---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sat 05/04/13: 8 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:58 AM - Re: How to test engine ground? (Eric M. Jones) 2. 10:15 AM - Re: Re: How to test engine ground? (Robert L. Nuckolls, III) 3. 10:38 AM - Re: Re: How to test engine ground? (Robert L. Nuckolls, III) 4. 10:57 AM - Re: Re: How to test engine ground? (Eric Page) 5. 12:19 PM - Re: Re: How to test engine ground? (Robert L. Nuckolls, III) 6. 12:35 PM - Re: How to test engine ground? (Eric M. Jones) 7. 12:38 PM - Re: Re: How to test engine ground? (Henador Titzoff) 8. 02:40 PM - Re: Re: How to test engine ground? (Verso Electronics) ________________________________ Message 1 _____________________________________ Time: 05:58:37 AM PST US Subject: AeroElectric-List: Re: How to test engine ground? From: "Eric M. Jones" Big conductors and low resistances are usually measured by the "voltage drop method at a specific current". But just feeling the ground strap to see if it gets hot is a great way to go. Note: There are temperature indicating materials available from: http://www.omega.com which are easy to apply to e.g. high-current lugs. Color change=loose or failing connector. BTW: More stuff to worry about in the middle of the night....bad things happen when ground currents pass through bearings. Sometimes the designer catches these things...sometimes they don't. -------- 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=399940#399940 ________________________________ Message 2 _____________________________________ Time: 10:15:09 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: How to test engine ground? At 07:57 AM 5/4/2013, you wrote: > >Big conductors and low resistances are usually measured by the >"voltage drop method at a specific current". But just feeling the >ground strap to see if it gets hot is a great way to go. True. But placing the touchy-feely technique into context, I rather imagine that any component that exhibits an extra-ordinary rise in temperature after a few seconds under load is on the verge of driving over the cliff of precipitous failure. For example, I would think that dissipation local to the 'touch point' must toss some goodly watts heat. Consider the 1' foot wire segment between battery(+) and the contactor in the figure below. 0.00025 ohms x 200A = 50 millivolts of drop. 50mV x 200A is 10 watts. A 10 second 'cranking event' may produce detectable rise but would you be able to tell if the rise were say TWICE the normal amount? The 200 millivolt drops I hypothesized for each contactor is a total for up to 6 metallic joints in the path that includes wire to terminal, terminal to contact post, contact to armature, armature to contact, contact post to terminal and terminal to wire. EACH of those joints is very low in resistance but NOT zero. The drops in components and joints can all add up to a significant total but no single joint produces a predominantly obvious drop. I think I once suggested that there's no such thing as a "12v starter". I made that assertion based on a hypothetical not unlike that pictured below. Emacs! This figure illustrates the reasoning behind the notion for measuring a battery's ability to deliver a current to a terminal voltage on the order of 9 volts. We like to see numbers in the 400+ amps range. This demonstrates that with a 200 amp load, voltage drop within the battery will be about half thus leaving us with 1 to 1.5 volts of 'head room' to toss off in cranking circuit components and still get 8-9 volts to the starter. If one observes a change in cranking performance the prime suspect will be the battery. It's either not fully charged or nearing end of life. Look at the battery voltage under load first. The starter is a second order suspect. Measure its terminal voltage under load. If 'high', then for what ever reason, it's drawing less than normal current (high internal resistance) and is probably self destructing. If the voltage is low, then start looking at the remainder of the cranking loop voltage drops. There's a lot of opportunity for loop resistances to go up with the most likely prospects being contactors. Any contactor who's voltage drop has risen so much as to affect cranking performance will probably be smelling bad but might not demonstrate a marked temperature rise detectable by feeling the outside surface of the enclosure. This narration is the foundation for the starter circuit analyzer. An 8-channel, a/d complimented with data integration software could take a 10 second look at a cranking event and instantly highlight the probable culprit for poor starter performance. The probability of identifying a 'warmer than usual' component in a suite of components that warms up in normal situations is somewhat problematic. Bob . . . ________________________________ Message 3 _____________________________________ Time: 10:38:37 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: How to test engine ground? > >BTW: More stuff to worry about in the middle of the night....bad >things happen when ground currents pass through bearings. Sometimes >the designer catches these things...sometimes they don't. Yeah. Some years back we discovered root cause of poor bearing life on starter-generators. It seems that the steel shaft down through the center, while thought to be in an area of "zero net flux" was "excited" with microvolts of induced EMF shorted out by micro-ohms of starter frame through the bearings at each end. In retrospect, I'm not sure that the frame of the starter-gen didn't see similar inducements. A mysterious stress on bearing life went away with incorporation of ceramic bearings or bearing liners. Just because some stimulus is 'tiny' does not necessarily negate its effects. Bob . . . ________________________________ Message 4 _____________________________________ Time: 10:57:57 AM PST US Subject: Re: AeroElectric-List: Re: How to test engine ground? From: Eric Page Is this bearing wear a result of microscopic arcing and pitting as the balls roll in their races, making and breaking electrical contact? Eric On May 4, 2013, at 1:36 PM, "Robert L. Nuckolls, III" wrote: > > Yeah. Some years back we discovered root cause of poor bearing life on starter-generators. It seems that the steel shaft down