---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 08/15/08: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:56 AM - Re: Starter Contactor (Robert L. Nuckolls, III) 2. 07:12 AM - No sidetone driving me insane! (keithmckinley) 3. 07:59 AM - Measuring "wiggly" currents . . . (Robert L. Nuckolls, III) 4. 08:33 AM - Re: Re: Battery Choices - what is too small AH capacity? (Robert L. Nuckolls, III) 5. 05:44 PM - Re: No sidetone driving me insane! (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 05:56:13 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Starter Contactor At 06:14 PM 8/14/2008 -0700, you wrote: > >Sorry if this has been covered before... > >What is the purpose of the additional starter contactor on the drawings? >If my ND starter has a solenoid, isn't that the contactor from the start >button? Why would I install a second relay? Or is this for another type of >starter that does not have a solenoid? > >Seems like more parts to fail... See: http://www.aeroelectric.com/articles/strtctr.pdf also Figure Z-22 and associated note on page Z-4 of . . . http://www.aeroelectric.com/articles/Rev11/AppZ_R11M.pdf Bob . . . ________________________________ Message 2 _____________________________________ Time: 07:12:32 AM PST US Subject: AeroElectric-List: No sidetone driving me insane! From: "keithmckinley" Hi, I've got an Icom a200 radio connected through a pm 1200 intercom. When I got the plane it had no side tone at all. Pulled the radio and tried to adjust the sidetone pot to no avail. Turned off intercom and still no side tone. I've tried numerous different headsets. I did notice what seems to be a disconnected wire(s) at the molex connector but don't no if that's an issue. The wiring job is shoddy to begin with but I'd hate to rip it out and start new if it's actually a radio issue. radio transmits and receives just fine and the intercom is awesome at canceling out noise in my very loud warbird. Just hoping for some last chance advice before I send the radio out for a bench test. Thanks, Keith -------- Wizard Read this topic online here: http://forums.matronics.com/viewtopic.php?p=198719#198719 ________________________________ Message 3 _____________________________________ Time: 07:59:19 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Measuring "wiggly" currents . . . At 11:59 AM 8/14/2008 -0400, you wrote: > >If you need to know actual current draw, check out >www.sears.com/shc/s/p_10153_12605_03482369000P. DC clamp-on ammeter, works >well for this kind of situation, not too expensive. Just be sure you're >clamping around the wire that you really want to read. It's easy to get on >the wrong side of a terminal. (Don't ask how I know -- I know!) This brings up a topic that I've been meaning to do an article on . . . but not all ammeters are the same . . . and some are decidedly unsuitable for some kinds of measurements. When we're sizing batteries and alternators, the REAL questions go to deducing the amount of ENERGY we need to store and generate. You can buy ENERGY meters but they are decidedly more expensive than the common mulitmeters and very few folks really need to make detailed energy studies. To review, energy is power over an interval of time. Like the Joule is 1 watt for one second, i.e. 1 watt-second. You pay for killowatt-hours recorded on the meter at the back of your house. While an alternator may be rated at 60A and 14v (840 watts) the energy you need from it is spread over a period of a flight and might turn out to be something like 600 watt-hours. A tidy number that accumulates total consumption that doesn't care if the current draw was 210 amps for seconds, 5 amps for minutes, 16.2 amps most of the time an 31 amps for a few minutes. Making measurements to deduce energy requirements can have some pitfalls . . . from two major sources. Accuracy of the instruments at the levels of interest and response of the instrument for integrating the true energy measurement from a reading that is anything but steady. Light bulbs, fans, radios, etc. tend to have steady current draw requirements. Their energy requirements are pretty accurately measured with the product of volts x amps x time. some devices in the airplane do not present steady, current draw signatures. Placing an ammeter in series with these devices is problematic. First, digital multimeters have some electronics that does an analog to digital conversion for display. This is a stone simple task . . . when the stimulus to be measured is steady. But depending on the instruments choice for a/d processing, currents that wiggle can cause erroneous if not wild swings in displayed readings. Systems like electronic fuel injection, pulse pumps, ignition systems, and strobes tend to demand current from the system with jumpy characteristics. Years ago I wrestled with these measurements by crafting an operational amplifier integrator that was fed by an ammeter shunt in series with the measurement of interest. The first time I did this was to deduce the batter size needed for this machine: http://aeroelectric.com/Pictures/Misc/Mobilizer_3s.jpg During a patient load-unload cycle the current draw of the various motors was all over the place. But the integrator would sum the current values per unit time whereupon I could multiply by battery voltage and deduce watt-seconds of energy per patient handling cycle. It's exactly this kind of measurement philosophy that's needed to deduce energy requirements for the "jumpy" systems aboard your airplane. This has always been a bit of tone in my shoe when dealing with suppliers of accessories to aircraft. The product data sheets give max current draws (sizes wire and breakers) but for things like strobes and pumps, there was no integrated total-energy value (sizes batteries in the alternator out mode). How does all this relate to the topic at hand? First, it is unlikely that a clamp-on DC ammeter of the type cited will be very useful for measuring current draw of an EFCI. First because the measurement of interest is large compared to the accuracy of the device. If it has a published accuracy of say 3% of full scale for a 50A scale, that's plus or minus 1.5 