Complete Electrical Failure In-Flight

[Raluttio]

Yesterday, about 20 minutes before the end of civil twilight, I had a complete electrical failure. EFIS, Radio, Lights - everything. Luckily, I had been testing out the accuracy of my EFIS groundspeed reading vs what I was getting from Foreflight. My stratux (with an ahrs chip) runs off of a battery pack so I was able to calculate an estimate of indicated airspeed based off of my ground speed. I managed to get back on the ground safely... only to get a flat tire trying to get off the runway with two other planes in the pattern at a non-towered field. I felt very exposed in the dark with no lights and radio. It was not a great end to an otherwise great flight.

I had an obligation I needed to get to so I was unable to take off the cowling and start looking around for the failure. I would appreciate some suggestions of where to start looking when I can get out to the plane tomorrow. Some details:
Third owner Sonex A
Aerovee 80hp
Stratomaster Enigma
XCOM radio
Stock voltage regulator (I believe)
Odyssey battery (less than a year old)
None of the circuit breakers tripped
I was checking temps in a climb 15 minutes prior and I took a picture - 12.5 volts and +22.9Amps
Only 2-3 minutes prior I was checking volts and amps with and without location and strobe lights on. I remember voltage being 13.something and amps being above 40 with the lights off.

I have a backup battery installed for the Enigma but clearly that didn't work. I just read in the manual last night that it should have been part of my preflight checklist to turn off the master with the battery on to check battery status. There are no records from the previous owner regarding the backup battery. I already know I will be replacing it and adding the check to my preflight.

Will a fried voltage regulator take out all electrical? I've rebuilt the engine but I haven't dug into the electrical system.

Thanks in advance for any help.

[BRS]

Wow, 20 amps seems like a lot of current! It's hard to speculate what happenend without much more information.

What battery do you have? My plane has a EarthX battery which must be carefully charged at idle (keep in mind I've a revmaster R2300) otherwise I'll frie the alternator which is rated at 18 amps. What is the capacity of the Aerovee alternator? So disconcect and check the battery for a start. For comparison, with a charged battery and all lights etc on, my sonex only draws about 6 amps max.

How is your ammeter wired. It can be between the regulator/alternator & battery (which shows charge current as well as load) or wired between the battery and buss (which shows load and not battery draw). Since you were showing 20+ amps I'm thinking it's wired to show current between the alternator and battery, and that your battery (uncharged) was the lion's share of the current draw.

Divide and concur. You said that no breakers were 'popped'. That many narrow things down quite a bit. Mentally break the system in half at the point where your power enters the buss. Since no breakers were open you then can 'guess' that the issue is before the buss. So start with the big wire to the buss and follow it back to the regulator then to the alternator output. A multimeter checking resistence to ground might be of help. Open the electrical path along the way and check on each side.

Good luck. Tell us what you find.

[Bryan Cotton]

I'll second the question about the ammeter wiring. Would be helpful to understand the high current.

I'd disconnect the battery and see if it recharges and is happy.

I'd disconnect the VR, run at 3000 RPM, and measure AC voltage. Should be about 26V at 3000 rpm IIRC.

The AeroVee alternator is only rated at 20A. When you add up all your loads what do you get?

Edit: this recent thread has info and links to other recent threads. A lot of them are on the first page of the electrical section.
viewtopic.php?f=6&t=7904

[daleandee]

Do you have a constant duty solenoid installed?

Dale
3.0 Corvair/Tailwheel

[Bryan Cotton]

Do you have a constant duty solenoid installed?

Dale
3.0 Corvair/Tailwheel

That's a great question. Would explain the total failure.

Not totally related but here is a pitch for my mechanical master switch which saves an amp.
viewtopic.php?f=6&t=2009

[BRS]

Not totally related but here is a pitch for my mechanical master switch which saves an amp.
viewtopic.php?f=6&t=2009

That was an interesting thread (read all of it). I like that idea. I see on ama zon that there are even aluminum bodied switches like that.

[Raluttio]

The ammeter is the MGL Magnetic Sensor that is a small exposed circuit board and is on the lead between the battery and the main contactor/solenoid.

Main contactor/solenoid: It is a continuous duty solenoid. I found a photo I took of the firewall back in May. I can only make out some of the numbers on the label. I am 99% certain this listing is what is installed --> https://www.aircraftspruce.com/catalog/pnpages/11-03161.php

The battery is an Odyssey - not sure the exact model - most likely the PC625.

Plan of action today is battery check followed by contactor check followed by VR check. Hopefully it's a straight-forward contactor failure and I can just pop in a new one.

Thanks for the discussion so far everyone.

[Raluttio]

I dug in and found the problem after work today.

The 14 gauge wire leading from the contactor to the master switch had an in-line 20amp blade fuse holder that had been spliced in at some point. That fuse was completed destroyed. When pulling out that spliced assembly I noticed that one of the butt splice connectors was miscolored. I took the heat shrink off and discovered it had melted underneath. I sent a photo to my dad (an electrician) who caught that the two wires were different gauges. The main wire is 12 gauge. He explained that there are no butt splices for those two gauges. There is 10-12 and 14-16 but not 12-14. So, the hypothesis is that in the past when the wire was under heavy load it would heat up but was still able to handle the load. Eventually the thermal cycling became too much and weakened the connection to the point it turned into a heater and blew the fuse.

After hooking up the wire I flipped on everything in the plane and it works just fine. I ordered some tefzel wire that should arrive by Monday.

I will be leaving the inline fuse out unless someone can tell me why that is a good idea. Everything has a circuit breaker so why put a 20amp fuse under the cowling where it can't be accessed in flight? In fact, the improper installation of the thing caused an inflight emergency.

I checked the EFIS backup battery as well which was only reading 2 volts. The replacement arrives tomorrow.

All in all this has been a great learning experience. I have a much better understanding of the electrical system now.

[kmacht]

When you say everything has a circuit breaker. Does that include the line running from the contractor to the main switch that used to have the fuse? What happens if that wire chafes and starts to short out? Does a breaker trip somewhere if that wire shorts or does it have a direct path back to the battery? Did the original builder include a wiring diagram with the airplane? If so I would review it to see if that fuse was shown and what it’s intended purpose was.

[Bryan Cotton]

The master switch usually just provides a ground to the coil on the contactor. That is never fused. It should see about an amp of current.

The hot connection from battery positive and the contactor is not protected, but is very short with a small possibility of failure. Note this connection covers both contactor input and the hot side of the coil.

Do you mean a 20A fuse between the contactor and main breaker? Or is there a main on-off switch for your panel that you are calling the master?

A little schematic would really help.