Bryan Wood

Bryan Wood

Well Known Member
My RV has an intermittant electrical problem that has been bothering me, but it doesn't last long enough to know with certainty where the problem lies. Today a new symptom emerged and it has left me scratching my head. Also the plane is definetely broken now and seems to be in the failure mode so tracking the problem should be possible. :rolleyes:

For clarification I used the Van's wiring harness and wired per the factory prints without exception. Everything has been working great for 600 hours over 4 years. Any help, ideas, cures, or known problem areas offered up that will help to cure my problem will be greatly appreciated. This problem is so odd that I'm embarrassed to give a description, but here goes. Honest, this is what is happening.

The problem began with the breaker for "Instruments" popping when turning the ignition key to the start position. This was traced back to the ignition switch and I ordered one. I learned that moving the switch quickly from off to both and so forth about 20 times or so would help the problem and the plane could be started. This is what led me to believe the switch was bad. Trying to get one local flight in while waiting on the switch to arrive the following happened. With the key to "Start" the Instrument breaker popped again. I turned off all power and the moved the key back and forth and then the plane started right up without the breaker popping. Reaching for the flap switch to raise the flaps the breaker for the flaps popped when the switch was engaged. Resetting and trying again yielded the same results several times so naturally the flight was aborted and any future flights are now on hold until above problems are solved. With the engine now off and the flap breaker reset, master switch on, the flaps were tried again. Engaging the flap switch popped the breaker, but not until it somehow engaged the starter and drove the propeller thu about 1/2 blade! :eek: This simply couldn't be possible so I regrouped and checked everything. Other breakers were pulled to isolate and the flap breaker reset. Flap switch up, prop turning, breaker popped. It is now that I realize that if for any reason the flaps would have been raised in the hanger that my propeller would have likely cut thru the Piper Cubs wing that parks in front of me. The thought of this scares me to death. I never wanted a Cub and certainly I don't want one with a wing that is destroyed. Then the idea of hurting somebody on a ramp or whatever enters my mind. The plane is grounded, the breakers are all pulled, and the canopy is locked so that nobody can touch the flap switch and I wait on the starter switch to arrive.

Some time passes... Installed the new starter switch and engaged the starter. Pop goes the breaker. The flap switch is tried and the flap breaker pops, but the prop doesn't move any longer. Coincidence? At this point I closed the hanger door and came home. I'm pulling out the prints tonight and looking for anything that could cause this, but suspect that it will not be found this way. The thought of a wire bundle eaten by a mouse or whatever is now swimming thru my brain. I'm truly clueless at this point. Help...:eek:
 
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Hey Bryan, have you done a really thorough visual of the wiring harness? Be especialy curious around all of the points where you have cable clamps or tie-wraps. Look in corners where the harness makes 90 degree turns, and any place that a gromet may have fallen out. Our F-16 jet wiring harnesses are prone to chaffing in some of these same areas.
 
Sounds like a chaffing issue to me too, somewhere there is a few wires that are worn.
 
Bryan Wood said:
(snip) Any help, ideas, cures, or known problem areas offered up that will help to cure my problem will be greatly appreciated. (snip)
The thought of a wire bundle eaten by a mouse or whatever is now swimming thru my brain. I'm truly clueless at this point. Help...:eek:
Click to expand...

Bryan, have you tried one of these?




You can sometimes find them on eBay or if you have a friend who works on British cars...
 
Ground strap?

If the current is trying to return to the battery using your panel instead of engine's ground strap... strange things can happen. Also check any other ground connections you have.
 
Strange electical problem

I would be checking and cleaning all grounding wires. Make sure the engine is bonded to the engine mount and to the airframe. Clean and polish all the grounds behind the instrument panel, it doesn't hurt to apply a small dab of dielectric paste between ground connections. Good luck
Chuck Ross RV4
 
I'd certainly start where the last two posted pointed out. Your symptom is almost 100% classic as to a fault with the engine to airframe ground. Not saying I know this is for certain your problem, but almost every time someone has a bad engine to airframe ground it causes a similar set of gremlins to appear.

