AeroElectric-List Digest Archive

Wed 10/10/18


Total Messages Posted: 3



Today's Message Index:
----------------------
 
     1. 08:54 AM - Re: Re: B lead circuit breaker (Robert L. Nuckolls, III)
     2. 10:20 AM - Re: Re: B lead circuit breaker (FLYaDIVE)
     3. 07:15 PM - Re: Re: B lead circuit breaker (Robert L. Nuckolls, III)
 
 
 


Message 1


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    Time: 08:54:05 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: B lead circuit breaker
    At 09:21 PM 10/9/2018, you wrote: > >The vast majority of electrical problems are due to bad >connections. Check every connection in the charging circuit and in >the strobe circuit. Take apart connectors, clean them and put them >back together. I disagree . . . I can recall only one 'degraded connection' that was so elusive that it took several 'teams' over a month to chase down . . . but only because it was so buried in the hardware (pushed back pin in a pressure bulkhead connector) and only manifested at low temperatures requiring a test flight to 41,000 feet to cool the thing off before we could even begin to look. All other bad connection manifested with rather gross symptoms like those we've discussed here on the List concerning switch failures, burned terminals, etc. This problem would be easy to 'divide and conquer' if you had a data acquisition system you could clip to the bus and watch for transients that might be antagonizing the ov protection system on the alternator. Assuming that the design dynamics for the ov sensor are correct, an ov trip can originate from one source only . . . the alternator. A too high output from the alternator suggests that the regulator has lost control due to failure. On thing you might try is to replace the 5A breaker. This will help you decide if the 5A breaker has (1) degraded with age (rare but not unheard of) but is indeed being 'crow barred' open by a triggering of the alternator's ov protection. Does this alternator have an externally mounted ov module? Early versions of the PP machines did. It was a plastic box mounted to the back of the alternator. A wire ran into the alternator through a cooling hole. Bob . . .


    Message 2


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    Time: 10:20:23 AM PST US
    From: FLYaDIVE <flyadive@gmail.com>
    Subject: Re: B lead circuit breaker
    On Wednesday, October 10, 2018, Robert L. Nuckolls, III < nuckolls.bob@aeroelectric.com> wrote: > At 09:21 PM 10/9/2018, you wrote: > > > The vast majority of electrical problems are due to bad connections. > Check every connection in the charging circuit and in the strobe circuit. > Take apart connectors, clean them and put them back together. > > > I disagree . . . > Barry - I have to TOTALLY AGREE! I do aircraft repairs weekly and the number of non working, lights, intercoms and antennas that come into the hanger almost weekly is probably way more than all the fellows here on the list see in a their life time... Just had one last week Friday. If I had to put a number to it, 90% were due to bad contacts due to corrosion. You can not visually inspect a ground connection. It must be undone, wire brushed, NEW star lock washers replaced and tightened securely... Yes, tightened even beyond specs. Then, you can spray some chromate paint over the connection for a bit more corrosion protection. Wait a second Bob, aren=99t you the one the advocates the use of Diel ectric Grease on connections just to prevent corrosion? I agree with the Dielectric Grease idea. Been doing it for decades. Talking about tracing CRAZY electrical issues. TWICE, I have come across bulbs that check good on continuity yet DO NOT LIGHT! No, it was not corrosion, not this time. Care to take a SWAG at it? I would bet the airport that no one would guess. The failed bulbs were Marker Nav Light Bulbs. =94- hint, hint. On a 12 VDC system the bulbs are really a 24 VDC bulb. And on a 24 VDC system, yes you guessed it, they are really a 48 VDC BULB. It is done that way to extend the life of the bulb. Vibration is your enemy as well as weather. So, what happens is the filament breaks but stays in contact with the =98post=99. I have seen the problem happen twice and both time s it was at the mounting post of the filament. The low current of the DMM checks the bulb as good. But when operational voltage and CURRENT is applied the break heats up and opens. My Rule: Do not believe the DMM, apply a separate and full voltage & current to the bulb. If it lights, LQQK elsewhere for the problem. Good time to Check Grounds. Barry -- Barry "Chop'd Liver" If you wash your hands before you go to the bathroom you may have the makings of a Crew Chief.


