AeroElectric-List Digest Archive

Sat 12/06/08


Total Messages Posted: 2



Today's Message Index:
----------------------
 
     1. 06:32 AM - Re: Z-11 Questions (Robert L. Nuckolls, III)
     2. 06:48 AM - Re: Dancing ammeter and alternator drop outs (Robert L. Nuckolls, III)
 
 
 


Message 1


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    Time: 06:32:05 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Z-11 Questions
    At 07:14 PM 12/5/2008, you wrote: > >Hello Listers, > >A few questions for my RV-7, Z-11 system, E-Mag/P-Mag. > >1. Can I run the Main Bus feed from the Alternator side of the ANL60 >Current Limiter? The wiring run would be slightly easier and there's >a secondary reason... How about the system side of the ANL? The reason the ANL would open is because of a fault in the alternator or its feeder. This is an exceedingly rare event but it would take down the whole system if you feed from the alternator side. >2. If I can do #1, would that provide sufficient protection for the >8AWG feed line to the Main Bus? That feed has no protection in Z-11 >and it seems like it should. I foresee little risk of that line >shorting to ground, but the consequences would be significant. FAT wires in airplanes that feed large busses and connect starters and batteries together do not require protection. You won't find such protection in any certified light aircraft. Here's an excerpt from FAR23 http://www.aeroelectric.com/Reference_Docs/FAA/Part23_electrical_A.pdf Check out paragraph 23.1357 . . . >3. If I can't do #1, can I / should I use a 12AWG fusible link to >protect the Main Bus feed line? Not useful . . . >4. My Battery Bus feed line will exceed 6". It's roughly the same >run length as the Main Bus feed, something like 24". Can I / should >I protect it with a fusible link? Same rationale as the Main Bus >feed. It would be a 14AWG run (Battery bus is source for the E-Bus >Alt Feed) with an 18AWG fusible link. No, that 6" thing is a design goal. The world does not spin down to a halt if it is longer. Treat this feeder with the same concerns for design, installation, and maintenance as your prop bolts. Satisfy yourself that there is NO way this wire's functionality can become compromised. >5. This is more FYI and for comment, but I'm wiring my E-Mag and >P-Mag each the same way: >- E-Bus to 2A panel breaker to mag for power >- SPST switch and shielded P-lead for each mag > >My thinking is that they should be wired identically and treated >much the same as mags. E-Bus 'cuz their important, the individual >breakers will allow me to power down the P-Mag to test it, and >finally the shielded P-leads allow me to switch to traditional mags >if ever needed. It is far less complicated than many schemes I've >seen and uses cheaper switches (albeit two pricey panel breakers). >Any holes in my plan? The switching arrangements shown in Z-11 for Emagair products are consistent with their recommendations and consideration of the effects of possible failure modes. This is your airplane . . . if you have comfort requirements that go beyond these recommendations, by all means, address them. >6. Finally, is there any problem with feeding those panel breakers >through a fuse on the E-Bus? My only other panel breaker, the Field, >will be fed through a fusible link from the Main Bus screw terminal. Breakers fed with like sized fuses will never operate. The fuses are 10x or more faster than breakers. You might as well use switches . . . which are already part of the suggested design. If you have a desire to incorporate breakers, then the battery bus fuses need to up-size to 30A devices and the feeder wire from bus to breaker should up-size to 14AWG or so. It's my recommendation that you wire the airplane as suggested in Z-11. This architecture was developed over 15 or so years of considerations for the uniqueness of the OBAM aircraft community based on 40+ years of experience in the TC aircraft world. Changes can and should be made if you find the recommendations lacking in some way for (1) minimizing weight, parts count and/or cost, (2) operational convenience or (3) safety. In these cases proposed changes should be evaluated by everyone as a candidate for revising Z-11 as published. But it's your airplane . . . your safest operational mode requires that you need to fly it with comfort and understanding. Bob . . .


    Message 2


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    Time: 06:48:48 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Dancing ammeter and alternator drop outs
    At 04:11 PM 12/5/2008, you wrote: ><thomas.n.gautier@jpl.nasa.gov> > >Bob, > > Our club Arrow IV has recently experienced a spate of alternator and >related electrical system maintenance issues. The symptoms that the club >members complained about centered on alternator drop outs which could often, >if not always, be cured by turning the alternator off and then back on. >There may have been an outright alternator failure of some sort as well. I >haven't followed the maintenance in detail since I haven't, until today, >flown the plane in the last month. By "drop out" do you mean that the alternator shuts down completely? Do you get a low voltage warning or does the ammeter go to zero and stay there? > The upshot of all the maintenance is that first the voltage regulator >and then the alternator were replaced. The symptom reported after voltage >regulator replacement but before alternator replacement was that the >alternator was dropping out every 10 minutes in the last half hour of a >cross country trip. I was the first to fly the plane after the alternator >replacement and I found the system to still be misbehaving. > > In my flight immediately upon starting the engine and switching on the >alternator the alternator ammeter (a load meter, I think) showed 70 amps, >pretty steady, recharging the battery I presume. Then, in less than a minute >the ammeter began swinging from 30A to 70A 2 or 3 times a second. I've read >your dancing ammeter posts so I assumed this was not particularly >troublesome (except that these swings were larger than I had seen before). >Then, after my first turn around the pattern, I noticed that the alternator >had dropped off line. It came back after cycling the alternator switch, >however the ammeter dancing was now as large as 0A to 70A. This behavior >continued for a couple more turns around the pattern, with full stop >landings, as I watched what was going on. I had to reset the alternator >twice more over the span of 20 minutes. I'm trying to deduce if you're speaking to an intermittent operation. A lack of ability for the alternator to deliver any power at all . . . or an unstable condition where the alternator is always developing some power but the regulation is unstable. > So, the plane's electrical problems are not solved and I'm trying to >help the owner and his mechanic figure out what is really wrong. I dug some >of your posts about dancing ammeters out of the archive and I'm ready to >show them to the plane's owner. However I'd like to get your opinion as to >whether I'm on the right track. Can the aging wiring problem that causes >dancing ammeters also cause the alternator to frequently drop off line? You use the words "dancing ammeter". Go to http://www.matronics.com/searching/ws_script.cgi Search the AeroElectric List archive using search string . . . dancing & ammeter You will unearth a lot of conversation about a phenomenon common to older airplanes where the voltage regulator senses bus voltage through the same wire that supplies field current. This sets up the possibility for a "negative resistance" (read oscillation) of voltage regulator stability that can be anything from barely noticeable to quite severe. It has nothing to do with the alternator or the regulator and everything to do with condition of ALL wires, components and joints between the bus and the regulator. The 30-year fix is to replace ALL these components. If you're describing an oscillating voltage condition, then the discussions and recommended fixes described in the archives are the road to Nirvana. If you're describing an intermittent functionality where the alternator output goes to zero and stays there for some observable time interval . . . you're chasing a loose connection. Bob . . .




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