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  #161  
Old 05-22-2018, 09:53 AM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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Originally Posted by Pukauma View Post
Much cleaner diagram(s), Dan. I have been considering running an AWG 6 "fat wire" to the switches for the EFI bus. According to Nuckolls he feels it does not require fusing. Eliminates another component and connections.

http://www.vansairforce.com/communit...uckolls&page=2

Any complaints with that?
Can I take a stab at that? I think the other responses were good, but I don't think the basic philosophy is clear yet. The following is my interpretation of what Nuckolls is saying.

It's not a universal truth that 'fat' wires don't need fusing (protecting). If it's a very short run (say, 6" or so), the danger to the wire is so low that you can make a 'sure bet' that you can get away with no protection. But if it's an extended run, there are more opportunities for faults. Now there are various ways to protect, and a contactor (relay) is one legit way to protect. It just requires a human in the loop to trigger the protection. That's what we do with a battery & master contactor in the back, and the fat feeder running to the front of the plane.

For my E-dependent engine bus, I wanted the engine to be as independent from the rest of the plane *as possible*, as we're accustomed to with a magneto ignition. My power paths:

battery>fusible link >fat wire>high current switch>engine bus<>high current bus tie switch<>main a/c bus<fat wire<master contactor<battery.

I'm contemplating a high current diode wired across the bus tie switch, pointing toward the engine bus. This will allow uninterrupted power to the engine bus if the engine power switch fails. If the master contactor fails, the airframe would go dark (EFIS has its own battery backup) until the bus tie switch is closed.

The bus tie switch provides one-switch redundant power feed to both the engine bus (from the main bus), and to the main bus (from the engine bus).

This is a two identical alternators, single battery system.

FWIW...

Charlie
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  #162  
Old 05-22-2018, 12:29 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by rv7charlie View Post
SNIP...

This is a two identical alternators, single battery system.

FWIW...

Charlie
I offer that assuming you have not abused it, the battery(s) is the most reliable element of your electrical power system. That reliability however ends at the battery terminals.

I also offer that the second alternator in a single battery system protects from only one risk, the loss of the primary alternator. While this may be the single most likely risk, it is not the majority of risk. Twin airplanes with two alternators have lost all electrical power (both engines still running and both alternators still working). There are lessons to be learned from these failures.

This translates to designs with two batteries and a single alternator provide opportunity for a far more robust power distribution design when compared to two alternators and a single battery designs. Add a B&C 20 amp standby alternator on the vacuum pad to take the design to the next level. Just be very cautious on how elements are connected and buss faults isolated.

Carl
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  #163  
Old 05-22-2018, 01:16 PM
Pukauma Pukauma is offline
 
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Location: West Covina, Ca
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So, given all the responses......(very informative)

Ross....adapting Charlie's power path (using two batteries):

battery1>fuse>fat wire>high current switch>engine bus<>high current switch<fat wire<fuse<battery2.

How much would I need to rate the fuse(s) and switch(s) for an EFI system? I am thinking 30amps? (I realize the fuse protects the wire, but let's assume we go with fat wire for safety).

I think the rub here is whether the power wire to the EFI bus is switched/fused/relay controlled. Welcome any additional thoughts.
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  #164  
Old 05-22-2018, 01:30 PM
rv7charlie rv7charlie is offline
 
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No vac pad on this engine; not a Lyc. I'm also not limited by the limited capacity of a low output 'backup' alternator, so my bus systems can be simpler. (either alternator can carry the full load of the a/c.) In addition, I'm able to carry only an additional ~10 lbs of alternator instead of 15-20 lbs of extra battery, and after one alternator failure, I still have unlimited electrons instead of those left in the batteries. Fuel is still the limiting factor of any single flight, instead of battery capacity.

Your point is well taken that the area around the battery can potentially be a single point of failure. But one alternator directly feeds the battery; the other feeds the load side of the master contactor. Even if the 'battery area' develops a fault, one of the alternators will still feed the system. (With a long background in electronics, I'm not in the camp that thinks an alternator will go insane without a battery attached.)

And, as you point out, even twins with redundant everything (not just alternators) can and have gone dark. It's not hard to make the jump to bad (certified) architecture as the cause, since even operator error should have a really hard time making an entire twin go dark.

Ultimately, we have to pick our poison. I've been tempted to add a 2nd battery, but the added weight, and more importantly, the added complexity, has driven me to this compromise, rather than the 1 alt/2bat compromise, or the much higher complexity of the 2/2 system.

Charlie
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  #165  
Old 05-22-2018, 04:39 PM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by Pukauma View Post
So, given all the responses......(very informative)

Ross....adapting Charlie's power path (using two batteries):

battery1>fuse>fat wire>high current switch>engine bus<>high current switch<fat wire<fuse<battery2.

How much would I need to rate the fuse(s) and switch(s) for an EFI system? I am thinking 30amps? (I realize the fuse protects the wire, but let's assume we go with fat wire for safety).

I think the rub here is whether the power wire to the EFI bus is switched/fused/relay controlled. Welcome any additional thoughts.
My airplane uses a 30 amp ATO fuse and a 25 amp switch. If you intend to run both pumps at the same time, you should use a switch (or relay or contactor if you prefer) rated for 30 amps. The surge current for the pumps is pretty high, being driven by DC motors.

