Very high amps draw indication on Dynon D120 and 912ULS

I would have two guesses as to the cause of this problem: either the wire connections at the current shunt are loose or corroded, or there's a mechanical problem with the shunt itself that's causing an intermittent change in its resistance.  I would remove all wires from the shunt, inspect the shunt for damage, clean the wire terminals, shunt studs and nuts to bright metal, then retorque the connections.  If you find any corrosion, apply something like ACF50, CorrosionX, LPS 3, battery terminal protector or dielectric grease to prevent a reoccurrence.

I'm a Flight Design service center and have been working on Flight Design's since 2006 and have 2K hours in them. The most common causes of this is lose battery terminal screws, lose ground wires (there are five to tighten really tight), the shunt behind the pilot side instrument panel has two wires on each side and they should be unscrewed and cleaned with a scotchbrite pad on the wire eyelets and the shunt surface and then apply a dab of dielectric grease and screw them back on. flight. The one last item is make sure the two yellow wires at the voltage regulator are firmly in place and make sure the brown plug with the wires is firmly pushed in place. If you have questions give me a call.

Great, thank you both for the detailed responses! I will check out those things mentioned today and follow-up with what I find.

Good to know you are an FD service center Roger, we are just a quick flight away from GEU.

Everything seems to be resolved, at least for now. Unfortunately for my testing interest, the plane got taken to a local shop earlier in the week because the voltage had dropped into the 11's since I last flew it. So, the shop already did the checking/cleaning of the regulator plug and that resolved the low charging voltage. However, the log entry said it did not resolve the erratic amps draw and they thought it was related to an issue w/ the Dynon display (they didn't touch the shunt according to the log entry).

So, I removed the -battery cable and started checking out the shunt. It looked ok from visual inspection and still felt like it had a tiny bit of dielectric grease on it. I removed the 4 screws/wires and cleaned everything off with a shop towel, re-applied grease, and re-assembled. Ground testing several power draw scenarios and the ammeter looks to be working as normal and we were not seeing anything greater than -5 amps.

Side note, do you guys have a manual reference for servicing the shunt or generic wiring like that? I searched through the FD and Rotax manuals and could not find anything specific to the shunt & wiring (to put in the log entry as reference). EDIT: I just used AC 43.13-1B Ch. 11-4 for the reference.

One odd thing I did notice on the battery terminal cables is that whoever installed it previously put 3 different sized washers on. 1 large one under the 2 ring terminals (supposedly to increase the contact area of the small battery terminal?), then 2 smaller ones of different sizes on top of the ring terminals so the small bolt could be tightened into the terminal. Naturally I forgot to take a photo, so hopefully that makes sense. Seems like there should be a better solution for securing the cables to the battery terminals (Odyssey battery).

Hi Justin,

Nothing to do to the shunt, but remove those four wires and clean them. In the CT you will always have an amp bounce between -4 to + 6. Did you tighten the five grounding points? The washer differences on the battery terminals is because of the difference in the wire eyelet size and the battery terminal size. Without the smaller washers the eyelets will go over the battery terminal and cause a poor contact. Now here is another better upgrade to reduce these issues. The Odyssey battery is only 12v and 100 CCA which was used in the begining. They don't use them anymore and most of us have switched. They use the Earth-X 680c. 13.2V and 320 CCA. It is only about one inch taller and longer and comes with a new mounting box from Aircraft Spruce. This takes care of several little issues including the amp issue and some starting issues. It takes about fifteen minutes to swap them out.

• Voltage: 13.2
• Weight: 3.9lbs (1.8kg)
• Cold Cranking Amps (CCA): 320
• Peak Cranking Amps (PCA): 680
• Amp Hour (1C Rate): 12.4
• Chemistry: Lithium Iron Phosphate (LiFePO4)
• Case Size: C
• Dimensions: 5.9" L x 3.4" W x 4.5" H (150mm L x 86mm W x 115mm H)

Call me if you have any questions