Don,
Your description of Peukerts Law is a good summary of the premise behind the concept, but there is much more to Peukert's work than just that. In fact, the concept was known for many years before Peukert was able to quantify the relationship between the load and capacity lost. Here's a link to a page that explains the Peukert Effect is greater detail:
http://www.smartgauge.co.uk/peukert2.html
The content can be a little difficult to work through, but it is correct. There are additional pages that provide validation of their version of the formula, where the results can be verified against the published specs of almost any battery. If you don't want to work through all of the math in the middle of the page, the second to the last paragraph refers to how different battery types have different Peukert's Exponenets and what that can mean.
If you can accept that different batteries can have different Peukert Exponents depending on how they are made, then the following link shows graphically how a different Peukert Exponent affects the available capacity of different batteries. Look about halfway down the page, in the section labeled "The Peukert Effect":
http://www.vonwentzel.net/Battery/00.Glossary/
Finally, while few manufacturers publish their specific Peukert Exponents, some do and some other numbers have been published for common batteries. Peukert Exponents are typically calculated through empirically measured capacity at different loads. Here are a few examples (values closer to 1.0 are better):
Trojan T-105 = 1.25
US Battery 2200 = 1.20
Optima 750S = 1.109
Concorde AGM = 1.06
You can compare the capacity at 50A of the flooded US Battery 2200 (PE = 1.20) to the capacity at 50A of an AGM (PE = 1.08) that falls between Optima and Concorde. For 120Ah of flooded battery, the available capacity of PE 1.20 at 50A is about 56Ah. For the same size (120Ah) AGM battery, the available capacity of PE 1.08 at 50A is about 88Ah. That works out to 57% more available capacity from the AGM battery over the flooded battery, when both batteries start with identical 20hr ratings.
Another difference between the two battery types that is relatively easy to check is the battery's internal resistance. The AGM has a low internal resistance so less energy is lost during charging and discharging due to heat. If you typically have high amperage draws, that lower internal resistance allows for a greater available capacity and faster charging, basically higher amps in both directions.
That said, AGM are much less tolerant of high voltages than flooded batteries, requiring a different charging profile than their flooded brethren. But a charger that is correctly matched to AGM batteries will not overcharge the batteries or cause them to vent. Most of the AGM batteries that meet an early death have been charged incorrectly.
I believe all of the information that I have presented is basically true, and that most of the battery manufacturers agree with that opinion. Whether or not you believe any of this is up to you, but given the formulas, anyone here that wants to go through the effort, can perform the calculations and verify the results through real-life measurements.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "desulfator" <desulfator@...> wrote:
>
> Hi Eric,
>
> Perhaps you can provide a link to the study done that demonstrates that,
>
> "AGMs have an advantage over FLA in that they do not suffer as much from Peukert's Effect"?
>
> Were these studies done with AGM and FLA side by side or merely a tests done with AGM alone as opposed to published data of FLA?
>
> I am highly suspect of any studies done with AGM in an air conditioned test chamber. :)
>
> My understanding of the 1897 Peukert's Law is simply that lead-acid battery capacity is inversely proportional to load. Simply stated it is that the Amp Hour rating of a battery decreases with increasing load.
>
> Given that AGM and FLA have similar plate and electrolyte chemistries, I find it puzzling that AGM would outperform FLA allowing for 50% increase in range?
>
>
> Don
>
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