overvolts on G model
 

sorry to bring Alternators and overvolts up again but need some new ideas.
I have a G model with the two regulators (one for each engine)
occasionally Im getting the overvolt situation with both alternators shutting down and red overvolts light on.
Sometimes say on a two hour flight 5his can never happen. Other times it could be three or four times.
I've tried running on Front alt only and it NEVER happens.
But it does on Rear alt only, same as with both running.
I've tried swapping regulators but it does not transfer the fault.
I've checked alternator voltage and it seems correct. around 28 with both running under losd add 26. 5 ish on only one alternator. Both regulators are the solid state Zefftronic/Electrodelta type with no adjustment.
where now too look. I had the diode board changed some years ago and physically it looks ok
Anyon3 had the dame issue on the G model pleaee and how did you eventually resolve it ?

There is only one proven solution - upgrade to true parallel alternators like the 400 series twins. I've sold many of this upgrade to members of this site, with excellent feedback.

Installation requires approximately one hour.

Search this site and you can find detailed info on the upgrade. Or contact me directly at dfwaircraftparts at gmail.com

Cost is $595 deliverd in the CONUS, with tech support included. 30 day money-back guarantee.

True parallel alternators are the solution.

Edit: The exact voltage at which the over voltage light comes on is fully adjustable. Have you verified that it is set at the correct voltage?

1973 337G…. Has had 3 separate over voltage issues.

See my detailed post on circuit breaker panel.

The second was a landing gear related.

The third was replacing these 2 diodes on front firewall. One had a physical break on the post. Once this was fixed…, I’m 99.9% over-voltage free.

I had the same symptoms as you. No problem running only on rear. Running on just front or both alternators, problem present.

The diode for the front had the broken post.

Hopefully the photo attaches to this post.

overvolts
 

thank you MSHAC and Edasmus.
The voltage regulators in my aircraft are the solid state type and I thought they were not adjustable. how do i set the voltage that triggers the overvolt shutdown please.
i will inspect the diodes as soon as.

Pertinent Shop Manual Pages
 

I've attached all the pertinent shop manual pages for your perusal.

Since we're limited to 5 attachments per post, this is the 6th and final attachment from the previous post.

I may contact you on this... My rear alternator light intermittently turns off/on

Cessna's Pawnee plant engineers had never designed an electrical system with two alternators. And never would they again! Why they didn't use the proven system the 400 series aircraft uses probably has something to do with "Not Invented Here Syndrome" and rivalry between the two production plants.

Whatever the reason, the dual alternator charging system on our 337's is a Rube Goldberg like design. The alternator electrical outputs are not placed in a parallel circuit where they may be properly managed by the regulators.

The Electrical Upgrade Package includes two used regulators pulled from a 400- series twin ($595 - 30 day warranty through me), or two new regulators from Cessna($1495 - 90 day warranty through Cessna). Also included are specific installation instructions and diagrams, including the addition of the parallel circuit wire. Finally, there is a sample 337 form that has been approved many times by many FSDO's. Your A&P can use it to file the 337 for the upgrade.

Kit installs in about an hour.

Blinking alternator lights will be a thing of the past.

Please let me know if I may be of assistance.

Will your upgrade work with the zeftronic regulators? (My very first R&R was installing those and already invested in a set. Hate to go backwards to mechanical regulators.) I have low volt front winking at idle, disappears with increased throttle. Also new alternator, wiring and diode.

Unfortunately it will not. The regulators must be designed to use the parallel circuit.

My understanding is that Zeftronics produces voltage regulators that incorporate the parallel circuit (that is so critical to balanced charging), but they would require a 337 field approval as well.

That fact that my system is basically copied from other certified twin Cessnas probably makes the 337 approval process a little easier. YMMV.

Check your over voltage sensor. I had one of our planes doing that and found a corroded pin

Gotchya. I'm expecting it's corrosion somewhere and have been on the hunt for it when not dealing with other issues.

overvolt issue
 

Just to let all out there know , I have resolved my overvolts issue.
The rear alternator was faulty . We found chaffed wires in it.
So , replaced it with a new Plane Power alternator at great expense ( we are in Europe)
Also replaced the diode on circuit board that sits on bulkhead in front engine compartment ,
In fact we replaced both front and rear diodes .(only cheap, even here)
System now works normally.
Hope this may be useful to others out there.

Happy to hear your success! These planes are so enjoyable when all is right with the maintenance! Safe flying! 😊

Thank you Edasmus.
In fact you were on the money when you mentioned
those diodes in your earlier post.
about 20 years ago I replaced the whole circuit board due to
corrosion, so suppose those origonal diodes lasted well !
Cheers
Sunnysky