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 1^st rate

C2 = Capacity at 2^nd rate

R1 = hour rate at 1^st C rating

R2 = hour rate at 2^nd C rating

Or, you can use our calculator and avoid a headache. Find it here.

Calculating what battery will run your load

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

Converting AC to DC

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