    Message 3


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    Time: 07:15:22 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: B lead circuit breaker
    >If I had to put a number to it, 90% were due to bad contacts due to corrosion. >You can not visually inspect a ground >connection. It must be undone, wire brushed, >NEW star lock washers replaced and tightened securely... Yes, tightened even >beyond specs. Then, you can spray some chromate paint over the connection >for a bit more corrosion protection. I've never seen this kind of effort expended on a ground to the airframe. A bizjet has HUNDREDS of such grounds. All are made up with flat and clean faying surfaces assembled to the proper compression specs (torque). The natural crush that occurs in the terminal creates the gas-tight interface that excludes moisture+air; hence corrosion. A ground connection can look pretty bad on the surface of components but still maintain electrical integrity if assemble properly in the first place. >Wait a second Bob, aren't you the one the advocates the use of >Dielectric Grease on connections just to prevent corrosion? >I agree with the Dielectric Grease idea. Been doing it for decades. It sure doesn't hurt but recall that the purpose of the grease is to fill voids in the surfaces that did not get closed when the joint was made up in the first place. A void full of grease won't admit moisture+air. Here's a ground cluster in the nose of a Beechjet http://aeroelectric.com/Pictures/Grounding/MVC-699X.JPG Bright? yes. Clean? yes. Grease? No, Overspray? No. This installation was in s/n RK24, an experimental flight test aircraft which was 20+ years old at the time. If the airplane is operated in a particularly wicked environs, like the sea coast, the surfaces on and around such joints will enjoy protection from accelerated corrosion but if the joint was properly made up in the first place, the service life of the joint is probably not extended much. >Talking about tracing CRAZY electrical issues. TWICE, I have come >across bulbs that check good on continuity yet DO NOT LIGHT! >No, it was not corrosion, not this time. Care to take a SWAG at it? >I would bet the airport that no one would guess. >The failed bulbs were Marker Nav Light Bulbs. hint, hint. >On a 12 VDC system the bulbs are reaally a 24 VDC bulb. >And on a 24 VDC system, yes you guessed it, they are really >a 48 VDC BULB. It is done that way to extend the life of >the bulb. Where is this idea published? In chapter 12 of the 'Connection I speak to the relationship between applied voltage and life/current/intensity of the typical incandescent bulb. Emacs! For every ~5% reduction in voltage from the bulb's design center, life approximately doubles. So in your hypothetical 50% drop from design center, bulb life goes up HUNDREDS of times. At the same time, light output drops to about 10% of the design center . . . and in fact is quite redish in color. Emacs! An exemplar navigation lamp is in the 21-26watt class and operates at a color temperature strongly suggesting a design optimized for light output/color . . . and NOT de rated for service life. > Vibration is your enemy as well as weather. Also discussed in Chapter 12. In fact, we suggested a keep-warm circuit to hold incandescent lamps at about 10% of nominal operating voltage when turned OFF. This keeps the tungsten filament ABOVE the brittle/ductile transition temperature making the bulb more resistant to both vibration and warm-up shock when turned ON. Yeah, the air around the airplane can carry a host of antagonistic stressed into vulnerable locations, like the metal parts of a lamp socket. Dielectric grease on the shell and tip of a lamp base is a good thing. >So, what happens is the filament breaks but stays in contact with >the =98post=99.=C2 I have seen the problem happen twice and both >times it was at the mounting post of the filament. >The low current of the DMM checks the bulb as good.=C2 But when >operational voltage and CURRENT is applied the break heats up and opens. So does the bulb come back on when it cools only to immediately go dark again? Bob . . .




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