---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 03/20/19: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:12 AM - Still noisy voltmeter (Achille) 2. 06:14 AM - Re: Still noisy voltmeter (user9253) 3. 08:15 AM - Re: Battery BMS failures? (Robert L. Nuckolls, III) 4. 11:38 AM - Re: Battery BMS failures? (Eric Page) ________________________________ Message 1 _____________________________________ Time: 05:12:46 AM PST US Subject: AeroElectric-List: Still noisy voltmeter From: "Achille" Hi all, I send a message because I have since months a noisy voltmeter after the total change of my electrical system. And I tried to resolved it without good evolution. I have used the book of bob, and it's the Z19 electrical diagram or very close to. I have 2 votmeters, one for main batterie and the other one for the aux bat 7amp/h bat. Set with one 2 way switch. The both voltmeters are on the same place and the wire of each other are a wire harness. This wire harness pass below my VHF. And just the voltmeter 1 (Main system) is noisy. The other not. (pictures below) My voltmeter 1 was set on the ESS bus bar after the diode. I tried to connect it before the diode. And in this case it's a bit (but still noisy) less noisy. I have the noise a low level when I set voltmeter in ON and intercom ON, and when I set radio in ON the noise is higher. In all case if I set my voltmeters in OFF no more noise. Voltmeters switch ON but voltmeter 1 disconnected no noise... [Rolling Eyes] Any idea ? Thank you Read this topic online here: http://forums.matronics.com/viewtopic.php?p=488163#488163 Attachments: http://forums.matronics.com//files/voltmeter_246.jpg http://forums.matronics.com//files/voltmeter_2_173.pdf ________________________________ Message 2 _____________________________________ Time: 06:14:09 AM PST US Subject: AeroElectric-List: Re: Still noisy voltmeter From: "user9253" How is voltmeter 1 grounded? I suggest to NOT ground the voltmeter to the airframe. Instead, twist the positive and negative wires together all of the way from the voltmeter to the battery. At the switch, loop the ground wire around the switch, then continue the twisted pair to the battery. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=488164#488164 ________________________________ Message 3 _____________________________________ Time: 08:15:43 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Battery BMS failures? >Bob, > >Speaking of BMS, perhaps you can explain (since EarthX seems >unable) why EarthX batteries, with their 'full BMS', have a limit on >alternator current capability based on their battery capacity. I am >unable to see why a BMS that can manage individual cell charging, >and protect individual cells plus the entire battery, is unable to >limit overall charge current to the battery to a safe level. I've >repeatedly asked that question of their spokesperson on the VAF (RV) >forum, and gotten words without answers. > >Charlie Interesting question . . . I've oft asserted that batteries are like houseplants. Given the right treatment in proper proportions and protected from deleterious stress, they will 'bloom' and thrive. But the term 'battery' is not quantified and the selection of a battery is to craft a kind of marriage between a host of players not the least of which are the engine driven power source(s) and design goals for normal and abnormal operations. Lithium cells are the orchids of the battery family . . . capable of extra- ordinary performance in some respects but exceedingly sensitive to stress largely tolerated or shrugged off by the likes of Flooded, SVLA, gell and NiCad technologies. Lithium is extra-ordinarily vulnerable to over and under voltage conditions. Hence the 'real' BMS will strive to operate the array of cells between about 20 and 90 percent of charge. This is a goal stated by the electric and hybrid car folks. No doubt, EarthX has their own numbers but what ever the numbers, ignoring them risks premature battery failure. Then there's temperature . . . stuffing energy back into a lithium array MUST raise the chemistry's temperature as does prolonged heavy rate discharge. So the agile BMS watches temperatures and strives to limit those effects on the cells irrespective of system demands from the outside. External hard faults cause spectacular current flows with a new constellation of risks for catastrophic failures. A BMS tailored for engine cranking expects to see some really high current flows for short periods of time . . . but it must differentiate between starter inrush/engine spin-up and a hard fault. I've mentioned that the enclosure for a True Blue, TC/TSO battery is filled with electronics . . . electronics with agility and robustness to accomplish all these things to prevent premature failure while packaged to keep the rare catastrophic failure from migrating to the rest of the aircraft. True Blue batteries are used on twin turbine aircraft with starter generators up to and including 400A per side or 800A of recharge capability. Starter inrush is typically 1500-2000 amps followed by spin-up currents on the order of 500-700A lasting 20-30 seconds. My hat is off to the folks who crafted an array of silicon that can operate in series with those loads yet meet design goals for safety and battery life. AeroVoltz seems to be moving toward offering an EXTERNAL BMS for their product line . . . methinks a fine idea. That way you don't trash a bunch of perfectly good transistors along with a shot battery. The most