---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 03/21/14: 8 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:24 AM - Re: New Over-Voltage Protection Architecture (user9253) 2. 07:01 AM - Re: New Over-Voltage Protection Architecture (Eric M. Jones) 3. 07:45 AM - Re: Re: New Over-Voltage Protection Architecture (Charlie England) 4. 09:22 AM - Re: New Over-Voltage Protection Architecture (David Josephson) 5. 09:59 AM - Re: Earth-X lithium (D L Josephson) 6. 10:06 AM - Re: Re: New Over-Voltage Protection Architecture (Jeff Luckey) 7. 11:17 AM - Re: Re: New Over-Voltage Protection Architecture (Robert L. Nuckolls, III) 8. 12:00 PM - Re: Re: New Over-Voltage Protection Architecture (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 06:24:00 AM PST US Subject: AeroElectric-List: Re: New Over-Voltage Protection Architecture From: "user9253" A voltage regulator is not likely to fail unless overheated. An over-voltage protection device is less likely to fail because it is usually not subject to excessive heat. What is more likely to fail is an electrical connection or switch somewhere between the main bus and the voltage regulator. Good workmanship, strain relieved terminals, and a dab of grease to prevent corrosion, will all help. Even if properly installed, switches and connections can corrode over time. These problems are unlikely to be detected during annual inspections. Many modern avionics can operate on voltages between 10 and 30, and can withstand minor voltage excursions. Over-voltage protection is like buying insurance. Is it worth the premium? Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=420718#420718 ________________________________ Message 2 _____________________________________ Time: 07:01:46 AM PST US Subject: AeroElectric-List: Re: New Over-Voltage Protection Architecture From: "Eric M. Jones" I learned to fly in a club with five Cessnas, and the only alternator failure I was personally involved with was an alternator bracket that broke from fatigue. (There was one "failure to charge" whose cause I never learned.) If you look at all the ways an aircraft can fail, I think alternator failures are low on the list. I have not heard of a NEW (not rebuilt) Nippondenso alternator that failed at all, save overheating, drowning, old age, etc. This might be true of other manufacturers as well. Any reports to the contrary? Rather than trying to protect the electrical system from a failed alternator, perhaps some effort in determining when an alternator should be replaced would be a good approach. 1000 hours, engine TBO? Most electrical parts benefit from not being driven too hard, and being kept cool. If this is done, count me as unconvinced that OVP is necessary with an internally-regulated modern alternator. -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge, MA 01550 (508) 764-2072 emjones(at)charter.net Read this topic online here: http://forums.matronics.com/viewtopic.php?p=420721#420721 ________________________________ Message 3 _____________________________________ Time: 07:45:35 AM PST US From: Charlie England Subject: Re: AeroElectric-List: Re: New Over-Voltage Protection Architecture On 3/20/2014 2:11 PM, Robert L. Nuckolls, III wrote: > > > At 10:58 AM 3/19/2014, you wrote: >> You might be approaching a situation where "the cure is worse than >> the disease". You have to be careful when stacking widgets on top of >> gizmos in pursuit of greater reliability. That approach quite often >> leads to greater complexity & lower reliability. > > Good put. > > What is the line of thought that drives the > notion that simple removal of field voltage from > a runaway system is inconsistent with our > assessment of risk? > > I'll have to ask around . . . I've been disconnected > from the field service loop in regulators for some > years . . . but I don't recall any controllers ever coming > back to B&C where a regulator fallen from grace > was blessed with salvation by the ov protection > system. > > I'm not suggesting that such failure rates are zero but > they ARE quite small. Further the prudent response > to a competent FMEA dictates that we include such > protection in spite of those low failure rates. > > It's been a long time since I've observed a car > approaching me at night with lights that were too > blue/bright demonstrating the fact that a poor > battery was doing its best to stand off a > runaway alternator. > > I'm also reading anecdotal bits about stock, > automotive alternators being incorporated onto > aircraft sans ov protection. It MIGHT be that > contemporary regulators have achieved 10 to the > minus 9 or better failure rates that suggest > the ov protection is no longer necessary/useful. > > If anyone runs across such an incident, I'd like > to hear about it. > > > Bob . . . Are you asking for incidents of *non* failures with internally regulated alternators & no protection? I've been running a Denso on an RV-4 Lyc O320 for about a decade. Not a lot of hours (probably around 400), but no issues with OV. This is a very simple VFR a/c that only recently acquired a transponder, so my financial and safety risks have been pretty low. I'll probably incorporate some type of protection on the -7 I'm building, just because I'll have more money tied up in the panel. Charlie ________________________________ Message 4 _____________________________________ Time: 09:22:13 AM PST US From: David Josephson Subject: AeroElectric-List: Re: New Over-Voltage Protection Architecture > What is the line of thought that drives the > notion that simple removal of field voltage from > a runaway system is inconsistent with our > assessment of risk? Only that removal of field