Charging System/overhaul questions from bad alternator

[gcball]

I have questions regarding my T337B '67 Charging System. I recently (last month) had an annual performed and the front alt was removed, inspected, cleaned and commutators turned. The rear alt was removed and replaced with an exchanged unit and a new battery was installed. After two flights total time 3hrs the battery started to discharge. I tried switching alt's and reg's and cycled the master nothing changed, the battery continued to discharge. After reaching my destination I charged the battery and flew home with the battery continuing to discharge. What is the next step, Reg's, contactor, wires in between? Help.

Gavin

[Mark Hislop]

Gavin:

Have you checked the field circuit breakers? I find it hard to believe that both alternators have failed.

Mark

[gcball]

Mark,
I have checked the Circuit Breakers on the Breaker panel (inside). Are the field Circuit Breakers at the unit (Alternator) or inside on the panel? I too find it hard to believe that both Alternators went out at the same time. Still troubleshooting.

Thanks,
Gavin

[docbob]

It is not unknown, but not necessarily common, that old regulators will not work with new/rebuilt alternators. The voltage limiter adjustment in the regulator is, ideally, adjusted to meet the requirements of the specific airplane. Often these can be CAREFULLY adjusted to work with new alternators. This is the ONLY adjustment that I know of on the transistorized regulators.

The Cessna Charging System Manual lists the following as probable cause for a discharged battery:
-Charging circuit resistance too high (loose or dirty connections, for example)
-Voltage limiter malfunction or low setting (could be)
-Accessory load too high (doesn't sound like your probloem)
-Corroded or loose battery cable connectors (probably not but I'd check anyway)
-Metal chips in field relay core gap (I suppose?)
I'm wondering if the alternators were installed correctly and were ever working at all. Depending on the circumstances is is not impossible that a new battery could work for 3 hours. What did the ammeter and/or voltmeter tell you?
I'd do everything simple first then attack the regulators.
Good luck, Bob

[rick bell]

if a coupling fails the carging systems turns to garbage. fooled around with mine for over a year. did everything and it turned out that the coupling would work on the low end and as a load was placed on it would taper of on voltage and the alt lits would keep blinking unti they finally stayed on. (73p) you can stick your finger into the alt and see it turns. if so maybe that is where the problems lies.

[Pete Somers]

Gavin

The only way to check the system is with a voltmeter.
You need to check that there is 28 volts on the F terminal of both alternators.
Also check there is 28 volts on the BAT terminal of the alternator.

If you start up both engine what is the bus bar voltage, should be 28.75 volts.
Select the standby regulator, is it still the same.

If you have no voltage at the F terminal you have a U/S regulator check with either regulator selected.

There is a fuse involved with the system and it is mounted down by the battery box.

Hope this helps, let me know how you get on.

Pete

[Ron Ball]

Gavin is out of town, I'm his Dad. The 1967 T-337-B is now back at the Mechanic. He says he found the bearing and parts of the new ex-changed alternator, on the bottom of the rear engine compartment. Has contacted the Manufaturer and they are sending out an insurance adjuster. They say needs a complete inspection, tear down of engine. cost 8000.00. Hopefully they pay for it. But down for min of 6 weeks....Engine has 800-900 hours, or so on it. Maybe should re-build, while it is torn apart???? Does the crank need to be replaced. Was a factory re-man in 1990 or so.

[WebMaster]

Check wiht Continental about the crank.
The timing is suspect, and if they crack the case, open it up, you will have to replace the crankshaft.

[Kim Geyer]

If your engine was a factory reman @1990 I would almost bet it's got a VAR crank
Kim

[WebMaster]

Kim,
Would the same be true if the engine was overhauled?

[Kim Geyer]

Larry
You are correct, I think it was middle 1980's when it was mandatory to put VAR cranks in. I would have to look at the AD
Kim