some light on odd electric issue

[mbodak]

well..a mechanic has troubleshot this and feels it may be a bad, old alternator field circuit breaker that controlls both fields? how does that idea sound?

[Pete Somers]

The field circuit breaker would be a good place to start as it does supply both alternator as your 337 has one voltage regulator to supply both alternators, using the run/stby switch overrides the voltage regulator and is used for alt restart in the stby selection.
If the field circuit breaker does not cure the problem let me know.

Pete

[mbodak]

thank you so much for that insight...my wife and i do appreciate an informed source helping us understand our 337 issue..we have owned this same 337 for 12 years now....could you please explain the run/stby system a little.....when this odd electric issue, of no charging of our battery, would show itself...we could, by selecting "stby", establish charging again but.. only if we turned the master switch off too...

[Pete Somers]

If the regulator drops off line and both alternators stop charging the battery, you would first select the other regulator or to restore the system 1. Master switch off, 2. RUN/STBY to STBY this will restore the electrics. The reason you have to select Master off on your 337 is that there are diodes in the system that block the STBY system when in normal mode, however with the Master off and the switch in STBY current from the battery will flow through the diodes to the field, allowing both alternators on line with the Master off, turning the Master back on will restore the charging system to the battery.
This is a alternator restart system which allows you to restore the charging system in event of a flat battery.

This is a big clue to your charging problem, if you cannot restore the system by selecting the other regulator, then it has to be that you lose power to both regulators and the common parts are the bus bar, circuit breaker, or wiring. Should not take much finding.

Regards
Pete

[mbodak]

thanks again for shedding light on our skymaster...we think it is a wonderful aircraft and your insight is truly apperciated...we will advz what the a&p's do and how it works

[stackj]

Mbodak

See your original post too. I have posted some information there as well as given a reference for a wiring diagram that may be easier to read than the one in the manual.

[GMAs]

Hello...

I don't usually get back on this board but we have our own that we maintain tech data on the 337 Skymaster. I was asked if I would comment about your problem.

One can do a lot of trouble shooting of the electrical problems by using a simple volt meter. Here you can measure across the devices and find out if they are in fact bad. By doing so ...if the Ckt Breaker for instance is bad and you close it.. you would see a voltage across it.... if good you would not see any voltage across it.

Now as to your problem. Your mechanic can short across the field ckt breaker if he doesn't own a volt meter and find out if the charge suddenly comes back on line... or he can measure the voltage at the field terminal of the alternator to see if it has the proper setting. (simple)

However, shotgunning is not a acceptable methode to find problems.

As others have said .. voltage settings on the alternators is critical... one does not want the rear and the front set to the same voltage... as Pete has said it will cause osc in the two alternators...one wants the front one set a little lower than the rear.. which should be set a little high. In this way the rear one is always taking the first loading.. once it max'es out then the front one will come on line and pick up the loading from their. Yes the rear will wear faster but it keeps the system in operation. Of course you could just simply shut down the front or rear by pushing the field switch off.. too.

Suggestion...

First off. How long have you had the master Slnoid. We have found that the master ones do go bad after 5 years.. and all should be replaced in the master and engine starters. If the vibration is getting to the master it will cause the battery to come off line and cause the alternators to shut down due to no loading.

Then I would go check the alternator coupler... the drive section of them sometimes go bad... lord ones are natourous for debonding... and while the alterntor will drive at low current it will slip when the power is needed... check by using the turn finger methode on the cooling fins of the alternator rotor...

Last but not least is the battery itself.... how old... if over 2 years... replace.

Most mechanics and IA's right now are not doing the section of the battery "Contenued Airworthness" requirement. One then wonders how they can retrun the aircraft to service AT ANNUAL if they fail to do the load test on the battery once a year as directed by the manufacture. (BUSTED BIG TIME)

Check out the battery manufacture web site and look for the "compliance for Contenued Airworthyness" both Gill and Concord have them in their owners manual... most mechanics are not keeping up with the program and the FAA is now being a bug about it...

