Cessna Generator Troubleshooting

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LSK

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Anyone have and willing to share a flow chart troubleshooting guide for the 1965 cessna 172 generator system in terms of what should and should not have continuity and acceptable resistance between various points - obviously we are having a issue with the generator and working with our A&P to try to figure it out - thanks in advance for anyone who might have something
 
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Gonna need more information for your particular aircraft as Cessna made a couple of different ones and the systems are not all exactly the same ...

Paging @Dan Thomas
 
I'm assuming you've got a Delco-Remy generator and a Delco-Remy regulator. Zeftronics sells a solid-state regulator for the Delco generator. Not sure if it's TSOd, but their installation manual includes key resistances:

1709538328168.png
The full manual can be found here:


I have had considerable problems with my generator/regulator over the years. Here's a web page I put together with some background on these systems:


Here's the Delco manual for the generator:


Here's the Delco manual for the regulators:


Ron Wanttaja
 
The Zeftronics generator regulator is PMA for the Cessna generators.
They are great. As Ron said they have a very good troubleshooting guide.
 
A specific complaint would be a good starting point. You can't go to the doctor and say "I'm sick" and expect him to diagnose the problem on that much information.
 
While waiting from your reply to Dan:

Suggest you have lights and avionics OFF while diagnostic running .

I’m not a MED so my belief is the best Docs are pediatricians and

veterinarians per his previous comment.
 
Dan Thomas said:
A specific complaint would be a good starting point. You can't go to the doctor and say "I'm sick" and expect him to diagnose the problem on that much information.
Click to expand...

Specifically the complaint is the generator is not charging the battery -
Things we have done/checked:
-Grounded field wire and ran engine up for a few seconds and used a voltmeter to determine generator is increasing output with engine rpm and it was
- installed a new delco VR and flashed field a few times and the red warning light would flicker around 1600 rpm but never go out and it wouldn't charge
- cleaned contacts on master switch and checked most of the wire terminals and verified continuity in wiring, should have checked resistance then but didn't
- got a zeftronics from a friend and put it on, started the engine and about 12-1400 the warning light went out and the voltmeter showed it was charging - we thought problem solved
- week later start it up and at 1000 rpm the warning light was dim and flickering some so that seemed normal, light went out and gen as charging during run up - all seemed normal
- somewhere between upwind and turning to the west the warning light came on bright red and it stopped charging -

All was seemingly good until it wasn't - frustrating and I guess going to have to bite the bullet and install an alternator - my optimism that it's something simple is waning
 
If the Gen is operating normal with Field grounded then it’s likely

the issue lies in the Regulator Circuit.

The Master is a dual pole single throw switch with one side

completing Ground Circuit for the Battery Contactor and the other

makes or breaks the Field Circuit.

Suggest you jump the Field side.

Rather than do it at the Switch you want to jump from the

Field terminal on Gen to the Field terminal on Regulator.
 
LSK said:
Specifically the complaint is the generator is not charging the battery -
Things we have done/checked:
Click to expand...
Has anyone checked the generator brushes? They do wear out. A Cessna inspection checklist:
1709663059932.png
1709663035585.png
1709663109526.png

Look at item 23. Notice that it refers you to Note 4. Note 4 demands a brush check each 200 hours. Most generators and alternators never get checked until they start acting up, or quit altogether. Alternators also need checking, but less frequently. Even the much-ballyhooed Plane Power alternators are just automotive alternators adapted for aviation use, and they have brushes that need checking. The Plane Power documents state that, too. Alternators in aircraft turn much faster than they do in cars, so brushes wear out faster.
Worn-out brushes can start acting up when they get hot.

So, back to square one. Check those brushes. And the commutator; it might be getting smeared with insulation from between the commutator segments.
 
The best troubleshooting is to toss the generator in the garbage and put on a Plane Power alternator. This is what I did after so many generator issues. That Zeftronics regualtor failed on me and I had unregulated voltage. Modern avionics loves that........... Plane Power has been on for a good 5 years now. Zero issues. I should have done this 20 years ago.
 
I replaced/repaired the generator 5-6 times over 15 years. Nothing but a headache. Let me know what money your saving as everything gets melted running 20+ volts. Alternator seems cheap compared to replacing all your avionics and every bulb on the plane.

Toss the generator in the garbage and move on. There is a reason why no one uses these old heavy generators anymore.

By far the best mod I've done to my C150 to date.
 
Magman said:
If the Gen is operating normal with Field grounded then it’s likely

the issue lies in the Regulator Circuit.

