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fabian-pagel avatar image
fabian-pagel asked

High voltage on MPPT 75/15 battery output, when BMS closes due to temperature

Dear all,

I try to figure out, if the behaviour I see is per design or not. In my van I have installed a Victron LifePo4, a BMS12/200 and a MPPT75/15 with 2x110W solar panels. Due to the current cold weather conditions (<5°C), the battery and the BMS shutdown the battery charging.

Whenever there is sun available, the voltage on my BMS load and the MPPT battery output increase to ~17V. I assume this is due to the battery shutdown for charging. As soon, as the battery is open (>5°C), the voltage decreases to a normal level.

Is that expected? I thought the MPPT will reduce somehow the voltage when there is no charging in progress.

Why I am asking the question? If put the MPPT battery charging minus on the BMS load pin, where all my other load is also connected to. Now I have ~17V on all my devices, as long as the battery is shutdown. Is my design correct or do I need to change something?

best regards,

Fabian

MPPT ControllersBMSsolarvoltage
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Check the battery voltage the mppt is set to.

Update the mppt firmware, if not current version v1.46.

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5 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Is the MPPT set to lithium? If not you'll maybe get this high voltages due to the temperature compensation.

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kai avatar image
kai answered ·

The underlying issue is the low temp (the BMS cuts out to protect the battery). Are you able to re-design the system with supplementary heating to keep the battery (& BMS) above the low temp threshold?


e.g.

https://community.victronenergy.com/questions/38030/lifepo4-low-temperature-protection.html

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fabian-pagel avatar image
fabian-pagel answered ·

@kai Unfortunately I can not heat up my batteries. So I need to solve the problem by configuration and that was my initial question, if I may have an configuration issue?

@M.Lange Yes, it is set to Lithium for sure. I read about absorption, is that maybe something, what I need to configure?

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kai avatar image kai ♦ commented ·

sorry, that's about it from me. I don't have hands on experience with the MPPTs; don't know their expected behaviour if the battery is disconnected.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

Do you have the 17V permanently or is it just a short peak?

Without battery the MPPT should maximal go to the absorption voltage.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Fabian Pagel

Do the answers to this question describe what you are seeing?

https://community.victronenergy.com/questions/38304/using-a-smartsolar-mppt-10030-with-a-common-port-b-1.html

Or is it something else?

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kevp avatar image
kevp answered ·

I have a LiFePo battery that can be charged down to -20 deg. Check to see if yours is restricted to the default 5 deg. If not, you can switch it off in the battery settings of the MPPT.

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petajoule avatar image petajoule commented ·

> I have a LiFePo battery that can be charged down to -20 deg.

No it can't. Neither °F nor °C. It can be discharged down to -20°C, but charged only down to 0°C (better 5°C).

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