Good luck.. thanks Larry for keeping the board up... I owed you for the ride home... what a fun time it was... that customs guy was a hoot... (not to mention the people at TC)
still have that palm hat.... you flew over and trimed the tree with... (smile)

Fly Safe.. GMAs

[Pete Somers]

GMAs
It is not my intention to talk out of turn here but I will make some comments on your trouble shooting ideas, and the little quiz.
I do not think a simple volt meter is good enough to start measuring voltages and resistance as they are not accurate and libel to errors. As i have seen when measuring across a circuit breaker you will need to load it as a bad connection inside the breaker would not show until loaded.

On the '65 337 both alternators are fed by one regulator so you cannot compromise between the front and rear, so any oscillation problem are down to wiring, connection, and the condition of breakers etc. On all 337's with dual regulator system this is not a problem as each regulator output can be adjusted to suit.
By the way GMAs what should be the voltage at the alternator field on a '65 337 and just for fun what should it be on the '77 337, just a little quiz for you all.

You seem to go a lot for the master or starter relays, and your failure rate seems high and over here we have 30-40 year old aircraft flying quite ok and never had a relay go down. Most of the Cessna range use this relay with no problems.

Change a battery after 2 years, no way, to expensive and not necessary if the battery is maintained properly.

I do not understand your shotgunning is not an acceptable method, please explain.

These are just my thoughts and would be interested in the reply/comments.

Cheers
Pete

[GMAs]

Hi Pete

I'll take it one at at time for your answers IN DIFFERENT TEXT

GMAs
It is not my intention to talk out of turn here but I will make some comments on your trouble shooting ideas, and the little quiz.
I do not think a simple volt meter is good enough to start measuring voltages and resistance as they are not accurate and libel to errors. As i have seen when measuring across a circuit breaker you will need to load it as a bad connection inside the breaker would not show until loaded.

TRUE. I WAS ASSUMING THAT YOU MEASURE THE ITEM WHILE ITS IN OPERATION... THAT IS HOW WE DO IT HERE... UNLESS YOUR DOING A STATIC CHECK. VOLTMETERS ARE ONE OF THE BETTER TOOLS TO DO ANY TROUBLE SHOOTING OF ELECTRONIC/PLANE CKTS. ONE WITH A CONTENUITY CHECKER BUILT IN (TONE OR BUZZER) IS EVEN BETTER FOR CHECKING WIRES AND SWITCHES BECAUSE YOU DON'T HAVE TO LOOK AT THE THING. WE ALSO USE O-SCOPES TO LOOK AT THE ELECTRICAL TRACINGS AND FOR CHECKING MAGS.... THEY ARE EXPENSIVE AND MOST MECHANICS ARE NOT ELECTRONICALLY TRAINED TO UNDERSTAND THEM. A GOOD VOM (EITHER DIGITAL OR ANALOG) IS THE FIRST TOOL OF CHOICE.... I DON'T KNOW HOW YOU SET VOLTAGES OR OTHER TESTING WITHOUT ONE.

On the '65 337 both alternators are fed by one regulator so you cannot compromise between the front and rear, so any oscillation problem are down to wiring, connection, and the condition of breakers etc. On all 337's with dual regulator system this is not a problem as each regulator output can be adjusted to suit.

DUAL REGULATORS WE HAVE SEEN HAVE INDIVIDUAL VOLTAGE ADJUSTMENTS BUILT INTO THEM.. AND ARE ADJUSTABLE ONCE INSIDE. IF YOUR SINGLE REGULATOR IS SETTING ACROSS BOTH FIELDS.. THE FIRST THING I WOULD DO IS UPGRADE IT TO A DUAL SPLIT... OR YOU WILL ALWAYS HAVE PROBLEMS ...BOTH ALTERNATORS WILL NOT PERFORM THE SAME ALL THE TIME... NO MATTER HOW HARD YOU TRY.

By the way GMAs what should be the voltage at the alternator field on a '65 337 and just for fun what should it be on the '77 337, just a little quiz for you all.

