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Physical construction of Z101 engine bus & battery bus
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m.whiting(at)frontier.com
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PostPosted: Fri Jun 12, 2020 4:27 pm    Post subject: Physical construction of Z101 engine bus & battery bus Reply with quote

I was simply addressing the question as posed, at least my understanding of the question. It seemed to be suggesting that one battery replaced every 2 years was more reliable than two batteries each replaced every 4 years since on average the one battery was newer than the combination of the two. I don’t think that is a correct assumption.

I certainly would take two alternators and one battery over one alternator and two batteries as well, and that is a scenario I posted earlier today in regards to my soon to arrive S-21 kit and 915iS engine. Unfortunately, of the two generators in the 915iS, it appears that only one is actually accessible for non-engine power supply. So, that configuration actually needs 3 in order to have two available for pitot heat, lights, avionics, etc.
However, I would take two batteries (alternated every other year) and one alternator over one battery (new every 2 years) and one alternator.
Matt

Quote:
On Jun 12, 2020, at 6:55 PM, Charlie England <ceengland7(at)gmail.com> wrote:

I think that when doing failure analysis, you don't really pay that much attention to odds; you play 'what if'. (Actually, 'when it fails'; the assumption when doing failure analysis is that anything we can back up *will* fail). You do have to take uncontrollable stuff out of the equation; we can't carry an extra set of wings, for instance, and most of us accept the risk of a single engine, in order to be able to fly at all.
Once that's out of the way, then 'what if' starts. What if the alternator fails? It's taken off line and battery backs it up. What if the battery fails? It's taken off line and the alternator backs it up (contrary to popular internet lore). If the engine isn't electrically dependent and we're VFR with nav on our phone, we don't even care about backup at all. The what if of both failing in a single flight is considered to be so unlikely that most are willing to treat a double failure like a wing or other structural failure; we're just not going to go there.
My personal choice with a high-amps-need engine control system is to not accept the limited and continuously decreasing duration (capacity) of a standard battery, nor to accept the weight penalty of a much bigger battery or multiple batteries, in order to keep the engine running to the end of the flight. For me, that only leaves the choice of dual alternators.
FWIW,
Charlie




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