voltage is impossible with a permanent magnet alternator and inconvenient with an internally regulated one. ________________________________ Message 5 _____________________________________ Time: 09:59:46 AM PST US From: D L Josephson Subject: AeroElectric-List: Re: Earth-X lithium Just as lead-acid electrochemistry is fairly well understood, lithium cell vendors and types are well known. Every maker of small "aviation" lithium batteries uses the same LiFePO4 18650 cell type as far as I know, which is also the same as Tesla uses in their car battery packs, and the same chemistry used in most smartphones today. There are various quality levels available, with the leader seeming to be the Panasonic NCR18650A, which is honestly rated at 2.9 amp-hours at 3.2 volts (more than 2.9 can be claimed by assuming a lower cutout voltage, which requires more precise low voltage disconnect to avoid damage.) Packs are made of strings of 4 cells in series, which is why you see 8-, 12-, 16 etc. cell "batteries." At last year's CAFE Electric Aircraft Symposium, Eric Darcy from NASA, who is responsible for designing the lithium batteries for the Space Station, gave some pointers on testing these ubiquitous cells for quality (you measure open circuit voltage over a few weeks -- cells that droop faster than the norm are suspect) and the measures that need to be taken to assure safe charging and low voltage disconnect. We learned that quality was primarily related to clean shearing and even winding of the internal foil materials, with failures mostly due to minute stray particles of the sheared material causing leakage, or misalignment of the wound structure allowing the edges to touch. Ideally each cell is charged separately. Next best is to charge each pack of 4 cells separately. The trick comes in designing a battery management system inside the box that manages charge current for multiple packs and at the very least alerts you if something is wrong. A battery company that will actually explain how they are doing these things, and takes the time to explain why a watt-hour of lithium cells might be more useful than the same watt-hour of lead acid, would be worth paying attention to. ________________________________ Message 6 _____________________________________ Time: 10:06:41 AM PST US From: Jeff Luckey Subject: Re: AeroElectric-List: Re: New Over-Voltage Protection Architecture =0A=0A=0A=0A________________________________=0A From: David Josephson =0ATo: aeroelectric-list@matronics.com =0ASent: Friday, Mar ch 21, 2014 9:21 AM=0ASubject: AeroElectric-List: Re: New Over-Voltage Prot Josephson =0A=0A=0A=0A>- - - What is the line of thought that drives the=0A>- - - notion that simple removal of fi eld voltage from=0A>- - - a runaway system is inconsistent with our =0A>- - - assessment of risk?=0A=0AOnly that removal of field voltag e is impossible with a permanent magnet =0Aalternator and inconvenient with an internally regulated one.=0A=0ADavid,=0A=0AI've never had occasion to f iddle with a PM alternator. =0A=0AI've always thought of a run-away conditi on as=0Aa regulator failure where it is no longer "regulating" =0Aand apply ing full field current.=0A=0ACan a PM alternator "run-away"?=0A=0A-Jeff=0A =========================0A =================== ________________________________ Message 7 _____________________________________ Time: 11:17:48 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: New Over-Voltage Protection Architecture At 11:21 AM 3/21/2014, you wrote: > > >> What is the line of thought that drives the >> notion that simple removal of field voltage from >> a runaway system is inconsistent with our >> assessment of risk? > >Only that removal of field voltage is impossible with a permanent >magnet alternator and inconvenient with an internally regulated one. That's why all the z-figures that incorporate pm alternators use a disconnect relay paired with an ov sensor to effect a disconnect . . . This unique characteristic of the PM alternator is what suggested that they be called a 'dynamo' to separate them out from the herd of engine driven power sources. B-lead disconnect has also been suggested in Figure z-24 of the 'Connection's collection of architectures. Bob . . . ________________________________ Message 8 _____________________________________ Time: 12:00:41 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: New Over-Voltage Protection Architecture At 08:23 AM 3/21/2014, you wrote: A voltage regulator is not likely to fail unless overheated. An over-voltage protection device is less likely to fail because it is usually not subject to excessive heat. What is more likely to fail is an electrical connection or switch somewhere between the main bus and the voltage regulator. Good workmanship, strain relieved terminals, and a dab of grease to prevent corrosion, will all help. Even if properly installed, switches and connections can corrode over time. These problems are unlikely to be detected during annual inspections. There are two approaches to system reliability analysis. One approach assumes NO backup . . . either because such features are too costly/bulky/heavy/etc or simply not possible. If any of these features are critical to comfortable termination of flight, they get designed and tested for very high probability of meeting a 'design service life' that is generally some multiple of 'practical service life'. For example, flown long enough, the wings on EVERY aluminum airplane are going to break off. This is because aluminum, unlike steel, has a stress-to-cycles plot that never goes 'flat'. If you stress and relieve a steel part to maxiumum ever expected loads 10,000,000 times without