---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 10/18/20: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:22 AM - Alternator modify to external regulation (Graeme Coates and Sharon Beaman) 2. 09:58 AM - Re: Alternator modify to external regulation (Robert L. Nuckolls, III) 3. 12:23 PM - "Load Dump" revisited (Robert L. Nuckolls, III) 4. 10:45 PM - Re: "Load Dump" revisited (Bob Verwey) ________________________________ Message 1 _____________________________________ Time: 12:22:33 AM PST US From: Graeme Coates and Sharon Beaman Subject: AeroElectric-List: Alternator modify to external regulation For easy mods to alternator that are completely reversable look at Kitplanes 2019 November p36-39. Graeme Coates Europa Tri-gear ________________________________ Message 2 _____________________________________ Time: 09:58:12 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Alternator modify to external regulation At 02:20 AM 10/18/2020, you wrote: >Beaman > >For easy mods to alternator that are completely reversable look at >Kitplanes 2019 November p36-39. > >Graeme Coates > >Europa Tri-gear I saw that . . . thanks for reminding us! Bob . . . ________________________________ Message 3 _____________________________________ Time: 12:23:17 PM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: "Load Dump" revisited The term is part of the vernacular of both automotive and aviation worlds but they have similar but not equal definitions. The term is somewhat self explanatory . . . a big alternator load is suddenly removed. The resulting event is something akin to the ice cream social game of tug-o-war. Two opposing but relatively equal forces compete with each striving to satisfy disparate goals in physics. In this case, the ALTERNATOR, under command of a regulator, works within its limitations to maintain the system bus at some pre-set voltage. The totality of system loads team up to comprise a total LOAD on the alternator. Their demand tends to pull bus voltage down while the alternator/regulator is working to sustain the bus at the regulator's set point. At such time that total LOAD is very high, sometimes equal to the alternator name-plate limit, when have the electrical equivalent of two teams of individuals pulling on a rope from each end. It's easy to visualize the prospects for a sudden change of equilibrium if the LOAD should suddenly reduce . . . perhaps even go to zero. The rope breaks, load is zero. Half of a crew looses traction and fall, the load is greatly reduced. In either case, the tension impressed on the 'alternator' side goes down. The alternator was already balls-to- the wall before the reduction. Sudden release of tension allows the bus voltage to rise suddenly and before the regulator's response dynamic can react, the voltage will rise quickly to some limit defined by (1) percentage of load reduction and (2) time it takes for the regulator to regain control. Now, here's where the automotive and aviation communities diverge a little when considering the cause/effects of a load-dump. When one reads the literature for mitigating load dump in cars, virtually every condition speaks to disconnection of the battery as worst case root cause of the voltage transient. For example, suppose you've had a hard start on the vehicle and the battery is flagging. The car starts and the alternator rises to the call and begins the task of recharging the battery. It's daytime and weather mild . . . no headlights, no HVAC motors . . . the BATTERY comprises the greatest load on the system because it's being demanding replenished from a largely discharged state. Now, unhook the battery and . . . you got it . . . the alternator is now lightly loaded by system accessories and the alternator/regulator overshoot/recovery characteristics prevail. Further, the system loads are light and the PRIMARY load-dump mitigator, the battery, is out to lunch. This is the automotive description of the perfect storm of load dumps and yes, it's the worst case scenario for a load dump in a battery-alternator DC power system. But the really BIG question is, how does that battery become unhooked? Pretty rare event on a vehicle-by-vehicle case . . . but there are tens of millions of them out there. It's kinda like lightning strikes . . . doesn't happen often but risk is not zero and the quality of workmanship for battery installation and maintenance is not as rigorous as in airplanes. In airplanes, we have the perfect configuration for generating the ultimate load dump: the battery contactor(s). In most piston aircraft, DC power controls are configured for BATTERY ON BEFORE ALTERNATOR and ALTERNATOR OFF BEFORE BATTERY. It's the legacy split-rocker on many production aircraft and the DP3P(progressive) toggle switch in a lot of OBAM aircraft. Except for conditions arising from poor craftsmanship or maintenance, the battery is pretty tightly wedded to the bus. There ARE still rare disconnects with root cause in contactor failure . . . but in the whole constellation of contactor failures, what proportion occur during a heavy battery recharge condition? Aviation's load-dump events have been extensively studied over the last 100 years. MIL-STD-704 and DO-160 qualifications combined with sundry TSO requirements suggest that power generation and control systems be designed and qualified to limit load dump excursions to 40/80 Volts (14/28 Volt systems). Accessories are designed and qualified to stand off those same transients. Just how the system designers choose to meet those goals is not dictated. They