difficult thing for a BMS to do is throttle currents . . . in either a charge or discharge mode. The series connected control devices are either switched on hard (saturated) or totally open (off). This offers the smallest form factor of electronics to manage such current levels. Battery recharge limits are largely a thermal management issue. The very low internal impedance of the lithium cell COMBINED with its low mass raises concerns for overheating during prolonged high rates of charge. True Blue isn't immune to these forces either but they're designed to work in a world of currents a magnitude greater than piston driven light aircraft. EarthX and contemporaries are not immune from the need to make compromises in design goals. They are marketing good cranking performance and light weight. Light weight generally brings extra-ordinary requirements in thermal management. Light weight and small size puts limits on capacity . . . largely independent of short term cranking ability. Given the fact that a BMS cannot 'throttle' current into or out of the battery, they must be cognizant of the risks for marrying their 'orchid' to a system recently divorced from a 'bromeliad' that may not easily bloom but it doesn't lay down and die when insulted. So what's the responsible supplier of light cranking batteries to do when marketing to relative technical novices about the care and feeding of their products. To be sure, lots of their batteries are being married to systems that already have alternators that are too big. If the engine starts easily when smartly cranked time needed to recharge is limited even if too fast. If the operator NEVER allows the battery to be deeply discharged followed by an in-situ recharge by the ship's too-big alternator . . . then risks to the battery are low. At the same time, the operator purchased "light" and "whippy-starting" and made no demands for electrical and thermal robustness. So it makes sense that EarthX would recommend limiting the size of the alternator depending on size of battery . . . not a very realistic expectation but a good CYA move nonetheless. This raises a recollection of experiences with another shotgun wedding between poorly matched components. Waayyy back when we got all exercised about what was then a big quantum leap in light weight, robust cranking batteries with flooded NiCads. After setting a few airplanes on fire with a marriage of nicad and twin turbines, powers-that=be decided that the BEST thing to do was add a remote reading battery temperature meter paired with yellow warning and red danger lights designed to assist crews in managing their 'orchids' to prevent overheat and thermal runaway. I argued then that we could craft an accessory to the starter-generator controllers that would automatically adjust bus voltage in response to battery overheat. That wasn't well received so we added another thing on the panel that was harder to install and drove up pilot work loads. The same thing could be done here. The BMS for the alternator/lithium marriage could easily include an regulator that would prevent an alternator of ANY SIZE from abusing the battery . . . maybe AeroVoltz will do it. Bob . . . ________________________________ Message 4 _____________________________________ Time: 11:38:18 AM PST US Subject: AeroElectric-List: Re: Battery BMS failures? From: "Eric Page" Charlie England wrote: > Speaking of BMS, perhaps you can explain (since EarthX seems unable) why EarthX batteries, with their 'full BMS', have a limit on alternator current capability based on their battery capacity. I am unable to see why a BMS that can manage individual cell charging, and protect individual cells plus the entire battery, is unable to limit overall charge current to the battery to a safe level. I've repeatedly asked that question of their spokesperson on the VAF (RV) forum, and gotten words without answers. My guess is that it's a limitation of the cell balancing circuitry in the BMS. As a cell within the battery reaches full charge, the BMS puts a resistance across it (either a fixed resistor hard-switched across the cell or a linear-mode transistor) to burn the current that would otherwise overcharge the cell while the others continue to charge. There must be a limit to the power that this system can dissipate, which may explain the alternator output limitation. Robert L. Nuckolls, III wrote: > After setting a few airplanes on fire with a marriage of nicad and twin turbines, powers-that=be decided that the BEST thing to do was add a remote reading battery temperature meter paired with yellow warning and red danger lights designed to assist crews in managing their 'orchids' to prevent overheat and thermal runaway. Indeed, the deHavilland DHC-8-202 that I flew in a previous life was fitted with battery temperature gauges on the overhead panel (just below the left fire t-handle in the linked image). https://bitly.com/2uj9V9F+ The airline I worked for operated them in the desert southwest, where ambient temps routinely exceed 100F. Given the short-hop, quick-turn nature of the flying we did, and the eye-watering current required to start a >2,000shp engine, we kept a close eye on those gauges. Eric Read this topic online here: http://forums.matronics.com/viewtopic.php?p=488170#488170 Attachments: http://forums.matronics.com//files/dhc_8_batt_temp_855.jpg ------------------------------------------------------------------------------------- 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.