Electrical Problem

[Ronnie Godfrey]

Well, after two weeks of aircraft ownership, I'd say my partner and I are really getting the experience.

The plane passed pre-buy/annual ($800), but had a few squawks that we just got fixed this week (estimated at $400). Among them was a bad seal on the parking brake cylinder. When the mechanic tried replacing the seals, the cylinder still leaked, so then we had to get a new cylinder ($200). So now we are at a total of $1400 within two weeks of buying this plane. It's worth noting that the same mechanic has done the pre-buy and all the repairs.

Today, I go to pick up the plane for a breakfast run. The engine won't turn over and the battery sounds weak. So we jumped it off, thinking perhaps the mechanic left the master switch on too long and the battery drained. We fly to breakfast, go eat, and come back to the plane, only to find that the battery is still dead and required yet another jump. As we are flying home, my backup comm flickers, then my 430 shuts down. I make it home with only my backup comm running on the circuit.

I texted my mechanic and he says it sounds like a bad voltage regulator, or possibly an alternator. Has anyone else had this issue before?

We are first-time aircraft owners and I'm hoping that this will eventually be a little less headache and expense, or at least not so frequently! A little reassurance would be nice, even if it's a lie lol!

 

[GRG55]

These are "little things".
Could be something as simple as the brushes in the alternator need replacing.
Could be the voltage regulator, or even low electrolyte level in the battery.
Start with the cheapest and simplest things and trouble-shoot it systematically. This is the sort of thing that I like to troubleshoot myself before getting my mechanic involved to repair it.

Don't get discouraged. These are not uncommon things on the older airplanes most if us fly. You'll probably find there's things like this that come up in the first little while you own the plane, especially if the plane was not being flown much by the prior owner before it was sold.

 

[Ronnie Godfrey]

These are "little things".
Could be something as simple as the brushes in the alternator need replacing.
Could be the voltage regulator, or even low electrolyte level in the battery.
Start with the cheapest and simplest things and trouble-shoot it systematically. This is the sort of thing that I like to troubleshoot myself before getting my mechanic involved to repair it.

Don't get discouraged. These are not uncommon things on the older airplanes most if us fly. You'll probably find there's things like this that come up in the first little while you own the plane, especially if the plane was not being flown much by the prior owner before it was sold.

Thanks for the advice and encouragement. I know that the previous owner only owned the plane for a few months and did not fly it much during that time. I've already put a good 12 hours on it in the last couple of weeks.

So assuming I'm a complete noob, how would you recommend troubleshooting the problem? I'm fairly mechanical and not afraid to get my hands dirty, but I have never done much work on an airplane and I don't want to create an even more expensive problem. The plane is currently parked at the mechanic shop and I am reluctant to do another jump start as I've read this can cause the alternator to fail, also.

 

[Matthew K]

I'd have to agree these are "little things". Not much different from buying a house and having to throw some money at it when you first buy it. Of course, if there are too many of these "little things" it becomes a BIG problem.

Congratulations on the purchase though! I hope it is not to far down the road till I'm able to own my own plane.

 

[Ronnie Godfrey]

I'd have to agree these are "little things". Not much different from buying a house and having to throw some money at it when you first buy it. Of course, if there are too many of these "little things" it becomes a BIG problem.

Congratulations on the purchase though! I hope it is not to far down the road till I'm able to own my own plane.

That's just it--these little things are starting to add up, and fast! I don't want to skimp on maintenance, but I also don't want to hemorrhage money every week lol!

 

[MauleSkinner]

So assuming I'm a complete noob, how would you recommend troubleshooting the problem? I'm fairly mechanical and not afraid to get my hands dirty, but I have never done much work on an airplane and I don't want to create an even more expensive problem. The plane is currently parked at the mechanic shop and I am reluctant to do another jump start as I've read this can cause the alternator to fail, also.

What were your ammeter indications in flight, and what exactly are they telling you? (alternator output vs. battery charging, for example)

 

[Matthew K]

That's just it--these little things are starting to add up, and fast! I don't want to skimp on maintenance, but I also don't want to hemorrhage money every week lol!

I know you haven't figured out the current issue, but $1400 right after buying isn't really much compared to the value of the plane(I assume this is true with yours too at least). While not very encouraging, these expenses you have mentioned are reasonable and somewhat expected in the world of airplanes. Hopefully you'll get these initial expenses over with shortly though and not have anything big.

 

[Ronnie Godfrey]

What were your ammeter indications in flight, and what exactly are they telling you? (alternator output vs. battery charging, for example)

My ammeter was reading anywhere from 5-20 amps on the way home today. It's a Cherokee 140, so that's really all the information the airplane gives me.