AHHH TRICK QUESTION THEIR PETE.... WHAT VOLTAGE SHOULD THE BATTERY BE CHARGED AT IS MORE THE RIGHT RESPONSE... CHECKING THE MANUFACTURES MANUAL IS THE PROPER ANSWER.. AS SETTING IT TO WHERE HE WANTS FOR HIS BATTERY IS THE CORRECT REPLY... (CESSNA HAS SOME GOOD READING MATERIAL IN ITS SERVICE MANUAL ON THIS SUBJECT)

You seem to go a lot for the master or starter relays, and your failure rate seems high and over here we have 30-40 year old aircraft flying quite ok and never had a relay go down. Most of the Cessna range use this relay with no problems.

WELL... CHECKING THE MANUFACTURS (CESSNA) IT SAYS THAT THEY SHOULD BE REPLACED EVERY 5 YEARS. NOW I KNOW A LOT OF OWNERS WHO HAVE NOT REPLACED THEM SINCE THE FACTORY... I ALSO SEE A LOT OF THEM THAT BURN UP STARTERS WHEN THEY HANG AND OR LOTS OF PROBLEMS WITH OTHER ELECTRICAL ISSUES WHEN THE MASTER SELO IS ...OLD. MOST OF THE TIME THE OWNERS FOLLOW THE MANUFACTURES SUGGESTED INSTRUCTIONS TO KEEP FROM HAVING PROBLEMS. OTHERWISE WHY WOULD THEY WRITE IT???

Change a battery after 2 years, no way, to expensive and not necessary if the battery is maintained properly.

WELL... AGAIN MAYBE THEY DO IT THAT WAY OVER THEIR.. BUT HERE ON THE LEFT COAST MOST OF THE GILL 242'S AND OTHERS DON'T MAKE THE LOAD TEST.. I.E THEY ARE LOSING CAP AFTER 2 YEARS. (NOW WHY DOES THE MANUFACTURE WANT YOU TO LOAD TEST THE BATTERY EVERY 11 MONTHS.... WELL ITS SO THAT WHEN YOU HAVE A PROBLEM YOU MIGHT JUST HAVE ENOUGH BATTERY TO MAKE IT BACK TO LAND WITHOUT CAUSING A BIG EMERGENCY) THE ISSUE OF BATTERY DEATH IS REALLY FOUND IN TWO AREAS. THE USED AND THE UN-USED. USED THE PLATES GET EATEN UP INSIDE BY USEAGE... THE UN-USED... THE BATTERY SULFATES AND IT THEN ALSO LOSES IT ABILITY TO PROVIDE THE CURRENT SPEC'ED FOR. OF COURSE RUNNING THEM LOW ON LIQUID/WATER ALWAYS HELPS SHORTEN THEIR LIFE DUE TO HEAT AND LACK OF ACID SUPPLY. (PLATE WARPING CAUSES SHORTED SECTIONS OF THE CELLS)

I WILL NOW TURN THE TABLE ON YOU PETE.... BY ASKING THIS QUESTION. HOW MANY MIN AND AT WHAT AMPERAGE SHOULD YOU BE TESTING THE BATTERY AT/ AND WHAT EQUIPMENT SHOULD BE USED TO TEST IT FOR COMPLIANCE WITH CONTENUED AIRWORTHY? (YEP ITS OPEN BOOK SO YOU CAN GO LOOK IT UP)

WHEN WAS THE LAST TIME YOU DID A LOAD TEST ON A SKYMASTER BATTERY... AND WHAT WERE THE RESULTS. (MOST MECHANICS JUST CHECKTHE LIQUID LEVEL AND CALL IT GOOD... BUT THAT IS NOT CORRECT WHEN YOU HAVE YOUR PLANE INSPECTED.

OH AND FINAL QUESTION.. WHAT / WHEN SHOULD YOU DO THE TEST ON THE BATTERY?

I AM SURE THAT IF WE CAME OVER AND TESTED 10 SKYMASTER WE WOULD FIND THAT THEY ARE FLYING WITH DEFECENT BATTERIES... AVG IS THAT 3 OUT OF 10 WILL FAIL. IT IS THEN THAT THESE PLANES ARE NOT AIRWORTHY AND BECOME A ISSUE FOR FLIGHT.

I do not understand your shotgunning is not an acceptable method, please explain.

