Message-Id: <3.0.3.32.19990826161347.030a5100@olsusa.com>
Date: Thu, 26 Aug 1999 16:13:47 -0400
To: lancair.list@olsusa.com
From: Marvin Kaye <marvkaye@olsusa.com>
Subject: Batteries
Mime-Version: 1.0

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          <<  Lancair Builders' Mail List  >>
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>>
The following is reprinted from another mail list that I subscribe to, as
it contains quite a bit of useful information that is certainly germane to
our interests here as well.  Lines with >> are the questions, and > are the
responses.  Enjoy.

   <Marv>


>Al Fuller wrote:
 
>Hi guys.  I took the liberty of sending the original query to someone who
>does aircraft electrical work for a living, AND is active in the
>homebuilding arena.  His responses follow below:

>Date: Thu, 26 Aug 1999 08:35:50
>
>>I did not quite understand how to identify a pending battery failure
>>when we discussed ignition systems a couple of months back.  I have
>>the following questions:
>
>>1.  Is low voltage a sure sign of impending failure (provided th rest
>>of the charging system is healthy)?
>
>Voltage alone is not a very good indicator of anything. The two
>conditions that voltage alone will call out are (1) if the alternator
>is running and the bus voltage where it belongs (13.8 to 14.6 volts)
>then the charging system is carrying all sytem loads with something
>left over to charge the battery. IF the battery is CAPABLE of
>storing a useful amount of energy for later use, it will do so
>under these conditions. (2) if the alternator is NOT working and
>the bus voltage is greater than 10.5 volts, then there is SOME
>energy still left in the battery. Again, the question goes to
>CAPACITY which I'll address below.
>
>>2.  How about specific gravity?  Do the testers that float the little
>>balls work?
>
>Hydrometers have been around since the first acid was dropped
>between two lead plates to run the first electric cars.  While they
>will yield some useful information about battery condition, they're
>totally useless in recombinant gas, sealed lead-acid batteries.
>Personally, given the outstanding performance of the RG/SLA
>batteries, I wouldn't even consider putting a wet battery into
>and airplane. I just replaced the wet battery in my GMC van with
>an RG battery.
>
>>3.  Just what are the 'load testers' used at the parts / tire stores
>>and how do they work?  Where can I buy one of these?
>
>Load testing speaks mostly to the ability of a battery to
>deliver power fast enough to crank an engine . . . while loosely
>associated with battery condition, it's not a good measure
>of battery capacity. You "load test" your battery every time
>you successfully crank the engine. None-the-less, I'll suggest
>that 1/2 of all single-engine airplanes flying today have
>FAILED batteries aboard . . . if the alternator craps, there
>is insufficient energy stored in the battery to be a practical
>second source of power. None the less, the battery probably
>got the engine going . . .
>
>I'm doing some work on the AGATE program for Raytheon (Beech).
>I'm going to propose an automatic battery capacity tester
>be included on board the airplane so that the owner can
>make periodic tests of battery capacity and replace them
>based on good data as opposed to waiting until they no longer
>crank the engine.
>
>>My concern is having what I think are 2 healthy batteries, only to
>>find that they have only about 20% storage.  This will not last long
>>with an EFI fuel pump sucking on it.
>
>This is why we developed the two battery, yearly swapout
>technique for electrically dependent airplanes.  Install
>two, RG batteries of identical size in your airplane. Use
>"main" battery to power engine essentials during alternator
>out ops and the "aux" battery to power panel essentials.
>Swap out the main battery into the aux slot each annual and
>put a new battery into the main slot. Now, you always have
>one battery less than one-year old and no batteries more than
>two years old.  The CAPACITY of your on-board energy storage
>system is proven and can be relied upon to get your wheels
>back on the ground with comfort. The goal is to make sure
>that batteries have 75-80% of original capacity before you
>go flying.
>
>>At this point I am in favor of 2 alternators unless I can be sure of
>>identifying a battery that is prepairing to die.  But 2 batteries and
>>2 alternators on what is a basically day VFR plane???  Sounds like to
>>much weight and complexity to me.  Maybe 2 alternators and 1 battery
>>is a better idea.  The idea of eliminating failure modes has several
>>permutations here, but I was not educated enough in our last visit on
>>this subject to make an informed decision.
>
>Two alternators is an excellent idea . . . especially IF you can
>deal with an all-electric panel.  B&C has light weight alternators
>in the 8 and 20 amp class than fit on the vacuum pump pad of
>the engine. Wiring for these systems is shown in diagrams
>downloadable from http://www.aeroelectric.com/errata/Z8_0299.pdf
>
>I would still have two batteries so that each alternator
>runs it's own stand-alone electrical system . . . see
>drawings.
>
>However, you can comfortably run one alternator and two
>batteries as well if you're willing to remove "a perfectly
>good battery" from the aux slot every year . . . the $50-70
>expense of this exercise is trivial compared to the total
>cost of airplane ownership and it affords a level of reliability
>that is unequaled in ANY single engine, type certificated
>airplane flying today.
>
>It's not a big deal. The design criteria lend themselves
>very well to analysis of the energy needed to meet your
>mission requirements. You just need to think and act a
>little bit "outside the box" . . . your experiences with
>TC'd airplanes are best filled in the "how not to do it"
>category going instead with a considered, calculated and
>MAINTAINED approach to fabrication and operation of your
>airplane.

>Bob {Nuckolls}. . .


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