Dual LSI - Sanity Check

[RV7ator]

Consider also your terminals. A dozen back-up batteries are worthless if some itty bitty terminal lug or connector contact serving the ignition decides to fail (in a number of ways). Nearly an axiom in maintenance, if the electrical goodie isn't working, check the connections first.

Lightspeed ignitions are excellent, but power sourcing is why I now use P-mags despite their early problems.

John Siebold

[Kahuna]

Originally Posted by rocketbob

One of my good friends had the battery contactor fail in flight in his RV7. The coil shorted internally. Total shutdown of the electrical system. As he was diagnosing the problem, he shut the alternator off and it wouldn't come back on due to the field wire requiring battery power to energize. The alternator I use does not require battery power to excite. I tested this in my -6.

A few years ago I had a battery in my Jeep fail shorted. Instantly shut everything down. I doubt this is very likely in an AGM-type battery but probably is still possible.

All it takes is a small 4-5aH battery isolated with a diode and a resistor or mosfet to limit charging current to have some insurance.

This is a good point. Yes contactors do in fact fail which is why the EI power should be on the hot side of the contactor and as close to the battery as possible to reduce failure modes of contactors, terminals and the like.

[Walt]

Contactors do fail, but they usually will show some anomoly prior to totallly failing. For example, I had a master contactor that started not engaging fully when I put the switch on the first time, if I reset it it would engage the 2nd time. The next day that relay was in the garbage and a new one on the way, I didn't wait for it to fail totally.

Good maintenance is listening to your aircraft, it will usually tell you about problems, the hard part for many is to not ignore it, take that cowl off and fix it! Don't ignore the signs of trouble, it usually means impending failure is at hand.

BTW, when I was changing the master contactor I also changed the starter contactor... preventive maintenance.
I also replace my battery every 2-3 years... I don't like problems.

[pvalovich]

Dual LSI's Aero Connection Z13-8 architecture with alternator, back up SD-8 alternator and single battery.

Or dual P-Mags.

[Walt]

Originally Posted by pvalovich

Dual LSI's Aero Connection Z13-8 architecture with alternator, back up SD-8 alternator and single battery.

Or dual P-Mags.

This is what I run now.

[rocketbob]

I can, with relative ease, poke quite a few holes in Z11 and describe several single points of failure. Some of them are alarmingly simple. This is why I don't have a Z11-style system in my Rocket.

[Gonzo24]

I'm setting up a dual LSI in my -7 now. Single PC-680 batt, SD-8 back up alt. Not using smaller back up batt as shown in LSI manuals because of the use of SD-8. Both LSI power inputs run to the batt buss that is wired directly to the 680. The SD-8 also comes to the batt buss through a separate terminal other than the batt buss main power feed.

Of course all of this could fail statistically....right after i get struck by lightning and the random asteroid.

[rocketbob]

Originally Posted by Gonzo24

Of course all of this could fail statistically....right after i get struck by lightning and the random asteroid.

Think so eh? Ever think about what would happen if the ground strap on your engine failed?

[Gonzo24]

Bob, actually no I didn't think of that. Thanks for bringing it up. I was assuming that the braided grd strap would be tolerant of the engine to airframe vibration difference. However, that link could make things interesting if it failed.

[rocketbob]

Another thought: if the SD8's regulator is set to a slightly higher voltage than the main regulator's voltage, it will be supplying ALL the current required to your system, and thus can be easily overloaded. So just make sure its adjusted to be well below the main regulator's output voltage.