question

snoobler avatar image
snoobler asked

Temperature compensation and output of remote monitoring.

Having trouble interpreting the output of VictronConnect


Components/parameters:

  • Smart SCC 150/100
  • Smart Battery Sense networked with SCC
  • Quattro 5K/48
  • Color Control GX
  • 48V Trojan battery bank, 58.8V absorption


Remote monitoring via VRM, VictronConnect on PC.


Trojan says -5mV/°C/cell

24 cells

24*5 = -120mV/°C


I can directly see the Smart Sense when local and able to access it on bluetooth. I do not see that I have a way to access it directly via VRM.


I entered -120mV/°C in temperature while it was at the uncompensated absorption level. Voltage immediately increased about 1V as expected based on 34°C, and it didn't seem to be adjusting current to lower it. Shocked me a bit, so I flipped the sign and immediately saw a lower voltage. Head melted, and I just turned it off.


Questions:


  1. Does temperature compensation adjust the measured voltage and make it read higher for °C above 25°C?
  2. If #1 yes, had I been patient and given the SCC more time, would I have seen the current reduce and the voltage settle to the absorption voltage?
  3. When I connect to the SCC, is the temperature reported in the app/PC VictronConnect (PC version shown below) from the networked smart sense or the SCC internal temp?
  4. If not the smart sense, is there a way I can see the smart sense via VRM?


Thanks!

VRMVictronConnectSmart Battery Sensetemperature compensation
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1 Answer
blue-sails avatar image
blue-sails answered ·

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.

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