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revenson(at)comcast.net
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 Posted: Mon Apr 13, 2015 2:07 pm Post subject: Do I Have a Problem? |
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On a flight a couple of months ago I noticed my endurance bus voltage lower than usual. It was showing 12.5-12.9 volts, where I usually see 12.9-13.3 volts. Since it was time for my annual, and I have 5 years and 460 hours on the plane (and the voltage regulator), I 'threw' on a new Standard VR166 regulator without any diagnosis. At subsequent start-up, I noticed what looked like a healthier 13.5-13.8 volts, so I thought I guessed right, and also thought maybe my previous 13.0 volts had been a bit low for the entire 5 yrs. I've been flying! (I get about a 0.5 voltage drop from my 4-diode bridge rectifier).
A couple of days ago, 35 minutes into a 1 hour flight, I got my very first low voltage alarm (which is set at 12.4v). Voltage was 11.2-11.9. My GRT EIS records engine info each second. The log showed the low voltage lasted only 6 seconds.
At 40 minutes, it tripped again, lasted 17 seconds, showed 11.2-11.6 volts.
It alarmed a third time at 54 minutes into the flight, lasted 13 seconds, and again showed 11.2-11.9 volts.
I later checked the EIS log, and noted that each time the bus voltage went down, the field voltage went down, and the total load ammeter also went down. Any clues there?
I think I have an issue that deserves more diagnosis, but then again, maybe it's just an artifact of having an EIS that just provides too much information. After all, we're talking about only 36 seconds out of a 1 hour flight. What do you think? And where should I start looking? I'd certainly rather investigate now, and not wait for a total failure while away from home.
Background and a couple more questions:
Wired Figure Z-11, with the B&C OV protection module.
In addition to the externally-regulated (40A, B&C) alternator, the field wire goes to both a sub-panel connector (per Z23 and note  ; and also to an aux input on the EIS. (I WONDER NOW IF THIS WAS OK).
A load test on the battery showed it still 'in the green', but only barely so. At 3.5 years old, I'm replacing it now.
Can the Crowbar OV module go bad and cause the regulator to perceive lower bus voltage?
My Crowbar OV module ground is connected first to the Master Switch, then from there goes to the common firewall ground tabs. I note this because I looked at the current Z11 figure and see that there the module ground is shown going directly to ground. But electrically, this should be the same, right?
Your help will be much appreciated.
Roger. RV-7A, Tucson.
[quote][b]
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user9253
Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan
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| Posted: Mon Apr 13, 2015 4:41 pm Post subject: Re: Do I Have a Problem? |
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I think that the low voltage alarm set-point should be closer to 13 volts to give a more advanced warning.
Quote from Bob's book Appendix Z note 8 paragraph (C).
| Quote: | | Check for increased resistance in regulator field supply wiring and components. Breakers, switches, over-voltage relays, and connectors are all contributors to regulator instability when their resistance ages upward a few milliohms in resistance. |
| Quote: | | but then again, maybe it's just an artifact of having an EIS that just provides too much information. |
Not at all, there is a problem that needs to be corrected.
| Quote: | | and also to an aux input on the EIS. (I WONDER NOW IF THIS WAS OK) |
Definitely. The more information the better.
| Quote: | | Can the Crowbar OV module go bad and cause the regulator to perceive lower bus voltage? |
Highly unlikely
| Quote: | | But electrically, this should be the same, right? |
Should be, but more connections mean more possible failure points.
I suggest you take some voltage measurements with the master switch on and the engine off. Use the positive bus as a reference point for the voltmeter red lead and measure voltage at various points between the bus and alternator field terminal. A voltage drop indicates resistance in the circuit.
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_________________
Joe Gores
Last edited by user9253 on Tue Apr 14, 2015 4:16 am; edited 2 times in total |
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paulf(at)hughes.net
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| Posted: Mon Apr 13, 2015 5:45 pm Post subject: Do I Have a Problem? |
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I would also suggest you verify nice "gas tight" connections on
everything in the charging circuit, including all of the regulator
wires, the alternator wires, and don't forget your grounds. As Joe
said, lower voltage indicates resistance in the circuit, and that is
often a lose connection. Fortunately, it is also one of the easiest
things (cheapest!) to fix!
Just a suggestion...
Paul
On 4/13/2015 7:41 PM, user9253 wrote:
| Quote: |
I think that the low voltage alarm set-point should be closer to 13 volts to give a more advanced warning.
Quote from Bob's book Appendix Z note 8 paragraph (C).
> Check for increased resistance in regulator field supply wiring and components. Breakers, switches, over-voltage relays, and connectors are all contributors to regulator instability when their resistance ages upward a few milliohms in resistance.
> but then again, maybe it's just an artifact of having an EIS that just provides too much information.
