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jeremy-h avatar image
jeremy-h asked

Turn on Heater for winter, with relay?

Hello everyone,

I’m new to the solar world and trying to prepare for my first winter. My system is comprised of the following components:

Smart Battery Sense 12/24/48V

Smart BMV (BMV-712)

Smart Solar MPPT 150/100

4 x 12V 100 AH battery, wired in series and parallel for 24V x 200 AH


I have 3 primary questions:

1 - Is there a way to have a small heater kick in at 8 C and kick out at 15 C, to protect the batteries over the winter? There seems to be relays that can be triggered on the Smart Solar and the BMV, could I use one of these?

2 - I’m measuring midpoint on my BMV and when I get close to 100% charge, around 28.4V (29.2V is manufacturer full), I start to get alarms. Is this an indication of my individual batteries being at different charge levels? If so is there any way to remedy this, short of disconnecting and topping each up individually?

3 - I seem to be struggling to get my BMV set properly with SOC, but this may be related to point 2. I‘ve watched a number of different videos on this, but don’t seem to be finding the right settings.

battery charging
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2 Answers
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snoobler answered ·

1) You're being a little paranoid. There is no reason to hold LFP above freezing except for charging. Even below freezing lower current charging will not cause damage. Insulation is preferable to heating unless you have a separate power source. You don't want to drain your batteries trying to keep them warm while not charging them.


2) I'm guessing you have cheap 12V like LiTime or any of the ~$300-ish units. They are notorious for having balance issues. If you did not individually charge to full and and then parallel charge the 12 volts, you need to. Additionally, 29.2 is excessive regardless of specs. 27.6 held for about 2 hours will reduce/eliminate top balance protection events and give more time for balancing.


3) charged 27.4. Tail current 2%

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jeremy-h avatar image jeremy-h commented ·
Thanks so much for the great comments
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kai-fuchs avatar image
kai-fuchs answered ·

Hey, sadly Victron does not enable enough data sources to turn relays on or of… e.g. you can not control the relay by temperature.

A way around would be using tank heater pats for RVs they are expensive but they have a temperature control build in. As said before this only makes sense if the battery’s are insulated and even in winter you generate enough energy to run the heater of the solar.

If you want to switch this on or of based of battery temperature you would need a Cerbo GX



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snoobler avatar image snoobler commented ·

The BMV-712 can trigger its control relay based on temperature, so replacing the SBS with a BMV temp sensor would allow for battery-based temperature control.

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jeremy-h avatar image jeremy-h commented ·
Thanks so much
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