Dual LSI - Sanity Check

[shamer]

Rocket Bob wrote:

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

This seems like it would be a very rare event, maybe up there with the lightning strike and asteroid hit. (With that said, I probably just insured mine will fail tomorrow).
What else do have on Z-11 that you don't like? Since I used that example on my -6, I'm interested in what you have to add.
It might also be helpful to take this to the Aerolectric List. A good back and forth discussion between knowledgeable folks is a good thing. Maybe you and Bob Nuckolls could have an enlightening conversation for the rest of us.

[rocketbob]

Originally Posted by shamer

Rocket Bob wrote:

What else do have on Z-11 that you don't like? Since I used that example on my -6, I'm interested in what you have to add.
It might also be helpful to take this to the Aerolectric List. A good back and forth discussion between knowledgeable folks is a good thing. Maybe you and Bob Nuckolls could have an enlightening conversation for the rest of us.

Pretty simple. An internally shorted battery is going to render the whole thing inoperable. Unlikely? Perhaps. Probably. Until that old Murphy guy makes an appearance. That said, a dual battery/dual contactor setup is going to be a little bit more bulletproof and simpler to implement than the Z11 system. Or a simple backup battery charging/isolation circuit for the ignitions. In other words, there are simpler ways to accomplish what Z11 does with a higher degree of redundancy and a significantly less cost of implementing and maintaining.

[Finley Atherton]

Still trying to get my head around this dual EI backup battery/alternator issue.

I stand to be corrected but using the aux battery Lightspeed diagram and assuming that the pilot would quickly recognise and alternator failure, then the only event that the aux battery is protecting against is an internal dead short (low resistance between the terminals) in the main battery

IF this is correct then the next question would be, is anyone aware of an Odyssey type battery failing with a internal dead short??

It also occurred to me that if the battery failed with an internal dead short in a two alternator/one battery system then both alternators would be useless as neither could operate with a shorted battery

Finally, can an Odyssey type battery fail in the opposite mode such as an internal open circuit in the battery (very high resistance between the terminals). If this were to happen then I presume the alternator would continue to provide regulated power but the voltage may be more spiky without the dampening effect from the battery

Please educate me

Fin
9A

[dmaib]

A friend finishing his Lancair II with dual LSE's and no backup power could not get that setup past the DAR recently. He ended up using the backup battery for his MGL, through a switch, to power one of the LSE's and the DAR was happy.

[RV10inOz]

David.....You are kidding me?

That is plain stupid....And I know you would never do that, but could you not talk him into doing it far better than that even? This is a Lancair not a kitfox or something similar.

Cheers

DB

[dmaib]

Not kidding DB, but maybe I did not make the setup very clear. Both of his LSE's run off ships power normally and one of them has access to the MGL backup battery pack for backup power. Does that make more sense?

[Lars]

For what it's worth, the Z11M architecture has the alternator field powered off the main buss, not the e-buss. So you still have the problem of the alternator shutting down in the event of a master contactor failure (assuming your alternator requires battery power to keep the field energized).

You can move the field supply wire from the main buss to the e-buss, but now the e-buss diode/alternate feed has an additional 5 amps (or what ever the field draws) going through it.

[Walt]

Originally Posted by Lars

For what it's worth, the Z11M architecture has the alternator field powered off the main buss, not the e-buss. So you still have the problem of the alternator shutting down in the event of a master contactor failure (assuming your alternator requires battery power to keep the field energized).

Your assumption is incorrect, the alt will happily supply it's own field current and power the bus with the master relay open.

[rocketbob]

Not all alternators work without the field wire excited by the battery. The ND alternators I use do work fine. But I don't know how stable the output is in that condition.

Did you guys see the B&C alternator Rick Gray just sold in the classifieds that was factory repaired? $500 alternator that had the diodes replaced by them for $363. No flippin thank-you.

[Lars]

Originally Posted by Walt

Your assumption is incorrect, the alt will happily supply it's own field current and power the bus with the master relay open.

No assumptions, other than the rhetorical your alternator. While my experience with alternators in airplanes is limited, I've had plenty of them in ground-bound vehicles. Some do, some don't. Irritatingly so.

My point was that the Z11 architecture wouldn't have helped rocketbob's friend when his master contactor failed. The Z11 diagram has been on my mind as I am wrapping up my own electrical system, and happen to be using it, more or less. The alternator field source was something I pondered last night. I have a Plane Power alternator, supplied in Van's FWF kit. I'm guessing it can sustain itself in the event of a master contactor failure, but I plan to test that before I fly.