Important recommendation relating to avionics installations

[Aviation Engines]

This was sent to me from Peter Howe (Composite Technologies)
I would like to urge everyone to check that they have the specified capacitor installed and make that it is correctly wired up.




Filser Electronics has advised us that the standard regulator used by Rotax in the 912/914 series has output voltage peaks of up to 70V. Most equipment is specified for up to 16VDC operation. Spikes which may occur at the output of the regulator may be attenuated to some degree by the wiring, the battery and the avionics equipment itself.



Due to equipment failures from over voltage, German ultralight manufacturers are to starting to use an alternate regulator, which does not exhibit this problem. You may want to look into this in the long term.



In the short term, I have observed in several cases in South Africa, that a 20,000uF capacitor is not connected across the output of the regulator, as specified by Rotax. This capacitor will help to smooth the output of the regulator, and will reduce the level of the voltage spikes to a point where damage from over voltage may not occur.



If there are aircraft flying without this capacitor, I urge owners to fit this without delay. The Rotax installation manual specifies the value and voltage rating. Companies such as RS Components stock suitable capacitors.

[Griffin]

Let me understand this. Rotax have a defective design and, instead of recalling the product and correcting the problem at their expense they make it the customer’s responsibility to fit a capacitor. A capacitor on its own is not an effective way of correcting the problem but, if you destroy your expensive radio/GPS/MP3 it is your problem! Wish my customers were gullible and accommodating.

BTW this is a Rotax issue. I am not pointing a finger at Niren and Aviation Engines & Accessories

[Aviation Engines]

The system is not defective!

The Rotax installation manual is quite specific about the installation of the capacitor as an over voltage protection and it is the responsibility of the engine and avionics installer to ensure that such protection is put in.

Over voltage protection is a standard part of an aircrafts electrical system and even a microlight is an aircraft.

The requirement from Rotax is capacitor 22000uf 25V minimum.

[Rudix]

I can assure you a capacitor is a very crude and quite inaffective way of preventing over voltage/regulating voltage ! Once the cap is charged it will provide NO protection. The only thing it will do is remove ripple (AC ripple) from DC, as it charges on the ups and discharges on the low parts smoothing out the voltage, this is not the problem in this case........

There are other, more effective way of preventing over voltage, like TRUE regulators or clamping diodes.... Why not use a common car voltage regulator ?

Happy flying,
Rudi

[Aerosan]

I agree with Rudix. Surely Rotax can make availeble a circuit diagram to do the job propery