question

bwilliams24 avatar image
bwilliams24 asked

solar charging lithium batteries

Hi, my question is about the mppt 100/30 controller. I have two lithium leisure batteries in a Motorhome with 300 watts of solar. Like all lithiums they maintain a voltage of around 13v down to 90% or more discharge. As a result the controller looks at the voltage each morning and sets a minimum time for absorption of typically an hour or less. At that point the controller moves to float charging and much of the solar output is blocked because the lithiums easily maintain 13.8 volts with around 50 watts charge - the remainder of panel output is wasted and the batteries are not charged properly. Should I set a temporary float value of 14.4 volts to deal with this problem and rest to 13.8 when the batteries are charged? Brian

Lithium BatterySOC
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3 Answers
klim8skeptic avatar image
klim8skeptic answered ·

The SmartSolar controllers with inbuilt Bluetooth are good to update to v1.42. They will get fixed absorption time.

The Bluesolar controllers with add on Bluetooth can get v1.43 (there is v1.42 firmware for 100-30 rev2 hardware)

v1.43 – 8 July 2019
Released only for four models below. For all other models, v1.42 is still the latest version:
⦁ BlueSolar Charger MPPT 75/50 – Product ID 0xA040
⦁ BlueSolar Charger MPPT 150/35 – Product ID 0xA041
⦁ BlueSolar Charger MPPT 100/30 – Product ID 0xA044
⦁ BlueSolar Charger MPPT 100/50 – Product ID 0xA045
v1.43 still does variable absorption time.

Instructions for manually updating firmware https://www.victronenergy.com/live/victronconnect:start Look at 8.2 for self supplied firmware. Read all instructions and warnings and changelog. Update at your own risk.

Got a link for the NDS system?

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klim8skeptic avatar image
klim8skeptic answered ·

Hi B,

"Should I set a temporary float value of 14.4 volts to deal with this problem"

I wouldn't, as when the charge controller is at float, it will compensate for any load being placed on the battery.

Foy my setup, the battery will loose 1% of capacity from its 100% "absorb" voltage state, until the battery settles down to its "float" voltage state and the controller resumes supplying current for the loads.

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solardude avatar image
solardude answered ·

13.8V is the MAX you should float Lithiums. If you look at a LiFePo4 voltage curve, you will see that 13.8V represents about 95% capacity. Anything over that is risking over charge and really doesn’t give you much more usable power.

Lithiums will last much longer if you don’t take them above 90% capacity, and not below 10%.

I would say you have it set up correctly now.

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