question

I do not know if the information below applies to your particular problem, but I thought they might be related.

I recently watched a video from Surrette Rolls batteries & Morningstar. The technical services manager of Rolls’ batteries said the following regarding the time spent in Absorb mode, and it made me wonder, if this could be related to the temperature coefficient.

Does anyone know?

https://youtu.be/Rxo7ECDnn3w

The discussion starts at around 20-minutes into the video.

[Please notice that there is a temperature coefficient for MPPT solar chargers based on solar panels; there is, also, a temperature coefficient for batteries.

In addition, there is battery temperature compensation, and there is, also, a term for temperature correction, and in general there seems to be a lot of confusion regarding the terminology, and it’s application.

The manual for the BMV-712 leaves does not clarify in this regards.

The discussion below is for Rolls Surette LEAD batteries:

ONLY THREE MODES ARE IMPORTANT (BULK, ABSORPTION, FLOAT)

IGNORE ALL OTHER MODES SUGGESTED BY CHARGERS

FOR BULK MODE:

Bulk mode is 2.45 - 2.50 volts per cell

In Bulk mode you reach ONLY 80% charge.

FOR ABSORPTION MODE:

Absorption mode is 2.45 - 2.50 volts per cell & Time of absorption

More on time of absorption below.

Many chargers will change from a blinking light to a solid light when Bulk mode is complete, and users think the charging is done.

So users stop the charge process. This would be incorrect. The process has completed only the Bulk mode, and it is about to enter Absorption mode. This is all the change in LED lights show.

However, the most important mode is Absorption mode. DO NOT TURN IT OFF.

It is imperative that the Absorption mode be completed at least once per week. Otherwise, you are undercharging your batteries.

Time of absorption = 0.42 x (C / 20) / (Nominal current)

Time of absorption = 0.42 x (C / 20) / (I)

0.42 is the assumption that you will loose between 50% to 60% of your overall charging current while in Absorb mode. It is not related to the depth of discharge

C / 20 = The battery capacity at the 20-hour rate

Nominal current = nominal charging current while in bulk mode. Usually will de-rate the maximum current by 20%.

Take an actual current reading.

Example:

500 Ah battery bank @ 48-volts

1,000 watt PV array: 21-amps peak; 15- to 18-amps nominal

2,000 watt PV array: 41-amps peak; 30- to 35-amps nominal

3,000 watt PV array: 62-amps peak; 50- to 55-amps nominal

0.42 x (500 Ah / 18 amps) = 11.7-hours or 11-hours and 40-minutes

0.42 x (500 Ah / 35 amps) = 6-hours

0.42 x (500 Ah / 55 amps) = 3.82-hours or 3-hours and 49-minutes

FOR FLOAT MODE:

Float mode is 2.19 - 2.20 volts per cell (1.5% to 2% of C / 20 for 60-minutes)

Your batteries will loose capacity below 77°F, but with care they can recover.

Your batteries will loose cycles above 77°F. This is permanent.

In any case, let me know what you think.