AeroElectric-List Digest Archive

Sun 11/14/10


Total Messages Posted: 4



Today's Message Index:
----------------------
 
     1. 01:48 AM - Re: LR3C and overvoltage (Linda Walker)
     2. 09:55 AM - Re: Re: LR3C and overvoltage (Robert L. Nuckolls, III)
     3. 04:41 PM - Re: LR3C and overvoltage (Clarification) (Robert L. Nuckolls, III)
     4. 08:38 PM - Recommend a digital multimeter? (Ralph & Maria Finch)
 
 
 


Message 1


  • INDEX
  • Back to Main INDEX
  • NEXT
  • Skip to NEXT Message
  • LIST
  • Reply to LIST Regarding this Message
  • SENDER
  • Reply to SENDER Regarding this Message
    Time: 01:48:13 AM PST US
    From: Linda Walker <l.p@talk21.com>
    Subject: Re: LR3C and overvoltage
    Bob. I have a B and C LR3C (?) regulator watching over my electrical system batt ery and alternator. I also have a Vision Micro Systems VM1000 instrumentation. In monitoring the elec system voltage the VM uses a lead from my main bus, and normally shows between 13.6 and 14.2 volts. I have recently, yesterday, fitted a Dynon D-10A and on its screen it shows a voltage of 15 -15.3 volts. The Dynon is powered from the main bus. I also have two auxilliary outputs from the main bus to power a standby han dheld gps and handheld radio. The gps also monitors its input voltage and also shows 15 volts. My questions are: Could the LR3C be faulty and should it be replaced? How c an the VM1000 see a different voltage to the Dynon and standby gps? Is the VM1000 at fault? Any help in identifying which is correct and which isn't would be much appr eciated. Patrick C Elliott G-LGEZ. PS: Presently in Indonesia on our rtw trip from the UK, so getting things r epaired isn't so easy!


    Message 2


  • INDEX
  • Back to Main INDEX
  • PREVIOUS
  • Skip to PREVIOUS Message
  • NEXT
  • Skip to NEXT Message
  • LIST
  • Reply to LIST Regarding this Message
  • SENDER
  • Reply to SENDER Regarding this Message
    Time: 09:55:05 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: LR3C and overvoltage
    At 03:44 AM 11/14/2010, you wrote: Bob. I have a B and C LR3C (?) regulator watching over my electrical system battery and alternator. I also have a Vision Micro Systems VM1000 instrumentation. In monitoring the elec system voltage the VM uses a lead from my main bus, and normally shows between 13.6 and 14.2 volts. I have recently, yesterday, fitted a Dynon D-10A and on its screen it shows a voltage of 15 -15.3 volts. The Dynon is powered from the main bus. I also have two auxilliary outputs from the main bus to power a standby handheld gps and handheld radio. The gps also monitors its input voltage and also shows 15 volts. My questions are: Could the LR3C be faulty and should it be replaced? How can the VM1000 see a different voltage to the Dynon and standby gps? Is the VM1000 at fault? Any help in identifying which is correct and which isn't would be much appreciated. You are suffering a common malady known as "too much data". We're all operating vehicles from airplanes to cars, trucks, boats and lawn tractors that feature DC power systems. The vast majority do not have voltmeters and when they do have voltmeters, their veracity is seldom questioned. Obviously, only one of the readings you've cited can be "most nearly correct". I say "most nearly" because all measurement devices have accuracy specifications (and perhaps drift with age) that contribute to errors in displayed readings. Just for grins, I just gathered up a flock of 5 multimeters from various hiding places around the shops and vehicles and hooked them to a power supply on the bench. I set the power supply to 15.0 volts output based on it's 3-digit display. The various meters read as follows: Micronta (radio shack brand) 15.00 Digital Instrumets Co 15.05 Radio Shack 15.07 Fluke Model 75 14.96 Fluke Model 8000 14.94 If I average the total of 6 displays I get 15.003 which is a very strong suggestion that the power supply is indeed putting out 15.00 volts. This isn't a very good illustration because the devices I choose to keep in my toolboxes are of known reliability and are periodically checked. Nonetheless, if I were to split hairs, I'd have to say that the REAL output voltage was probably closer to 14.95 volts. Why? Only because of my experience with instruments crafted with John Fluke's name on them. Now, what's the significance of these tiny variations? In an airplane or any other vehicle, obviously none. What you're experiencing is the uncertainty generated by non-agreement of multiple instruments. This is compounded by the fact that you don't know which if any of the instruments were crafted with the skills and quality exemplified by John Fluke's test equipment. The preponderance of evidence suggests that your bus voltage is indeed on the order of 15.0 volts. Assuming that the VM1000 is not being "tricked" into some lower reading as a result of configuration (conductor voltage drops throughout the system) then the major suspicion of error is on the VM1000. The best thing to do is get a multimeter of some known calibration and use it to referee the contest. A fresh Duracell AA battery is very close to 1.60 volts at room temperature. Get a Radio Shack AA battery holder for 8 cells (Catalog #: 270-387) Emacs! An populate with fresh AA cells. Measure the terminal voltage on the holder. If your meter reads 12.8 volts, it's close enough for government work. If it's something else, make note of that difference. Let's say it's 12.5 volts. Okay, any reading in that range is 0.3 volts high. Now, go measure the bus on your airplane. Apply any observed calibration offset to the reading and THAT becomes your benchmark for evaluating the veracity of the other displays in the airplane. Your LR-3 senses the main bus so if your meter suggests some adjustment is called for, then there's a plug button on the side of the LR-3 that covers an adjusting screw. This reading is best taken while in flight and with normal loads on the system. So it might take several observations and subsequent adjustments to achieve what you want. On the other hand if you find that the bus is 14.2 to 14.6 volts under all operating conditions in flight, then I'd leave it alone. Just make note of the correction factor you now need to apply to any ONE instrument that displays voltage and ignore the rest of them. Many moons ago, the RM series mercury cells could be depended upon to offer a 1.345 volt calibration source over a wide range of temperature. Of course, we can't buy those any more. Bob . . .