Grounds are funny things and account for a large percentage of electrical issues. Seems weird considering we're flying metal planes, but even so, they can be extremely difficult to pin down.

Other than that, I'd have to systematically start looking at pieces of the puzzle one at at time to eliminate them as problems.

My 2 cents as usual.

Cheers,
Stein
 
Grounds and...

...one specific wire to look at.

The starter should only turn if the starter solenoid is activated with 12 volts.

It is not a wire to ground to activate it like the Master solenoid, it needs an actual 12 volts.

I would check the grounds as mentioned, but specifically look along every inch of the starter solenoid activate wire from the solenoid to the starter switch.

Could a bundle be damaged and a flap motor wire be shorted to this starter solenoid wire?
 
On a similar note.......

There I was, flat on my back, airspeed zero, and ......... Oh, wait, that's a different story.:rolleyes:

The related story is that I was flying a trusty old F-4B having launched from the USS JFK for a routine sortie in the Mediterranean. We did a bit of yankin' and bankin', and in the middle of the simulated dogfight I felt a big "Thump", and thought I'd flown through wake turbulence, or as we called it "jetwash". Upon landing, discovered that all missles, racks, including 2 sidewinders and 2 sparrows, were gone. Squadron CO was NOT a happy camper.

Fortunately for me, the maintenance troubleshooters discovered a chafed always-hot wire very near a chafed wire for the jettisoning circuit. Junior officer absolved of wrongdoing, WHEW !

Electrons where they don't belong, not a good thing. AZ-Gila may be onto something.
 
Engine to sirframe ground.

I'm afraid I have to go along with the "ground" solution. Strange electrical problems are almost always traced to a faulty ground. One of the main things I look for during my inspections is a sufficient ground from engine to airframe. This ground wire must be as large as the starter current wire. I even had an A&P argue with me that with all the other small ground wires, there was sufficient ground. This would cause starter current to flow through instrument wires. Sounds similar to your problem.
 
<<The problem began with the breaker for "Instruments" popping when turning the ignition key to the start position. This was traced back to the ignition switch and I ordered one.>>

Potentially a red herring. At first glance you might think the instrument breaker pop is due to some internal fault in the off-left-right-start key switch. However, there is no path that brings instrument breaker output to the key switch internals. I'd be inclined toward an intermittent connection external to the switch, due to airframe shake during starter engagement.

<<With the engine now off and the flap breaker reset, master switch on, the flaps were tried again. Engaging the flap switch popped the breaker, but not until it somehow engaged the starter>>

In this description the key switch is no longer involved. Those pesky electrons are leaking from your instrument feed and flap feed to your start solenoid feed. As Gil said, the start solenoid has a single + feed to its coil, and a case ground. Follow the electrons; battery->batt contactor->main buss->flap breaker->flaps and start contactor. "And" means an undesired connection (chaffed wire or similar). The combined load exceeds the breaker rating.

I'd examine the main buss assembly and the wires in the panel vicinity. That's probably the only area where the start, flap,and instrument feeds are near each other.

Disclaimer; given the physical variations possible in the custom-built fleet, electrical diagnosis by long distance is pretty much a crapshoot....but it is fun to think about <g>
 
electric gremlins

Try disconnecting all the wires to the affected components, including their grounds. Use a multi meter to check for any continuity between the two components. If any connection found, start tracing that wiring to where it might contact and look for chaffing. Also check for any connection to ground with all the wires disconnected. If that fails, try the start sequence again with those components disconnected. If that looks ok, reconnect one component and try again. When something pops, recheck all the above. Something should show its ugly head, then smack it with a gremlin swatter. Also, check any reostats or relays concerning the components the same way. Hope this will help a little.
 
Yep - engine ground. The instance of the starter kicking over when selecting flaps clinched that diagnosis. You've got current trying to find a path back to the battery through routes other than the original spec. Ditto with popping the instrument breaker on startup - you've got starter current backfeeding through the panel, probably hitching a ride onto the panel via the throttle and mixture cables.
 