amps. Furthermore, the electronics within the instrument may not handle the wiggly nature of current draw for injectors that get pulsed at 10A for milliseconds and once per cylinder-firing. A modern version of the instrumentation I described above would be useful. A 10A, 50Mv shunt would provide the current sample. We would want to put a gain of 100 on the 50Mv signal to get it up to the 5 volt range. The output of the gain stage would drive an integrator with a low dielectric absorption capacitor (like a Panasonic ECQE1106K). With a 1M integrating resistor and 10uF capacitor, our amplified shunt signal would drive the charge on the capacitor to 5 volts in 10 seconds. This is the order of magnitude for integrator gain and time constant useful to our tasks. See: http://aeroelectric.com/Pictures/Schematics/Ammeter_for_Wiggly_Currents.pdf Hooking this shunt in series with your wiggly system power, let us assume that you get a reading of 3.6 volts at the end of ten seconds. We know that 10A for 10 seconds raises our instrument's output to 5 volts. The reading of 3.6 volts represents an integrated current value of 10 x 3.6/5.0 or 7.2 amps. It matters not how much the measurement thrashes around, as far as your BATTERY is concerned, it needs to deliver 7.2A x 12v x 2 = 173 watt- hours of energy to keep that puppy running for two hours. When you have the integrated value of current draw for ALL endurance loads, you're prepared to go into the battery performance charts and select a battery that meets your design goals. I know this is a lot of info that most folks don't need. But if anyone is interested in getting the real numbers on their system's performance, this kind of tool is quite useful. But be aware also that the plain vanilla ammeters have limitations for accuracy at levels of interest and performance for dynamic (wiggly) loads. Bob . . . ________________________________ Message 4 _____________________________________ Time: 08:33:26 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Battery Choices - what is too small AH capacity? At 01:15 PM 8/13/2008 -0700, you wrote: > >Ken, > >You wrote: 8 AH Dekka AGM batteries > >Can you describe the battery terminals on these Dekka batteries? Even a >digital photo would be helpful. I have #2 welding cable with #2 lug >terminals from the main contactor to the main battery terminals. I'm a bit >concerned my existing battery terminals are too small for long term use & >vibration resistance. The driving considerations for battery selection are (1) capacity at endurance loads, (2) internal impedance at cranking loads and (3) ability of the terminals to carry cranking currents. (1) Capacity is another discussion. (2) For a battery to be a successful engine cranking source, 10 milliohms new is a pretty fair benchmark for maximum internal impedance. I mention this because there are very compact technologies with limited capacity (1 a.h. or so) that will dump over 1000 amps of short circuit current! Smoke from a flash-in-the-pan blew through the marketplace about 10 years ago when Bolder Technologies attempted to launch a thin metal film battery about the size of a c-cell. A host of products sprang up using this device. "Start Stick" was shown around OSH several years. I think Sears marketed a very compact car cranking accessory for a time. These cells didn't make it for reasons of process limitations. They couldn't keep a good electrical grip on the edges of the films . . . and had some sealing problems too. They're gone now, but they (or something similar) will be back. For the moment, our practical choices for cranking batteries are probably not smaller than 10 a.h. or so. B&C has a little 12 a.h. battery that will crank engines: http://www.bandc.biz/BC103-1.pdf Concorde used to have a 10 a.h. device that would crank but I don't see it listed any more. (3) Terminals. You can get a 17 a.h. battery with .25" faston tabs, and fat-wire connection posts. Both batteries are capable of cranking engines with respect to internal construction but fast-on tabs are obviously not capable of delivering that kind of current. IF you find a battery with a very low internal impedance, then terminals should be on the order of 1/4" bolts through hefty metal tabs -OR- 10-32 (4mm) minimum screws into brass inserts. To prevent damage to your battery's connections due to vibration and stress . . . make all connections to batteries with 4AWG welding cable between battery(-) and ground; battery(+) and battery contactor. This is a good thing to do even if the rest of your airplane is wired with 00 fat-wires. After (2) and (3) are satisfied, then capacity is a function of meeting design goals for weight, cost of ownership, and battery-only endurance. Bob . . . ________________________________ Message 5 _____________________________________ Time: 05:44:05 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: No sidetone driving me insane! At 07:08 AM 8/15/2008 -0700, you wrote: > > >Hi, > >I've got an Icom a200 radio connected through a pm 1200 intercom. > >When I got the plane it had no side tone at all. Pulled the radio and >tried to adjust the sidetone pot to no avail. Turned off intercom and >still no side tone. > >I've tried numerous different headsets. I did notice what seems to be a >disconnected wire(s) at the molex connector but don't no if that's an >issue. The wiring job is shoddy to begin with but I'd hate to rip it out >and start new if it's actually a radio issue. > >radio transmits and receives just fine and the intercom is awesome at >canceling out noise in my very loud warbird. > >Just hoping for some last chance advice before I send the radio out for a >bench test. Sidetone is not subject to variations in headsets. If you can hear anything else in the headsets and no sidetone, then it's not the headsets. I looked at the installation manual and didn't spot any mention of sidetone . . . are you sure this radio supports it? Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ---------------------------------------- ------------------------------------------------------------------------------------- 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.