| I'm with you completely Chris on the battery tender concept. I've been using them on a VRLA Concorde battery that costs $1800. I received more than 5 years life on the last battery. I maintain the Legacy batteries on charge as well with a different make.
But testing is a different story and maintainers can't guarantee capacity. Load testing is the only way to determine some faults. My batteries failed under load in the Legacy but not on the ground. When I pulled gear up everything died including my Avidynes. It took a lot of investigation and help with B&C before we finally tracked it to a problem with the Odyssey and they were replaced, I think they were 2-3 years old. The starting amperage for the hydraulic pump caused the battery to fail under load. My point was that for someone like Bob who wanted to know his capacity, that test will give him a number and a trend each year. But since you mention the discharge issue I have calculated some figures and I am open to corrections and comments of course.
Assuming the PC925 discussed earlier, the 10-hour discharge rate capacity is 27AH (2.7a for 10 hours). The 20 hour capacity is almost identical at 28AH. The reserve capacity is 52 minutes at 25A discharge rate so you have two bookends to use.
If an owner wanted to discharge at 25A and got 80% or more of the 52 minutes before voltage dropped to 10,5v then I would suggest that battery is good.
If the test was performed at a more conservative C10 rate (2.7A) then the battery would have to stay above 10v for at least 8 hours (80% of 10 hours).
Since Odyssey provides those high and low amperage benchmarks I believe you can determine remaining capacity using a wide range of rates and keep those batteries at long as they perform.
Paul On 2010-06-21, at 6:39 PM, Chris Zavatson wrote: Paul, Changing the discharge rate during a capacity check will alter the results Going higher in current will yield less capacity while using less current will produce a higher capacity. The battery has internal resistance that also uses up power (turns into heat) during the discharge test. This loss is roughly a squared function of the current, therefore changing the discharge current will alter the results. I highly recommend keeping batteries on a maintainer while not in use. Once I started using these, my batteries (Concorde 25XC) would retain over 90% capacity even after five years of use. I can now replace them based on calendar time instead of performance. Chris Zavatson N91CZ 360std
From: paul miller <paul@tbm700.com>
To: lml@lancaironline.net
Sent: Mon, June 21, 2010 5:20:51 AM
Subject: [LML] Re: Odyssey batteries with very limited warranties
To avoid tossing a good battery you can do a test similar to that used on our Concorde batteries. Take the amp-hour rating (C1) and draw a load and measure the amps and time down to the threshold of 10v or 20v depending on the battery. If we can get 80% of the rated A-H capacity we keep it. But, we use a normal discharge rate in the airplane, not a full draw at C1 as I think that is unnecessary. So, maybe something like 20% of C1 discharging through some lights for example or a rate that duplicates a discharge rate in the airplane in your worst condition so that it will show up any faults under load. Take a measurement every X minutes and get your capacity. I'd do it on the bench out of the airplane and track the capacity between annuals.
We previously tossed these expensive batteries based on calendar life but we can now leave them on condition using these tests.
Paul On 2010-06-19, at 3:01 PM, Robert R Pastusek wrote: Just had two of my four Odyssey PC680 batteries crap out after 2 years of service although an identical set on the other buss are fine… Robert,
I have a similar setup in my IV-P and had planned to replace two of the four batteries every two years, expecting them to last for four years…but I never looked at the expected/advertised life; I was just following a practice used for lead/acid batteries. Two of my batteries are coming up on two years old; the other pair are coming up on four years, and I’d planned to replace them during the condition inspection next month. I’d appreciate your thoughts/experience on this. Thanks, Bob
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