umgibso1(at)yahoo.com
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 Posted: Wed Sep 13, 2006 6:21 pm Post subject: alternator vs. second battery |
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Thanx for the reply Ken, sounds like good advice!
I'll take it!
Tony
From: Ken <klehman(at)albedo.net>
Subject: Re: Debating on an alternator or two
batteries?
--> AeroElectric-List message posted by: Ken <klehman(at)albedo.net>
Hello Tony
Personally with an electric dependant engine, I'd happily trade 4 lbs
or so of battery for a small permanent magnet alternator and I suspect
the alternator would be the lighter option if you have a few hours of
fuel on board.
Bob just posted some references on battery discharging that you will
want to look at.
For a primary battery with no alternator I'd suggest multiplying your
hours of fuel by 2.5 amps and then picking a battery that can supply
that (from its spec. sheet) and then doubling it. Another battery
characteristic is that the deeper you discharge them, the fewer
discharge - charge cycles they last so planning for a 50% discharge
when
the fuel runs out might be reasonable. That would also allow for other
sub optimal conditions such as temperature.
Ken
Tony Gibson wrote:
> Hi Group, my name's Tony Gibson, I've been a lurker on the list for
> almost a year now and am building a Sonerai 2L - read 550lb slightly
> underpowered two place! 
>
> I'm trying to take as much weight out of the plane as I can by
keeping
> it simple. There's a lot of reasons I'm considering two batteries
> rather than a battery and an alternator. But saving a bit of weight
> isn't the main reason, the fact that I can move the weight of
battery
> where ever I want in the plane is a big bonus for servicing it
> nevermind balancing, and ....the last thing I will do is put lead
> weight back into it!
>
> I have an ignition system that draws ~1 amp and a single fuel pump
> that draws another amp. I decided against the starter and the only
> other amp draws will be two small Stratomaster instruments drawing
> less than half an amp together. Total draw would be less than 2.5
Amps
>
> With the right warning system to indicate a low primary battery
> I'm wondering if something like a 3 - 5 Ah battery would be large
> enough for a backup? What about the primary?
>
> The downside of course is what would I do on a crosscountry trip?
> Argh!
>
> Thanx a lot, appreciate any help and opinions!
> Tony
>
[quote][b]
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