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Light speed ignition system protections, vulnerabilities

M

Md11av8r

Member
Hi guys,
I am interested in you opinions as to the vulnerabilities of the dual electronic ignition system to electrical faults which could render both systems inoperative. What protections are there in this system to guard against an electrical fault taking out both of these units? I currently have the dual Lightspeed Plasma III with the backup battery.
My reason for asking is due to a recent experience I had related to a poor battery ground. Recently while attempting an engine start, I experienced a very slow starter rotation, and then noticed an electrical smoke smell. On further investigation, it was discovered that due to a poor or loose battery ground during engine start the lightspeed ground wires (which are connected directly to the main battery) overheated due to the excess load. It was also discovered that one of the cannon plugs connected to one of the power boxes showed signs of heat damage. We replaced the wiring and the cannon plug, and on run up both Ignition sources checked out fine, so I flew the A/C home. Just before descent into my home field I performed an inflight mag check and noticed an EGT rise on 1&3 Cyls and no rise on 2&4 on the A ignition system. Once on the ground I accomplished another MAG (IGN) check, and when I selected the A IGN to OFF the ENG quit.
I have not received the full report from my mechanic as of yet as to the cause, whether it is a failed IGN or just a wiring problem, but it did get me thinking about the dual electronic IGN solution and its suspectibility to a possible main electrical system fault causing both units to fail simultaneously and rendering ones power plant inoperative.
My question then is what if any safeguards are incorporated within the Lightspeed Ignition system to guard against such a scenario? Would it be a better, and safer solution to have one electronic IGN and one MAG?
Your would appreciate your insights based on your understanding and knowledge of this system and safeguards.
Thanks,
David Johnston
 
The simple answer to your question is as you pointed out in your own post, one magneto and one EI.
Each has its own failure modes and you touched on the many issues that can occur with electronic ignitions and potentialy shut down your engine.
I have been tempted to replace my one impulse coupled mag but decided to stick with my set up of one LSE and one Slick.
 
Md11av8r said:
Hi guys,
I am interested in you opinions as to the vulnerabilities of the dual electronic ignition system to electrical faults which could render both systems inoperative. What protections are there in this system to guard against an electrical fault taking out both of these units? I currently have the dual Lightspeed Plasma III with the backup battery.
My reason for asking is due to a recent experience I had related to a poor battery ground. Recently while attempting an engine start, I experienced a very slow starter rotation, and then noticed an electrical smoke smell. On further investigation, it was discovered that due to a poor or loose battery ground during engine start the lightspeed ground wires (which are connected directly to the main battery) overheated due to the excess load. It was also discovered that one of the cannon plugs connected to one of the power boxes showed signs of heat damage. We replaced the wiring and the cannon plug, and on run up both Ignition sources checked out fine, so I flew the A/C home. Just before descent into my home field I performed an inflight mag check and noticed an EGT rise on 1&3 Cyls and no rise on 2&4 on the A ignition system. Once on the ground I accomplished another MAG (IGN) check, and when I selected the A IGN to OFF the ENG quit.
I have not received the full report from my mechanic as of yet as to the cause, whether it is a failed IGN or just a wiring problem, but it did get me thinking about the dual electronic IGN solution and its suspectibility to a possible main electrical system fault causing both units to fail simultaneously and rendering ones power plant inoperative.
My question then is what if any safeguards are incorporated within the Lightspeed Ignition system to guard against such a scenario? Would it be a better, and safer solution to have one electronic IGN and one MAG?
Your would appreciate your insights based on your understanding and knowledge of this system and safeguards.
Thanks,
David Johnston
Click to expand...

David,

I'm not sure I understand why a bad battery ground would have any effect on the Lightspeeds, if they're installed according to the manual? As you note the power and ground are both directly connected to the battery so other wiring shouldn't matter. There's not supposed to be any cannon plugs involved, but perhaps you mean the D-sub connectors that connect to the ignition boxes? One of these could certainly be loose and cause a bad connection. Its also quite possible that one of the ignition boxes has a fault.

If installed correctly I don't see how one electrical fault could take out both ignitions, if you have a dedicated backup battery that can power one ignition.
 
Sometimes despite best efforts to keep systems truly independent, there is something that is missed that will provide a common mode failure of otherwise dual redundant systems. Often that is the grounds.

It sounds like you didn't build your electrical system and so you would need to gain insight into the system design. Most people who have dual electronic ignitions, also have an independent (isolated) back up battery for one of the EI systems.

That would be advised, and as a part of that, the grounds should be kept independent.

You can consult AeroElectric for typical wiring diagrams for dual power systems.
 
All good advice.

Do things like using separate ground points so one bolt/screw doesn't bring you down.

One failure point that surprised me was when someone on this forum had an alternator belt snap and take out the wire(s?) to the timing board, or whatever it is called. He lost both ignitions and all his backup hardware did him no good.
 
N941WR said:
One failure point that surprised me was when someone on this forum had an alternator belt snap and take out the wire(s?) to the timing board, or whatever it is called. He lost both ignitions and all his backup hardware did him no good.
Click to expand...

Bill,

That one surprised me as well. As I recall the post all the timing wires from the Hall effect sensor board were routed together. The newer Lightspeed sensor modules are separate, which makes it easy to route the wires separately. Replacing the alternator belt at regular intervals is also seems like a good idea.
 
You have found some common faults with installing Lightspeed Ignitions. Luckily you get to reflect and fly another day.

We had 3 RV-8s built at the same time, all with Dual Lightspeed Plasma II+ igntions. We came up with a power distribution system that assured power to at least one igntion regardless of the fault. The backup battery Klaus calls for in his instructions is better than nothing, but as you found out it can fall short.

