Electrical Problem

Discussion in 'Maintenance Bay' started by warren.mcilvoy@asu.edu, Dec 24, 2005.

  1. warren.mcilvoy@asu.edu

    warren.mcilvoy@asu.edu Filing Flight Plan

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    Warren McIlvoy
    1980 C182Q Ser #18267373
    Electrical Problem/Problems
    To date my partner and I have replaced the battery, the alternator (after my partner had to hand prop the AC at a remote airfield)the alternator circuit breaker, the master switch and master contactor in an effort to solve the following intermittent problem/problems.

    Scenario 1-- Occasionally prior to start nothing comes on line when
    the Master switch is turned on. Using a volt meter there is no
    indication of voltage to the bus. After a short amount of time with the switch on, the system comes on by itself.


    Scenario 2--With the master switch on, engine not running, the system shuts down by itself. Recycling the master switch brings everything back online.

    Scenario 3--With the engine running and the ammeter operating what appears to be normally, the ammeter needle goes to one needle width on the discharge side and goes inop. When a load is put on or taken away ie flaps up and down, lights on and off the needle stays fixed one needle width left of center. To bring the gage back into operation it is necessary to recycle the Alt switch.

    This fixes the problem sometimes for only a short time and sometimes for many minutes or even the duration of the flight.
    When this condition happens a digital volt meter on the cigar lighter shows 28 +/ - volts.

    Scenario 4-- Occasionally the cylinder head temp gage also drops off line. This happens even after our mechanic has checked the probe several times.

    At this point we are starting to think that we have more than one problem. We are thinking that we might have a wire issue from the master switch to the master contactor and a separate ammeter/ cylinder head gage problem.

    HELP!!!!
     
  2. Don Jones

    Don Jones Line Up and Wait

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    Warren,
    Sounds to me like Senario 1 & 2 are going to be connection related, probably in
    a bad ground connnection somewhere. There is a strong probability it will fix everything. Sounds like time to clean and inspect every ground connection there is. Particularly the ones which connect to the airframe where corrosion can build up and cause high resistance. I went through a similar long diagnosis process on my Piper and found a lot of crappy grounds. Since the master switch supplies ground for the master relay that is the first place I would start by tracing the ground to the switch back to the source. The cylinder temp thing is probably a seperate problem, however if the meter is losing ground it could be tied to the other problems as well.
    Good luck,
    Don
     
  3. Steve

    Steve En-Route

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    Have you checked the voltage regulator?
     
  4. gismo

    gismo Touchdown! Greaser!

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    I agree with Don about the likelihood of a ground problem. Chances are you do have more than one problem though. Also the issue with no bus voltage when the master is first turned on could be a bad master contactor. Most have three terminals, a few have four with two tied together. Two of the terminals are larger and one of those goes to the battery and the other to the main bus. If there's only one small terminal it will go to the master switch.

    If you can put a meter on those terminals when the master is on and you have no buss voltage, you should be able to determine where that problem lies. Measure from each terminal to airframe ground. If the battery terminal is dead, check both battery leads. If the switch terminal (small) has more than a volt or so, the wiring to the master switch is the problem (including the swtich). If the buss terminal is at the same voltage as the battery, the wire from the contactor to the main bus is open.
     
  5. Richard

    Richard Final Approach

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    Why do you think it is a gnd problem? Is it because it is easier to troubleshoot than checking the master sw? I think it is connectivity at the master sw.
     
  6. Stache

    Stache Pre-takeoff checklist

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    Being an A&P/IA, I would say you may have a bad connection/ground issue. I would start with the battery connections. Next look at and clean the terminals on the terminal block. This is one area that never gets cleaned during any inspection I know of. However be very careful when cleaning the terminal block, make sure the battery cables is disconnected first. Take one terminal off at a time clean it and reinstall in the same manner it came off with the washers in the same location.

    Next if you have breakers I would pull them and push back in. This will clean off any corrosion on the breakers. If you have fuses take them out one at a time and clean them and reinstall.

    I also ran a check of the AD’s and Alerts for your aircraft CE-182-Q and found two on the electrical system and one alert as follows that should be looked at again.

