Essential Bus

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11-22-2014, 09:31 AM
henrysamson

Essential Bus

OK, here is a Burning Man story from my flight out to the desert this summer.

While at Burning Man I gift rides over the city. I also gift rides up to some hot springs about 30 miles north of the city. It gets pretty hot during the day and I am usually done flying by early afternoon and cover my panel with an aluminized mylar "space blanket" to keep the electronics cooler. But the heat can take its toll.

The morning before the event was over I was giving rides over the city. On what turned out to be my last ride, I had just taken off from the dry lake bed and was about 400ft AGL when there was a loud explosion and the cabin filled with smoke. The smoke was obviously coming from under the panel and at the time I thought it was perhaps the filter capacitor. The low voltage warning light came on also (wired into the Rotax voltage regulator/rectifier). I declared and emergency, flew the pattern at 400 ft and was back on the ground in about two or three minutes. We found my passenger another airplane and pilot to take her on a ride. I parked my plane and took the cowlings off.

It was indeed the filter capacitor. It had exploded and apparently took the voltage regulator with it. So, what to do? When I built my airplane I put what I considered to be essential items on a separate bus that is diode blocked from the main bus so power can flow from the main to the essential but not the other way. When activated, the essential bus is separately and directly powered from a switch and does not activate a solenoid. So, all of the power goes to the essential accessories and none to energize a solenoid. There are some diagrams of the concept in the Aero Electro Connection book.

So, what did I need to fly home? My engine instruments, my trim and a few indicator leds. Everything else was not needed (I carry a full set of paper charts). Both items are on the essential bus. Other items I could turn on as needed that are on the bus are the radio, transponder, efis, and gps. The turn coordinator is also on the bus but I did not need that so I unplugged the connector from the back. I had a full battery and perhaps a little over an amp of power was needed to fly with the trim and engine instruments on. I also have a solar panel mounted under the turtle deck. It can be seen here:

http://www.flyinglowandslow.com/blog...-storm-andrea/

I tested everything that afternoon and the battery was actually charging with the trim, instruments, and gps on when in full sun. I realized that if I ran the battery too low I would not be able to start the engine and would need to let it sit in the sun for a few hours or find a battery charger.

I took off the next morning a couple of hours after sunrise and the voltages stayed in the 12.5-12.6 range on the first leg so I was confident the battery would be able to start the engine. After refueling and having some lunch, with the solar panel in full sun the entire time, the engine did indeed start. Also, the low voltage light did not come on! The voltages were over 13 at idle so the regulator was now working. I'm not sure why but it has worked since then. If it recovered during the first leg I would not have known as the regular master switch was not on. I had to turn it on to start the engine.

So, any of you who are working on your panel design may want to consider having an isolated bus for essential items. It does complicate the design but the essential bus plus the solar panel got me started on my way home and I'm sure I could have made the entire 1400 miles that way if need be although I would not have flown as late in the afternoon as I was able to do with the regulator working. If you look through my blog you can see some panel pictures that show the circuit breakers in two groups. The "B" bus is the essential bus. The new filter capacitor is mounted forward of the firewall!

When I designed my panel I never contemplated using the bus as I did when leaving Burning Man. I was concerned with having the solenoid powering the main bus failing while in flight and being left with nothing. But after landing and taking stock of the situation I realized that it allowed flying the aircraft in a mode that uses very little power. Even if I did not have a solar panel it still would have allowed me to fly to a real airport for maintenance.

Hank
11-22-2014, 09:44 AM
Danzer1

Re: Essential Bus

Hank,

Good info for all. Can you post a link to the solar panels you used?

Greg
11-22-2014, 10:23 AM
Av8r_Sed

Re: Essential Bus

Any idea on why the cap blew up? What was its voltage rating, value, type and how old was it? I've got an aluminum electrolytic in mine and I'm not fond of in-flight surprise explosions.
11-22-2014, 12:17 PM
Dave S

Re: Essential Bus

I have come to the conclusion that if a person shares a cockpit with an electrolytic capacitor for enough hours/years, the opportunity of experiencing this kind of excitement increases.

I have had friends with normally certificated aircraft as well as experimentals have one go - always the same - a real good pop, smoke, stink etc that indicates it is well to land soon. Fortunately none of the incidents resulted in fire although the effects were certainly indicative of fire.

In my meager understanding of electrolytic capacitors, I hear a few things can cause one to pop including 1) reversed polarity (including a diode failure or short in the case of an alternator used in a DC charging system - which I understand can expose the cap to alternating current) 2) Overheating - which may be an effect of some other problem, 3) Physically decayed or corroded internally - that can happen with the liquid in the mat over time in a cap; and, 4) overloading (which likely results in overheating or internal shorting if the voltage is too high). Don't know the validity of the source; but, there was some scuttlebut about capacitors out of certain companies in Taiwan in the late 1990's and early 2000's with excessive failure rates.