Send me your email and I will send you the power distribution design. The design is to support IFR flight after a power component failure.

Note - after 300 hours the Lightspeed ignitions were removed as we experienced mutilple failures. They have been replaced with pMags which have been flawless for 700 hour or so. I continue to use the power distribution scheme even though we don't use Lightspeed.

Carl
 
I will admit that I am somewhat ignorant of how my system was wired, given that I did not build this aircraft. I do have an ignition system backup battery installed to protect against a main electrical system failure. My concern, and question is- does the Lightspeed IGN system have safeguards to prevent such a scenario from happening, and if not, is there a wiring solution which will accomplish this goal. If these safeguards do not or cannot be accomplished, then it appears to me that the one Electronc IGN/one MAG solution will be the way for me to go.
 
N941WR said:
Unless you have a CS prop. Taking one of those off is a major pain in the butt!
Click to expand...

Don't I know it! It gets easier with practice though, and really is more tedious than difficult. I've had mine off several times in the last ten years and always take advantage of the opportunity to replace the belt.
 
ground

Alan Carroll said:
I'm not sure I understand why a bad battery ground would have any effect on the Lightspeeds, if they're installed according to the manual?
Click to expand...
Hi Alan, Just speculation obviously, but it sounds like the ground strap from the engine to the battery failed, and then the electrons flowed through the path of least resistance (which they usually do) which was through one of the lightspeed ignitions. This can be bad if it's the electrons related to starting the engine, since there are a lot of them - more than the wires used on the lightspeed are designed for. I'm quite impressed that the ignitions worked after that incident, even after replacing some of the burned wires.

It is recommended by those much smarter than I am about electricity to have two independent ground straps to avoid this kind of thing.

About the original question, the only thing you can do is to scour the literate about possible failures modes, and do what you can to either eliminate the risk, mitigate it, or accept it. As mentioned by Dan, I'd start with aeroelectric.com which is an amazing resource.
 
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Md11av8r said:
I will admit that I am somewhat ignorant of how my system was wired, given that I did not build this aircraft. I do have an ignition system backup battery installed to protect against a main electrical system failure. My concern, and question is- does the Lightspeed IGN system have safeguards to prevent such a scenario from happening, and if not, is there a wiring solution which will accomplish this goal. If these safeguards do not or cannot be accomplished, then it appears to me that the one Electronc IGN/one MAG solution will be the way for me to go.
Click to expand...

David,

If you go to the Lightspeed Engineering site you'll find the the installation manual, which might help in figuring out whether your system is wired as recommended.

I'm not sure you'll find a definitive answer to your question about safeguards. Klaus Savier and others would certainly argue that they do exist, but other reasonable people such as Carl have come to a different conclusion. There are quite lot of these units in the field, and dual PlasmaIII's are used by Cub Crafters and I believe some other manufacturers. There are some past threads on this topic that might be worth reading.

I do think you should figure out for sure whether the problem you have is really with the Lightspeeds, or with some other aspect of the electrical system.
 
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rv8ch said:
Hi Alan, Just speculation obviously, but it sounds like the ground strap from the engine to the battery failed, and then the electrons flowed through the path of least resistance (which they usually do) which was through one of the lightspeed ignitions. This can be bad if it's the electrons related to starting the engine, since there are a lot of them - more than the wires used on the lightspeed are designed for. I'm quite impressed that the ignitions worked after that incident, even after replacing some of the burned wires.

It is recommended by those much smarter than I am about electricity to have two independent ground straps to avoid this kind of thing.

About the original question, the only thing you can do is to scour the literate about possible failures modes, and do what you can to either eliminate the risk, mitigate it, or accept it. As mentioned by Dan, I'd start with aeroelectric.com which is an amazing resource.
Click to expand...

Hi Mickey,

I see your point, but the ground wire for the Lightspeed that apparently overheated is connected directly to the battery. Unless I'm missing something its not able to serve as an alternate ground pathway for the starter, because its only connected to the engine by way of the grounding strap that failed. Its a little unclear though whether the problem was the connection between the engine and firewall, or firewall to battery. Perhaps the OP can clarify?
 
As I understand it the draw on the positive side of the battery caused an equal draw from the ground, which was insufficient due to poor grounding. The current therefore chose the only path to ground available, which from my (limited) understanding was through the ground wires going to the IGN modules.
 
dual ground straps

Lack of ground can be very nasty when the path it takes is something like a braided fuel line. This is one of the reasons why two ground straps are recommended. They need to be bolted to different connection points on both ends to avoid the failure mode of a nut coming loose, for example.
 
Thinking about this some more, the Lightspeeds could provide a ground path for the starter if the timing modules are grounded to the engine. I'm guessing that the shields for the sensor wire assemblies might be? If so then everything makes more sense.

As others have noted, a well maintained engine ground (or redundant grounds) would eliminate this problem.
 
I have about 1,300 hours over the 14 years that I've flown my RV-8 (after 5 years of building) with dual LSE ignitions (with the crank-angle flywheel pickups).

Both systems are independent, with separate batteries. Wired per the manual and the invaluable "Aeroelectric Connection" by Bob Nuckolls (if you don't have a copy, buy it).

I have a single engine ground strap which is easily visible from the oil filler door.

The only problems that I've ever experienced with the ignitions has been the result of a single point of pulling MP off the #3 cylinder.

Once I had a intake manifold gasket (those cheap 35-centers) fail, and I also had the hose the runs from the cylinder head back to the brain boxes go wonky (entirely due to stupid action on my part).

Other than those two failures, Klaus' gear had run flawlessly, and he's been a source of ready help and advice when I've needed it.

As I like to tell people, the only moving part in the system is the flywheel, and if that comes off, I've got other problems. :D
 
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