Help with setting Peukert's Equation

Chinolbz wrote:
I have a E-Meter (Link 10, Checkmate, Energy Manager)That needs to have it's "n" value reset for a larger battery bank. Default number is 1.25.
I have increased my capacity to 500ah with 4 AGM 125ah batteries. Any ideas? Fasinating I know but I could use some help! Thanks Chino

I don't use Peukert's Equation since I don't believe it actually represents any lost charge.

What it does try to do is to take into account the higher current rates related to the batteries internal impedance when discharging, or the batteries internal voltage drop.

So the "n" is related to specific battery types and battery condition.

Oh, and this also means the "n" changes as the battery ages.

I would just solve for n based on battery specifications...

AFAIK, that number (different for type of battery. 1.25 is in the middle) is to help keep the accumulated AH figure correct which is used to estimate the SOC where you pick a number for bank capacity.

IMO your bank capacity changes so much with temperature, whatever you enter for capacity will be wrong, so the est for SOC using the accumulated AHs will be wrong too just from that.

So no point is using the correct Peukert figure--the 1.25 is close enough so you won't be any worse off in the estimated SOC WAG

Cruising sailboat owners had to learn the hard way that setting the n only reduced the error intelligently if the n factor correlated to agreement with an ampere hour meter TO a hydrometer. These gimmicks (another gimmick is displaying the "percentage of charge remaining") are there to sell the gizmo to the customer.

When they make a meter that tells me what mood a woman is in (from a distance) then I'll take a closer look at peukert compensation for anything other than high demand loads.

Stick with 1.25 unless the chemistry changes. The peukert factor just helps estimate the power available from different discharge levels. Discharging at 100 amps vs 10 amps is not linear and the 1.25 factor helps estimate the difference.

Now if you move to AGM you might go 1.1 and litium-ion maybe 1.04 etc but stick with 1.25 on the wet cell.

Thanks for the thought's guys! They are AGM so I might try 1.1 just too see if there is a difference. I have just left it at 1.25 in the past so I guess I was close. Chino

http://www.batterystuff.com/kb/tools/peukert-s-law-a-nerds-attempt-to-explain-battery-capacity.html

Or you could get the Peukert spec from the battery manufacturer.