Interesting day today, lots of smoke in the cockpit!

[EXflyer]

I was an aircraft mechanic for several years before going into auto/truck repair. That short cable to ever what one uses as a disconnect can cause problems. The shorter the better would be my rule and many installations I have seen over the years, yes home built and owner repaired certified AC also have been very bad and have caused problems have seen autos burned to the ground because of it. One of the worst was the fellow on here who connected his starter cable to ground next to the starter. A switch can be welded shut but have never seen any type of solenoid do the same. Just my FYI as I think those who came before us on how aircraft things like this should be handled knew quite well what they were doing.

[KeithB]

I got to our hanger not long after the smoke event occurred and saw the damage. It's was an eye opener.

I've been thinking about my wiring and decided to add an in-line fuse from the aux battery (4Ah EarthX) that is mounted on my firewall. Even though I have a fuse in the cabin, there is probably 2 feet of unprotected wire between the battery and the fuse.

I'm going to add another fuse forward of the firewall just a few inches away from the battery terminal.

I similarly got thinking about my wiring. I have a single wire from the battery to an essential bus switch, bypassing the master relay. That wire is going to get a fuse link on the firewall side by the battery.

Thanks, Walt, for passing on an important lesson.

[rightrudder]

Related thought...make sure there's a rubber boot on the positive battery terminal. Without one, if you drop a wrench when, say, removing the cap from the brake fluid reservoir (directly above battery on some RVs), it could instantly short out against the firewall. Not much space between the two.

[airguy]

It's the little things that can get you, too. I am guilty of releasing some of the magic smoke myself, from some wire that I really never thought about...

I ordered an Allan Nimmo cowl flap device for my 9A to control high oil temps during hard climbs and installed it, and it worked great (and still does). When I put it in I figured the wire itself would serve as a pretty good fusible link and declined to install a fuse inline for the supply power as the instructions dictate. Fast forward about 150 hours, and one day while working on an unrelated item in my panel I buttoned it back up and flipped on the master, and was amazed at the quantity of smoke coming from behind it.

Come to find out, after shutting everything down and inventing some new vocabulary, all I'd done was smoke about 3 feet of the 28-guage wire for the cowl flap - it attaches to power/ground and has some mating female/male pins to extended wiring for longer runs - but the male pins are on the power/ground side of the connection rather than the load side. The result is that under the panel you can inadvertently tug on wires while working on other items under there and these can easily disconnect at the extension point - which leaves one hot pin and one ground pin exposed - and the hot pin grounded against my 430W case. When I flipped the master, the magic smoke escaped.

I called AntiSplat Aero, and they sent me new wiring at no cost - which was not expected nor asked for, and for which I'm grateful - but I also mentioned to them the problem and the cause and recommended they reverse the pin location. They responded that this was supplied by a third party and they don't have control of that - but I do, and I changed it on my airplane as well as adding a fuse.

Be careful up there.

[Aluminum]

Originally Posted by EXflyer

A switch can be welded shut but have never seen any type of solenoid do the same.

A quick googling for "stuck starter solenoid" shows how ridiculous this statement is. Several such events have been described here at VAF over the years. Battery switches, on the other hand, are designed to reliably break a thousand amps using sliding contacts. Since they never have to do that in normal operation, the one time you really need them to in a choking panic they are highly unlikely to fail you.

Originally Posted by EXflyer

Just my FYI as I think those who came before us on how aircraft things like this should be handled knew quite well what they were doing.

If that were true our experimentals would not be outnumbering "certified" designs today. Such attitude almost ended the U.S. auto industry in the 1980s.

[gasman]

Originally Posted by Aluminum

A quick googling for "stuck starter solenoid" shows how ridiculous this statement is. Several such events have been described here at VAF over the years. Battery switches, on the other hand, are designed to reliably break a thousand amps using sliding contacts. Since they never have to do that in normal operation, the one time you really need them to in a choking panic they are highly unlikely to fail you.

Just looking at your switch and the key it uses, it looks like a press contact switch. As the key is turned, a tab on the key rides on a cam that forces the contacts closed. A spring is expected to force the contacts apart when the key is turned back.

An easy test..... push the key in without turning and see if contact is made. If it is truly a sliding contact, then you do have a reliable disconnect switch.

[160kt]

The Blue Sea switch that Dan posted a link to seems to be a great idea to me.

There are remote switches that can be mounted at the battery in the engine compartment and mechanically operated from the cockpit. IIRC there are some examples of this in the certified world albeit in very old airplane and more likely a starter switch. Consider this switch that comes with a T-handle and an 18” linkage:
https://www.summitracing.com/parts/sum-830051

As a mechanic it is ingrained that the first thing to do before working on electrical is to disconnect the battery. Although the design may have been faulty the destruction caused was not the designs fault. It was the fault of the one who did not follow this well known procedure. I hope original poster is not charging the owner of the damaged plane for the damages he caused.

[Aluminum]

Originally Posted by gasman

Just looking at your switch and the key it uses, it looks like a press contact switch. As the key is turned, a tab on the key rides on a cam that forces the contacts closed. A spring is expected to force the contacts apart when the key is turned back.

An easy test..... push the key in without turning and see if contact is made. If it is truly a sliding contact, then you do have a reliable disconnect switch.

H'm, now that you've planted the seeds of doubt, I think I'll buy another switch and cut it apart to study.

I can confirm that pushing the key in does not make contact.

FWIW, this design didn't elicit any comments from the airworthiness inspector (who asked that I put a rubber boot over the negative battery terminal as well, go figure). It was also endorsed by a high time pilot and homebuilder who is a retired professional electrician.

[160kt]

You might find out how the switch is made without buying another one by contacting Blue Sea Systems technical support
https://www.bluesea.com/products/600..._Key_-_Red/FAQ

Click on Frequently Asked questions then on Contact Technical Support

The ratings of the switch are very good. It is ignition and water proof. The key design is for locking when removed and the amp rating and surge rating are such that one would think it is a properly designed battery switch.

[rv7charlie]

For those that think using a high current master switch (without master contactor) will bring down the wrath of some deity like the FAA, here you go:

http://www.vintagepiper.co.uk/vpac-h...gram-for-pa22/

IIRC, some of those old designs even had the battery in the back, and a 'hot' feeder all the way to the panel mounted master switch. Obviously a terrible idea, but blessed by the FAA.

Charlie