporarily drawing more than alternator can handle ?

I was at the Yakima factory today and was trying to finalize my build sheet. And a concern was raised that I am going to exceed the electrical capacity if I did all of the following:

- Full IFR with pitot heat
- 100w Landing light with 10amp
Breaker
- 100w taxi light with 10am breaker
- TA245 USBC dual (45w each plug) so there is another 90w / 10amp breaker

 

[Neal]

I moved this post out of the landing lights MOD discussion, probably best for its own thread in configuring a new FX-3 to be built by the factory.

Probably some questions to send to [email protected] and get Pete's help.

It was stated by @earthxbatteries not to use the 1200, the 900 is the correct battery for us.

At some point increasing electrical demands is going to go beyond the design and circuit, yeah, not stating anything we all know. So there certainly has to be limits in what is used IMHO. I don't think you can throw an "extreme" upsize to the alternator without needing wiring, fuses, on and on to support the loads.

If no one can help then I'd say you really need to dig into the documentation to pull the electrical specs for each and every LRU, component, etc. The ole AI / chatGPT on and on may help but needs to be verified.

 

[Cactus Charlie]

2) What does a heated pitot draw? I assume there is an on / off switch for the heated pitot?

There are two verions of the heated pitot. CubCrafters usually fits the GAP 26-10 which is the uncontrolled version. That means it is either on of off as set by the switch.

Like all resistive heaters the current depends on the probe temperature. When the probe is turned on there will be a large current peak but current will quickly reduce to a steady state value that is influenced by ambient temperature.

I cannot tell you the peak current because G3X logged data is heavily lagged. When I turned on my GAP 26-10 the data log shows a peak current of 6.5 A and stabilized current of 4.9 A with ambient 36 deg F. Actual peak current at switch-on would have been greater than 6.5 A but less than 20 A CB rating.

 

[Cactus Charlie]

3) In a scenario where you are drawing more than 40amp, can you damage the alternator? Or will it just supply 40amp and then the battery will be discharging?

Don't know for sure. I expect the alternator will supply over 40 A but will overheat and may fail. I would expect the voltage to reduce as current draw is increased and that would eventually limit the current it can supply.

Since alternator is critical for sustained flight I would be inclined not to overload it.

I have an amber alert for alternator current greater than 35 A. It tripped once very briefly after a difficult engine start.

 

[Cactus Charlie]

1) Does anyone know what the electrical draw is for a full IFR panel on a FX3 (G3X, G5, GNC355, two Comms, etc).

I don't have that configuration but remember that peak avionics load will be when transmitting with AP engaged and servos at peak torque.

I did some battery current measurements on my system (standard G3X VFR plus GPS 175 and G5) a while ago, Here are my notes -

With engine running the ignition load will be about 2.5 A, not the zero increase shown in the table. Transmitting will add about 3 A.

It's easy to go over the top with added equipment. Think about what you really need for the way you plan to use the aircraft. Don't add weight, cost, and complexity for equipment you don't need for your mission.

 

[Cactus Charlie]

Here is a plot of alternator and battery current for a typical flight in my FX-3. Strobes on, lights wig/wag, no autopilot, no pitot heat. Peaks were correlated to radio TX and fuel pump use.