WELL.... SHOTGUNNING IS NOT ACCEPTABLE METHODE BECAUSE FIRST OFF IT COST THE OWNER/OPERATOR TOO MUCH MONEY. SECOND ITS NOT SAFE.
SHOTGUNNING IS NOT TROUBLE FINDING. YOU ARE JUST REPLACING THE BLACK BOX THAT FAILED... YOU DON'T KNOW WHY OR WHAT CAUSED IT... THINGS DON'T JUST HAPPEN... CAUSE AND EFFECT.... AND VISE VERSA.
IN THIS CASE CHANGING THE REGULATOR, CKT BREAKER AND ALTERNATOR ALL ARE EXPENSIVE AND MAY NOT BE NECESSARY... THIS IS CALLED SHOTGUNNING. IF CHANGING THE REGULATOR FIXES THE PROBLEM CURRENTLY ONE GOES OFF FLYING THINKING THAT THEY ARE GOOD TO GO... BUT IN REALITY ITS THE ALTERNATOR DRIVE COUPLER (FOR INSTANCE) AND NOW THE ALTERNATOR FAILS IN FLIGHT... SENDING PARTS AND PIECES INTO THE CAM GEAR WHICH THEN TAKES OUT THE OIL PUMP GEAR SHAFT AS WELL AS RUPTURING THE ENGINE. ALL BECAUSE SOMEONE DIDN'T TAKE THE TIME TO FIND THE REAL PROBLEM... THEY THOUGHT IT WAS THE REGULATOR...THUS NOW OUR PILOT NOW .. IF HE MAKES IT BACK TO THE GROUND WITHOUT GOING THUD... HAS A BIGGER EXPENSE TO DEAL WITH... SHOTGUNNING IS A BAD WAY TO WORK ON AIRCRAFT. THAT IS WHY WE TRAIN MECHANICS TO THINK... AND FIND THE BAD PART CAUSING THE PROBLEM. SYMPTOMS ARE THE EFFECT THAT THE BAD PART CAUSES.
THEN AGAIN YOU ALREADY KNOW THIS TOO...

KEEP UP THE GOOD WORK.

fly safe GMAs

[GMAs]

For those who are not up to speed on their ships battery in the issue Pete and I are discussing you can go to this web site if you have Gill battery (the pink one) in your plane. (chapt 7.7 Ppg 19- is of particular interest to you and your IA)

http://www.gillbatteries.com/battery...ice_Manual.pdf

Please don't get us wrong... discussing different issues has always been a healthy approch to improvement as well as insight into different experances... those of you reading along should not assume that we are bickering... no instead you should also go look up the issue and see if it applies to your plane/experiance... food for the head.

[GMAs]

As to the Sulfating of the ships batt from setting... to answer the other question I got... you can go to the internet and look up why they do it better than we can re-write the issue here.

We did a extensive study on the problem and what can be done to keep the ships battery from having it happen.
We tested several pieces of manufactured equipment to find out if they really did what they claimed. We got down to just 3 manufactures. One even improved their product further after he reviewed our testing data. The currently are the No. 1 aircraft battery charger/desulfator and highly recommended to the members of the Skymaster groups.

This charger/de-sulfiator can be left on the ships battery indefinately. It uses a microprocessor to sense the battery and keep it peaked.

Here is the best of the best that we tested... and their new aircraft specific appliance

BatteryMINDer
AviationSpecific Battery Charger

12-24 Volt 2,4,8 Amp

The BatteryMINDer is a 3-mode charger /maintainer /conditioner that extends performance and life of all types of 12 Volt or 24 Volt lead acid batteries. These include maintenance-free, marine, sealed gel, AGM, dry and valve-regulated batteries.


The voltage settings and charge rates (both user selectable) have been chosen, after conferring with leading aviation battery makers in the U.S. By providing each of these BatteryMINDer units with an “At-the-Battery” temperature compensating sensor, batteries can be safely charged and maintained for extended periods in temperature extremes from 32°F to 125°F. Without this type temperature sensing, batteries will be under-charged in colder temperatures (<70°F to 32°F) and over-charged in high temperatures (>80°F to 125°F).

Both models include full-time pulsed de-sulfation circuitry designed to safely dissolve sulfation build-up on the battery’s storage plates, restoring lost cranking power and extending life. Our de-sulfation method is fully automatic, does not use potentially damaging high voltage and is exclusively protected by two U.S. patents.

