Author Topic: Airplane electrical wtf? (Read 486 times)

Wolfala · « **on:** October 23, 2007, 12:15:23 AM »

This is a 2000 SR-20 with a Lamar MCU and is relatively simple.

The other day, the alternator wasn't getting field excitation. So, we went through the usual suspects, checking the connections, battery and alternator, and belt. Hooked a meter up to the alt to see if there was any field getting to it - sure enough, nope. So checked the switch and it wasn't closing - so we bypassed the switch and the alternator came back alive.

So today, replaced the switch and put everything back the way it was. Hit the battery master, it sat there like a dumb ****. Unhooked the battery again, checked the connections underneath the dash, took the MCU cover off to see the battery solenoid - didn't see anything special. Had a guy come over with an volt/ohm meter - he put his leads on the solenoid when I put the Battery master on: Keep in mind these are his words - my head was underneath the dashboard and I couldn't see where his hands were. His words "I'm not getting any volts" Then - wham - comes to life.

I hit the battery master, a few seconds - he was doing something and then by some stroke of jedi magic the power came back. I don't know what he did, but i'm confused.

For one, the switch removed now magically had continuity which it did not have yesterday. Figure maybe it had oxidation or something. But the main power not coming on, the guy not seeing voltage for awhile and then it appearing - has me scratching my head.

Could it be a grounding issue that could've been exposed, or maybe somewhere between the battery and the battery contactor there is an intermitant short?

I don't believe in jedi magic, but this 1 has me stumped.

Wolf

Heater · « **Reply #1 on:** October 23, 2007, 06:04:13 AM »

Check the ground for corrosion / contact, as you have a short / open circuit

Phaser11 · « **Reply #2 on:** October 23, 2007, 06:54:06 AM »

OK,
Odds are what he did is grab the ground side of the battery near or at where it connect to the airframe and moved it around (THIS IS NOT A FIX). This is a very common problem in many aircraft. It could also be corrosion on\or a failing contactor (battery Relay). Remember you must CLEAN OFF CORROSION not move it around.
Go find your Jedi Night and find out what he did, get and answer. There should be a second write-up in the forms now for the second problem. These are 2 different problems, get them both in the forms.
And for gods sake, don’t fly the damn thing until your sure what happened.

Phaser11, Aircraft Electrical & Environmental Systems Craftsmen, USAF, Ret.

BlueJ1 · « **Reply #3 on:** October 23, 2007, 10:10:52 AM »

Quote

Originally posted by Phaser11
OK,
Odds are what he did is grab the ground side of the battery near or at where it connect to the airframe and moved it around (THIS IS NOT A FIX). This is a very common problem in many aircraft. It could also be corrosion on\or a failing contactor (battery Relay). Remember you must CLEAN OFF CORROSION not move it around.
Go find your Jedi Night and find out what he did, get and answer. There should be a second write-up in the forms now for the second problem. These are 2 different problems, get them both in the forms.
And for gods sake, donï¿½t fly the damn thing until your sure what happened.

Phaser11, Aircraft Electrical & Environmental Systems Craftsmen, USAF, Ret.

I second everything he just said.

BlueJ Aviation Electrician, USN

Wolfala · « **Reply #4 on:** October 25, 2007, 03:44:09 AM »

Update:

Spent most of the afternoon tracing out the electrical system. Connections on the battery were clean and no corrosion found elsewhere. The alternator master appears to be functioning normally as the battery was still charging. The battery master when initialized once today had about a 1 second hesitation before powering up. That basically leads me down the road of an open circut, but more specifically in the form of a Solenoid - with corrosion on the contacts. Naturally this is one of those items that is invisible from the outside, because all you see is a mini beer can from the outside. Based on the behavior - this is what I think it is. Any other possibilities?

Phaser11 · « **Reply #5 on:** October 25, 2007, 06:39:09 AM »

OK,
First, I am no longer qualified as an aircraft electrician. Any advice I give you is just that. You must get an FAA inspector to look at the aircraft after any work done before flight.

This is what I would do.

Disconnect the battery.
Remove the ground lead from the battery switch, using an ohm meter look for any resistance on that segment. It should be a strait short to ground.
Reconnect the battery switch.
Remove the GND ROWER RELAY. Safe the wires with some type of insulation (VERY IMPORTANT).
Connect the battery and test it again. By the diagram the GND ROWER RELAY is not required for battery operations and you can eliminate that entire segment by removing the relay.
It could be the battery relay, but it really sounds like the control power has to build up to energize the relay. Before you change the relay shoot the following wiring,

Disconnect battery,
Battery positive terminal to battery relay, 0 ohms on all scales
Battery switch ground to battery relay (ground control circuit) 0 ohms all scales (at airframe connect point)

Things to look at
Remove all paint from the airframe at all ground points in the circuit. Just scrape it away with a screwdriver or something. Where you might get a 0 ohm reading, it won’t be able to handle the amperage.

Bottom line, I AM NOT AN AIRCRAFT TECH ANYMORE.
Good luck.