Not at all, there is a problem that needs to be corrected.
> and also to an aux input on the EIS. (I WONDER NOW IF THIS WAS OK)
Definitely. The more information the better.
> Can the Crowbar OV module go bad and cause the regulator to perceive lower bus voltage?
Highly unlikely
> But electrically, this should be the same, right?
Should be, but more connections mean more possible failure points.
I suggest you take some voltage measurements with the master switch on and the engine off. Use the bus as a reference point for the voltmeter black lead and measure voltage at various points between the bus and alternator field terminal. A voltage drop indicates resistance in the circuit.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=440814#440814
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nuckolls.bob(at)aeroelect
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| Posted: Tue Apr 14, 2015 6:38 am Post subject: Do I Have a Problem? |
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On a flight a couple of months ago I noticed my endurance bus voltage lower than usual. It was showing 12.5-12.9 volts, where I usually see 12.9-13.3 volts. Since it was time for my annual, and I have 5 years and 460 hours on the plane (and the voltage regulator), I 'threw' on a new Standard VR166 regulator without any diagnosis. At subsequent start-up, I noticed what looked like a healthier 13.5-13.8 volts, so I thought I guessed right, and also thought maybe my previous 13.0 volts had been a bit low for the entire 5 yrs. I've been flying! (I get about a 0.5 voltage drop from my 4-diode bridge rectifier).
Expected readings . . .
A couple of days ago, 35 minutes into a 1 hour flight, I got my very first low voltage alarm (which is set at 12.4v). Voltage was 11.2-11.9. My GRT EIS records engine info each second. The log showed the low voltage lasted only 6 seconds. At 40 minutes, it tripped again, lasted 17 seconds, showed 11.2-11.6 volts. It alarmed a third time at 54 minutes into the flight, lasted 13 seconds, and again showed 11.2-11.9 volts.
I later checked the EIS log, and noted that each time the bus voltage went down, the field voltage went down, and the total load ammeter also went down. Any clues there?
Wow! Symptoms quantified with numbers . . . and field voltge too? Be still my beating heart . . .
I think I have an issue that deserves more diagnosis, but then again, maybe it's just an artifact of having an EIS that just provides too much information. After all, we're talking about only 36 seconds out of a 1 hour flight. What do you think? And where should I start looking? I'd certainly rather investigate now, and not wait for a total failure while away from home.
You cannot have too much information. It's possible to mis-interpret data and having lots of it might be distracting . . . but ALL of my most challenging failure studies began with getting the data acquision systems installed with a hope that the problem would repeat and be captured on hard-drive. One test involved routing a long piece of 30 conductor ribbon cable from the hell-hole on a Beechjet, out the baggage compartment door under the seal, tapped to the side of the fuselage and thence into the cabin through the main door seal. Only then was I able to watch and record a library of events surrounding a problem that would only repeat after 30 minutes or so at 41K feet. Turned out to be a pushed back pin in a pressure bulkhead connector. The airplane had been out of service for several weeks at killobux per day while un-informed studies were conducted. Only after I got them to put the airplane in 'experimental license' and convinced the pilots that we weren't going to suck the tape and wire into the engines did we GET THE NUMBERS. The airplane was back in service the next day.
Background and a couple more questions:
Wired Figure Z-11, with the B&C OV protection module.
In addition to the externally-regulated (40A, B&C) alternator, the field wire goes to both a sub-panel connector (per Z23 and note ; and also to an aux input on the EIS. (I WONDER NOW IF THIS WAS OK).
A load test on the battery showed it still 'in the green', but only barely so. At 3.5 years old, I'm replacing it now.
Can the Crowbar OV module go bad and cause the regulator to perceive lower bus voltage?
No . . . the CBOVM will OPEN the field breaker to effect a permanet shutdown of the alternator. It is incapable of intermittent operation you describe.
My Crowbar OV module ground is connected first to the Master Switch, then from there goes to the common firewall ground tabs. I note this because I looked at the current Z11 figure and see that there the module ground is shown going directly to ground. But electrically, this should be the same, right?
The CBOVM can be grounded to any sturdy location.
If field voltage drops coincident with drop in bus voltage, there is a DISCONNECT between the bus and the alternator field terminal. It can be anywhere along that path INCLUDING a bad alternator switch, misbehaving regulator, even a bad breaker, or perhaps a poorly crafted joint.
This has the 'smell' of a poor connection . . . so if you've not already done so, check the tightness of screw terminals, tug firmly on crimped terminal joints, the usual suspects. Given that the gross failures of alternator output occured after you changed the regulator, I'd pay particular attention to the terminals and crimps associated with that device.
The next time the symptoms manifest, cycle the breaker and the alternator control to see if the action immediately clears the symptoms.
Bob . . . [quote][b]
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