    Message 3


  • INDEX
  • Back to Main INDEX
  • PREVIOUS
  • Skip to PREVIOUS Message
  • NEXT
  • Skip to NEXT Message
  • LIST
  • Reply to LIST Regarding this Message
  • SENDER
  • Reply to SENDER Regarding this Message
    Time: 04:41:53 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: LR3C and overvoltage (Clarification)
    <snip> . . . populated with fresh AA cells. Measure the terminal voltage on the holder. If your meter reads 12.8 volts, it's close enough for government work. If it's something else, make note of that difference. Let's say it's 12.5 volts. Okay, any reading in that range is 0.3 volts HIGHER THAN WHAT IS DISPLAYED ON THE METER so your correction factor is to add 0.3 volts to the reading. One reader asked why you couldn't check the meter calibration with one cell. Two reasons: (1) Many meters measure 15.0 and 1.5 on different scale settings which may not exactly track each other for %of error. In the example I gave, a single cell would have been measured on the 2 to 4 volt full scale settings while 15.0 volts was measured on 20 to 40 volt full scale settings; same settings as those used to investigate the situation in the airplane. If Radio Shack had an 9-cell holder, it would be better yet for qualifying your investigative instrument. (2) Instruments have several kinds of errors. Linearity, scale factor and offset. See instrumentation chapter in the 'Connection. By doing your calibration in the same neighborhood as the voltage of interest, the effects of linearity error are washed out. Effects of offset and scale factor are largely combined together in the hypothesized 0.3 volt error factor. This is a good example of how an instrument with terrible accuracy characteristics is still useful as a reasonably precise 'transfer standard' once its shortcomings are known. Now, go measure the bus on your airplane. Apply any observed calibration offset to the reading and THAT becomes your benchmark for evaluating the veracity of the other displays in the airplane. <snip> Bob . . .


    Message 4


  • INDEX
  • Back to Main INDEX
  • PREVIOUS
  • Skip to PREVIOUS Message
  • NEXT
  • Skip to NEXT Message
  • LIST
  • Reply to LIST Regarding this Message
  • SENDER
  • Reply to SENDER Regarding this Message
    Time: 08:38:01 PM PST US
    From: "Ralph & Maria Finch" <ralphmariafinch@gmail.com>
    Subject: Recommend a digital multimeter?
    I just discovered my faithful old Radio Shack DMM is wonky, the little scale at the bottom of the LCD displays reads correctly between 0-30, but the digits don't correspond. Time for a new DMM. I could just go back to the Shack and get whatever they have, but would like to check here for a recommendation. Mr. Nuckolls, any advice? A brief search using Google reveals many nifty new features in DMMs these days. Anything an airplane builder should look for? Thanks, Ralph Finch Davis, California, USA RV-9A QB-SA




    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
  • 7-Day List Browse
  •   http://www.matronics.com/browse/aeroelectric-list
  • Browse AeroElectric-List 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.

    -- Please support this service by making your Contribution today! --