Matronics Email Lists Forum Index Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
 
 Get Email Distribution Too!Get Email Distribution Too!    FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

ACS key ignition switches

 
Post new topic   Reply to topic    Matronics Email Lists Forum Index -> Europa-List
View previous topic :: View next topic  
Author Message
JonathanMilbank



Joined: 14 Apr 2012
Posts: 383
Location: Aberdeen area

PostPosted: Tue Dec 26, 2017 1:59 pm    Post subject: ACS key ignition switches Reply with quote

This topic comes up from time to time and my belief is that if Rotax and Ducati felt that there was a problem, then they would have put out a written warning years ago. Yet there are many who swear that these ACS key switch units cause ignition and rough running problems. What's the proof of this?

Here's an opinion which someone passed on to me, even though he's about to change to separate toggle switches for grounding his Ducati ignition modules:

"My local airport is KGVT, Greenville, Texas. It is home to the defense contractor L3 – Mission Integration Systems. L3 employs thousands of engineers. I am fortunate to rub shoulders with many of these engineers both active and retired.

I spent much of the day with a pilot/electrical engineer who has over 35 years designing and specifying aircraft electrical systems. We discussed the magneto switch when used with the Rotax Ducati ignition system. He agreed the notion of a magneto switch causing a failure of the solid state module with some type of "feedback" was poppycock. He also agreed the AC voltage on the Ducati kill circuit was less damaging to a switch than the P lead circuit on a magneto ignition.

Let’s look at the facts, how the system operates, and possible failure modes.

The Rotax Ducati ignition uses a shorting wire to “kill” the ignition. It is only grounded on engine shutdown and during ignition checks. The shorting wire is grounded through the “mag” switch. If the shorting wire is disconnected or breaks, the engine continues to run. The only electrical things that could damage the ignition module are overvoltage and improper or shorted wiring.

The Rotax engine dynamo supplies power to the modules. Voltage is limited by engine rpm. Current is physically limited by the size of the dynamo coils. It is impossible for the dynamo to supply excessive voltage or current to the modules. The vast majority of Ducati ignition module failures are wires breaking inside the insulation close to the module due to vibration.

The premise that AC voltage present on the grounding circuit is too high for a magneto switch is unfounded. The voltage involved when grounding a Ducati module is similar to the voltage present on the P lead of most magnetos. The internal arcing with AC voltage is less than what would be present with a pulsed DC signal from a magneto. There is no reason to assume one or more toggle switches will last any longer than a standard magneto switch.

While we have no doubt some standard type magneto switches have failed while in service on the Rotax engines, we do not believe they are the cause of ignition module failures. If the contacts on the magneto switch were to corrode or burn to the point where they no longer make continuity, the respective module would simply not shut down with the switch in the off position. I don’t think LEAF, Lockwood or anyone else can explain how an open kill circuit due to a bad switch is the cause of ignition module failure.

Advising aircraft owners to change the magneto switch to toggle switches is questionable. The magneto switches are aircraft quality devices with large contacts capable of handling high voltage and current loads either AC or DC. Magneto switches are used successfully on many Rotax 912 equipped aircraft without incident. The replacement toggle switches are largely unspecified. A 250 volt toggle switch can be a totally inadequate miniature device capable of only 0.5 amps. with quality or origin unknown.

In summary, the Rotax Ducati ignition module kill circuit is not likely to damage a magneto switch or a replacement toggle switch. Nor is any switch, magneto or toggle likely to cause a failure of the ignition module.

John Pitkin"


- The Matronics Europa-List Email Forum -
 

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Europa-List
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Matronics Email Lists Forum Index -> Europa-List All times are GMT - 8 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Powered by phpBB © 2001, 2005 phpBB Group