The Master is a dual pole single throw switch with one side

completing Ground Circuit for the Battery Contactor and the other

makes or breaks the Field Circuit.

Suggest you jump the Field side.

Rather than do it at the Switch you want to jump from the

Field terminal on Gen to the Field terminal on Regulator.
Click to expand...

We messed with it some more tonight - no luck - see what you can make of this

- we removed the wires from the VR - attached bat and arm together and started the engine, yes with avionics off, then touched the field wire to ground - ran engine up slowly and around 1300 the voltmeter started up and by 1700rpm was putting out about 13.3 volts - (we assume this indicates the generator is/can charging)

- Also, since we were grounding the field wire, we assume this verifies the master switch connections are good - as I read the diagram the field wire goes from VR to master then to the field terminal on gen - can you confirm or refute

- next we removed the zeftronics and installed another delco VR we had - gen would not come online - just to see if we could get it to charge we grounded the field wire on the VR, expecting it to start charging but it didnt -

- nothing I have read explains to me why grounding the field wire will result in charging if the bat and arm wires are connected but it they are installed on their respective VR terminals then directly grounding the field wire doesn't work

- in checking continuities and resistance we found no readings of extremely high resistance

- We did flash the generator following the zeftronics instructions of grounding the field wire, master on and touch together bat and arm for 3-5 seconds and repeat

- The only readings we got that is a mystery at least to us is - we measured .6 volt of residual current with master off at the arm terminal on gen - after flashing we got a reading of 1.6V and after running the engine and verifying that it was not going to start charging we shut down the engine and turned off the master and again checked the residual got a reading of 0V

I recall reading that the zeftronics needed to see a min of 1.5V residual to activate -

Not sure if my issues are related this lack of residual V or maybe we are not checking it correctly

As far as someone asked about checking the brushed, yes the brushes and springs were inspected a few months ago during annual and reported to look serviceable

The generator has done a good job the past 5 years until this issue - if it's something simple we are missing would like to run the gen a few more years but at the moment it's starting to look like an alternator is in the near future
 
it seems you have proven Master is defective.

If I understand correctly when grounded “ F” it charges.

With wiring in normal condition it does not charge.

I’m quite sure Field wire goes as you described.

“F” on Gen, through Master and on to “ F” on Reg.

Running in this condition takes the Master out of the picture.

Some aircraft have separate Switches to control to Gen .

Combining batt and Gen. in one switch makes little sense and folks

are not aware of the Gen portion.


Switching to to an Alt is not exactly “ plug and play” if done properly.

Bolting it on is easy. But you are still looking at other things.

ALT output is higher so this will necessitate upgrading Fuse/ CB.

For the same reason the Power Lead must have a higher rating.

Attaching to the Bus is not easy either. I did discover at least some

Cessnas have a section of the Bus that can be removed to facilitate

soldering . I hate to solder overhead!

You still need to address switches and warning lights.

IMHO Alts are nice but not essential.
 
A couple more suggestions:
1. When you polarize the generator, ground the field through an ammeter and check for around 2 amps of current.
2. I would not trust the months old inspection, as a failure could have occurred since. Remove the generator and re-inspect brushes, springs and commutator. While you have it removed, ground the field and connect a battery to the armature terminal (and case ground of course). It should spin like a motor.
 
Fast Lane said:
Toss the generator in the garbage and move on. There is a reason why no one uses these old heavy generators anymore.
Click to expand...
I would advise exactly the opposite. The generator system is stone-simple, reliable and a heck of a lot cheaper to fix than dropping $2K on an alternator kit.

I'm sorry I can't tell you exactly what is wrong, but I do know this:

1. Don't replace the expensive parts (generator, regulator) until you've checked ALL of the cheap parts (wiring, switches, breakers).
2. Brushed DO wear out and are cheap to replace. Needs to be done on a regular basis though, don't wait for them to fail.
3. Zeftronics regulator is pretty bullet-proof. Diagnostic lights are helpful and instructions are spot-on.
4. These planes are old (mine is a '62). Over the past 20+ years of maintaining mine, 90% of the issues have been due to old wiring, connectors, switches, etc. not the big items that people go to first.

C.
 
camorton said:
I would advise exactly the opposite. The generator system is stone-simple, reliable and a heck of a lot cheaper to fix than dropping $2K on an alternator kit.
Click to expand...
In the flight school we had alternators in most of the airplanes. No trouble with them at all as long as the brushes and other internal stuff were checked on the recommended schedule.