Circuit breakers dont care which direction the over current is going, or comming from. This can often cause a bit of wild goose chasing looking in the wrong circuit.

Airguy sure sound right on the money.
 
Back when I did a bunch of wiring problems in cars I use to use a current draw meter, you simply run it over the wires while the circuit is on, we also put a resetable breaker in the suspect circuit. It would pop and then reset, all the while going over the wires with the current meter, little small device with a bent metal guard that you run the wire close to. This would always find a short because as you got closer to the short the amps would go up. Very useful tool for finding shorts.
 
Interesting but unfortunate problem!

I don't see how a ground or lack thereof could be involved. Assuming you have a starter contactor for the starter and not a master type solenoid, you need to apply 12 volts to the contactor to engage it (as Gil pointed out).

It would seem to be prudent to verify that the starter solenoid is indeed not a master type (which actuates by grounding its terminal). While that situation would not in itself cause this problem, it would change the diagnosis a little. If the solenoid is correct, it would seem the only explanation is that the wire to activate the solenoid is intermittently shorting to a wire involved with the flaps. If the solenoid is incorrectly a master type, then the ground for the flaps "up" position may be shorted to the solenoid terminal wire. Since the flaps breaker is popping, it would seem to be the "hot" line that is crossing with the starter solenoid terminal, which would rule out the contactor being the master type. How many amp is the flaps breaker? I believe the solenoids only take about an amp or two.

Bad grounds will indeed do strange things, but I do not believe this is one of them.

Good luck!
 
Gentlemen,
Do you think it would be a good idea to disconnect the battery while you are not troubleshooting or with the aircraft?

Brad
 
Wow, you folks have been busy while I was asleep. Thanks for you inputs and I'm going to use the advice given.

1. Engine to firewall ground... This has come loose before on my plane, and as recently as Osh this year. I had the cowl off and a friend was pulling on wires and the like and found the loose connection at the engine. He tightened it while I worked on replacing a bad alternator so I could get home. This connection could easily be bad again. That will be the first thing I check this morning.

2. Before ordering the starter switch I jumped 12v from the battery to the firewall mounted solenoid, which is the proper one for the application. The starter engages and the prop turns with no popping of breakers. This was however with the master off because I didn't want the dumb thing to start obviously. This would have likely popped the breakers if a second person was there to hold the breaks so the master could have been on and is apparently where my troubleshooting when awry. An assumption was made based on a bad test. What do you think?

3. Engine to firewall ground cable... The one provided with the FWF kit is the same size as the supply cable to the starter and that is what is being used. It should be good if tight. :eek:

4. Jiggling the key consistantly made the thing start without popping breakers, while the problem was repeatable every time without cycling the key. This is why I went to the switch instead of a chaffed wire in my mind. There was no shaking from the propeller because the breaker would pop before the prop would turn.

Thanks again and I'll keep you all posted on what I find. I'd like to have a picture of the expression on my face when the flap switch was engaged and the prop turned. There are some things that a person is just not mentally ready to observe with their airplane.
 
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Flap/start switch?

Just food for thought, if I found all of the grounding in good condition the next thing I would do is start at the start solinoid wire to the start switch. I would physicaly look at every inch, open any adells that it's going throuh and look for carbon traces or chafing. I would bet there is a place that the insturment and flap wires parallel and are bound together with the start wire.

Good luck, keep the smoke in.

Randy
 
Starter Switch - could be???

Suppose the starter switch IS bad (shorting to the starter relay pos and neg) - assuming that you feed the switch from the same buss as the flaps, etc. Hit the flaps switch and you complete a circuit to ground that would send 12V to the contactor. Yes?

Forrest
 
Electricity must be made of smoke, cause the only time I can tell it around is when I see smoke.....