may use a sprinkling of transient voltage suppressors or simply configure limit/withstand those levels by design. In any case, the highest risk condition is set up by an inadvertent disconnect of a badly discharged battery. Folks who travel on the ground are many times more likely to experience this than folks who fly . . . who are supposed to KNOW better! Bob . . . ________________________________ Message 4 _____________________________________ Time: 10:45:48 PM PST US From: Bob Verwey Subject: Re: AeroElectric-List: "Load Dump" revisited Thank you Sir...illucidating as usual! On Sun, 18 Oct 2020, 21:32 Robert L. Nuckolls, III, < nuckolls.bob@aeroelectric.com> wrote: > The term is part of the vernacular of both > automotive and aviation worlds but they > have similar but not equal definitions. > > The term is somewhat self explanatory . . . > a big alternator load is suddenly removed. > The resulting event is something akin to > the ice cream social game of tug-o-war. > > Two opposing but relatively equal forces > compete with each striving to satisfy > disparate goals in physics. In this case, > the ALTERNATOR, under command of a regulator, > works within its limitations to maintain > the system bus at some pre-set voltage. > > The totality of system loads team up to > comprise a total LOAD on the alternator. > Their demand tends to pull bus voltage down > while the alternator/regulator is working > to sustain the bus at the regulator's > set point. > > At such time that total LOAD is very high, > sometimes equal to the alternator name-plate > limit, when have the electrical equivalent of > two teams of individuals pulling on a rope > from each end. > > It's easy to visualize the prospects for > a sudden change of equilibrium if the LOAD > should suddenly reduce . . . perhaps even go > to zero. The rope breaks, load is zero. Half > of a crew looses traction and fall, the load > is greatly reduced. In either case, the > tension impressed on the 'alternator' side > goes down. The alternator was already balls-to- > the wall before the reduction. Sudden release > of tension allows the bus voltage to rise > suddenly and before the regulator's response > dynamic can react, the voltage will rise quickly > to some limit defined by (1) percentage of > load reduction and (2) time it takes for the > regulator to regain control. > > Now, here's where the automotive and aviation > communities diverge a little when considering > the cause/effects of a load-dump. > > When one reads the literature for mitigating load > dump in cars, virtually every condition speaks to > disconnection of the battery as worst case root > cause of the voltage transient. For example, suppose > you've had a hard start on the vehicle and the battery > is flagging. The car starts and the alternator rises > to the call and begins the task of recharging the battery. > > It's daytime and weather mild . . . no headlights, no > HVAC motors . . . the BATTERY comprises the greatest > load on the system because it's being demanding > replenished from a largely discharged state. > > Now, unhook the battery and . . . you got it . . . > the alternator is now lightly loaded by system accessories > and the alternator/regulator overshoot/recovery characteristics > prevail. Further, the system loads are light and the > PRIMARY load-dump mitigator, the battery, is out to lunch. > > This is the automotive description of the perfect > storm of load dumps and yes, it's the worst > case scenario for a load dump in a battery-alternator > DC power system. > > But the really BIG question is, how does that battery > become unhooked? Pretty rare event on a vehicle-by-vehicle > case . . . but there are tens of millions of them out > there. It's kinda like lightning strikes . . . doesn't > happen often but risk is not zero and the quality of > workmanship for battery installation and maintenance > is not as rigorous as in airplanes. > > In airplanes, we have the perfect configuration for > generating the ultimate load dump: the battery contactor(s). > In most piston aircraft, DC power controls are configured > for BATTERY ON BEFORE ALTERNATOR and ALTERNATOR OFF > BEFORE BATTERY. It's the legacy split-rocker on many > production aircraft and the DP3P(progressive) toggle > switch in a lot of OBAM aircraft. > > Except for conditions arising from poor craftsmanship > or maintenance, the battery is pretty tightly > wedded to the bus. There ARE still rare disconnects > with root cause in contactor failure . . . but > in the whole constellation of contactor failures, > what proportion occur during a heavy battery recharge > condition? > > Aviation's load-dump events have been extensively > studied over the last 100 years. MIL-STD-704 and > DO-160 qualifications combined with sundry TSO > requirements suggest that power generation and > control systems be designed and qualified to > limit load dump excursions to 40/80 Volts (14/28 > Volt systems). Accessories are designed and qualified > to stand off those same transients. > > Just how the system designers choose to meet those > goals is not dictated. They may use > a sprinkling of transient voltage suppressors > or simply configure limit/withstand those levels > by design. > > In any case, the highest risk condition is > set up by an inadvertent disconnect of a badly > discharged battery. Folks who travel on the > ground are many times more likely to experience > this than folks who fly . . . who are supposed > to KNOW better! > > > 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.