Math Behind the Magic
Here are the formulas our calculators take into consideration while computing. What? You thought we would show our work step by step? You’re welcome to do it longhand if you like, but personally, I like my calculators better.
Peukert’s Law (As we use it in Finding Load Specific Run Time)
H is the rated discharge time, in (hours).
C is the rated capacity at that discharge rate, in (Ampere-hours).
I is the actual discharge current, in (Amps).
k is the Peukert constant, (dimensionless).
t is the actual time to discharge the battery, in (hours).
To find the Peukert constant, we must have two different ratings from the manufacturer. Most manufacturers will give a 20 hour rate AH rating as the standard rating, and also a 10 hour rate and possibly a 100 hour rate. With two of these, you can figure out Peukert’s number using the simple (J maniacal laughter) formula below.
n = Peukert’s constant
C1 = Capacity at 1st rate
C2 = Capacity at 2nd rate
R1 = hour rate at 1st C rating
R2 = hour rate at 2nd C rating
Or, you can use our calculator and avoid a headache. Find it here.
Here is gets complicated. In this formula we are trying to solve for C, the Rated capacity at a 20hr rate.
...Yeah, just use the Calculator
This one is simple, it’s Ohm's Law.
W = V x A
Wattage = Voltage x Amperage
or as we use it:
Amperage = Wattage / Voltage