question

The device inside that type of sensor is an LM335.

These will read high if there is stray resistance somewhere between the MultiPlus and the sensor.
For example, an additional resistance of 10Ω will result in a reading of 24°C when it should be 21°C.

Perhaps you could check the connections to ensure that they are sound and there is no stray resistance creeping in.

Thanks for the Answer yes I can also confirm the use of LM335 as the sensor. My test of the Victron sensor used only the sensor and wiring provided, which in my case reads +6.5C high. By chance, I had a couple of LM335Z wired to a data collection box from a work project 30 years ago! The result, the 30-year-old LM335Z's with calibration potentiometer read correctly +/1 0.5C.

Long story short, the specification for an "uncalibrated" LM335 can be up to 9 degrees C out at the extremes and 6C at 25C and still be within specifications. With a Typical error of best-case LM335A at 2 degrees C.

Using the LM335's are fine but need the calibration checked at manufacture (super easy to do) or add in the calibration potentiometer to adjust more finely. If the battery sensor is being used to protect the battery having such measurement errors in 2021 is really poor, I would expect the temperature sensor to be reading within a 1 degree C envelope either by device selection or calibration. So maybe better quality control would fix the problem.

For me, I'll be repurposing one of the old sensors with a calibration circuit for the application.

Figure 12, R1 is calculated to have 1ma of current flow at 25C.

Calibration table (below), I used in my calibration 0.1 degrees, the table below at least gives the voltage to within 1 degree for checking the sensors separately using the circuit above minus the calibration 10k ohm potentiometer.

LM335 Temperature C - voltage Table.

Hi Ray, the temperature reading can be calibrated/corrected within the Venus OS software.

To do so first you need to enable the 'Superuser' access level, that will reveal the related settings.

Instructions to set 'Superuser' access level are here.

Then go into the temperature sensor > Setup.

Then correct the reading with an appropriate Offset and/or Scale factor. The sensor voltage as measured by the Venus OS is also reported there, which can be helpful with troubleshooting.

my question is similar to above .. however a little different my system has
victron skylla i 3 charger, with its supplied temp sensor fitted to the house battery (neg terminal)
Victron BMV 702 shunt, fitted with (correct) optional temp sensor to same house battery. (pos terminal)

i recall from somewhere that victron uses two different types of temp sensors, and i think im correct that the two sensors in above situation are different.

my challenge is that the two report quite different readings (both connected to same battery bank)

eg BMV reports 23.0 at same time as skylla 18.7C.. & a check with infrared temp gun shows 23.5C
( a good match to BMV shunts temp sensor) but VERY poor tomthe skylla.
And its the skylla sensor that is used for its temp/volt compensation calculation etc
My batteries are “only” AGM, so probably less critical than if i were using Lithiums.

Whilst i know i can adjust the BMv shunts temp .. it doesnt need it..
However the skylla does ...

and help, comments welcome...

Thanks. I'm having a similar problem, the battery temp seems to be far too high. Easysolar with standard victron temp sensor on the negative terminal.

Am I right in saying, based on this thread, that the sensor is measuring the temperature of the battery terminal, and that there is an assumption that the terminal temp is the internal temp. Also that I can use an accuarte thermometer to measure the terminal temp and use that to correct the sensor inaccuracy using superuser mode?

Thanks in advance.

Hi,

If I want to create an additional sensor, by connecting an LM335, can I simply use 2 wires from the Cerbo temp ports to the ML335?