ALT restart batteries

DrDave · #1 09-09-20, 12:58 AM

Good evening:

You can't like any of that. It sounds like the front engine system is the closest to normal. I would adjust the front regulator to 28.4V. Once it's set there let's see how it handles the load. We also want to see a steady amp meter. If the amp meter is waving at you there is a problem in the field circuit. Let me know what you get and we will diagnose.

One step at a time will win the battle.

Report your findings.

patrolpilot · #2 09-10-20, 07:57 AM

Interesting and timely topic. I recently experienced a significant electrical event after takeoff; I thought I had documented it here but didn't and will add that topic today.

I wanted to mention that as the troubles were corrected, the amp meter continued to have a "hard, full-range cycle. On the ramp, I ran through the Electrical System Ops Check outlined in the POH, and at the end of the successful test, I realized that my amp meter indication had returned to the regular, light, small bumping on the meter.

My battery pack did not pass the Alternator Restart Test, so the batteries are being replaced now while the airplane is in maintenance. I found and purchased the SK337-46A Battery Pack Kit recently. Given what happened to my airplane, my mechanic might replace the existing pack with the kit.

As pilots, we are supposed to perform both the Electrical System Ops Test and Alternator Restart Test at 25-hour intervals. I remember this from attending Cessna Skymaster school in January '78. While in the airplane, the paragraph format in the Manual is tough to follow. I listed them out in checklist form in ForeFlight and also kept it as a document within the app (attached).

From experience, when you push on either electrical test button, push with a clockwise movement on the button. The button is thread onto the shaft of the switch, that shaft is free to rotate. It is impossible to get them too tight, but I have found them missing and on the airplane floor. I haven't experienced the loss since I started adding the rotation with the push.

DrDave · #3 09-10-20, 02:38 PM

Does the regular, small, bumping of the amp meter correspond to any known electrical load?

Dave

Learjetter · #4 09-10-20, 11:50 PM

Quote:

Originally Posted by DrDave

Good evening:

You can't like any of that. It sounds like the front engine system is the closest to normal. I would adjust the front regulator to 28.4V. Once it's set there let's see how it handles the load. We also want to see a steady amp meter. If the amp meter is waving at you there is a problem in the field circuit. Let me know what you get and we will diagnose.

One step at a time will win the battle.

Report your findings.

Rear alt field circuit to case= 15 ohms. Book value 10-12 ohms. Good diode test on real alternator.. Haven’t check front yet. Forgot about AC volt test, again.

Ran engines separately and adjusted both VR to 28.0v
Running both engines together showed 27.9-28.1v fairly steady, even with a load of full lights. Annunciators appeared to operate normally....but...rear alt out light would blink occasionally. Looking closely at warning board, we determined terminals 1&2 and 6&7 were wired backwards, with terminal 2&6 to cathodes instead of 1&7. Fixed that, re-ran front engine and it shows 30v. Gave up and came home to some 12 year old Glenfiddich and read old Tom Carr posts in the CPA forum.

I think I need to start over, but none of the troubleshooting guides in the service manual match these symptoms.

Kim Geyer · #5 09-11-20, 04:43 PM

don't forget to look at the trip out sensor.
had 2 of our 337s doing stupid electrical stuff and found the sensor had corroded pins.
re pinned the connector and everything good. The other one I replaced the sensor. Its located on the copilots side of the pedestal. little rectangle box about the size of a pack of smokes.

Learjetter · #6 09-11-20, 08:53 PM

Turns out, the wiring diagrams in the Service manual depict the printed circuit board in two places. In one drawing, it shows the circuit one way, and in another, it shows it differently.

When I ignore the drawing on page 4-3, and wired the board as in 4_2_1, magically, the system works. Annunciator lights come on when the switch is off. Adjusted each regulator to 28.0v to give 27.7v (book value with load on). And it all worked. Test flight soon to confirm.

Still have a jittery ammeter, but at this point, I'm willing to live with it until annual when we bring this airplane into the 21st century and install plane power R1224s and an EI Voltmeter/ammeter and pile all the ancient diodes and resistors and capacitors in the middle of the ramp and set fire to them.

That is, if I can convince the local FSDO to play ball and sign off my 337 form.