Is there a guideline on absorption charging cycle?

R Whitt

I have a Xantrex XW MMPT80 Charge controler,XW6048 inverter and 1200ah battery bank with 20 Schott 240Poly panels powering my entire home. My batteries are fully charged by 1 or 2 pm most days, the Xantrex equipment came with factory defaults of 180minutes on the absorbition cycle. I have the l16 DEKA batteries, the factory provides all the recomended charging voltages but I can not get an answer on how long they should be held in absorption before going to float. Any help please.

NorthGuy

Re: Is there a guideline on absorsion charging cycle?

R Whitt wrote: »

I have a Xantrex XW MMPT80 Charge controler,XW6048 inverter and 1200ah battery bank with 20 Schott 240Poly panels powering my entire home. My batteries are fully charged by 1 or 2 pm most days, the Xantrex equipment came with factory defaults of 180minutes on the absorbition cycle. I have the l16 DEKA batteries, the factory provides all the recomended charging voltages but I can not get an answer on how long they should be held in absorbsion before going to float. Any help please.

They should be kept in absorption until two things are accomplished:

1) Charging current does not decrease any more. You can watch it on your SCP.

2) Specific gravity has reached the level specified by a manufacturer. You can measure that with a hydrometer.

Cariboocoot

Re: Is there a guideline on absorption charging cycle?

Welcome to the forum.

There are two basic criteria used for selecting for Absorption time length.

The first is how long the Bulk charging cycle takes, as this is a fair indication of the batteries' relative state of charge. The longer the Bulk cycle takes, the lower the SOC and thus the longer the Absorb cycle needs to be.

The second is the decline in current, commonly known as End Amps. Once the current rate has drop to a low percentage of the batteries' capacity they are fully charged for all practical purposes. What this number will be depends on the capacity, manufacturer's recommendations (if any) and any concurrent loads drawing while charging (which has to be included in the setting).

Unfortunately Xantrex controllers are not the most accommodating for fine-tuning charging profiles.

BB.

Re: Is there a guideline on absorption charging cycle?

And, based on your measurements over time, you may find you need 2 hours of absorption in summer and 4-6 hours in winter (assming system is running 12 months a year).

If the system is not used (2-3 season use), you might keep it at two or even less hours when you are gone.

-Bill