Rear Alternator Condensor

bking · #1 05-06-21, 03:50 PM

In rebuilding my alternator failure board, I've decided to change out the front alt. capacitor filter and rear alt. condenser. The problem is, I cannot find the location of the rear condensor. It is not connected to the rear alternator directly and not located in the rear or front engine compartments or the avionics bay. Does anyone know where they are located?

Thank you,

BK

mshac · #2 05-06-21, 09:04 PM

It mounts on the alternator. Yours may have been removed at some point: http://www.337skymaster.com/messages...ight=condenser

JAG · #3 05-09-21, 05:55 PM

I have a 1966 337A. My rear condenser is mounted to the firewall just in front of the alternator. I have disconnected it, but have had no issues with noise or problems with the alternator or radios.

Jeff

bking · #4 05-10-21, 03:44 PM

Jeff, thanks for your comment and could you share why you disconnected the rear condenser?

Thank you,

Bill King

JAG · #5 05-10-21, 06:05 PM

Hi Bill,
Sorry - I should have mentioned why I disconnected it. I thought I had an output issue from the alternator, and in my troubleshooting, I disconnected it. It turns out, that was not my problem, but after sending out the alternator (no fault found), and then subsequently swapping it with the front one (not a fun troubleshooting exercise!), there was nothing wrong with that alternator or the system. It turns out, the one alternator just needs more RPM than the other to start producing output.

Long story, I know. I have not hooked the condenser back up yet, but have noticed no problems (noise) in the system not having it either.

Jeff

mshac · #6 05-11-21, 03:42 PM

Just know that a condenser and a capacitor are one in the same. They act as a small "reservoir" of current, catching small spikes, and smoothing temporary low voltage situations. If you've ever had an RV, think of it as the rubber bladder that stores a bit of water pressure before the pump has to kick in. Unless there is electrical noise or interference with your radios, I would not be overly concerned about it.

bking · #7 05-13-21, 11:36 AM

My apologies for not replying to you both sooner but was waiting to hear back from the Cessna/Textron piston support group. They were very helpful and took the time to pull the original electrical drawings that went back to the 336 days. The drawings did show a condenser connected to the rear alternator but the engineers could not explain why and suggest that if I had any radio noise that might be a fix.

I think i'll take mshac's advice and not worry about it.

Thank you,

Bill King

SkyMac · #8 05-13-21, 03:53 PM

I removed my rear condenser a couple of years back, no noticeable effect.

Dave

wslade2 · #9 05-13-21, 04:45 PM

As I understand it, condensers (noise filters) were necessary with the OLD radios. The newer audio gear more sophisticated with protection built in. Ergo, if you have even a 20-30 yr old panel, won’t notice it’s absence.

bking · #10 06-19-21, 06:54 PM

This afternoon was my first flight since completing this years annual. As I advanced the throttles to takeoff power, there was a noise in my headset that has never occurred before. At first, I thought the batteries went out in my Bose noise canceling headset but once the throttles were pulled back to 25” it stopped. I did a ground check before shutdown and the same thing occurred.

During the annual, my A&P replaced the rear starter and had both rear mags overhauled this year. Also, we replaced the alt out warning circuit board and the front alternator noise filter.

I haven’t talked to him on this but came here first for ideas since thats the first thing he ask when we have seemingly Skymaster related issues.

Has anyone had a similar problem or any idea where to start diagnosing the problem?

DrDave · #11 06-20-21, 08:51 PM

Greetings:

According to the alternator system wiring diagram for serial numbers 337-0001 thru 337-0268 and 337-0281 thru 337-0325 there was no filter capacitor on the alternator output. 337-0269 thru 337-0280 did not have a filter capacitor either.

Beginning with 337-0327 there was a filter cap on the output (B+) of both alternators. This practice was also associated with Cessna's practice of shielding the alternator output wires and the field wires. This was done in an attempt to clean up the AC hash on the line that was interfering with ADF's and poorly isolated audio amplifiers in the radio's and audio panels.

Fortunately the Skymaster was spared from the poor tactic of putting a capacitor on the field terminal at the regulator, this was a single-engine airframe practice. We don't want the regulator driving a capacitance load.

If you review the alternator system wiring diagrams for the later Skymasters the wire shielding practice was dropped but the output capacitor remained. There is nothing wrong with having a capacitor on the output terminal of the alternator.

During an electrical system freshening there is no reason to shield the alternator output leads. It's okay to shield the field wire from the regulator to the field terminal of the alternator. Best practice is to ground the shield at the regulator end only. If you are doing a charging system freshening, running a 16 gauge field wire to the rear alternator will help to balance the output sharing of both alternators. This statement applies to the planes that use one regulator for both alternators. The 2-4 amp field load can have a noticeable voltage drop over the long field wire to the rear alternator. The heavier field wire to the rear alternator will help balance the load.

Dave

Dave