Bob,

Robert Nuckolls is the author of a popular home buildi= ng electrical design book entitled The AeroElectric Connection (available at= http://www.= aeroelectric.com/), and is very active in answering associated qu= estions on the AeroElectric List (http://forums.matronics.com/viewforum.php= ?f=3D3).

He suggests that cranking abili= ty is a poor indication of a battery's capacity. In other words, energ= y capacity as would be required to drive your critical systems if your alter= nator failed at night or IMC should not be confused with short term power ge= neration required to crank an engine. You may lose lots of capacity wi= thout a noticeable drop in cranking ability.

In his= book and online he talks about ways to measure capacity. In simple terms, i= t boils down to applying a constant known load (like a load bank or just a l= ight bulb) and measuring voltage over time (or simply measuring the time unt= il the voltage has fallen below a preset voltage). See http://w= ww.aeroelectric.com/articles/battest.pdf for more info.

- Kyrilian

On Jun 21, 2= 013, at 11:59 PM, Robert R Pastusek <rpastusek@htii.com> wrote:

<= div>Angier wrote:

I installed two Ody= ssey PC545 batteries during the build in May 2008.
First fli= ght was back in February and about a month ago I thought I sensed a little l= ess cranking power on startup.
On start on the last flight, t= he prop would not pass through the compression stroke so I waited a bit, hit= the starter again and even through there was a bit of hesitation, motor sta= rted normally. So my uneducated guess is that these batteries are tired and h= ave lost a lot of there cranking power. They have always been maintained on a= n Odyssey Battery Minder and with a check on a battery tester, they're still= in the green. Anyway, two new PC545 will be installed today.
Everybody else having good experience with their Odyssey batteries?=

Angier,
Five yea= rs is pretty good service life for batteries, but generally, the Odess= eys should do better, especially since you've kept them in good condit= ion/lightly used.

I have two independent e= lectrical systems on my IV-P, using two PC 680s each. I replaced the pair of= batteries I bought in 2006 last year, and was planning to replace the 2008 &= nbsp;batteries at this condition inspection. Both sets still crank the airpl= ane well, but this is one area where I'm "second guessing," so I could = ;use some factual information as well. For example, is there a valid test fo= r power available, etc.

One other note. The= se batteries require a higher charging voltage than "regular" batteries. Be s= ure your regulator is adjusted to the specs called for in the Odessey litera= ture. Can send same if needed, but also available on-line.
<= /span>
Bob

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