Complete Electrical Failure In-Flight

[Raluttio]

My apologies - I was not taking my time in writing the last post. I didn't mean to say the master switch was fused and my wording conveyed the wrong thing. The 20A fuse was between the contactor and the breakers - it is included in red on the attached diagram. The breakers are pigtailed - essentially acting as the bus. Everything runs off of one of those circuit breakers.

A wiring diagram did not come with the plane. I started creating one today. IT IS NOT COMPLETE - but is what I have been able to confirm so far. Like I said, it's hard to contort my body in under the dash to make sense of the wiring.

All of the wiring FWF has an anti-chafing sleeve on it. All wires coming into the cockpit through the firewall are then run through a plastic conduit. I find the likelihood of a issue in the wire between the contactor and "main bus" to be exceedingly rare compared to the risk of an inline fuse with two butt splice connections - whether they are correctly done or not.

[Bryan Cotton]

Well done Rodger. I'd eliminate the 20A fuse. The pilot is the protection from the contactor to the breakers inside. If there is smoke or something bad happening you turn off the master.

[BRS]

Interesting that there was a 20 Amp fuse protecting 38 amps worth of breakers. What size is the wire on that 20 amp fuse and what is the actual maximum draw of all the items on the branched out fuses?

Personally, I like a fuse between the battery and buss (In my case it's between the battery and contactor). It would only, likely, get used if you bend metal. It really should be like 150% larger (wire too) than full load potential. If it opens then there must be something seriously wrong, not something you'll want to reset before investigation.

[mike.smith]

The wire from the master switch to the master contactor should not need to be a heavy wire. It's carrying very little voltage. It just energizes the master contactor post that closes the continuous high voltage circuit. That higher voltage never passes through the wire to the mater switch, so there is no high voltage wiring on the cockpit side of the firewall. I don't know of any reason why you would want to keep the fuse there.

I have an inline fuse between the positive battery terminal and the voltage regulator (to protect from over voltage), but long ago I changed it from a 20 amp to a 30 amp. Since the AeroVee has a 20 amp alternator, a spike can (and did on a couple of occasions) pop the fuse. The wire is 10 AWG, so no issue overloading the wire. Yes, I know that if the fuse blows in flight I can't fix it, but I don't fly at night, and it simplified my electrical system, so it was a choice I made.

I lost all electrical power recently, when the wire between the positive battery terminal and the master contactor decided it had a life limit of 10.5 years. A new wire with new connectors solved that problem.

[BRS]

Mike I believe we might not be reading the schematic the same way. The wire the 20A fuse is on seems to be the main wire that is carring all the load (current not voltage) to the main-"buss".

As stated by someone else, it is questionable if the 20 amp fuse is needed by argument can be made for it or it could be placed on the battery before the contactor. Much like a fusable link on a car. I do agree the obvous, that the solinoid wire from the contactor to ground (via master switch) is of low current and less often fused.

[mike.smith]

Mike I believe we might not be reading the schematic the same way. The wire the 20A fuse is on seems to be the main wire that is carring all the load (current not voltage) to the main-"buss".

As stated by someone else, it is questionable if the 20 amp fuse is needed by argument can be made for it or it could be placed on the battery before the contactor. Much like a fusable link on a car. I do agree the obvous, that the solinoid wire from the contactor to ground (via master switch) is of low current and less often fused.

The diagram came to me after my post :-)

[Bryan Cotton]

I have an inline fuse between the positive battery terminal and the voltage regulator (to protect from over voltage),

The EarthX battery has internal circuitry for this function. It works - I had a VR fail high, and at night. Soon after I found happiness in owning a John Deere VR.

[gammaxy]

I'm not completely convinced the root cause has been identified. I don't understand the 22A and 40A currents that were measured unless those are just a measurement anomaly/calibration/sensor error that was also seen on other flights and only noted this time when the fuse failed.

I'm also not sure how the butt splices would have caused the fuse to melt. Unless I'm not interpreting the picture of the melted fuse correctly, I think the butt splices would have been inches away from the fuse holder where any heat they were generating would not have melted the fuse. What I can believe is that the fuse blade or socket wasn't making good contact and heated up to the point that the fuse melted despite not exceeding the 20A rating of the fuse. I'm uncertain how this all fits with the high measured current--high current should have blown the fuse without melting it, unless the high current was due to the charging circuit.

Also, I suspect this is just an error from being upside-down under the instrument panel, but the primary Aerovee ignition is independent of the electrical system and should not be connected to that fuse as drawn. The ignition generates its own power from the flywheel magnets and a circuit completed to disable it from firing.

[BRS]

Back on topic, thanks Chris!
I'm looking forward to learning what caused the high current as well.

[daleandee]

I'm not completely convinced the root cause has been identified.

I'm also not sure how the butt splices would have caused the fuse to melt. Unless I'm not interpreting the picture of the melted fuse correctly,

I agree and also believe that the cause hasn't been found but I have witnessed a similar situation when a connection is corrupted and resistance occurs and that over time heat will build up and cause items to melt. Usually this will cause higher voltages from the regulator but that will depend on where in the system the high resistance occurs.

I do have a 30 amp fuse FWF for the power coming out of my 20 Amp Dynamo used on the Corvair engine. It has never blown. I also have an over voltage module that shuts down (by bias) the alternator. I have a fuse in that line (inside) and not a breaker. Even using a breaker it's likely not something I would reset in flight.

I'm extremely afraid of an inflight fire so I tried to so everything possible to prevent any issues ...

FWIW

Dale
3.0 Corvair/Tailwheel