through the center, while thought to be in an area of "zero net flux" was "excited" with microvolts of induced EMF shorted out by micro-ohms of starter frame through the bearings at each end. In retrospect, I'm not sure that the frame of the starter-gen didn't see similar inducements. > > A mysterious stress on bearing life went away with incorporation of ceramic bearings or bearing liners. Just because some stimulus is 'tiny' does not necessarily negate its effects. > > Bob . . . ________________________________ Message 5 _____________________________________ Time: 12:19:03 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: How to test engine ground? At 12:57 PM 5/4/2013, you wrote: > >Is this bearing wear a result of microscopic arcing and pitting as >the balls roll in their races, making and breaking electrical contact? Yeah . . . sort of. I'm not so sure that 'arcing' takes place so much as a kind of 'accelerated corrosion.' We're talking VERY tiny voltages at SIGNIFICANT currents. The area of contact between a spherical ball and its races is small and the pressures are huge. Hence the need for both harness and smoothness. An ionizing current flow across the tiny 'joint' cannot go unnoticed. Where the local magnetic fields are large and fluctuating, there is a coupling of energy between conductors. Making those conductors massive produces a potential for significant currents to flow at the tiniest of voltages. That once smooth surface begins to chip away as the little electron-hammers go to work on it. Those shafts run at 7 to 10,000 rpm and pretty high temperatures. Bob . . . ________________________________ Message 6 _____________________________________ Time: 12:35:28 PM PST US Subject: AeroElectric-List: Re: How to test engine ground? From: "Eric M. Jones" > Is this bearing wear a result of microscopic arcing and pitting as the balls roll in their races, making and breaking electrical contact? Maybe micro-welding more than corrosion. As I said...stuff to worry about in the middle of the night. -------- 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=399958#399958 ________________________________ Message 7 _____________________________________ Time: 12:38:46 PM PST US From: Henador Titzoff Subject: Re: AeroElectric-List: Re: How to test engine ground? Yes, Eric, it is due to making and breaking of metal surfaces as the bearin gs roll around.- Here is a good article on this phenomenon:=0A=0A-- - http://www.ien.com/article/insulating-ball-bearings/7642=0A=0A=0AKeep i n mind that grease and oil are not good conductors and therefore will intro duce resistance within the bearing.- As arcing occurs, it pits the metal surface areas as well as degrades the lubricants.- From thereon, it's a s nowball effect.=0A=0A-=0AHenador Titzoff=0A=0A=0A________________________ ________=0A From: Eric Page =0ATo: "aeroelectric-list@ma tronics.com" =0ASent: Saturday, May 4, 20 13 1:57 PM=0ASubject: Re: AeroElectric-List: Re: How to test engine ground? .com>=0A=0AIs this bearing wear a result of microscopic arcing and pitting as the balls roll in their races, making and breaking electrical contact? =0A=0AEric=0A=0A=0AOn May 4, 2013, at 1:36 PM, "Robert L. Nuckolls, III" wrote:=0A> =0A> Yeah. Some years back we disc overed root cause of poor bearing life on starter-generators. It seems that the steel shaft down through the center, while thought to be in an area of "zero net flux" was "excited" with microvolts of induced EMF shorted out b y micro-ohms of starter frame through the bearings at each end. In retrospe ct, I'm not sure that the frame of the starter-gen didn't see similar induc ements.=0A> =0A> A mysterious stress on bearing life went away with incorpo ration of ceramic bearings or bearing liners. Just because some stimulus is 'tiny' does not necessarily negate its effects.=0A> =0A>- Bob . . .=0A =========================0A =================== ________________________________ Message 8 _____________________________________ Time: 02:40:04 PM PST US Subject: Re: AeroElectric-List: Re: How to test engine ground? From: Verso Electronics Thank you Bob, Eric and Henador for the replies. Fascinating what goes on i n the invisible world! Eric do not archive On May 4, 2013, at 3:38 PM, Henador Titzoff wrot e: > Yes, Eric, it is due to making and breaking of metal surfaces as the beari ngs roll around. Here is a good article on this phenomenon: > > http://www.ien.com/article/insulating-ball-bearings/7642 > > Keep in mind that grease and oil are not good conductors and therefore wil l introduce resistance within the bearing. As arcing occurs, it pits the me tal surface areas as well as degrades the lubricants. =46rom thereon, it's a snowball effect. > > Henador Titzoff > > From: Eric Page > To: "aeroelectric-list@matronics.com" > Sent: Saturday, May 4, 2013 1:57 PM > Subject: Re: AeroElectric-List: Re: How to test engine ground? > > > Is this bearing wear a result of microscopic arcing and pitting as the bal ls roll in their races, making and breaking electrical contact? > > Eric > > > On May 4, 2013, at 1:36 PM, "Robert L. Nuckolls, III" wrote: > > > > Yeah. Some years back we discovered root cause of poor bearing life on s tarter-generators. It seems that the steel shaft down through the center, wh ile thought to be in an area of "zero net flux" was "excited" with microvolt s of induced EMF shorted out by micro-ohms of starter frame through the bear ings at each end. In retrospect, I'm not sure that the frame of the starter- gen didn't see similar inducements. > > > > A mysterious stress on bearing life went away with incorporation of cera mic bearings or bearing liners. Just because some stimulus is 'tiny' does no t necessarily negate its effects. > > > >&nbroElectric-List" target="_blank">http://www.matronics.com/Navigator? AeroElectric-Lista href="http://forums.matronics.com/" target="_blank">h ttp://forums.mat &nbs//www.matronics.com/contribution" t arget="_blank">http://www.matronics.co============ ===== > > > > > > > ========================== ========= ========================== ========= ========================== ========= ========================== ========= > ------------------------------------------------------------------------------------- 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.