Engineering options into an aircraft electrical system is certainly a route that can get a person out of the back country if something like this happens. I thought about that since most of the problems I experienced with normally certificated aircraft (or at least the ones I could afford to rent) involved charging system/electrical failures and I kept thinking nobody is going to flip start a rotax in the outback.

We took a slightly different route and used two complete and separate electrical systems - using the on board Rotax charging system for one and the optional auxillary alternator for the other - two busses, two alternators, two batteries (So I could be criticized for making the aircraft excessively heavy:eek:) two masters and a cross tie plus alternator breakers that can be pulled to disconnect if that becomes necessary - Normal operation - one system feeds the low draw equipment and the other system feeds the high draw equipment (the high draw equipment was the reason I wanted the aux alternator in the first place). A person can start and run the engine off either side or, use the cross tie to run both busses off either system with the other alternator & battery disconnected. The only real limit is no night flying if the low output rotax alternator is all that is left because it won't keep the radios and the lights going at the same time. (I know....there are LEDs available now, but that wasn't in equation when the plane was built.:o)

Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive
11-22-2014, 03:13 PM
henrysamson

Re: Essential Bus

Quote:

Originally Posted by Dave S

The only real limit is no night flying if the low output rotax alternator is all that is left because it won't keep the radios and the lights going at the same time. (I know....there are LEDs available now, but that wasn't in equation when the plane was built.:o)

Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive

I was looking at the same issue when I was building my airplane. I bought the lighting with the kit in '97. In the final months of construction I just replaced all of the bulbs with LEDS. Aircraft Spruce has the LED replacements for my Whelen wingtip nav and strobe light combo. I did not have to do anything but unplug the old bulbs and insert the LEDS. The only non LED lighting are the post lights on the panel but the current use is minimal and I wanted to be able to keep my low tech dimmer so they are original Now night flying is no issue as far as power is concerned. Actually, I keep all of the exterior lights on night and day for visibility.
11-22-2014, 06:07 PM
henrysamson

Re: Essential Bus

Quote:

Originally Posted by Danzer1

Hank,

Good info for all. Can you post a link to the solar panels you used?

Greg

http://www.aircraftspruce.com/catalo...clickkey=13768

The larger one. I have it mounted in a manner that makes it very easy to remove. There is extra cable at the panel so I can, if needed remove the turtle deck, remove the panel and place it a few feet away, outside the aircraft and pointed directly at the sun. Never have had to use this feature although if I was really stuck in a remote location with a dead battery I would. It is covered by the Kitfox Aircraft cover which I usually put on the aircraft when parked overnight on an airport ramp. Which is too bad but I like to have the plane covered.

The output from the solar regulator is connected to the battery through a 15 amp line fuse using a molex plug. I can disconnect the solar regulator and have adapted a battery charger so I can plug it in at the same location. Makes it easy to give the battery a couple of hours of charge if I have not flown it for a while. I don't have to remove the cowlings and the battery box cover. The fuse is to avoid problems if there is a short.

I can also plug the solar panel directly into a usb adapter that allows me to charge my tablet computer or phone In the desert, after flying I often plug my tablet in to let it charge for the afternoon.

Quote:

Originally Posted by Av8r_Sed

Any idea on why the cap blew up? What was its voltage rating, value, type and how old was it? I've got an aluminum electrolytic in mine and I'm not fond of in-flight surprise explosions.

The capacitor was provided with my firewall forward from Skystar back in '03 and flying since A/C completion in May '13. I still have it and will take a look next time I am at the airport and give the specifics and take a picture. The new one is the one sold by ACS and is much larger. I think that perhaps the extreme heat in the desert had something to do with it. It is pretty brutal. I also flew trough a lot of rain on the way there and perhaps some moisture made its way in although I had no other problems. Everything was working fine until it blew. I have an over voltage "crowbar" that would take the alternator offline on the DC side if the voltages go over about 16.3 volts.

Another pilot at the burn is an A&P and an authorized Rotax mechanic. He said that some of the newer light sport aircraft that he works on have dispensed with the capacitor completely. Perhaps the regulator/rectifier is not as sensitive as the earlier ones were reported to be. Also, I did use my radio, intercom and music after the regulator came back online and without the capacitor and there was no audio noise which is one of the reasons for having the capacitor in the first place. Along with protecting the regulator/rectifier.