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ted-burke avatar image
ted-burke asked

MPPT 75/10- too little Absorption time- why?

While on the boat and with loads on, engine off- the charge times average: Bulk 46%, Absorption 11%, Float 43%. The Absorption time seems too low and is not acting per my interpretation of the manual.

Have a new horizontally mounted 100 W marine installation with a SmartSolar MPPT 75/10, one 85 AH dual purpose lead acid house bank battery. While using the boat there are minor loads at about 5AH a day. The one major load is a DC powered compressor type refrigerator on all day, 5A while running, about 30% duty cycle, so about 40AH/day.

Absorption is often on less than 2 minutes and never over an hour at a time. Per the manual, Absorption time is set by either: 1) battery voltage at sunrise- which could drop below 12.2V- meaning the algorithm sets Absorption time to at least 4 hrs., or 2) the absorption stage can end when the “tail current” is less than 1A. The 11 recorded Absorption current levels last week ranged from 1.8 to 4.5A- none were under 1A. Only once, today, did the Absorption stage actually continue for 29 minutes and switched onto Float stage when the current dipped 0.9 A.

SO why is Absorption almost always terminating too early to be useful (not soaking the battery at the higher 16.2 V)??

Thanks

MPPT SmartSolar
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3 Answers
michelg avatar image
michelg answered ·

Hi ! Lead acid ? or GEL / ABS ? if lead acid (meaning you have to add distilled water to refill the battery), then your battery is probably sulfated. Give it a try by using the equalize function after the charge gets the float position.

Michel.

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spirou avatar image
spirou answered ·

With a small panel like that the option is also that by the time battery reaches absorption there is so little light that panel can't produce more than 1A thus triggering the tail current criteria.

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ted-burke avatar image
ted-burke answered ·

Thanks. New system. Trying to make sure it will do the job.

Regarding your “low end of day sun” comment- have logged many entries to try to figure this out. The charging day is 12-13 hours long here and there are typically 4-8 Bulk daytime charge events. Panel is typically 40-85 W with battery current at 3-4A at the end of the 14.4V bulk stage. So plenty of sun power to continue 14.4V in Absorption. Again why is the control switching out of Absorption so quickly?

And yes, it is a lead acid battery which has some sulfation. The controller’s Manual Equalization mode did nothing. In the one hour time limit, it never got above 14.5V. Did it 4 times. I don’t see how sulfation explains the controller switching.

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