The claim was made: "The edison cell has a peukert value of about 1. You can see how this works out at ____”.
Yet no support for this claim was offered except a link to a capacity calculator at the poster’s own website.
Extraordinary claims (in this case, Peukert Exponent of 1 for NiFe battery chemistry) demand extraordinary proof.
A P.E. of 1 effectively requires a battery with zero internal resistance and no irreversible electro-chemical losses.
For years, people have claimed P.C. of 1.0 for Lithium also, often parroting "Peukert only applies to Lead Acid". Only recently has this been disputed.
e.g. Peukert Exponents of 1.036 (Valence) and 1.056 (ThunderSky) estimated for 100ah and 90ah Lithiums respective.
Is 1.03-1.06 a Peukert Exponent “about 1”? That depends of course on your usage---i.e. %C that you will pull current out at. EV-scale Lithium batteries were claimed for years as having ZERO Peukert effect (Peukert Exponent of 1.0) and yet now we know otherwise. So why should I (as an Engineer of 30yrs and EV enthusiast for 17yrs) believe an unsupported claim that effectively Peukert doesn’t apply to NiFe? Sorry, credentials notwithstanding, I am skeptical.
What do we find on the Web regarding NiXX chemistry and Peukert?
It doesn’t take long with resources online to find evidence that NiMH batteries (eg this Panasonic curve below from research paper HERE) display the Peukert effect---this one with a Peukert Exponent of about 1.035. Given this for modern NiMH, why should we believe claims that Edison (NiFe) batteries exhibit zero Peukert effect? Modern NiFe are somehow better than modern NiMH?
I can’t tell you the number of times that I’ve heard “Peukert only applies to lead chemistries”.
The problem with this: The Peukert Equation was not derived based on the chemistry involved at all. It was simply based on detailed observations of reduced capacity as a function of current draw and a simplified exponential mathematical model found that matched it pretty well. Nothing to do with constraining its applicability to lead-acid or that if a battery’s internal resistance is small or zero that the effect doesn’t apply. Given its empirical basis, the way you “prove” a battery type doesn’t exhibit the effect is to show the data for your new battery type! You don’t prove it by simply making a claim that the Peukert exponent is about 1.0. Having said this, sure, a Peukert Exponent of 1.035 is very very good! And that should be celebrated.
-Myles
-----Original Message-----
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Steve Spence
Sent: Sunday, November 14, 2010 12:58 PM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Picking batteries
If you read battery chemistry engineering books, you would know that
Nickel based batteries have a peukert of virtually 1.00. I do not
"parrot", I do research and practical experimentation. I've lived off
grid for 6 years, and have over 25 years in electronics. I resent the
implications otherwise. My calculator is accurate.
Steve Spence
Renewable energy and self sufficiency
http://www.green-trust.org
http://arduinotronics.blogspot.com/
On 11/14/2010 03:36 PM, Myles Twete wrote:
>
>
> *>*A Peukert exponent of 1.00 means that there is no Peukerts effect at
> all and that the battery will deliver the same amount of energy at any
> discharge rate. I would guess that the Peukert's exponent for Nickel
> Iron batteries is higher than 1.00
>>Eric
>
> No doubt. References online claim virtually no Peukert effect for any
> of the Nickel chemistries including NiCd, NiZn, NiMH.
>
> I’m sure he just was parroting these. Worse, the weblink he offered
> drawing folks to his personal Peukert calculator page does not provide
> any support for the 1.0 Peukert exponent claim.
>
>
>
> From the brief looking I’ve done, I’d guess that the effective Peukert
> exponent for NiFe is below 1.05, and once you’re down that low, unless
> you’re drawing high-C loads, I don’t think you have to worry much about it.
>
>
>
> I think the major beefs against NiFe batteries are:
>
> · Cost
>
> · Relatively high self-discharge rates
>
>
>
> And those weigh enough against them that we don’t appreciate the
> uber-long life of them. Charge/discharge inefficiency isn’t much of an
> issue for many of us, but high initial cost and self-discharge rates are.
>
>
>
> -Myles Twete
>
>
>
>
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