I doube if your porblem is a bad ground...Sounds more like you may have a combination of problems...a couple of wires shorted up stream of the breaker and perhaps a short to ground after the breaker....The breakers are only going to trip when more than the rated current is flowing through them, a ground after the breaker and before the load will cause the breaker to trip and not a back feed. The goesouttes always equal the goesintas..

the first step in succesfful troubleshooting is to clearly identify the cause and effect then go after the cause. It is very easy to come to erronious conclusions regarding the cause vs effect.....

A couple of troubleshooting tricks I have used are: half splitting systems. Find a point in the system where you can determine that the first half is ok, then proceed to again splitting the remaining half again determining that the first half is Ok, continue this process till you've found the problem. The second technique is to start troubleshooting at a point where you can gain the most information about the problem with the least amount of work.

Good luck and lwet the forum know what you find.
 
Found It!

The wire between the ignition switch and the starter solenoid chaffed against a support under the panel and above the rudder pedals. The wire had the insulation melted as well as another wire that I haven't identified yet. The ignition switch that I had changed a couple of days ago also appears bad. I put a fluke across the switch, turned the key to check for continuity and 400K ohms was the lowest reading I saw after almost twisting the key off several times. Out of curiosity I opened up the switch and looked inside. There isn't much in there, but the contacts were worn much more than what I would have guessed from 600 hours of use. There was no visable signs of arcing or high current in the switch, just extreme wear. I'm starting to think that this wire thing played into my alternator failure a couple of months back.
 
Bryan, glad you are finding at least some of the culprits. The shorted wire from the starter key to the solenoid would seem to explain why you needed to cycle the switch, perhaps burning away a bit of the short each time. But, have you found any explanation of the flap wires cross talking to the starter wire?
 
Probably....

Bryan Wood said:
The wire between the ignition switch and the starter solenoid chaffed against a support under the panel and above the rudder pedals. The wire had the insulation melted as well as another wire that I haven't identified yet.
...... I'm starting to think that this wire thing played into my alternator failure a couple of months back.
Click to expand...

...the flap motor wire....:)

12 volts into the starter solenoid wire has to come from somewhere....:)
 
<<The wire between the ignition switch and the starter solenoid chaffed against a support under the panel and above the rudder pedals.>>

Lemme see if I can guess a bit of your wiring diagram. Power to the keyed start switch is supplied by the "instruments" breaker. Theory; you've not mentioned a "start" breaker...and if you had one, it should have popped given the start contactor feed shorted to airframe ground.

<<The wire had the insulation melted as well as another wire that I haven't identified yet.>>

I guess we're all hoping it is the flap feed wire.
 
PCHunt said:
There I was, flat on my back, airspeed zero, and ......... Oh, wait, that's a different story.:rolleyes:

The related story is that I was flying a trusty old F-4B having launched from the USS JFK for a routine sortie in the Mediterranean. We did a bit of yankin' and bankin', and in the middle of the simulated dogfight I felt a big "Thump", and thought I'd flown through wake turbulence, or as we called it "jetwash". Upon landing, discovered that all missles, racks, including 2 sidewinders and 2 sparrows, were gone. Squadron CO was NOT a happy camper.

Fortunately for me, the maintenance troubleshooters discovered a chafed always-hot wire very near a chafed wire for the jettisoning circuit. Junior officer absolved of wrongdoing, WHEW !

Electrons where they don't belong, not a good thing. AZ-Gila may be onto something.
Click to expand...

Ha! They started putting a thin red plastic film over the Jettison button in later years (Air Farce), kind of like sealing wax on a letter. The idea was if something like that happened and the film was still in place they could skip blaming the pilot. The opposite was also true - if the film were broken and you didn't notice during preflight, you were then guilty until proven innocent.

Almost make you think they didn't trust us...

:)
 
Flying Again

A quick follow up for those that helped on this problem. While replacing the wire between the starter switch and the starter solenoid a larger wire that was also burned and shorting to the solenoid wire and/or sometimes to ground was discovered. This wire came from the ammeter shunt. This is likely the cause of the alternator failure at Osh. There was also a third wire in the melted mess that became apparent when digging into this which was the "Flaps" which explains the weirdness of the original symtoms.
 
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