Dago · « **Reply #6 on:** October 26, 2007, 08:39:01 PM »

I hope the "we" includes an A&P in your maintenance work, or you are in violation of the CFR's, and your insurance will be null and void. The work you described exceeds owner authorized preventive maintenance.

Wolfala · « **Reply #7 on:** October 26, 2007, 11:43:17 PM »

Quote

Originally posted by Dago
I hope the "we" includes an A&P in your maintenance work, or you are in violation of the CFR's, and your insurance will be null and void. The work you described exceeds owner authorized preventive maintenance.

We includes the instructor from A&P class. We're very familiar with 14 CFR Pt 43.

Chairboy · « **Reply #8 on:** October 26, 2007, 11:55:47 PM »

Quote

Originally posted by Dago
I hope the "we" includes an A&P in your maintenance work, or you are in violation of the CFR's, and your insurance will be null and void. The work you described exceeds owner authorized preventive maintenance.

Dago, could you quote the specific piece of his description that exceeds owner maintenance rules? Battery care & maintenance is explicitly allowed, for example, sounds like the only thing he did was disconnect a terminal. Or did I miss something?

Wolfala · « **Reply #9 on:** October 27, 2007, 12:04:37 AM »

Quote

Originally posted by Chairboy
Dago, could you quote the specific piece of his description that exceeds owner maintenance rules? Battery care & maintenance is explicitly allowed, for example, sounds like the only thing he did was disconnect a terminal. Or did I miss something?

Easy Chair, its 14 CFR Pt 43.

Part 43 MAINTENANCE, PREVENTIVE MAINTENANCE, REBUILDING, AND ALTERATION

Things an owner can do per Part 43 Appendix A Paragraph C

Removal, Installation and Repair of landing gear tires.
Replacing elastic shock absorber cords on landing gear.
Servicing landing gear shock struts (adding oil, air or both).
Servicing landing gear wheel bearings (cleaning and greasing).
Replacing defective safety wiring or cotter keys.
Lubrication not requiring disassembly other than removal of nonstructural items.
Simple fabric patches.
Replenishing hydraulic fluid.
Refinishing decorative external coatings (not on balanced control surfaces).
Applying preservative or protective material (where no disassembly is required).
Repairing upholstery and interior furnishings.
Making small repairs to fairings.
Replacing side windows.
Replacing safety belts.
Replacing seats or seat parts with approved parts.
Repairing broken landing light circuits.
Replacing bulbs, reflectors and lenses of position and landing lights.
Replacing wheels and skis (NO W&B change required)
Replacing cowling (not requiring propeller or flight control removal)
Replace, gap or clean spark plugs
Replace any hose other than hydraulic connections.
Replacing prefabricated fuel lines
Cleaning or replacing fuel and oil strainers or filters
Replace or service batteries.
Cleaning balloon burner pilot and nozzles.
Replacement or adjustment of non structural fasteners.
Interchange of balloon baskets.
Installation of anti-misfueling devices.
Removing or replacing magnetic chip detectors.
Any inspection and maintenance specifically identified in the AC type cert or any STC.
Remove/replace self contained front instrument panel mounted NAV or COMM device (excluding DME, Transponder and AP)
Updating self contained navigation databases.

That about covers what you can do without supervision, and you can do anything an A&P can do with their direct supervision.

Hope this helps.

Wolf

Chairboy · « **Reply #10 on:** October 27, 2007, 12:16:15 AM »

I know part 43 well, I was asking what he thinks you did that busted it. That's why I said "Battery care & maintenance is explicitly allowed, for example".

Wolfala · « **Reply #11 on:** October 27, 2007, 12:26:27 AM »

Doesn't matter in this case since it was supervised to begin with. Naming names wasn't relevant to the post since it was still largely troubleshooting, and electrical issues are perhaps being the most difficult to track down.

We've got a lot of good wrenches that hang out on these boards - so I defer my observations to them - and take their cautionary prescriptions with me every evening to class 6 hours per night - and in the days following continue the proud tradition of hunting gremlins under the teachers eye.

Dago's just making sure everyone is safe - nothing wrong with that and I applaud him for it.

Wolf

Chairboy · « **Reply #12 on:** October 27, 2007, 12:32:26 AM »

Maybe, but saying "The work you described exceeds owner authorized preventive maintenance." is a pretty direct statement, and unless I misread your description, I don't see what specifically you did that would have exceeded the boundaries defined by part 43.

Considering how carefully I studied that part of the rules before doing work, I'd love to know what he saw in your post that I didn't.

Wolfala · « **Reply #13 on:** October 27, 2007, 12:39:49 AM »

Not necessarily - if you R&R a switch, which is what was done when the Alternator wasn't getting field excitation - that is not preventive maintenance. At the same time neither is R&R on 3 jugs, but i've done that too.

Its the insinuation that the work was not supervised is what Dago was getting at - which is a legitimate concern if you don't know the persons background IMO.