    AD 79-08-03
    To prevent an inflight electrical system failure, smoke in the cockpit, and/or fire in the wire bundle behind the instrument panel, accomplish the following:
    A)Disconnect the wire, at the ammeter or at the electrical system bus as applicable, that connects the bus to the cigar lighter receptacle. (The wire is connected to either the bus side or equipment side of a circuit breaker or to the ammeter.) Following the disconnection of this wire either:
    1)Reconnect the wire to the electrical bus by using an existing or newly installed circuit protection device that is properly rated to protect the wire gauge used for this circuit, or
    2)Disconnect the wire from the lighter receptacle at the opposite end and remove it from the airplane, or
    3)Protect the wire by insulating its disconnected end, fold this wire end back against the wire bundle in which it is routed and secure it to that bundle.

    AD 79-25-07
    To preclude the possibility of electrical or electronic component damage or an in-flight fire due to a short between an ungrounded alternator and flammable fluid carrying lines, accomplish the following:
    A)Perform either 1 or 2 below:
    1)Install an additional ground strap, Cessna P/N 1570102-22, between the ground stud on the alternator and the lower left hand mounting stud on the engine auxiliary drive pad in accordance with Cessna Single Engine Service Information Letter SE79-59. An equivalent ground strap fabricated per FAA Advisory Circular 43.13-1A appropriate for the alternator rating is also acceptable.
    2)Modify the alternator installation by installing a different engine mount leg per Cessna Service Kit SK210-84 (Reference Cessna Single Engine Customer Care Service Information Letter SE79-5, dated February 26, 1979) or for the 182 Series, Cessna Service Kit SK182-55A (Reference Cessna Single Engine Customer Care Service Information Letter SE79-58 dated November 23, 1979).

    AC 43-16 Alerts for Cessna 182
    Starter Solenoid, P/N S1577-A1
    During installation of radio equipment and testing of the equipment using aircraft power, the battery current began to get a little low. When the maintenance crew turned the aircraft master switch on a short time later, the prop began rotating and the engine started while still in the hangar. No external power was connected. An identical incident was reported relative to a new Cessna 182.

    Just one man’s opinion.

    Stache
     
  7. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser!

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    I had something similar on an airplane in which one of the terminals on the ammeter was loose.
     
  8. Tom-D

    Tom-D Taxi to Parking

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    Has any one cleaned the battery ground strap to airframe contact?

    Does your A&P know how to do a voltage drop test? Across each and every contact.
     
    Last edited: Dec 25, 2005
  9. Richard

    Richard Final Approach

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    So, it is agreed that the likely suspect is an IR drop at a connection and not neccessarily a bonding issue? But which connection, right?
     
  10. Tom-D

    Tom-D Taxi to Parking

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    I hate on line trouble shooting it is a stab in the dark at best.
     
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  11. gismo

    gismo Touchdown! Greaser!

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    You got that right. At best we might suggest the right places to start looking, anything more and it's like speculating on the cause of a crash with nothing but the type of aircraft and the ground weather at the time.
     
  12. warren.mcilvoy@asu.edu

    warren.mcilvoy@asu.edu Filing Flight Plan

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    Regarding the "ground strap". I asked our mechanic about that and he said that this does not exist on the 24-volt system. He said that this was a common issue on the 12-volt system as it was located under the battery case and was subject to random corrosion. He also checked the wire from the master contactor to the (new) master switch and found it to be ok. Yesterday, I turned-on the master and.............nothing. After about 5-minutes or so, I happened to turn on the nav light switch and, walla, everything came on. We are going to have him replace all (6?) switches. It might have been just a coincidence that everything came on but, who knows, the problem could be in the wiring associated with these switches.
     
  13. wsuffa

    wsuffa Touchdown! Greaser!

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    Warren,

    I had a problem with a corroded/pitted contactor that was similar. When there was enough current to bridge the resistance, current flowed well enough. 12 Volt system, different type of plane, but I'd look for corrosion, pitting, and bad connections in the contactor system.

    My $0.02.
     
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  14. Don Jones

    Don Jones Line Up and Wait

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    Man Warren, I sure would not just throw a set of switches at it. These things can be diagnosed right to the failed part/connection. You have already replaced the switch involved. It sure gets expensive replacing things it does not need.
    You also mentioned checking the wire from the switch to the contactor. What about the wire from ground to the switch? There is a bad connection lurking there somewhere, just gotta find it. I bet the nav light thing was a coincidence.
    Or it wiggled the bad connection somehow when you flipped it on.
    Don
     
    Last edited: Dec 29, 2005
  15. gismo

    gismo Touchdown! Greaser!