breaking it, the part is considered 'golden' and will last forever. Aluminum has no such feature . . . it eventually fails at any stress loading . . . the cycles may be very high but there is no flat spot on the s/n curve to failure. Hence you see a totally different approach for the design setting service limits for qualification of structural parts on airplanes. Approaches that have continuously evolved over the years particularly in response to incidents like this . . . http://www.aloha.net/~icarus/243a.jpg Emacs! An alternative technique for making design decisions can be adopted for items that are not immediately catastrophic. The generally categorized by criticality level not unlike software under DO-178 . . . (a) Catastrophic - Failure may cause multiple fatalities, usually with loss of the airplane. (b) Hazardous - Failure has a large negative impact on safety or performance, or reduces the ability of the crew to operate the aircraft due to physical distress or a higher workload, or causes serious or fatal injuries among the passengers. (c) Major - Failure significantly reduces the safety margin or significantly increases crew workload. May result in passenger discomfort (or even minor injuries). (d) Minor - Failure slightly reduces the safety margin or slightly increases crew workload. Examples might include causing passenger inconvenience or a routine flight plan change. (e) No Effect - Failure has no impact on safety, aircraft operation, or crew workload. For OBAM aircraft, we're free to tighten up our spectrum of criticality level. Depending on the design of our plan-B, we can generally drop to 3 categories . . . (a) Engine stops and we're going to descend . . . NOW (b) Some appliance goes dark and finding our way to comfortable landing . . . preferably at airport of intended destination . . . is at risk. (c) Some appliance goes dark but while convenient, is not critical to continued flight, navigation, approach to landing and parking the airplane. These three categories focus on system components like fuel pumps, ECM, nav receivers, orientation aids, panel lighting, electronic ignition, comm, and perhaps xponder. The builder/pilot has to decide what order of important fits their particular project and the environment in which they intend to fly. Then an architecture and hardware compliment needs to be crafted such that no single failure takes down more than one accessory and all really useful or critical accessories have a plan-B. The elegant solution minimizes weight, cost, volume, parts-count and pilot work loads. It takes an appreciation of the thoughts outlined above to understand the rationale for careful consideration before ov protection is no longer in your plans. Recall that MTBF numbers say NOTHING about the behavior of any single part. If one strives for predictable behavior, then you venture into the world of 'established reliability' accessories where a great deal of money has been spend to design, test, manufacture and perhaps even screen finished goods to weed out infant mortality . . . The easiest way to deal with SYSTEM reliability with internally regulated alternators is to ASSUME it will fail and install a plan-b . . . as long as that addition is not a significant cost/weight adder. OV protection adds little overhead. Second alternators add some weight and up-front costs but minimizes cost of ownership. Second batteries are probably cheaper up front but add more weight and perpetual cost of ownership burdens for preventative maintenance and r/r costs common to an expendable commodity. Don't forget one super-significant feature of the engine driven power source: It's an inexhaustible source of energy . . . at potentially high voltages (100+ volts). The alternator is unique in this regard. The battery can deliver a lot of current but its energy reservoir is limited. The alternator is current limited but for all practical purposes, it's output voltage and total energy is not limited. These features are foundations on which you build your personal failure mode effects analysis. An analysis that could not care less about anecdotal reliability narratives and builds a foundation of system reliability on logic assembly of simple-ideas irrespective of any perceptions of probability. Many modern avionics can operate on voltages between 10 and 30, and can withstand minor voltage excursions. Over-voltage protection is like buying insurance. Is it worth the premium? OV protection is not about minor excursions. It's about unleashing the flame thrower first against your battery (by the way, if it's a tiny lithium super-cranker, it will toss in the towel much faster than your 18 or 24Ah SVLA brick) and then upon system accessories. Just a few steps from where I sit right now is a lab where these features and effects have been studied for years. It's not a concept to be dismissed lightly. A runaway alternator is the acme of electrical disasters on about any DC power system. If you're willing to buy into the anecdotal 'never heard of it happening' . . . then ask the supplier of your alternator/regulator combination if he'll guarantee replacement of electro-whizzies on your panel if his gizmo fails? This is why we elected to bring the B&c alternator controllers to market as a TRIO of accessories that offered a very favorable FMEA. The thought was that if the customer wanted to go a different route, they're certainly free to do so . . . but not with our product. Proceed with both caution and confidence borne out of lessons learned . . . Bob . . . ------------------------------------------------------------------------------------- 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.