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tom56 avatar image
tom56 asked

SmartSolar lithium battery storage settings?

I have a solar setup with 2x100Ah lithium batteries and two solar panels about 120w each, connected in parallell. 5-6 months of the year (wintertime in Norway) the system/cabin is not in use. Temperatures are well below zero parts of the winter, see temp. chart. In summertime and clear conditions, batteries are generally fully recharged in less than 2 hours the next day with perhaps an average 300Wh charge.


I am pretty sure the batteries (data sheet attached to this post) where delivered to me at storage voltage 13,17v each. The batteries are supposed to have a "Under temperature charge protection" (0C/32F).

What are the best SmartSolar 100/20 settings for "storing" the lithium batteries over the winter under these conditions?


MERITSUN LFP100-12.8.pdf

Lithium Batterysmart solar set-up help
temperatures.png (48.9 KiB)
meritsun-lfp100-128.pdf (475.8 KiB)
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Fideri avatar image Fideri commented ·

Hi @Tom56 I’m thinking of getting 4 modules of the unsupported Meritsun battery. With Meritsun, I would get over 900ha compared with about 400ha of the officially supported PolyTech us3000.
What is your personal experience with Meritsun, including support?
The sales agent, who incidentally promotes Victron as a system compatible with Meritsun batteries, told me the Victron system “works” provided the correct battery parameters are entered in Victron and there is no communication between Meritsun and Victron.
If it helps, The Victron gear I have are the MPPT 250/100; a Quattro 10,000 VA and a CCGX device.
Fideri

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Fideri avatar image Fideri Fideri commented ·

*That is 900 vs 400ah, not “ha”. Sorry!

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5 Answers
thomassolar avatar image
thomassolar answered ·

I would suggest:

Absorption voltage: 13,30V

Float voltage: 13,10V


Then you keep the battery close to the storage voltage you mentioned.


(I am not a Victron employed, so maybe someone else gives you a better advice. But with the settings i suggested, the battery should be very little stressed. And as long as you don’t have consumption of electricity those months, a voltage around 13,0-13,3V should be pretty safe)

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Sten avatar image
Sten answered ·

I would suggest setting both Absorbtion and float to

13.2V - 13.3V. There is no need to cycle betwen 2 different voltage.

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thomassolar avatar image thomassolar commented ·

You are probably right! I suggested a lower float than absorption to prevent charging all day... But as long as the voltage settings are below the max charging voltage (14,6V), it doesn’t harm that the charging goes on all the way to the tail current is down to 0 ampere..?

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Sten avatar image Sten thomassolar commented ·

The reason to set both Arbsorption and float to the same voltage, is that the solar Controller start with a New bulk fase every morning. Then it doesn't mater witch fase the Controller is in. My thought about this is kepping the batteri in a SOC from 60 to 70% and My experiense is that 13.2 to 13.3V does that. As Daniel Boekel also says number one is disconecting the battery, but if a gx device is connected and the goal is to supervice the system i think this is the Best way.

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Alistair Warburton avatar image
Alistair Warburton answered ·

My advice... Set whatever the datasheet for the batteries tells you to and make sure the system is applying temperature compensation. Below 13C and definatly below 0C lithiums ability to be charged is seveerly limmited to the point where charging at all may be a poor plan.

Have you got the batteries in an insulated box? potentally even with a small heat source.

If you need to charge in very low temps it would be worth while using some power to heat the battery enclosure so that a charge can be accepted. It isnt like you would wasting any power, if you cant charge then whatever solar you are getting is wasted anyway. Insulation is importent because quicklly heating the air in the enclosure will not heat the batteries, you need significant soak time. You will need to test this. or monitor the heater load for a given setpoint.

When the heater load falls to the rate your insulation is leaking heat the batteries are warm, if the heater is running longer/harder then the batteries are still cold and absorbing heat.


Al

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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

If a system is not used for 5-6 months, and no power needed, I would advice to disconnect the batteries from the system completely.

Because Lithium batteries are best stored not fully charged (for longer life), disconnecting them when they are about 50% SOC is best.

The same goes for lead-acid batteries, but these are best to be fully charged before disconnecting.

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tom56 avatar image
tom56 answered ·

Thank you all. Since there may be some need for lights etc at the cabin during winter, disconnecting the batteries may be a bit laboursome.

At the time I leave the cabin in fall, batteries are probably fully charged. I dont think draining them to 60% SOC is easily done, I have no big load to attach to the system that I can think of. So when I set the SmartSolar absorption and float to 13,3V like @Sten suggests, will the batteries drain to 13,3V, 60%-70% SOC?

Can I expect the BMS of the batteries to disconnect the charging when temperature falls below 0C, or should I add the Victron Smart Battery Sense to the system?


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Sten avatar image Sten commented ·

You don't have to drain them to 60%. If you start with full battery. Setting the solarcontroller to 13.3V will just try to keep the batterys at this voltage. If there is a consumption from the battery it will setle around this soc, as long the solarcontroller can keep up with the consumption.


I look into the specs you attached, and your lithium seems to disconect if temperature go under 0 deg. So I would think the BMS will disconect at low temperature.



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