Temperature sensors connected to Gerbo GX differ by 5 Deg F

DIY
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1

Folks,
I have two temp sensors. One came with the Cerbo GX and one came with the Multiplus II. I plugged them both into temperature inputs on the Cerbo. I did not see the point of plugging one into the temperature port of the Mulitplus, but perhaps that was my mistake. The report temperatures that differ by 5 degrees F. They are physically hanging in the battery bay, within a few inches of each other. Unlikely the air temp is really that different.
Can someone explain why they are not showing the same values?
Thanks
ANdy

2

Because these are not the highest accuracy sensors and you can have slightly different temperatures unless they are attached together.

There is a facility in the temperature sensor setup menu to add an offset or a multiplication factor to correct the displayed value. See screenshot below.

IMG_20250502_205156
IMG_20250502_205156767×453 18.1 KB

3

5 deg F is over 2.5 deg C that is a big difference for any electronic temperature measurement. Dose anyone know if these thermocouples or thermisters?
Andy

4

The device is an LM335. This device comes with a third calibration terminal, but this is not used.

5

I like it that you can work around it with help of the settings. Problem solved I would say.

6

PW
Are both devices the same? There seem to be multiple temp sensors on the Victron web site.
The three Victron part numbers I see on the victron page are
ASS000001000 ASS000100000 ASS000020000

Also, should the multiplus have an external temp sensor to do compensation? Or does it have an internal one? I dont find LM335 on the Victron site
Thanks
Andy

7

Andy,

  1. I looked at an old post I made, my Victron sensor was about 1.3°C different to a Ruuvi.
  1. The 3 Victron temperature sensors are all different sensing elements and are not compatible, you need to make sure you have the right one for the right service. See link below.
  1. The LM335 quoted is the actual sensing element used. Many of us have purchased LM335 sensors in the TO-92 case and made our own because we do not want to have a large battery lug as the measurement device. See link to the sensor and building info.

Peter.

8

Just to add to this, if you’re building your own ASS000100000 (for Cerbo or Multiplus) equivalent, use an LM335A or LM235Z. They’re more accurate than the basic LM335 (and you’ll probably find an LM235Z to be cheaper!). If you put it in a lug, there should be no electrical connection to the lug.

For the ASS000100000 (for the shunts/battery monitors) - you need a NTC 150 Kohm B 4730K thermistor with one side connected to the lug. A Vishay NTCLE100E3154GB0 is suitable. Those specs were determined by measurement of an actual ASS000100000.

I’m not sure about the ASS000020000.