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  #1  
Old 01-29-2015, 01:47 PM
DaleB's Avatar
DaleB DaleB is offline
 
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,331
Default What do you think of this idea?

I really want a keyed ignition/start switch that will disable all the bits needed to start the plane, but I'm not wild about paying over a hundred bucks for the usual mag/start switch, which has features I simply don't need. I plan to use P-mags, so I have a separate plan for the power and P-lead wires.

So I'm thinking this may be a solution. A marine type 3-position keyswitch (OFF/IGN/START) controls the main battery contactor and functions as a MASTER switch. The main bus from the master contactor supplies power via fuse blocks (or breakers if you prefer) to everything else. The starter contactor is controlled by the START position on the keyswitch.

There would be no traditional MASTER rocker or toggle switch. Just an ALTERNATOR switch. In case of an in-flight electrical emergency (like a fire) you could turn the keyswitch off, dropping power to everything -- but the P-mags would still fire under their own power until switched off.



Anyone see a problem with doing it this way? Anything I missed or got horribly wrong? This is by no means complete or finished, I am many moons out from doing the panel and FWF wiring. Just hashing out how I want things to work. I got a lot of ideas from the Nuckolls book, but I see those diagrams as a starting point rather than a final solution. This looks awfully simple, but I can't see that I'm giving up anything. And for the record -- the mission is day VFR (maybe day/night VFR depending on rules changes), and I'll have backup instrumentation for airspeed, altitude, and heading that don't rely on ship's power.

I'm open to comments and suggestions.
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Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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  #2  
Old 01-29-2015, 05:53 PM
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JohnInReno JohnInReno is offline
 
Join Date: Jun 2005
Location: Prescott Valley/Chandler AZ
Posts: 352
Default Hidden APRS

I used a marine type 3-position keyswitch (OFF/IGN/START) with a traditional master. The IGN position controls the APRS transmitter.
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  #3  
Old 01-29-2015, 06:44 PM
PaigeHoffart PaigeHoffart is offline
 
Join Date: Jun 2005
Posts: 375
Default

Quote:
Originally Posted by JohnInReno View Post
I used a marine type 3-position keyswitch (OFF/IGN/START) with a traditional master. The IGN position controls the APRS transmitter.
Not much of a secret now
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  #4  
Old 01-29-2015, 07:03 PM
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Snowflake Snowflake is offline
 
Join Date: Oct 2009
Location: Sidney, BC, Canada
Posts: 4,282
Default

Another option:

Separate toggles for each mag, momentary toggle or pushbutton for start, and either one or two toggles for Master and Alternator(as fits your opinion of whether they need to be separate or not). If you're concerned about security or safety when parked, a hidden (behind panel somewhere) "master enable" switch could kill everything. And: no need for another key on your keychain.
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  #5  
Old 01-29-2015, 07:37 PM
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DaleB DaleB is offline
 
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
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Default

Quote:
Originally Posted by Snowflake View Post
Another option:

Separate toggles for each mag, momentary toggle or pushbutton for start, and either one or two toggles for Master and Alternator(as fits your opinion of whether they need to be separate or not). If you're concerned about security or safety when parked, a hidden (behind panel somewhere) "master enable" switch could kill everything. And: no need for another key on your keychain.
Thanks for the comments. Originally I had the two toggles for the mags (as it is now), one for master/alt, and a start button. I really don't mind having a key, and it would live on its own key ring with the hangar key - which worked perfectly for me when I was in a flying club. It wouldn't be more of a hassle than groping around for a hidden switch.

I'm not terribly concerned about security, since I haven't heard anything about a rash of RV thefts, but it's a factor. I"m more thinking about safety when parked in a spot where I may not be with it constantly. I know some guys don't bother with a keyed switch, but if something did happen - either safety or security related - I'd hate to spend time explaining why I thought something as basic as a keyed ignition switch was unnecessary.

Another spin I had on this idea was to use a 3-position toggle OFF/BATT/ALT master switch, then put the engine related bits (boost pump, mag power and alternator field) on a separate bus with the keyswitch controlling a 30A relay for that stuff. That way you could have the EFIS and cabin lights on without needing the key, but would still need the key to do anything dangerous.