 

[Ronnie Godfrey]

I know you haven't figured out the current issue, but $1400 right after buying isn't really much compared to the value of the plane(I assume this is true with yours too at least). While not very encouraging, these expenses you have mentioned are reasonable and somewhat expected in the world of airplanes. Hopefully you'll get these initial expenses over with shortly though and not have anything big.

I agree. It's just that we had only intended to spend $1200, which turned into $1400, and now potentially more. I know it's not much money relatively speaking, but I don't think many people that fly Cherokees consider $1400+ to be chump change.

 

[Skip Miller]

First, tell us about the plane. Make/model? Hours? Your general location? (down south/Alaska/where)? Hangar or outside tiedown?

Generator or Alternator? Loadmeter or ammeter?

Got a voltmeter, or one in a engine monitor? What does it show as you first turn things on, then after starting? What does it show in cruise flight? After landing at the hundred dollar (cough, cough) burger location? How old is the battery? Do the log books show any recent work on the electric system?

This could still be a simple problem. How well do you know the seller? Any chance the seller is the AME/prebuy guy? If yes, well... I wont make any accusations but he seems to be on all sides of this transaction. Get a different mechanic.

-Skip

 

[MauleSkinner]

My ammeter was reading anywhere from 5-20 amps on the way home today. It's a Cherokee 140, so that's really all the information the airplane gives me.

Is that 5-20 amps of alternator output, or 5-20 amps of battery charge, or...?

 

[Skip Miller]

My ammeter was reading anywhere from 5-20 amps on the way home today. It's a Cherokee 140, so that's really all the information the airplane gives me.

Cherokees usually have loadmeters, not ammeters. On the ground, engine running at idle, turn everything on.

A Loadmeter will never show a discharge, instead it shows the load on the generator/alternator. An ammeter will (should) show a charge as you increase rpm. This may not be enough to power the electronics and charge the battery too. If that is the case, you may have a bad diode in the alternator (assumes alternator not generator). Diode replacement won't break the bank.

-Skip

 

[Ronnie Godfrey]

First, tell us about the plane. Make/model? Hours? Your general location? (down south/Alaska/where)? Hangar or outside tiedown?

Generator or Alternator? Loadmeter or ammeter?

Got a voltmeter, or one in a engine monitor? What does it show as you first turn things on, then after starting? What does it show in cruise flight? After landing at the hundred dollar (cough, cough) burger location? How old is the battery? Do the log books show any recent work on the electric system?

This could still be a simple problem. How well do you know the seller? Any chance the seller is the AME/prebuy guy? If yes, well... I wont make any accusations but he seems to be on all sides of this transaction. Get a different mechanic.

-Skip

It's a '69 Cherokee 140 with about 5000 hours on the airframe. I'm in East Texas, and the airplane is tied down under an open-sided T-hangar.

All I have is the ammeter in the airplane, and it reads anywhere from 5-20 amps. Usually the lower readings come when the engine is idling and no electronics are active. The 20 amp reading shows just after run-up and right before takeoff. When I was in flight today and might avionics began to flicker, the ammeter was reading as low as 5 amps, and as much as 20.

The mechanic is independent of the seller, and he's local to me. I think he's a good guy, and he has a large client base, so I'm confident in his opinion and his work. I know that things break on these old airplanes, and that it's part of the deal.

 

[Skip Miller]

OK, that all sounds good. Glad the mech is independent of the seller. -Skip

 

[Ronnie Godfrey]

OK, that all sounds good. Glad the mech is independent of the seller. -Skip

So does it sound to you like it's the alternator, the battery, or the voltage regulator?

 

[Dan Thomas]

Old airplanes cost as much to maintain as new airplanes. Often they cost more, because so much stuff has been neglected or is wearing out. Maintenance will never be a percentage of the airplane's value. Shop rates are the same as for new airplanes. Parts prices are the same or more, since many parts for old airplanes are scarce or produced in small numbers. There is no such thing as a cheap old airplane.

Electrical system troubles defeat a lot of mechanics. They start replacing parts until the issue goes away. A new battery might be Ok for a few days until that weak alternator or regulator or master contactor kills it. It takes some careful testing to narrow the problem down without spending a big pile of money trying to fix it.

Charge the battery and see what the specific gravity of the electrotyte is. New is 1.280; much less than 1.270 is not good. Batteries are often ruined by people who don't read the stuff that comes with a battery, which tells you to top up the battery with distilled water while it is actively charging. Tap water often contains alkalinic minerals that neutralize the acid. Topping it up to the bottom of the split ring when it's not on charge will result in so much expansion of the electrolyte when the alternator sends big amps through it after startup that the electrolyte will blow out the caps and overboard. The guy tops it up again, with water, diluting the remaining acid. This happens over and over until the electrolyte is so weak that starting the airplane is impossible.