In our experience, 2 batteries and 1 alternator is preferable to 2 alternators and one battery. We see many people going 2 batteries and 2 alternators (one driven off the accessory pads) on RVs these days as they may have more room with one or more of the mags gone.

My RV10 was fitted with dual batteries and dual alternators as the airports are further apart up here than in the US.

Below is a typical RV10 installation with B&C backup alternator that more people are considering or fitting these days.

__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 420 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #166  
Old 05-22-2018, 04:58 PM
rv7charlie rv7charlie is offline
 
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Hi Ross,

I tried to detail my thought process that led me to the 2alt/1bat configuration. However, I'm not flying and you've been flying auto-style engine control for quite a while. Can you summarize or refresh my memory as to why the 1alt/2bat system is better? I know we're all trying for 'best', and while I've tried to think of all the variables, I don't doubt that I've missed a few.

Thanks,

Charlie
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  #167  
Old 05-22-2018, 06:09 PM
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rv6ejguy rv6ejguy is offline
 
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Batteries can't overvoltage and the AGM ones we've used hold a good charge for many months (designed for UPS applications). They have been completely reliable. No moving parts in a battery. They are not expensive either.

Disadvantage is more weight (AGM anyway) and the AH capacity is your limiting factor for duration compared to an alternator.

If you do lithium, you can save weight but are subject to their unique operating characteristics which might not inspire total confidence as a backup power source. The AGMs will actually fire coils and run pumps down to 9V or so. Not sure on the lithium but I know one guy who did not have such great luck with one as a backup. You'd want to test one under load and see where it signs off.

2nd alternator needs a regulator and preferably a crowbar. Starts getting expensive there.

If I was doing a -10 again, especially with a lot of glass and for IFR, I'd install 2 batteries and 2 alternators again. The pad driven alternators are pretty light for Lycs.

With one battery, if it goes wonky (say shorted cell or something like that) and you have to disconnect it, how will your alternator regulators reference voltage to control output? Should test for that too.

Test all this stuff on the ground and see what it does. You don't want to find out in a real emergency that something doesn't work the same as you thought it would- especially on a dark and stormy night IFR.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 420 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm



Last edited by rv6ejguy : 05-22-2018 at 06:16 PM.
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  #168  
Old 05-22-2018, 08:02 PM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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My 6-year-old PC680 failed open with an internal broken weld. You can read about it here:
http://www.matronics.com/forums/view...4fa1960b22b54f
At first it was an intermittent condition. The first sign of a problem happened when the throttle was closed for landing. The EFIS (no backup battery) rebooted because the Rotax alternator does not generate at idle and the battery internal weld opened up.
Like Charlie said, the alternator will not go insane without a battery. But the battery is needed to stabilize the alternator. I have conducted an experiment by disconnecting the battery while flying. Without a battery, the Rotax electrical system voltage varied plus or minus 3/4 of a volt or 1.5 volts total.
Based on this experiment, the Rotax charging system needs a battery for stability. While the electrical loads worked OK, high and low voltage alarms can be annoying. A pilot would not want that distraction while flying IFR.
Although rare, batteries can fail suddenly without warning.
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  #169  
Old 05-22-2018, 08:47 PM
rv7charlie rv7charlie is offline
 
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Hi Ross; I appreciate your thoughts.

If I were flying IFR with an E-dependent engine, I'd probably go whole hog with 2/2, as well. And it sounds like we agree on the quality/reliability of AGM batteries (and the not-yet-provens of lithium), too.

On the subject of alternator choice, I don't fear controllable IR alternators, and OV modules are very inexpensive these days. I have less than $250 in a pair including OV modules, so, less money than one pad mounted backup alt (which I don't want anyway; each of mine can support the whole plane). Alternator regulators don't look to the battery the battery for their voltage reference; otherwise, how would they know what voltage to supply a battery in some state of discharge? Any regulator will have its own internal voltage reference; typically involving a zener diode.

And believe me, I will be testing on the ground. :-)

With what I've seen so far, it really does seem to come down to an individual's comfort zone. I will continue trying to maintain an open mind if/when more more info becomes available.

Thanks again,

Charlie
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  #170  
Old 05-22-2018, 09:07 PM
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rv6ejguy rv6ejguy is offline
 
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As I always say guys, use what you want and test it well on the ground first.

Don't assume because one brand or type does something connected in one way that it will behave the same way when combined with other parts or in other ways.

It would be instructional for folks to shoot some video of their battery/ regulator/ alternator experiments and share the links.

As for the Odyssey batteries, yes we've read of a few failures here on VAF but I'm thinking there are thousands of these installed for decades now. Maybe we should start a poll and see what the real percentage failure rate might be. I got 11 years out of my first (still cranking the engine and passing the annual load test), on the 5th year with my second. Mine are FW aft, not exposed to temperatures they were not designed for and not sitting on a trickle charger like some folks seem to be doing. Look at the bottom of this chart for operating temp specs. http://www.odysseybattery.com/extrem...ery_specs.aspx

Anything can fail but I'll bet a dime that Odyssey batteries are 100X more reliable than one brand of alternator commonly fitted to RVs...

You'll only find out how smart you were at the end of 10 or 20 years of flying. Share the good and the bad experiences so we can all learn and improve.

BTW, I use a Powersonic 18 AH battery for backup. http://www.power-sonic.com/images/po.../PS12180NB.pdf
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 420 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm



Last edited by rv6ejguy : 05-22-2018 at 09:34 PM.
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