What is Sulfation (sul-fay-shun) and
How Does It Affect Batteries?

When batteries are improperly maintained (over-under charged or left uncharged for extended periods) small crystals of sulfuric acid from the battery’s electrolyte (liquid or paste) form on the battery’s charge plates. They act as a resistor (barrier) preventing the battery from ever again accepting a full charge, no matter how long a charging source may be connected. Once this occurs, the cranking power of the battery is severely reduced, as well as its life. Aviation batteries are affected the most because they have been designed for maximum performance in the smallest-lightest case possible.

VDC Electronics has developed simple, but highly effective circuitry, able to safely dissolve sulfation, restoring much, if not all, of the lost power, providing the battery’s cells are not shorted or structurally damaged. This U.S. Patented approach is believed to be the most effective method for eliminating even the oldest hardened sulfate. By generating safe, wide-band, random frequency electronic pulses, we are able to cover the full range of sulfate crystals sizes, in the shortest possible time. Depending on the amount of sulfate and its age, complete de-sulfation can occur within several days to several weeks. De-sulfation takes place automatically, while the battery is being bulk or maintenance level charged.
FEATURES

• For all size and type 12-Volt and 24-Volt aviation batteries (or two 12-V in series = 24-V) including sealed AGM-maintenance-free and filler cap maintenance type
• Guaranteed never to over-charge, regardless of time or temperature (32°F – 125°F) with correct battery type setting and ABS-248 or 124 temperature sensors correctly installed on either battery terminal connection
• Push-button selector for charge rate and battery types = ensures 100% compliance with major aviation battery makers’ specifications
• Auto-restart after power failure
• Safely charges up to 200% faster than conventional chargers
• Maintains from 1 - 6 batteries at a time (parallel connected)
• Automatically dissolves power-robbing sulfation using safe low voltage pulse technology (U.S. Patented)
• Microprocessor controlled pulsed output ensures 100% full charge
• Temperature compensation extends battery life by more than 200 Cycles (full charge-discharge cycles) with ABS temperature sensor1
• High efficiency design = low monthly operating cost of less than 50¢2
• Weather-proof enclosure
• Optional 12 or 24 Volt PowerPlug (fused) allows charger to be easily connected to battery via input 12 v or 24-v power receptacle
• 1 year 100% money-back guarantee + five (5) year “no hassle” warranty
Size/Weight: 5-1/2” L x 5-1/2” W x 2 1/4” H / 3.0 lbs.

by the way... mention that your a 337 Skymaster Club person and you can get a manufactures direct discount for one. A lot of our club owners now own them and have had great results while the bird sits throught he cold long winter.

Only warning we suggest is that you not turn on the ships radios or master switch when its in operation. The de-sulfication break down pulse spike can exceed 30 volt and could damage sensitive electronics if allowed to be placed across the terminals.

Hope this helps

Fly safe...GMAs

[Pete Somers]

OK Gmas
I see your point on these matters, however we all have different approaches to troubleshooting a system and Although you keep saying refer fo the Cessna Service Manual for write ups and defect rectification, but have you found, ahah that what the defect and how to rectify from a Service Manual, no. It comes from experiance an pure hard work.
That quiz question was not a trick, it is a factual question and the answer does not lie in the Service Manual! and it does not matter about the battery condition. It does not matter what type of a/c you work on experience is the only thing that is going to matter weather it is a Tiger Moth or a King Air.

I use an AVO MK8 for most of my measuring of resistance and voltage, it is an old unit but it does the job right, then use a 4 digit DVM for any setting up work like alternators, but each to there own as they say.
A member mentioned about checking bonding across control surfaces using a DVM, no way you need a bonding checker to do this as a DVM does not go low enough to check the bonding.

Is there an STC to replace the regulators on the '66 337 so that each alternator is fed from it's own regulator, sounds an expensive mod to me?

The Manufactures are more and more covering there own rear end by putting a life on items, these parts were always on condition but we have become the sue and sue more society that it has been blown out of proportion.
In the Cessna 337 Service Manual it also says the seat belts should be replaced at 5 years, anybody done this. If they did this sort of thing to your car you would have something to say.