Put a voltmeter across the master contactor's big terminals. It should read battery voltage with the master off. Turn on the master; it should drop to zero volts, meaning that there's no big resistance across the internal contacts. Crank the engine and see that the voltage stays at or very close to zero; anything more than a small fraction of a volt means the contactor's contacts are burned or eroded or oxidized. Old contactors do that, and many batteries and alternators and regulators are replaced when all that was needed was an inexpensive contactor. Do the same with the starter contactor while you're at it. They get old the same way. This week I tested both contactors in an airplane that was cranking poorly and found a two-volt drop acrfoss the master. Two volts is a significant cut considering that the battery's voltage already falls a bunch when cranking. Assuming a 250-amp draw for the starter, we can figure a resistance in that contactor of 0.008 ohms. Doesn't sound like much, does it? But it is a big deal. Can't afford it.

Disconnect the alternator's field terminal from the regulator. Put an ohmmeter across that terminal and ground. See what it says. For a 12-volt alternator it should be between 3 and 5 ohms, and it should remain fairly steady if you rock the propeller some. Ten or 20 or 30 ohms is a bad sign, as is a jumpy reading when you move the prop. The carbon brushes run on copper slip rings to carry the field current to the rotor to make the magnetic field that generates the output in the stator, and if the resistance is high, that current can't reach max and the alternator will have a weak or intermittent output. Worn brushes, or brushes and slip rings contaminated with grease off the rear bearing of the alternator, or by oil off a leaky engine, will have high resistances. Failed diodes are very rare.

Voltage measurements can be taken at the regulator while the engine is running if one has the gumption to make a board with some terminals that have long wires to run to the regulator's terminals and ground so you can take readings from the pilot's seat while running up. One should see the field voltage ("F" terminal) rise when large loads like landing lights are turned on. One should see the voltage at the "A" terminal stay steady at the specified voltage, usually around 14 volts, even when the alternator is loaded up by turning on lots of stuff.

Like a doctor, look for the most common diseases first. Rule out the obvious stuff before throwing money at the problem.

 

[JAWS]

So does it sound to you like it's the alternator, the battery, or the voltage regulator?

Yes! lol

If you are really interested in making your plane safe and economical, I would suggest getting yourself a maintenance manual and start reading. You need to be in tune with your aircraft and know what is normal and not normal and be able to describe that accurately to your mechanic. Join a type club and start reading, such as Cherokee Chat. I know for a fact that there is a book or two on Cherokees that highlight common problems and offer troubleshooting help on their specific systems. Let Google be your friend! Also, get into your aircraft logs and make notes on when the alternator was last changed or repaired, or the mags last 500 hour inspection, or the last time the trim system was taken apart and inspected. This will help guide what you do from here on out. Do you know what you are legally allowed to do to the plane as an owner? More reading there.

As the current owner, you are buying the complete history of that aircraft - the good, the bad and the ugly! In my opinion, you are still in the good area! Just wait for the first annual!!

 

[paflyer]

Well, after two weeks of aircraft ownership, I'd say my partner and I are really getting the experience.

The plane passed pre-buy/annual ($800), but had a few squawks that we just got fixed this week (estimated at $400). Among them was a bad seal on the parking brake cylinder. When the mechanic tried replacing the seals, the cylinder still leaked, so then we had to get a new cylinder ($200). So now we are at a total of $1400 within two weeks of buying this plane. It's worth noting that the same mechanic has done the pre-buy and all the repairs.

Today, I go to pick up the plane for a breakfast run. The engine won't turn over and the battery sounds weak. So we jumped it off, thinking perhaps the mechanic left the master switch on too long and the battery drained. We fly to breakfast, go eat, and come back to the plane, only to find that the battery is still dead and required yet another jump. As we are flying home, my backup comm flickers, then my 430 shuts down. I make it home with only my backup comm running on the circuit.

I texted my mechanic and he says it sounds like a bad voltage regulator, or possibly an alternator. Has anyone else had this issue before?

We are first-time aircraft owners and I'm hoping that this will eventually be a little less headache and expense, or at least not so frequently! A little reassurance would be nice, even if it's a lie lol!

Welcome to airplane ownership.

As an aside, what kind of annual does one get for $800?

 

[paflyer]

How old is the battery? If it's more than a few years old I'd replace it. If it's been so deeply discharged that it won't start the plane, it's probably toast. Also check for clean connectors to the battery terminals.

 

[JAWS]

Welcome to airplane ownership.

As an aside, what kind of annual does one get for $800?

I missed that. Twice as good as a $400 annual?

I think the OP is ahead of the game at this point, even if he doesn't see it right now. Just wait until he has to comply with the new AD that just came out. I have an aircraft that will need that next year too, but it had SB 1006 completed a few years ago, so I am not overly concerned. I use a flexible boroscope to get into tight areas and I am confident that the new AD will go smoothly.

 

[paflyer]

I missed that. Twice as good as a $400 annual?

