VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > Main > Safety
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 04-25-2019, 06:58 PM
Paul 5r4 Paul 5r4 is offline
 
Join Date: Oct 2006
Location: Foley, Al
Posts: 630
Default

This thread has me thinking. I'm planning dual batteries with single alternator when/if I upgrade to full IFR. My question is this. With dual batteries and each one with it's own contactor that then join up next at the starter solenoid.... if one or the other contacter failed, how would you know? Seems everything would keep right on purring along. If the OTHER contactor or battery failed it would then become obvious.
__________________
Paul Gray
Foley, Alabama
N729PG..... 500+ hrs
RV 7A, Lycoming 0 320 D1A, Sensenich FP propeller
pilotforfun2001@yahoo.com
VAF supporter $$$
Reply With Quote
  #22  
Old 04-25-2019, 07:47 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,251
Default

Quote:
Originally Posted by Paul 5r4 View Post
This thread has me thinking. I'm planning dual batteries with single alternator when/if I upgrade to full IFR. My question is this. With dual batteries and each one with it's own contactor that then join up next at the starter solenoid.... if one or the other contacter failed, how would you know? Seems everything would keep right on purring along. If the OTHER contactor or battery failed it would then become obvious.
If one of the master solenoids failed in flight, and you took the step to have voltage monitored from each battery on your EMS, the battery with the failed master would be disconnected from the alternator. This will become evident with that battery voltage dropping from the normal alternator output voltage. This assumes you are not cross connecting the batteries in some other way - which I strongly recommend not doing as this could create a path for one fault to take out both batteries. This leads to powering your panel via stand alone relays connected to each battery instead of a common buss off the master solenoids. I have only non-vital loads off this common buss - like pitot heat, landing lights, nav/strobes, starter circuit and such.

Carl
Reply With Quote
  #23  
Old 04-30-2019, 12:30 PM
kaa kaa is offline
 
Join Date: Dec 2013
Location: Boulder, CO
Posts: 137
Default

Thanks everyone for comments. Looks like I'll have enough capacity of the backup alternator to merge both buses. I also realized that I already have an essentially backup contactor - right now it's used as a contactor for GPU connection. My plan now is to use it as a redundant master connector by connecting battery to it and wiring a switch to turn it on from the cockpit. This way I can avoid having an essential bus and high current switch in the cockpit. I haven't seen this arrangement before though, any thoughts on why it may not work?

Schematics is here: https://drive.google.com/uc?export=v...Zc790CtxwnM7HR
__________________
Konstantin Azarov
RV-7
Reply With Quote
  #24  
Old 04-30-2019, 01:02 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,251
Default

Konstantin,

Your power distribution scheme achieves two things over a standard design:
- Mitigates the loss of alternator risk
- Mitigates the loss of a single master solenoid risk

It still leaves the less likely, but more severe outcome risks. Look at a fault on the main buss - your immediate action will be to open the master solenoid, but the fault will reappear when you shut the second solenoid. You are left with no panel. Another example using your specific design is a high resistance contact on the battery side of the (left) master. You now have no path to power your main buss.

If you insist on a single battery design, recommend you take the step of powering your panel via two avionics relays or switches to the battery, half of the panel on each. That way a fault on one avionics buss will not take down the other (as in EFIS #1, COMM #1, NAV #1 on one buss, EFIS #2, COMM #2 and NAV #2 on the other buss). Doing so you can eliminate the second master solenoid. Such 30amp relays are cheap.

Keep all your non-IFR critical loads on the main buss from the now single master.

Carl
Reply With Quote
  #25  
Old 04-30-2019, 01:17 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,888
Default

I get the desire to have redundant redundancy, but how far should it be taken? Assuming proper downstream circuit protection (fuses/CBs on the bus), what fault could take down an entire bus? It feels like we're getting into the realm of carrying a spare wing spar....
Reply With Quote
  #26  
Old 04-30-2019, 01:26 PM
kaa kaa is offline
 
Join Date: Dec 2013
Location: Boulder, CO
Posts: 137
Default

Thanks.

What kind of bus fault are we talking about here? The only thing I can think of is that the main power wire from the master solenoid to the bus fails somehow, or the fuse block fails. How likely is that? These are all beefy wires and bolted connections.

I'll also have a battery in the D5, btw.
__________________
Konstantin Azarov
RV-7
Reply With Quote
  #27  
Old 04-30-2019, 03:17 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,251
Default

What can take down a single main buss?

- The feed wire to the common buss fatigues off at one of the connections.
- A high resistance common contact in the buss supply line, or a high resistance contact that ends up melting, or arcs shut. The latter happened to a neighbor?s Mooney gear motor resulting in a gear up landing after flying off an hour of fuel over the Everglades, in the dark with a dark panel. Luckily the cell phone worked to clear the runway for the belly landing.
- The 1960 approach of using a bare copper bar to tie in all the circuit breakers - then you find the screw that you lost behind the panel or that vibrated out of something during turbulence and it will of course short out the nice bare copper bar to the panel (ground). The smoke coming from behind the panel will be the tip off to open the master solenoid.

Point - I do not trust any single power or ground connection, be it a master solenoid or master solenoid terminals, either battery terminal or a feed wire to a buss. I offer these are low probability risks, but they result in severe consequences. Considering is it simple to avoid these and other single failure pitfalls I ask why not?

And the kicker - most people have dual everything these days in the panel. Why not dual and separate power to each side so that the worst case is you loose half the panel? This can be done with just a little wire and a couple of $5 relays.

Note - no extra wing spar required or desired.

Carl
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 03:27 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.