One airplane had a generator. What a hassle. Even though it was an old Champ, no lights, so day VFR only, we still had problems. It would not start generating until the engine was at 1200 RPM, at least. If a flight was scrubbed after startup for crosswinds or whatever, the battery did not get recharged, and sulfation set in. A few episodes like that and the battery was shot.

A generator weighs twice what an alternator does, and puts out half the power. It has big heavy brushes that are not that cheap to replace. As these things get older and older (nobody has made them for decades) you will find parts impossible to get. As their commutators wear out and get machined to get them usable again, you eventually run out of commutator depth, and now you need a new armature. Hah. Good luck with that.

The automakers abandoned generators for alternators way back in about 1965. That's almost 60 years ago. They never went back to generators. I am old enough to understand why: Sitting at some red light for a long time, at night, engine idling, the generator light is on, meaning that it's not producing. The headlights and everything else are dimming while you sit there. The battery couldn't keep up. If you were stuck in some freeway traffic jam, even in the daytime, and the weather was cold, your battery was going dead just from running the ignition, generator field, and heater motor. I remember holiday parades with old cars that the drivers sometimes had to stop, put them in neutral, and rev the engine to get the battery back up so the car wouldn't quit as the ignition died.

Night flights with a generator are a pain, for the same reasons. No power until you're in the runup.

The alternator will produce vast amounts of power even at idle. No problem with stuff going dead.
 
It ALWAYS helps to study the service manual. Always. This is the generator/master wiring diagram for the '61 and on 172s:

1710377430074.png

Note that the GEN section of the master switch is between the regulator's F (field) terminal and the generator's field terminal. No grounding is going on here. All the other 100-series schematics I checked show the same thing.

Now, that master/generator switch is way up high in the panel. A real pain to get at. We had one that wouldn't generate, and I traced it to that switch. I got it out. It looked like this:

1710379205585.png
No new one available. Used ones, but they'd be in about the same condition. Well, it was dead anyway, so I carefully bent those four little tabs up and removed that insulator plate. I found that the grease that was used at the factory to lubricate the contacts had hardened and dried and was acting as an insulator. I cleaned it all off all the contacts, relubed it with DC4, and put it back together. It worked.
 
If neither was installed I would prefer the Alt.

However: converting is not plug n play as in #15.

It can be simple as a brush hanging up or a commutator issue.

I dimly recall hanging on a Widgeon with sandpaper for the Gen on a Ranger

engine.

if you conn “F” on Gen to “F” on Reg you have bypassed the Field side

of the Master. If it works fine with the jumper then you have proven

a bad switch. You replace the switch per original or my preference

would be a split rocker as a Minor Alteration.
 
Owner takes 60 year-old airplane to the shop with charging issues.
A&P replaces generator, then the regulator, then the battery in succession - still intermittent problems!
Owner drops $2K plus another $1K in labor to install alternator conversion kit (which BTW happens to come with all new wiring, connectors, switches and breakers).
Problem suddenly solved! Conclusion: generators don't work, can't work, never did work. Alternators are the only way to go! LOL

OTOH, some people just love to dump money into their airplanes (guilty!). I say God bless 'em. Keeps the economy going and the doors of my local MX shop open.

C.
 
camorton said:
Owner takes 60 year-old airplane to the shop with charging issues.
A&P replaces generator, then the regulator, then the battery in succession - still intermittent problems!
Owner drops $2K plus another $1K in labor to install alternator conversion kit (which BTW happens to come with all new wiring, connectors, switches and breakers).
Problem suddenly solved! Conclusion: generators don't work, can't work, never did work. Alternators are the only way to go! LOL

OTOH, some people just love to dump money into their airplanes (guilty!). I say God bless 'em. Keeps the economy going and the doors of my local MX shop open.

C.
Click to expand...
That doesn't prove that generators are better. It just proves that electrical troubleshooting skills are the weakest skills in the majority of mechanics. Many can't read a wiring diagram, can't use all the functions of a multimeter, don't understand Ohm's Law, and don't understand the electromagnetic operating principles of alternators, generators, and their respective regulators.

So they start throwing parts at it.
 
If generators were so great, why when I order a new 182 it comes with an alternator? My 1966 C150 logbooks how generator issues since the 1960's. Always something. Alternator conversion is simple. No issues in 5 years. Clean stable power at any rpm. No brainer in my eyes.
 
I'd never say a generator is better than an alternator. All else being equal, I'd go for the alternator, too. But that's not the case here. The OP is looking to trouble-shoot an existing system that has worked well previously. If he can find the actual fault, the solution is probably a .50 cent connector or $2 wire. Suggesting that the best path is to rip and replace the entire system for $3K seems a bit rash.