I think the OP is ahead of the game at this point, even if he doesn't see it right now. Just wait until he has to comply with the new AD that just came out. I have an aircraft that will need that next year too, but it had SB 1006 completed a few years ago, so I am not overly concerned. I use a flexible boroscope to get into tight areas and I am confident that the new AD will go smoothly.

New owners haven't been exposed to AD fun; it's not a car where the mfr owns safety issues forever. Thanks for the lead on Cherokee Chat, never heard of it.

 

[Ronnie Godfrey]

Well, I got to looking in the logs today, and the last battery change was in 2013. The battery is a Gill G-35, and I feel like 4 years is a really long time for a lead-acid battery to last. So I think replacing the battery might do the trick, but my mechanic suspects that the voltage regulator is bad. What would be the symptoms of a bad voltage regulator?

 

[Glenn D]

Welcome to aircraft ownership... I have just completed my 2nd annual, and did replace some electrical parts, and a SCEET hose.. Installed a new electric clock with volt meter, and it cost me $450 total.... parts and IA work.. of course I did all the grunt work of opening up the plane and closing her up... installed the clock and the other items needed... IA supervised and preformed the compression check... the bill from my IA was $175. I like those prices!..

Power problems can be frustrating... Check each step of the process before replacing a bunch of parts. the battery at 4 years old may be almost dead if it was mistreated in the past... mine is 5 years and cranks great.... look at each subsystem and assure each is working correctly, then look at the interconnects. Get a volt meter to check the output voltage, and turn on lights and other gear one at a time to see the increasing load... if the voltage holds as the load increases, it is most likely not the voltage reg. or the alternator.

Do a load test on the battery, if it has high resistance then perhaps it is time to replace it. Charge it up first before testing the other systems in the plane and assure it will handle a high amp load. This is on a 1967 140, with a little more HP... O-360 power.

After the pre-buy was completed, I had about $3k worth of work preformed, as the price of the plane was reduced about 4k.. and have had no major surprises... The bigest thing is to get out there and fly her... note the issues and work with you mechanic as much as he will allow.... down load the parts manual and the service manual, then read them!... having knowledge will help tons in keeping maintenance cost down.

I did change all the light bulbs to LED's to reduce the electrical load, and it has helped.. with everything on, I see just over 5 amps total on the load meter.

 

[Jerry King]

Ronnie,
Dan Thomas has some good troubleshooting advice. He is correct that some otherwise good mechanics are a bit weak (I include myself) when it comes to troubleshooting electrical problems. Ammeter is near useless. If you have nothing else, plug a voltmeter into the cigar lighter socket for now to help you understand what is going on.
You need a voltmeter to diagnose problems
Jump starts are hard on a batteries
You must fully charge the battery before beginning testing and a slow charge is by far the best
Disconnect one terminal and see if battery maintains charge overnight.
Reconnect battery and again see if battery maintains charge overnight.
Remove & clean battery posts & terminals - look for signs of green corrosion & remove w/ wire brush
After cleaning & reassembly, I add a dab of grease.

The good side of our older airplanes with alternators is that the charging system is not complicated and the service manual usually has a good troubleshooting chart. There are only three areas to look at: ALTERNATOR / REGULATOR / WIRING.

All interconnecting wiring can be checked for continuity using an ohmmeter with power OFF. With power ON, battery voltage should appear at alternator A+ (hot) terminal. Watch for green corrosion. Don't forget that GROUNDS and bonding straps must be cleaned and checked too.

The regulator energizes the alternator through the field terminal. Some alternator systems apply a modulated voltage to the alternator field terminal, while others apply a ground. I don't know which type of system your Cherokee has. If you remove the alternator field wire (don't allow the loose wire to touch anything) and when engine is running BRIEFLY jump the alternator field terminal with 12 volts (or ground if that is what is required), full alternator output voltage should result. To stay away from the moving prop, I attach a long wire to the alternator terminal and bring the other end to the battery where it's a lot safer.

A fully charged 12V battery should read about 12.5 volts. If alternator is working, voltage should jump up to around 14V. If not, yank the alternator and see if an auto parts store can spin test it for you. You may need to tell the store that the alternator is from some oddball tractor if they ask, but some of testers are so computerized, that they require a CAR make & model to set things up. Ask beforehand.

BTW, don't ever disconnect the alternator A+ (hot) terminal from a spinning alternator.

Hope this helps,
Jerry King

 

[Ronnie Godfrey]

Well, for those who are interested, it turned out to be a bad voltage regulator, and the battery tested just fine. Should be back up and running tomorrow. In an interesting plot twist, my mechanic thinks that my bottom buttons on my 430 may have been disabled because of the voltage regulator and that the replacement may rectify that issue, also. He says those units are very sensitive to abnormal voltage and can malfunction under that circumstance. I’m cautiously optimistic, but here’s hoping!