Re: (ET) Peukert's Number

["David Roden (Akron, Ohio, USA)" <roden ald net>]

From:                   "Pestka, Dennis J" <Dennis Pestka mkg com>

> Can anyone let
> me know what "peukert's number is ?

Peukert modeled the behavior of a lead acid battery under varying 
discharge rates.  

The higher the current you draw, the fewer amp hours you can take from 
the battery.  This is expressed as amp hours at different rates; for 
example, a golf car battery might be rated for 220 amp hours at the 20 
hour rate (meaning those 220 amp hours are drawn over a 20 hour period), 
but only 140 amp hours at the 2 hour rate.  

Peukert's number is an exponent of an equation which approximates that 
behavior.

The higher the number, the more capacity you lose at high rates of 
discharge.  A high Peukert exponent is also usually an indication of high 
internal resistance, and thus of a more limited ability to deliver 
exteremely high instantaneous currents.

A Peukert number in the range of 1.1 is considered very good.  You will 
find these values in expensive sealed AGM batteries such as Optima and 
Hawker.  Values from 1.25 to 1.3 are considered rather poor, and are 
typical of 12 volt flooded marine batteries such as Trojan 27TM and 
SCS225.  Most golf car batteries are in the 1.2 range.

A very good source of battery information is Uve Rick's battery page at

   http://www.geocities.com/CapeCanaveral/Lab/8679/battery.html

This page includes a javascript calculator to figure Peukert's exponent 
from your battery's amp hour ratings at various times (say 1 hr and 20 
hr), and from there to extrapolate other ratings at other times.

Hope this helps!


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1979 General Engines ElectroPed 24vdc
1974 Honda Civic 96vdc
1970 GE Elec-trak 36 vdc