Regarding the starter relays: The CAA over here insist on the fitting of a simple light to show the starter in engaged and the relay is energized, so a failure of the starter relay would be detected by the light being on. Simple but saves a burnt out starter?

Trick question, not my style. But would like an answer.

GMAs I have enjoyed this discussion and I hope that we can have more of these, as you have said for owners that read this I hope it has given you some insight of what is involved in maintaining your airplane and the older they get the more of a problem they are (just like us!).

Thanks GMAs
Pete

[GMAs]

Pete....
I too enjoy a good tech discussion. Yes indeed you all do it different over their. Putting a light on the dash showing the engagement of the starter would not be hard today using LED's... but then again the wire weight and is it necessary if the plane is maintained.

I used to know a guy who could use two fingers across the voltage source and tell you if it was 120,240 or 480... he wouldn't try 660 because he said his hand got cramps after for a few days... Yes technology has come a long ways from the old days of the edison jar measurements. We have several of the fluke inst that we use here and they seem to serve well... We also use a low freq generator to do surface contact checking... however most of the time a good cleaning, alodining and then mounting takes care of the problem of skin resistance on parts.

Well the service manual is the bible... but yes experance is the key to "gettin 'er done" right the fist time.

Yes I think they did away with the old single regulator... never worked right in the first place... and put in the same as the current dual regulators on the fire wall using the same parts.. shouldn't be that expensive.. but, here in the States we can use a form 337 and get field approval for these types of mods... I don't think a lot of the older ones here are running single vr's anymore... of course cessna quit making the plane that did...336 and early 337... and went on to a better system.

If it were me.. I would change... but if it were too difficult or expensive over their.. I would put a switch in so that only one alternator was working on line... of course your limited in current then if you go by the rules... Yes I would upgrade to the dual vr ... one each for the alternators. Today technology has the VR's built into the alternators on the belt driven ones.. I think some of the EAA guys have converted the Cont drive to use the newer alternators... thus you would have the VR's built into the alternator and wireing would be a breeze to convert the system over... then each VR is right inside the alternator... and of course they are electronic controlled so no adjustment necessary at the source... only IR drop from the rear to front would have to be delt with. A single sense wire could take care of that.

As to your question....
I disagree... with your response... the set voltage is in the Service manual.. and also the battery manufactures publications... they are the guide that you are to follow. Anything else and your not going to get opt life out of the battery. I am still scratching my head about the "...and it doesn't matter about the battey condition" I think most will disagree... that it does... i.e if the battery is low ... how do you set the vr's correctly... the manual clearly states that one should have the battery charged up and full before attempting to set he VR's ... while the plane is running... of course you could set them up using a test jig...on the bench... but then that doesn't take into consideration the IR drop of the connections and condtion of the wires.

Take care my friend

Fly Safe GMAs

[Pete Somers]

GMAs
Sorry i will put that question in a different way.
On the ground no engines running you check the field voltage at the alternator, what will the voltage be on a '66 337 and what will be the voltage on a '77 337, just for interest and i hope all you guys are taking note.

Thanks GMAs
Maybe meet up soon time

Pete

[tropical]

Originally Posted by GMAs

For those who are not up to speed on their ships battery in the issue Pete and I are discussing you can go to this web site if you have Gill battery (the pink one) in your plane. (chapt 7.7 Ppg 19- is of particular interest to you and your IA)

http://www.gillbatteries.com/battery...ice_Manual.pdf

Please don't get us wrong... discussing different issues has always been a healthy approch to improvement as well as insight into different experances... those of you reading along should not assume that we are bickering... no instead you should also go look up the issue and see if it applies to your plane/experiance... food for the head.

Originally Posted by GMAs

Most mechanics and IA's right now are not doing the section of the battery "Contenued Airworthness" requirement. One then wonders how they can retrun the aircraft to service AT ANNUAL if they fail to do the load test on the battery once a year as directed by the manufacture. (BUSTED BIG TIME)

That section you refer to says "recommended", not "mandatory". It is not required for an annual inspection to accomplish to return to service.