And John - I like that idea! I honestly haven't decided whether to bother with APRS or not. Weird thing for a ham, I know, especially considering what's financing my build.
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Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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  #6  
Old 01-29-2015, 07:46 PM
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Ron RV8 Ron RV8 is offline
 
Join Date: Nov 2010
Location: Okanagan Valley BC, Canada
Posts: 500
Default

I used a marine ignition (Sea-Doo) switch as master, a push button start switch, and toggles for the rest.

The key ring also holds the key for the forward baggage so there less chance of taking off with the baggage door unlocked.

I make it a policy to never take the keys out of the baggage door unless it's locked...

The other plus is that the plane keys quick connect to my car key ring, making it less likely to go home and leave the master on.
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Last edited by Ron RV8 : 01-29-2015 at 07:48 PM.
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  #7  
Old 01-30-2015, 08:41 AM
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vlittle vlittle is offline
 
Join Date: Jan 2005
Location: Victoria, Canada
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Default

There be dragons here.

Your design is a potential fire hazard. You are using unprotected thin gauge 12V wiring to switch on the Master contactor and Starter contactor.

This could be overcome, but it is really an architectural problem. Conventional practices switch the ground wire to the Master contactor coil (not needing protection) and the starter contactor coil is fused before running through a starter switch.

The marine starter switch will not give you this directly. You could use it to switch the ground to the master contactor, then use a a relay connected to the other pole to switch a protected +12V to the starter contactor.

Something like this: http://www.vx-aviation.com/sprocket/...ics/MASTER.pdf, but with the marine switch controlling the master contactor and the starter contactor rather than the toggle/pushbutton combo I have shown. Both functions switch to ground, which is what you want.

My example is a bit complicated because I have a starter interlock function, but just ignore it for your application.
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Last edited by vlittle : 02-01-2015 at 07:55 AM.
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  #8  
Old 01-30-2015, 09:12 AM
krw5927 krw5927 is offline
 
Join Date: Aug 2010
Location: Wichita, KS
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Default

Quote:
Originally Posted by vlittle View Post
There be dragons here.

You design is a potential fire hazard. You are using unprotected thin gauge 12V wiring to switch on the Master contactor and Starter contactor.

This could be overcome, but it is really an architectural problem. Conventional practices switch the ground wire to the Master contactor coil (not needing protection) and the starter contactor coil is fused before running through a starter switch.

The marine starter switch will not give you this directly. You could use it to switch the ground to the master contactor, then use a a relay connected to the other pole to switch a protected +12V to the starter contactor.

Something like this: http://www.vx-aviation.com/sprocket/...ics/MASTER.pdf, but with the marine switch controlling the master contactor and the starter contactor rather than the toggle/pushbutton combo I have shown. Both functions switch to ground, which is what you want.

My example is a bit complicated because I have a starter interlock function, but just ignore it for your application.
Good point, Vern, but wouldn't a simple in-line fuse straight off the battery on the single wire going inside the cabin to the switch provide the necessary protection? Say a 5A fuse (which should be more than enough power to activate both contactors at once) and 18ga wire to the switch and both contactors?
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  #9  
Old 01-30-2015, 09:53 AM
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DaleB DaleB is offline
 
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
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Default

Quote:
Originally Posted by vlittle View Post
There be dragons here.
Good points, thanks for pointing them out. I revised the diagram.
  • START relay coil is now on a fuse.
  • ALT switch allows starting only with alternator field switched off
  • MASTER coil supply is 22 AWG (could use an in-line fuse just as easily)
  • Master/Start switch now switches to ground
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Dale

Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)

Last edited by DaleB : 01-30-2015 at 09:56 AM.
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  #10  
Old 01-30-2015, 09:54 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,237
Default

A momentary key switch can be used only for the starter. Here are a couple of examples:
Kigikey Keylock Switch
Mouser Keylock Switch
The Mouser switch is actually SPDT, ON (ON) per the manufacturer's datasheet. The Digikey switch has the same configuration.
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