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

[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.

[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.