Avionics master solenoid
 

I am going to power the avionics buss bar via a solenoid which will be activated with a switch. My plan is to only protect the switch as this will have a wire run from the main bus to the switch to the solenoid.
The solenoid will be next to the main feed[live bar which is fed by the main solenoid]
Therefore there is no wire run which is unprotected. My problem is,do I need to protect the solenoid ? What can really go wrong?
My thought is that at worst the solenoid stops operating or welds shut.
Both scenarios dont pose a serious flight risk for vfr flight.

My question is ; Have I missed something?

I have ordered a Aeroelectric book but still dont have it.

Avionics master switch
 

After reading the aeroelectric connection, you may change your mind about having an avionics master switch. Bob makes a pretty good case as to why they are a bad idea.

Do the avionics really draw enough juice to warrant a solenoid? Couldn't a switch handle the job?

Steve Zicree

If you must use a relay for your avionics master, switch the ground not the power and you won't need a fuse in the switch line.

I have to agree. Before reading Nuckolls' book, I always thought the avionics master switch was a really bad idea and shouldn't really be nescessary. After reading his book, I'm absolutely convinced.

Even if you want one, though (it's not the worst thing in the world :), I wouldn't use a solenoid. All it would do is add a few more possible points of failure, a current draw that doesn't need to be there and more weight.

If you really really want to use a traditional bus architecture and an avionics master, you may want to consider just using a quality Klixon breaker. You can switch it if you want to, and later on if you decide for yourself that an avionics master is a bad idea, just shove it in and forget about it.

Nuckolls' "essential bus" concept is better though, IMHO.

-John

Avonics master
 

I installed an avionics master switch on my C-172 after I fried a brand new Narco radio. I turned off everything I thought at shut down, except the radio. When I started back up the radio blew. Narco said that this happens often and suggested a master switch. The master is easier for me because I only have to remember turn off one switch.

My .02

Jeff

Well the word acording to ....
 

Bob is very convincing. He has great ideas and is right, omitting the master switch has merit, BUT many current avionics manufacture's and many very experienced avionics shops that actually install, maintain, repair, warranty and design new factory aircraft installations from small to large, recommend a master switch.

Bob claims avionics masters are old school and not needed with new avionics, which are internally protected. He assumes all radios have this protection. THEY DO NOT. He states they should or be shot for not having it. Well that's fine but many GA avionics do not have power filters. Many NEW avionics are NOT immune to voltage spikes. If it's built to Mil-Std DO160 it is. Radios like Icoms A200 or even the TSO version, do not have spike protection. Don't assume anyone is correct, check it, get another opinion. Many (experimental) EFIS systems I assume are protected, so I checked the Dynon EFIS D10 (which I have). It is protected. However.......

I do not want my radios or EFIS on during start, old school not. I also have a Icom A200 and an older transponder (also not protected). The cost and effort of a switch or two switches in parallel for redundancy is small. Last I love turning all radios on/off with one switch. Do what Bob says but NOT everything. I know Bob makes it sound like there is NO other choice but the one he promotes, when it's a matter of preference or opinion many times. Bob clamps down on a few facts, makes an assumption or two and makes it doctrine. Bottom line he is not correct, having (some) radios on during start and shut down can be bad, even new ones. If you want to "exercise" every individual radio switch each time you start and stop, OK. I like the master switch. :D

Pick the best ideas and make your own mind up. If you want a master (and I do) than put one in. Either way it is not super critical. George

PS I agree the less relays or solenoids the better. An avionics switch can be handled with it without a relay. However some folks are adding lots of avionics.

I hope I didn't come off like I was preaching. OF COURSE everything I say should be prefaced with a "IMHO" whether or not I explicitly say it or not :)

I wouldn't recommend starting an engine with avionics on either, but honestly it really makes no difference to me if the boxes can "take it" or not. I just shut everything off using the knobs before I hit the avionics master (just like I bring the mixture back to lean, kill the mags, secure the seatbelts etc). That's what all my checklists and instructors have always told me to do, anyhow, so I just do it automatically now. That being the case, the avionics master for me serves no purpose other than to add one more thing that can break to the mix. YMMV.

If you have parallel switches, that just adds one more thing to check during your preflight (you need to switch them one at a time to make sure they both work or one may be failed and you wouldn't know it). I guess you could add indicator lights, but now you have more complexity and yet another thing that can break.

That's why I suggested using a Klixon breaker (I know there are others, but I've used Klixons in the past and am comfortable recommending them). Incidentally, I don't believe this is something that Nuckolls' recommends at all, in case you're wondering (someone can correct me here), but from a design standpoint I believe it makes the most sense and is how I intend to wire my panel. It needs to be fused anyway, so why not just use a switchable breaker and make the agonizing over actually switching it a non-design issue?

just my usual ever-so-humble opinion :D

Absolutely
 

Not at all J, and also very good observations. I guess the worry of a switch (avionics master) not working after it is on is small, provide a good quality switch. Again to each his own and there is no right wrong at all. Cheers George
http://www.avweb.com/news/avionics/182015-1.html

Thanks for the reply guys, but still no one has told me if the solenoid must be protected.
Yes a combination c/b switch is a good idea . Its just that I am using really nice lighted rocker switches and would like to use one of these instead.

As far as Bobs opinion ,I have no idea what he says as I dont have his book yet.However despite of all the facts etc, I want a avionics master .Just a personal thing.
The things on the master will be :- AOA ,Trutrak ,GRT efis ,Kmd150 ,sl40 com,
gtx327xponder.
The ACS2005 engine monitor will be on the main buss. This I need on startup.