question

Where did you read that battery temperature compensation was always based on 20 degree celsius?

All parameters for a battery are given at 20°C by the manufacturers. So why should Victron define a different centre point?

https://www.victronenergy.de/upload/markets/Brochure%20-%20Off-Grid,%20back-up%20and%20island%20systems_rev%2013_EN_web.pdf

14. Effect of temperature on charging voltage The charge voltage should be reduced with increased temperature. Temperature compensation is required when the temperature of the battery is expected to be less than 10°C / 50°F or more than 30°C / 85°F during long periods of time. The recommended temperature compensation for Victron VRLA batteries is -4 mV / Cell (-24 mV /°C for a 12 V battery). The centre point for temperature compensation is 20°C / 70°F.

First, thank you very much for the links!

This makes this case really interesting because both documents describe the same products, the Victron gel and AGM batteries. The whole text is identical except the centre point part "20°C/70°F" vs. "25°C/70°F". But which document is correct?

I think none of it because did you check the Fahrenheit values:

20°C is not 70°F, it's 68°F

and 25°C is 77°F

So, if 25°C is the correct centre point, it should be 25°C/77°C

The document describing the settings of the MPPT chargers say only at this one point that the centre point is 25°C. If this is the case, I would assume, that also all other parametres are based on 25°C.

As a consequence, the parameters of manufacturers who base them on 20°C (like HOPPECKE, Germany) have to be converted to 25°C before entering in the settings.

Improvement:

Add a reference temperature setting, the entered values are based on as there are multiple (industry standards?) used in the world.

This would explain why the measured voltages are always incorrect and too high. But it does not explain, why the voltages in winter are too high. I saw 16V and more and voltages above 17.5V were logged as maximum. The destilled water went down from MAX to the MIN mark during winter (more than a litre per cell) and the bottoms were covered by 2-3mm of lead dust (the cells were brand new!).

The max voltages at 0°C and 15.08V (@25°) balance voltage should be then (delta = -25) 15.68°C but not above 17°C.

If I have time, I will do a reverse engineering using a potentiometer instead of the temperature sensor and record the measurings for each degree step.

You have written that you have a MPPT, a battery and using an app. So you need to read the manuals on all those three for the correct setup.

In the VictronConnect manual, it clearly says ”The base temperature for the compensation is 25°C (77°F)”: https://www.victronenergy.com/live/victronconnect:mppt-solarchargers

(there’s also a help-link from the app, with video explanations.)

In the manual for the MPPT, it also says where to place the MPPT if not using an external temp.sensor to get correct temp.reading. And if the internal temperature is used, its using the temperature read on the morning before the mppt itself starts to heat up (for example if its 10°C in the morning, and your batteries is getting up to 20 degrees in the evening, they still get charged with the 10°C value the whole day).

The data you have given:

Battery @20°C:

Abs: 14,4V

Float: 13,36.

Temp.comp. coef: -4mV/°K /cell

6 cells.

You then need to do the calculation to get the values needed in VictronConnect app:

@25°C

Abs: 14,28V

Float: 13,24V

Temp.comp.coef: -24mV/°C

Then, this chart shows MPPT charge, temperature compensated:

Hello everyone,

I have a solar system with Victron components since the beginning of 2020. I, too, have been busy entering the correct values in the components. This is not so easy. I read this chat with great interest. It is very funny for me that aspen quotes the Victron documents and refers to 25 ° C as the basis (see also his hardcopy "14. Effect of temperature on charging voltage).

If I open the Victron documentation today, the base is 20 ° C !!!!

But in the documentation of the MPPT 100/30 the reference temperature is 25°C

A little confusing for me......

what do the Victron experts think about this?