Ford edis with megajolt

[rv7charlie]

My statement:
Originally Posted by rv7charlie View Post
If you think about it, a modern battery is extremely reliable. If maintained properly, it's probably the most 'reliable' component in the plane. So why are there two?

Originally Posted by rv6ejguy

Batteries have been known to take an unexpected dump, especially some lithium ones. With a battery dependent ignition system, you lose a single battery, the engine stops. That's a good reason for a second one in my view. I have personal experience in this regard...

We never recommend anyone running two EIs in an aircraft to use a single battery.

Boy, the interwebs are a tough place to communicate.

1st, my mistake for not specifying 'modern *sealed lead acid* battery'. The various lithium chemistries are still a big wild card to introduce, especially when they interact with another other new variable.
Now that that is out of the way, aren't you making my point? If redundancy is highly recommended, shouldn't all single points of failure that negate the redundancy be eliminated, as well? If you'd quoted the rest of that post, you'd have seen:

Something that comes up all the time on the Aeroelectric List is not designing for reliability (which should be a given), but for redundancy. If you think about it, a modern battery is extremely reliable. If maintained properly, it's probably the most 'reliable' component in the plane. So why are there two?

That last question was rhetorical; Of course you want redundant power. But if the non-redundant delivery is the failure point, then it's just dead weight. (Pardon the pun.)

Last, I'm more comfortable with redundant generating systems (which will weigh less) with redundant paths , than with redundant batteries, which still have (highly variable) endurance limits even if they don't actually fail. Yes, you can do both, but should we add an extra set of wings, as well? (Rhetorical question.)

Charlie

[DanH]

Originally Posted by SMO

Even with two alternators? I have a Plane Power and an SD8.
Yep, I have cleaned the negative terminal of corrosion (green) on my Odyssey PC680.

Three thoughts.

One, I'm going to give IGN2 a separate ground, as corrosion could cripple the ground path at the main battery negative terminal.

Two, I never considered corrosion, as I've never seen it on any AGM battery. Yet it exists. Peer review is good.

Three, regarding dual alternators or dual batteries; as we've seen (again), God is in the details.

NOTE PLEASE: I much appreciate the peer review of specific wiring. However, let's not steer this thread off into general battery and alternator debate. It's about EDIS and Megajolt, ok?

[DanH]

Ignition #2 now installed. Useful data...

Current draw, per ignition, EDIS and MJ/E combined:

Switch on, engine not running, 90 mA

1200 RPM, 520 mA

1800 RPM, 800 mA

2700 RPM, 1.08 amp

Single ignition drop, 25~30 rpm

[rwtalbot]

Originally Posted by Mike S

Considering all the stuff in the prior pages about the drive speed of a six cyl mag/rotor assembly, I suspect your mag hole trigger may not be a viable option for me???

I also have a 6 cyl engine I'd like to try this with. I'm looking at putting one trigger on the front of the crank, and one on the rear for added safety. By my calculations an 18 tooth mag drive gear would bring the 1:1.5 drive ratio on the 6 cyl engines back to 1:1 while using a standard mag shaft. Such a gear would need to be custom made for our applications. Cut stock gears won't do it. These would need to be ground and case hardened.

I believe the existing 6 cyl mag gear is 10 DP, 20 PA. I can have them made using EN36A for approximately $250 if we order 10 at a time.

I have a design for a suitable housing to offset the larger gear in the case and allow timing to be adjusted. If there is sufficent interest I may post some Solidworks images of what I have mocked up.

[DanH]

Originally Posted by rwtalbot

I also have a 6 cyl engine I'd like to try this with. I'm looking at putting one trigger on the front of the crank, and one on the rear for added safety.

As a thought exercise, explore trigger location risk. Feel free to add to the lists.

Crank trigger:
1. belt breakage may take out reluctor bracket or wiring

Mag hole trigger:
1. torsional vibration issues
2. bearing issues
3. oil seal issues
4. machining error
5. component joining issues

What else?

