question

raymiller avatar image

What is the temperture measurement accuracy of Victron sensors?

I've purchased a new MulitPlus II with included battery temperature sensor but the sensor is reading many degrees high, while I'll be using the sensor on LifePO4 batteries the low-temperature reading is the most critical in my situation. What accuracy should I be expecting from Victron temperature sensors?

Can the temperature sensor be corrected with software?

What temperate sensor is glued into the battery sensor? is it just a simple LM335?

Regards

MultiPlus Quattro Inverter ChargerTemperature Sensor
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

4 Answers
sunnycoastgreg avatar image
sunnycoastgreg answered ·

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...

2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Mark avatar image
Mark answered ·

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.

screenshot-20210131-101132-chrome.jpg

Instructions to set 'Superuser' access level are here.

Then go into the temperature sensor > Setup.

screenshot-20210131-101032-chrome.jpg

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.

screenshot-20210131-101042-chrome.jpg


1 comment
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Thanks for the solution, I did not know about this.

cheers

raymiller avatar image
raymiller answered ·

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.

screen-shot-2021-01-31-at-75740-am.png

screen-shot-2021-01-31-at-81501-am.png

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.

TempC Voltage
0 2.732
1 2.742
2 2.752
3 2.762
4 2.772
5 2.782
6 2.792
7 2.802
8 2.812
9 2.822
10 2.832
11 2.842
12 2.852
13 2.862
14 2.872
15 2.882
16 2.892
17 2.902
18 2.912
19 2.922
20 2.932
21 2.942
22 2.952
23 2.962
24 2.972
25 2.982
26 2.992
27 3.002
28 3.012
29 3.022
30 3.032
31 3.042
32 3.052
33 3.062
34 3.072
35 3.082
36 3.092
37 3.102
38 3.112
39 3.122



2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

wkirby avatar image
wkirby answered ·

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.

2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.