Voltage Regulator Failure

Hi Eric,

Inspired by your comments & photo's, I dug out an old (1999) Rotax 912 ULS, Ducati PN 343620.

This was removed from my last 912 ULS powered aircraft.

Green rather than black potting compound - quit crumbly, so took some removing.

Circuit does not look like the one in your photo.

As you predicted, found a loose/unsoldered connection.

As the 34369 pre dates the last & current part numbers, I will not attempt to fix & install it as it may not be compatible with my Earth X battery voltage/current draw.😈

Hi Sean,

That potting compound indicates the regulator is an older version, either  PN 365347 (Ducati 343620) or 365345 (Ducati 343875). These precede the current version introduced in 2010, PN 365349 (Ducati 362001)

The instructions I posted previously only apply to the current version (Rotax PN 365349, Ducati 362001) with black potting compound. 

The older version regulator has a completely different failure mode and is “repairable” without un-potting it.

This version use two “button” case diodes as part of the full wave bridge. Because of the poor design and poorer thermal management choices these diodes unsolder themselves under higher current opperation. Fortunately the connections we need to access are available at the regulator’s socket/plug. An external 50 amp 1000V bridge rectifier can be added to bypass the inoperative internal parts. Simply clip off the new bridge’s negative lead (it’s not used), next connect the bridge positive lead to R or B+, then connect the bridges  AC leads to the regulator AC input (the generator wires must feed both the regulator and the new bridge rectifier.)  Installing the new bridge on a a heat sink is advisable. 

The attached files are spicific to Rotax PN 365347(Ducati 343620). 

Hi Mike,

Thanks for your inspirational electronic advice.

Its definitely a Ducati 343620.There is no Philips head screw in sight. My investigation, was purely academic. I have no intention of bringing the paperweight  back into service.😈

Some interesting & helpful commentary/advice from Vans Air Force;

https://vansairforce.net/threads/yet-another-voltage-regulator-failure.123402/

It beggars belief, that Rotax persist with the Ducati VR (including ineffectual upgrades).

😈

Vans has one of the highest failures of any Mfg because of where they mount the VR and they get too hot. I've fixed numerous Vans RV12 VR mountings to get cool air and they have never had a single failure. It's all about amp draw and too much heat. You need to make sure you don't get out of spec or you'll most likely have to replace one.