---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 08/31/16: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 10:55 AM - Re: Z13/8 with EarthX battery and dual electronic ignition (Robert L. Nuckolls, III) 2. 12:11 PM - Re: Z13/8 with EarthX battery and dual electronic ignition (John Morgensen) ________________________________ Message 1 _____________________________________ Time: 10:55:53 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Z13/8 with EarthX battery and dual electronic ignition I'm building an RV-14A that will have a full glass IFR panel and dual electronic ignition (still undecided about which brand of ignition but for discussion purposes let's assume it's not P-mags). I'd also like to use the EarthX ETX680 battery for the significant weight savings. Would you be comfortable using Z13/8 for this mission? A few specific questions I have: 1) Is the SD-8 with the parallel R/C circuit & PMR1C-14 regulator guaranteed to self-excite even if the alternator is brought online without a battery connected? The circuit (Z25) has been tested on numerous airplanes . . . I'll be testing it further on my drive stand . . . but yes . . . the SD-8 will come up without a battery when wired as shown. One possible failure mode is the physical connection to the battery, but my real concern is the unknown failure modes of the EarthX technology. It's more complex than a lead acid battery due to the BMS and newer chemistry and has a short track record thus far, so compared to an Odyssey PC680 I feel there's a greater chance that the EarthX may simply shut itself off or fail in a manner that is equivalent to having the battery completely disconnected. During normal cruise operations, stress levels on internal electronics is a small fraction of that experience when cranking the engine. We don't have enough data about internal workings to do the classic MTBF study . . . but there's a lot of these devices in service . . . the risk is small. Even PC680s have gone "open". I have on my bench now that will go to Wichita on my next trip . . . need to machine the top cap off to inspect the inter-cell connections. In this scenario I would assume the main alternator will no longer function reliably . . . why do you assume this? Alternators have been demonstrated to run self-excited after start up . . . so I need high confidence that the SD-8 will come online and produce 12-14 V, especially with both ignition systems depending on it. Your choice . . . but the p-mag features offer an exceedingly robust failure modes effects analysis . . . but even LightSpeed system operating directly from a battery bus are on a par with the p-mags . . . Operationally would you recommend having both alternators on all the time for normal flying? Or would you normally have the SD-8 off and only switch it on if the main alternator fails? I think that's what is described in the 'Connection. It seems one potential downside to having both alternators on all the time is if there's an overvoltage condition it may trip the field breakers for both alternators. You would not know which one failed and you'd have to reset one CB at a time to see which one works. Not a really big deal but it adds troubleshooting complexity. Actually that's not so. The LR series regulators are selective ov trip. If the main alternator runs away, field voltage will be greater than 1 volt. If the field voltage is LESS than 1 volt, the LR3 ov trip is suppressed. Further, with the limited output from an SD8, you're not likely to EVERY see an OV event if the SD8 is the only alternator running unless system loads are very light . . . and the main alternator is inop. But it's a moot point . . . leave SD8 off until needed. Z13/8 shows both electronic ignition systems connected to the Main Battery Bus. This seems ok for Pmags, but for ignition units without their own generating capability, I'm thinking it would make sense to move one of them directly to the + battery terminal with a fusible link. Do as you wish . . . but the wiring as shown is exceedingly robust . . . your getting wrapped around the axles of exceedingly remote probabilities. Z13/8 shows the main battery lead, battery bus lead, and fuselink for the SD-8 all connected to the same terminal on the battery contactor. While I'm sure this is a pretty robust connection, it's still a potential single point failure that could result in loss of your battery and both alternators (along with Main bus, E-bus, and Batt Bus) all at once. . . . I think I'm more concerned about colliding with an inboud meteor than I am for contactor stud failure. I know I could alleviate some of my concerns by going with an Odyssey PC680 and installing magnetos or Pmags, but the Odyssey battery is significantly heavier and the Pmags are still a concern for long-term reliability (I'm skeptical about how any electronic device can handle the heat exposure that is inherent in the Pmag design and have an MTBF of more than several hundred hours). I could also add another smaller battery and have a full dual batt/dual alternator architecture, but this adds more weight, complexity, maintenance, expense, etc, so I prefer not to go that route unless necessary. The p-mags don't really operate that hot. Modern electronics are not that fragile. One of the first temperature tests accomplished by a friend of mine is to throw the thing into the chamber at 100C to see that there are no weak compoents or joints in the build. If it were my airplane, I'd go with Z13/8 as published with p-mags. If you go any other ignition system, run from battery bus on separate switches. Should you ever get down to SD-8 only operation, turn off one ignition system. Run pumps off the battery bus too. Bob . . . ________________________________ Message 2 _____________________________________ Time: 12:11:21 PM PST US Subject: Re: AeroElectric-List: Z13/8 with EarthX battery and dual electronic ignition From: John Morgensen 6 months ago I installed an EarthX ETX900 in my RV9A with Z13/8 and dual pmags. 385 hours TTAF and no failures to date. I chose the ETX900 over the ETX680 because it is rated for a bigger alternator. The form factor is the same. Anyone contemplating the EarthX battery should be aware that the battery will accept all of the amps that the alternator is capable of producing. If you start on battery only and forget to turn on the alternator until the low voltage light comes on, then my Plane Power 60 amp alternator puts out 64 amps. It does not stay at that output for more than a minute but it is disconcerti ng. John Morgensen RV9A On 8/30/2016 11:09 AM, Mark and Kathleen Navratil wrote: > > Hi Bob, > > I=92m building an RV-14A that will have a full glass IFR panel and dual > electronic ignition (still undecided about which brand of ignition but > for discussion purposes let=92s assume it=92s not P-mags). I=92d also like > to use the EarthX ETX680 battery for the significant weight savings. > Would you be comfortable using Z13/8 for this mission? > > > Mark Navratil > > Spring Hill, KS > > RV-8A N2D built/flew/sold > > RV-14A #140017 finishing wings > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.