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Compass Marine How To | all galleries >> Welcome To >> LiFePO4 Batteries - Thoughts & Musings > Capacity Test #12 @ Cycle 550
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Capacity Test #12 @ Cycle 550

Here is a close up shot of the data the DC electronic load captures when set to battery Ah testing mode. (click the image to make it larger) I set the capacity tester to 30A so as not to over heat it by running at full bore for 10+/- hours. The unit is rated at 40A but like anything electronic it likes to be run at less and will last longer doing so.

It should be noted that both my charge source and DC Electronic Load tester both utilize dedicated voltage sensing leads that do not carry any current. This means accurate charging voltages physically measured at the battery terminals, and also accurate cut-off voltages, measured at the battery terminals.

The cut off voltage for this capacity test was set to 11.2V or 2.8VPC. A Cell Log 8 was used to trigger alarms if any cell dropped below 2.78V.

The Process:

#1 Charging = 13.8V and current allowed to taper

#2 Cell Temps = 76F - 77F

#3 DC Load = 30A constant

#4 Voltage Cut Off = 11.2V / 2.8VPC

#5 Capacity Measurements = Ampere Hours & Time At Load


Cycle Number = 550

DC Load = 30A

Ah's Delivered = 419.2 Ah's

Time @ 30A = 13:58:55

Do your self a favor and create a baseline capacity figure that is both repeatable and useful to you!


other sizes: small medium large original auto
Jim Kevern 10-Mar-2016 19:53
What about the propulsion engine start battery? Not sure I'd want to invest in LFP for that, but if we change the charge profile for the house bank I'm guessing there's no way to get the start battery fully re-charged (other than when plugged into shore power and using the Victron start battery terminals)

Would something like a PWM solar charger using the house bank as the power source instead of solar panels do the job?
Shane 22-Apr-2015 18:17
Outstanding article and information. Thank you for sharing your knowledge and obvious expertise on the subject and the techniques you have used. I am now considering LiFePO4 as a solution. Not sure what the "ideal" Ah capacity for a circumnavigation cruising boat should be?
Steve Moore 11-Mar-2015 04:29
Just a quick note to thank you for your forum posts & these articles on LIFEPO4. Tremendous effort & detail & I really appreciate it.
John Tully 15-Dec-2014 16:50
Thanks for the update Maine Sail.

Regards Typhoon