benl avatar image
benl asked

Victron SmartSolar MPPT 100/30 Controller low temperature cut-out

With regard to battery over- and under- temperature protection/cut-out (for LiFePo4 chemistry, where AIUI charging should not be performed when outside the range 0-40C): the VictronConnect - MPPT Solar Charge Controllers page notes that "In case there is no external source for battery temperature; charger uses its internal temperature for battery temperature compensation." and goes on to explain the idle requirements.

The next section notes that it will do under-temperature protection with an external sensor.

I presume from this that the SmartSolar will not consult the internal temperature sensor to consider if the temperature is too low prior to starting a charge cycle? Which is a pity as it would otherwise seem perfectly placed to do so: in cold conditions, if the device at ambient temp is below some low threshold (5C?) then just don't start charging.

MPPT Controllerstemperature
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3 Answers
Mark avatar image
Mark answered ·

The 'low temperature cutoff' function is only active if the MPPT is paired with another device that can provide it with a measured battery temperature (BMV, SBS, BMS, STS).

The MPPT internal temperature sensor is not reliable once the MPPT is active as the charger generates it's own heat. Even for voltage compensation due to temperature - it only takes a reading in the morning just before it starts up (which could be significantly different to later in the day).

It could be possible to use the same logic to disable charging commencing for lithiums, but it's still a risk as the MPPT would not know if the temperature dropped later.

On top of that the battery temperature could be significantly different to the initial MPPT measured temperature since;

-The MPPT is commonly located in a different area / compartment to the batteries

- The large thermal mass in a battery means that the battery temperature will significantly lag behind ambient temperature (for example the ambient temperature could easily be >5degC but the battery temperature is still <0degC

- The charge / discharge process will generate heat within the battery (a positive factor in this case)

In summary; it's not worth it for an expensive lithium battery, particularly when you can buy a 'Smart Battery Sense' device fairly cheaply and provide the MPPT with the correct battery temperature throughout the day.

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benl avatar image
benl answered ·

You've made good points as to why an external sensor co-located with the battery is better than the charger internal sensor. However in our case, it'll be once in a blue moon when we experience freezing temperatures (this is in a van with rare snow trips), and the fancy wireless sensor is over the top for this use case (pity there isn't a simple inexpensive wired/passive sensor).

It would have been nice to have the unit simply not charge until the ambient temperature was suitable; however I understand why Victron may have decided to do this, and we can manually work around it by simply disabling charging via the app if it gets too cold.

Thanks for the input!

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norbert avatar image
norbert answered ·

I searched for the same. Thanks for this.

Also in my case it would be enough to stop charging if the temp. is below e.g. 5°C in the ambient, and restart if it's above.

I do currently the same by disabling charging via the app.

I will need to buy the external sensor - not an issue - but the documentation of the mppt should/could be changed accordingly (mppt 150/35).

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Mark avatar image Mark ♦♦ commented ·

Hi Norbet,

Per explination in my answer, there is no ambient temperature sensor in the MPPT, it's internal and also effected by the heat generated by the actual MPPT unit during operation. So it's not a good/safe option and would only lead to issues and complaints from some systems/customers.

Regarding the documentation, I suppose that you mean the dedicated MPPT manual for your model?

Have you had a look at the online VictronConnect MPPT manual?

Also VE.Smart Networking;

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norbert avatar image norbert Mark ♦♦ commented ·

Yes, I only read the manual and not the live pages.

Thanks for the hints.

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