question

nofinsphil avatar image
nofinsphil asked

SmartSolar 75/15 temperature sensor, temperature compensation

I have three separate arrays and three SmartSolar 75/15's charging a single 24v AGM battery bank. Currently I have no temp sensing aside from that provided by the MPPT internal sensors. I set up the charge profiles provided by the battery supplier. However the adopted temperature compensation seems incorrect on at least one of the controllers. The ambient temperature is around 20deg C. Absorption voltage is set to 29.1V -32mV/deg C. However the charge controller is going onto absorption at 28.6V. This suggests that the controller thinks it is ((29.1-28.6)/0.032) = 15.6degC above the nominal 25degC baseline ie 40deg C.

I was wanting to check what temperature the charge controller thinks it is, in case it is faulty (as it appears to be). Any way to check? When I turn off temperature compensation the controllers all switch to absorption at 29.1V correctly.

MPPT SmartSolarsmart solar charging behaviourtemperature
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JohnC avatar image
JohnC answered ·

Hi @nofinsphil

You may not be aware, but your mppts only use their internal temp sensor once a day. When they fire up at the beginning of a solar day they'll set corrected target figures, which will remain the same for the rest of the day. This because the internal warming of a producing mppt isn't reliable. And the value isn't available. Typically, users would compensate their settings to allow for battery warming as the day progresses.

A bit rough, but usually adequate for many users of Pb batts. An external sensor is needed for more accuracy, like a SmartBatterySense, or one of the shunts (with optional sensor). Networked in via BT, the mppt will control to that reading continuously. Or users with a wired GX network might use the T from a Multiplus, say.

I can't explain why your one mppt seems off. Might be faulty or even a local thing. Networking something else in to supply a continuous T is the ultimate answer.

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nofinsphil avatar image nofinsphil commented ·
Thank you for the detailed reply. If I install a SmartBatterySense and connect into the network using bluetooth I presume that will fix the problem if I have a faulty sensor. With a Smart Battery Sense I presume the temperature compensation will I be applied continuously? Also, will I be able to see/graph battery temp through the Victron Connect app?
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regman54 avatar image regman54 nofinsphil commented ·

My setup is smaller than yours with only one 75/15 CC, one SmartBatterySense, and two 12V AGMs. To somewhat answer your question the 75/15 and SmartBatterySense will communicate together via VE.Smart networking. The 75/15 will automatically use the temp and voltage data from the battery sense and yes that data is supplied continuously.

Hopefully that answers some of your questions.

Screenshot from Victron Connect app:


screenshot-2023-10-29-at-35119pm.png

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screenshot-2023-10-29-at-35119pm.png (108.5 KiB)

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