Yes, I went with rear triggers, and I'm not going to say you shouldn't. On the other hand, I think the risk factors are higher with mag hole triggers, an inescapable result of parts count. The six cylinder compounds that problem, by adding custom gears and housings, and a somewhat higher chance of torsional vibration issues at some unknown RPM. They don't put rubber drives on 6-cyl mags without reason.

Even given the lower torsional risk of the 390 (short 4-cyl crank with pendulums), one key reason I've been flying an EDIS/Slick combination for a year was the opportunity for long term examination of the trigger unit drive gear. It was out for inspection last week.

If the single risk of a front trigger is belt failure (are there more?), a fella could turn out one heck of an armored shield with a a TIG and some 4130 plate.

[F1R]

Originally Posted by DanH

As a thought exercise, explore trigger location risk. Feel free to add to the lists.

Crank trigger:
1. belt breakage may take out reluctor bracket or wiring

Mag hole trigger:
1. torsional vibration issues
2. bearing issues
3. oil seal issues
4. machining error
5. component joining issues

What else?


If the single risk of a front trigger is belt failure (are there more?), a fella could turn out one heck of an armored shield with a a TIG and some 4130 plate.

OR ... you could have no front alternator , just a vac pump pad mount alternator and keep the nose ultra clean, light and simple on a day VFR only RV.

[F1R]

With a bit more work Dan, you could put some permanent magnets in the flywheel and make a brushless alternator out of the flywheel. That would also get rid of the drive belt on the front end.

[rv7charlie]

If you've already got a mag drive sensor for one ignition, why not use a crank trigger for the other, and consider the redundancy taken care of?

I did put a guard over the CAS on my Wankel installation, but I it's worth mentioning that I can't remember the last time I had an alternator/fan/water pump belt failure, on a car or a/c. Cars I can understand; most have spring tensioners that maintain proper belt tension, but I've had great luck, even with a/c engine belts. Current belt tech is pretty impressive.

Charlie

[rwtalbot]

Originally Posted by DanH

As a thought exercise, explore trigger location risk. Feel free to add to the lists.

Crank trigger:
1. belt breakage may take out reluctor bracket or wiring

Mag hole trigger:
1. torsional vibration issues
2. bearing issues
3. oil seal issues
4. machining error
5. component joining issues

Dan,

I don't disagree there are some considerations with the rear pickup and its engineering. However, I think you have somewhat understated the risk associated with two pickups on the crankshaft as anything that gets loose in there may well destroy both systems.

I am not overly concerned if the rear mounted system fails (and doesn't compromise the engine itself). Simultaneous failure of both pickups could result in a fatal accident.

The group may find the following accident report useful.

http://www.atsb.gov.au/media/5341498...37;20Final.pdf

[Toobuilder]

Originally Posted by rwtalbot

Dan,

I don't disagree there are some considerations with the rear pickup and its engineering. However, I think you have somewhat understated the risk associated with two pickups on the crankshaft as anything that gets loose in there may well destroy both systems.

I am not overly concerned if the rear mounted system fails (and doesn't compromise the engine itself). Simultaneous failure of both pickups could result in a fatal accident.

The group may find the following accident report useful.

http://www.atsb.gov.au/media/5341498...21%20Final.pdf

It seems that we are going down the familiar rabbit hole of trying to guard against the mere possibility of failure, rather than evaluate the probability, as Dan is wisely suggesting. After all, the entire accessory gear train in a Lycoming depends on a single 5/16 bolt securing the crank gear- yet we don't give that much thought. So back to Dan's point, aside from a belt coming loose (which is easily guarded against), or bad design/maintenance (as the Glassair accident suggests), what is the probability that something can "get loose in there" (behind the ring gear) that wouldn't cause engine stoppage anyway?

I'm not saying it can't happen, and I'm not saying that I'm not blind to my own logic/justification, but I'm not seeing a higher risk with a properly designed and maintained front pickup system.