Victron temp sensor reading high compared to Ruuvi

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northtown2022 asked Oct 1, '23

Victron temp sensor reading high compared to Ruuvi

Hello. I have sensors set up measuring ambient temperatures at the moment.

OEM Victron sensor that came with Cerbo is measuring ~ 4C higher than the Ruuvi sensor (which measures close to an outdoor thermometer hanging close to the other two sensors.

Is it common to have to make adjustments of this degree on sensors?

In Remote Console the Vic OEM Power House Tmp sensor Offest = 0 and Scale = 1.0, there does not seem to be any adjustment for the Ruuvi.

I have a few LM335Z analog sensors and plan to build another cable or two and will use them for comparison if they work ;) Also have more Ruuvi's on the way and next time I am here at the cabin will test for comparison as well.

Suggestions are welcome!

Temperature Sensor remote console ruuvi sensors

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Answer 1 · 2023-10-01T13:49:24Z

packrat1969 answered · Oct 01, 2023 at 01:49 PM

Just an idea…

I had some NTC BMS temp sensors that arrived with exceptionally short leads so I lengthened them even knowing that the additional wire length would affect the temperature readings. I recalibrated them by determining the temperature offset after freezing them in a container of water. This gave me a starting point of 32 degrees F (0 degrees C). I don’t know how linear their readings are but at least they’re consistent. I didn’t want to destroy them by putting them in boiling water.

pack rat

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northtown2022 commented · Oct 02, 2023 at 01:02 AM

I'm having troubles getting my head wrapped around this. Would ice not eventually get as cold (or warm) as its environment? Are you freezing in a thermometer or sensor known to report accurately?

Today I fabbed up and added a homebrew LM335Z temp sensor and taped it to the wall beside the Vic sensor and the Ruuvi.

Its reading even higher temps than the Vic sensor!

Ruuvi's should be in later this week and I'll try and find time to make more sensors but it's starting to look like I am going to be in need of a good calibration technique.

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packrat1969 northtown2022 commented · Oct 02, 2023 at 03:15 AM

No, I did not perform this freezing test in any scientifically controlled environment. I did not need that kind of accuracy. I just made the assumption that as long as the sensors were encased in ice, they was at the water's freezing point. I only needed to keep the ice frozen long enough to get a idea as to what the sensors' errors were. The sensors were then thawed, dried off, and transplanted to various locations in my battery pack (core and surface temps). The values offset from freezing were then incorporated into the my BMS settings. So far, nothing has exploded.

packrat

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Answer 2 · 2023-10-01T16:39:18Z

pwfarnell answered · Oct 01, 2023 at 04:39 PM

I have an LM335 sensor (red) that should read very similar to the Ruuvi sensor (orange). The trouble is Victron only report the hardwired sensors to whole numbers and the Ruuvi to 1 decimal place. The difference on mine varies from 0.8 to 1.8degC so on average the LM335 is indicating 1.3degC lower which I have not tried to calibrate away.

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northtown2022 commented · Oct 02, 2023 at 01:13 AM

Thank you for pointing this out. Not sure at this point what sensor IF ANY I should trust. Thinking I'll get set up a pile of thermometers in combination with wired temp sensors and Ruuvi's to see how they stack up.

Your LM335 seems to be reporting dead accurate compared to mine :)

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harold commented · Oct 02, 2023 at 08:26 AM

Mine are Ok too, 1x Victron sensor to the Quattro, 2x Ruuvi (1 on each battery)

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Answer 3 · 2023-10-02T04:53:41Z

kevgermany answered · Oct 02, 2023 at 04:53 AM

LM 335 sensors can be calibrated with a pot. Some are way off. I had a Victron sensor that was about 5C over reading. Was easier to replace, but there's a thread somewhere aon how to calibrate, again with a pot. Google's your friend

@NorthTown2022

@pwfarnell

@packrat1969

Moving this to modifications space.

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