battery charge rate

[john firth]

Years ago , I replaced my PIK 20E SLA starter bat with an 8AH
Odyssey; as it did not come with specific charging data, I used a
1A charger when needed .

Thanks to our EAA president, it appears that Odyssey bats should be charged
at a much high rate than SLA. 40% of the AH capacity, in amps
3 A for mine.

John F

[[email protected]]

On Monday, March 19, 2018 at 4:38:21 PM UTC-4, john firth wrote:
> Years ago , I replaced my PIK 20E SLA starter bat with an 8AH
> Odyssey; as it did not come with specific charging data, I used a
> 1A charger when needed .
>
> Thanks to our EAA president, it appears that Odyssey bats should be charged
> at a much high rate than SLA. 40% of the AH capacity, in amps
> 3 A for mine.
>
> John F

"Should" be charged at that rate, or "may" be? I'd say the slower the better, or at least not worse, as long as you have the time available.

[Charlie M. (UH & 002 owner/pilot)]

Agreed, other than time on charge, no issue with a slow rate charge.
In general, charging at a rate that warms the battery a bunch is killing a little life.

Note: decades ago, we slow charged NiCads (for RC car use) to "full". Then, just before a race, we hit them a few times to top off and warm them up.
Pulling power is a chemical process, usually the warmer the item the faster the process (energy dump) which is what we wanted.
Part of why a car battery seems weak when rather cold vs. a warm day.

The only time a high rate charge may be worthwhile is to help shed some plate sulfation in VRLA batteries. Even then, it is up for discussion.
Yes, in case someone brings it up, an equalize charge on VRLA/flooded cells can help with new batteries, but only a time or two in their life.
Taken from someone that made a living observing and monitoring batteries for datacenters and their UPS's.

[Eric Greenwell[_4_]]

wrote on 3/19/2018 1:49 PM:
> On Monday, March 19, 2018 at 4:38:21 PM UTC-4, john firth wrote:
>> Years ago , I replaced my PIK 20E SLA starter bat with an 8AH
>> Odyssey; as it did not come with specific charging data, I used a
>> 1A charger when needed .
>>
>> Thanks to our EAA president, it appears that Odyssey bats should be charged
>> at a much high rate than SLA. 40% of the AH capacity, in amps
>> 3 A for mine.
>>
>> John F
>
> "Should" be charged at that rate, or "may" be? I'd say the slower the better, or at least not worse, as long as you have the time available.

Odyssey says slower is definitely not better, and will shorten the life of the
battery.


According to the information that came with my 12 volt, 16 AH Odyssey batteries
(PC680), they should be charged at a minimum of 0.4 x 16 AH = 6.4 amps. In fact,
there is no current limit - they can be charged at 14.7 volts without limiting the
current. I use an 8 amp charger; of course, it doesn't stay at 8 amps
indefinitely, and the charge current begins to drop after while, and the charger
eventually switches to 13.6 volts.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

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This battery is a (sealed lead-acid) "starter" type battery, i.e., designed to provide a large current for a short period (rated 170 amps CCA). Perhaps there is something about a slow charge that may change the shape of the lead compounds on the electrodes in a way that will reduce that cranking ability? I don't know. But for the typical battery used in a non-motorized glider I still recommend a slow charge, generally no faster than the discharge.

A 0.4C charger is not terribly fast, it would take 2.5 hours for a full charge of an empty battery if the current was constant, which as you said it isn't, so more like 4+ hours. Of course you shouldn't ever fully discharge a lead-acid battery, thus it would rarely need a full charge cycle.

A lithium battery can be "fully" discharged (to the point where its internal controller says "no more") with less effect on its longevity. That means that, for example, a 10AH lithium battery will provide as much practical usage time as a 15 or 20 AH SLA. This doubles again the weight advantage. But still at 6x the price. For that reason I'm still using SLA. It helps that the modest gizmos in my glider allow me to fly 6 hours on a 5AH SLA battery. (I use the 12AH battery on strong days, that's my "ballast".) If the LiFePO4 price comes down another 2x, and/or I'm convinced of a long-enough life in years, I might spring for it.

[Charlie M. (UH & 002 owner/pilot)]

I am really curious why they state that.
In general terms, through many consumer battery chemistries, slower charge is better for the total life of the battery.
Some chemistries tolerate higher charge rates with less detrimental effect.

LiPo and Lion tend to be happier with high charge rates than NiCad and sealed/gelled LA.

[jfitch]

On Tuesday, March 20, 2018 at 9:28:22 AM UTC-7, Charlie M. (UH & 002 owner/pilot) wrote:
> I am really curious why they state that.
> In general terms, through many consumer battery chemistries, slower charge is better for the total life of the battery.
> Some chemistries tolerate higher charge rates with less detrimental effect.
>
> LiPo and Lion tend to be happier with high charge rates than NiCad and sealed/gelled LA.

Some manufacturers of AGM batteries recommend fast charge rates, at least occasionally, to drive the sulfate into solution again. Odyssey is a thin plate battery, their selling point is high charge and discharge rates without damage.

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I use a "desulphator" device to extend the life of old SLA/AGM batteries. It provides a very slow trickle charge on the average - but in short pulses that are high-current. Seems to help, if kept running for months. Great for the old batteries I use for running LED lamps at home in case of a power outage. But I wouldn't use a battery that is that old and tired in my glider. A new SLA is cheap and is good for several years of flying use, as long as you only discharge it halfway, recharge right away (slowly) with a good smart charger, and never store it where it is hot (as in a glider trailer).