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  #11  
Old 06-10-2016, 10:41 AM
Bill Palmer Bill Palmer is offline
 
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Location: Chino Hills, CA
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Default Dual Everything

Dual Alternators (B&C 40-amp Alternator and SD-8-amp Dynamo); Dual Batteries (EarthX ETX680C's); all through an EFII Bus Manager here.
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Last edited by Bill Palmer : 06-10-2016 at 10:45 AM.
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  #12  
Old 06-10-2016, 11:11 AM
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DanH DanH is offline
 
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I think it depends on the mission.

IFR? Dual batteries, dual alternators, dual regulators.

VFR? Big battery, schottky-fed small battery for second ignition, single alternator...KIS.
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  #13  
Old 06-10-2016, 11:36 AM
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rcpaisley rcpaisley is offline
 
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Location: Upland, CA
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Default electrical system evolution

Dan's got it right,
Electrical system complexity follows a progression:
1. One batt, one alternator
2. Two batts, one alternator
3. Two batts, two alternators

One batt, two alternators is a problem. If you lose the batt, all you have left is half wave rectified AC power off the alternator - this means unhappy electronics. There needs to be a functioning battery in the system to absorb the pulses from the alternator.

Robert
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  #14  
Old 06-10-2016, 12:36 PM
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Carlos151 Carlos151 is offline
 
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Location: Lebanon, TN
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Default

60 amp main alternator, SD8 standby alternator on vacuum pad, one battery. Split Main bus and Emergency bus. Aeroelectric book has the setup in one of their diagrams. No time limit this way as with a battery.
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  #15  
Old 06-10-2016, 01:37 PM
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erich weaver erich weaver is offline
 
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Location: santa barbara, CA
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Default

Quote:
Originally Posted by rcpaisley View Post
One batt, two alternators is a problem. If you lose the batt, all you have left is half wave rectified AC power off the alternator - this means unhappy electronics. There needs to be a functioning battery in the system to absorb the pulses from the alternator.
Im not enough of an expert to argue with you here, but I consider Bob Knuckolls to be, and he would disagree with what you say above. I tend to respect his opinion.

erich
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  #16  
Old 06-10-2016, 02:34 PM
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rcpaisley rcpaisley is offline
 
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Default batts and alts

There really isn't anything to argue, that's how alternators work.
An important part of the evolving aircraft electronics systems is the evolving electrical distribution to support the new systems.

Robert
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  #17  
Old 06-10-2016, 02:56 PM
Bill Palmer Bill Palmer is offline
 
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Location: Chino Hills, CA
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Default Alternator Output

Hi Erich,

It’s Bob Nuckolls (spelling). Through Aeroelectric Connection and his various articles, Bob has contributed a tremendous amount to experimental aviation. I’m somewhat following Bob’s z14j architecture myself substituting an SD-8 for the auxiliary 20-amp alternator and inserting the EFII Bus Manager into that architecture. Bob is definitely one of our “good guys!”

That being said, just because Bob offers a schematic, that doesn’t mean that there might not be component issues associated with the schematic that you need to research and understand yourself. Yes, the electrons will keep flowing from the alternators if the battery fails, but, as Robert correctly mentions, the alternators in absence of a battery deliver a wave form that some electronics like avionics or ignitions may not like. Yes, most will keep operating, but possibly with signal (noise) problems or other issues. Components like lights or fuel pumps are usually not as sensitive.

I should mention that Robert Paisley is an Electrical Engineer (Cal Poly) and has decades of experience designing, producing, and testing fuel and ignition systems for motorcycles, cars, and, over the past decade, aircraft. He definitely knows what he is talking about and is one of our “good guys,” too. Rather than posting a “put down” here on VAF requiring a response or pitting one experimental aviation “good guy” against another, it might be best to call or send a PM or email first. Assuming that Bob would disagree with Robert is a real stretch and is probably not the case.

Robert’s (EFII’s) phone is 951-317-3473, you can PM him here on VAF via rcpaisley, and EFII’s email is info@flyefii.com.

I hope this helps,
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  #18  
Old 06-10-2016, 03:06 PM
krw5927 krw5927 is offline
 
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Quote:
Originally Posted by rcpaisley View Post
There really isn't anything to argue, that's how alternators work.
An important part of the evolving aircraft electronics systems is the evolving electrical distribution to support the new systems.

Robert
All true, however can you please expand on "unhappy electronics"?

I've tested this very situation in my aircraft with dual alternators and a single battery. I took the battery offline by switching off the master contactor, to test whether the alternator(s) would continue providing power. The result was, if the main alternator field is already energized when the battery goes down, then it continues providing power. I even tried turning on and off various loads (pitot heat, landing lights, etc.) to test whether I could trick the alternator regulator (B&C) into going offline. Nope, still worked. Take the main alternator offline in addition to the battery failure however, and there's nothing left to energize the standby alternator field. (But now we're talking simultaneous, independent failures which is another debate altogether.)

Yes, you could hear the AC ripple noise through the intercom, but the electronics (full Skyview suite and Garmin IFR GPS navigator) kept happily humming along and sustained no temporary nor permanent damage.

edit: I do not have electronic ignition. Robert obviously knows more about his gear than anyone else, so if he says AC ripple is bad for his system then you can take that to the bank!
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Last edited by krw5927 : 06-10-2016 at 03:15 PM.
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  #19  
Old 06-10-2016, 03:57 PM
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Walt Walt is offline
 
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I want to be able to continue a flight with no disruption and without alarming my wife if the main alt fails so I have a BC 20a backup with a single main battery. I also have a small EarthX for an avionics back up which can be crosstied to the main bus if needed. In addition I also added a couple of large capacitors on the main and avionics bus in case the battery relay fails there will still be some AC filtering to keep the avionics happy.

I would also have no hesitation about departing with only the backup alternator operating (VFR). There will be no side trips to Autozone or O'Reilly's for me.

My wife (like most) doesn't want any excitement in the cockpit, if the main alt failed she would have no idea it happened and I probably wouldn't tell her until we got to our destination
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Last edited by Walt : 06-10-2016 at 03:59 PM.
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  #20  
Old 06-10-2016, 04:03 PM
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rcpaisley rcpaisley is offline
 
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Default robust electrical

There is always more than one way to solve any electrical requirement.
We use a very simple and robust scheme that doesn't include a master relay, or a typical aircraft right/left/both type switch. We also connect alternator outputs directly to batteries to avoid load dump. This is when an alternator gets separated from its battery and dumps its AC output through the rest of the systems.

Drawing 5A in our Bus Manager instructions (http://www.flyefii.com/media/Bus_Man...structions.pdf) shows how simple and robust, redundant electrical supply can be.

Robert
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