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    There's virtually no way the nave light switch has anything to do with your problem beyond possibly providing the vibration of some connection or contact that finally made the connection.

    The behavior you describe is typical of a bad master contactor, the coil in the contactor heats up and once warm enough the plunger becomes free to move and complete the circuit. Next time this happens, try rapping the contactor with something relatively hard (screwdriver handle hard) while the master switch is on. If it starts working then, you've probably found one of your problems. It could also be the master switch itself or the connections on it.
     
  16. Henning

    Henning Ejection Handle Pulled

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    First thing I would be looking at is the grounding loop. Check it from the battery all the way to the buss, make up a jumper lead that you can go direct from the battery post to the ground buss next time it acts up. If that gets the panel back on line, start looking for the corrosion. There is also a braided ground strap that connects the engine to the mount (those Lord/Dynafocal mounts are good insulators) to look at as well. Usually these sporadic type electrical problems are loose or corroded ground connections.
     
  17. warren.mcilvoy@asu.edu

    warren.mcilvoy@asu.edu Filing Flight Plan

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    Don, you may be correct but two of the switches have broken plastic rockers and since we have to replace two of them now, why not just do the rest? It may also be possible that while the "wrench guy" is in there doing that job, he may stumble upon something suspicious.
     
  18. warren.mcilvoy@asu.edu

    warren.mcilvoy@asu.edu Filing Flight Plan

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    I believe that we have solved our electrical gremlin. We had an "airplane guy" that specializes in avionics installations and aircraft wiring. After much testing and tracing, he found the power connection to the bus, was loose. He bolted it on and I test flew the airplane this morning. Everything worked perfectly. He is also going to replace the six rocker switches that had our attention during our problem solving efforts.
     
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  19. Mantoga

    Mantoga Filing Flight Plan

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    I know that this is resurrecting extremely old thread but I have the exact same issue. So in the end was it just a loose electrical ground? Thanks
     
  20. Dan Thomas

    Dan Thomas En-Route

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    Not a ground. There's a heavy wire between the ammeter and the bus bar. He said it was loose at the bus.
     
  21. Mantoga

    Mantoga Filing Flight Plan

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    Wow, OK, I guess I'll just start checking every wire I can the see if any are loose or corroded. My problem is when I turn on the master everything comes on but the 2nd you try to start the engine or put a heavy load like landing lights, clack! everything goes dark and the gyro start spooling down. I think it has to be master switch related because if I jump the pole on the master solenoid there are no issues
     
  22. Dan Thomas

    Dan Thomas En-Route

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    The contacts in the master solenoid get old, oxidized and burned. Even a low-time, 40-year-old airplane will have oxidized contacts. Contacts like that create a small resistance that isn't a big deal until you try to start the airplane. Voltage is equal to amps times ohm, which means, in this case, that a starter that draws 200 amps at 12 volts through a contactor that has a .05 resistance--a twentieth of an ohm--will have a 10-volt drop across the contactor. The remaining two volts aren't enough to keep the contactor closed. Things go dark.

    The starter contactor can do the same thing, but things usually don't go dark.

    Put a voltmeter's probes across the big terminals on the master contactor. Set the meter to 12 volts or whatever. It should read battery voltage (ground is provided for the tiny voltmeter current through the contactor coil and stuff like the turn coordinator). Crank the engine; the meter should drop to zero or very close to it. Anything over half a volt or so is cause for concern. Do the same with the starter contactor.

    Intelligent use of a multimeter--even a cheap multimeter--will save gazillions of dollars by pinpointing the problems.

    Another common problem is oxidized cables inside the big crimp terminals on battery and starter cables. Look for green crud on the wires.
     
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  23. Mantoga

    Mantoga Filing Flight Plan

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    Ok, I’ll give that a try. The master solenoid did get replaced but still it could be a bad one, I’m thinking possibly bad master switch but prob somewhere I have a bad ground or wire or both
     
  24. denverpilot

    denverpilot Taxi to Parking

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    FWIW our Master went bad a while back.

    This crap is 1970s electronics. It’s going to wear out.