My own A&P is a wiz with a socket wrench, not so much with a voltmeter. I suspect he's not alone.

C.
 
Fast

The Alt upgrade is a nice change but please don’t describe the install

as “ simple”. It does require skilled labor hours.

What method did you use for the connection at the Bus?

I have seen Installations where the wiring originally designed for

20 amps is now required to handle 50 + amps!
 
Magman said:
I have seen Installations where the wiring originally designed for

20 amps is now required to handle 50 + amps!
Click to expand...
Mechanics that don't or won't or can't read the installation instructions.
 
IIRC The Instructions do not include a updated wire size.

You are referred to AC 43.13- 1A instead.
 
Magman said:
IIRC The Instructions do not include a updated wire size.

You are referred to AC 43.13- 1A instead.
Click to expand...
If the referral to 43.13 is in the manual, the installer has no excuse. "Incorporated by reference" is the legal term we use here in Canada. Might be the same in the US.
 
The Agency that signs off the installation bears the burden of assuring

compliance with all pertinent requirements. If this does not take place the

aircraft would not be in Airworthy Condition and the Tech may be given a

violation notice.

My guess that how it happens is that the Owner requests a quote for

an installation. There may be comments made as to how” simple”

this task is. Later the realization that wire may have to be ordered

and tied in to the Bus both parties understand it won’t be finished for a

while. That means no flying and possibly tieing up a portion of a hangar.

End result could well be the Owner swearing that they will never use

more than the original 20 amps. Not good at all.


Since this thread started I got the word that a friend had his aircraft

catch on fire in flight and it is now ashes. No serious injuries.

It was not from an electrical problem though.. I’ll write it up

when the smoke settles.
 
Magman said:
My guess that how it happens is that the Owner requests a quote for an installation.
Click to expand...
It can also happen in a manner that can catch the installing mechanic off-guard when there was a previous “partial” upgrade to power generation system or with previous increases to the system load that were not properly complied with.

Everything looks good on the surface and adds up for installing a larger output alternator. Yet after the first run there are odd occurrences and smells. Then they realize half the behind-the-panel distribution is still set up for the original 40-amp alternator or that nice newer radio stack is all connected to the original AUX buss.

Regardless, it still falls to the installer to find this and correct it no matter how much the owner whines. Or walk away from the job. The hardest part for me was having to explain to the owner that I would need to repair existing issues from the previous owner’s time before I could install the current owner’s brand new alternator… “But they’re both 60 amps, I don’t understand…”
 
If you read the installation manual it says you can install a 30 amp breaker if you want or a 50, which is what the alternator can output. You have something seriously wrong if the alternator is pumping out 50 amps.

Its a fairly easy install. If your mechanic is having a hard time, I would suggest another mechanic.

If you really are hung up flying with a low output, heavy generator, have it tested at an AUTOMOTIVE starter/alternator shop and NOT a aviation mechanic. Take it off and drop it off. They will test its output. Bring your old school regulator with you too. I went through many regulators and one zeftronics. Once the Zef died I gave us on the generator. I have have every light and radio on and have a stable 14 volts at idle. Like I said, I should have done this years ago. The money I spend of repair the generator easily payed for the alternator conversion.
 
Fast Lane said:
If you read the installation manual it says you can install a 30 amp breaker if you want or a 50, which is what the alternator can output. You have something seriously wrong if the alternator is pumping out 50 amps.
Click to expand...
If the battery has been run way down on a cold start, that alternator could easily run up to its 50 or 60 amps at 1200 RPM, trying to get that battery back up. A 30-amp breaker would pop, leaving you resetting it and idling for a long time while the voltage slowly recovered.

Best to do the job right. Those of us that repaired electrical systems for many years learned how to do it right, or face angry customers and maybe angry government officials. We are bound by regulations, and regulations will point out reference materials such as AC43.13, which gives the requirements for breakers and wiring. All of this stuff was learned the hard way, with people dying in electrical fires or crashes at night or in IMC when critical stuff failed.
 
I agree with Dan’s comments.

On some aircraft it would be easier to just keep the existing 20 amp

fuse and not change the Power Lead. HOWEVER; this could result in

“ someone” later changing the fuse to 50 amps. End result could be 50 amps

going through a wire designed to handle 20 amps. What could go wrong?

I’m reasonably sure that “ someone” will not change the signature in the

Records too!
 
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