float - Lithium manufacturer says no?

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jpcirig asked Oct 20, '22

float - Lithium manufacturer says no?

Hello,

Our installer just installed a Victron Phoenix Smart 50 amp 3 bank charger to new 2 lithium battery banks (4 total). We didn’t know what to do about the float setting, as Victron’s website suggested 13.2V however the manufacturer's website said that a constant float charge will degrade the battery. See excerpts below.

Can the float setting be zero? What happens if I’m not on the boat for an extended period, but it’s connected to shore power?

Thank you for any help you can offer.

From Victron:

6.4. Lithium batteries

Lithium Iron Phosphate (LiFePo4) batteries do not need to be fully charged to prevent premature failure. The default lithium (and recommended) settings are:

Setting	12V system	24V system	48V system
Absorption voltage	14.2V	28.4V	56.8V
Absorption time	2h	2h	2h
Float voltage	13.2V	26.4V	52.8V

From the manufacturer:

Should I use float chargers or battery maintainers for my lithium battery?

No, LiFePO4 batteries should be disconnected from the charger when fully charged. Float charging, or maintainers are not good for lithium batteries. Keeping a constant float charge or topping off charge also can cause metal plating and will reduce the lifespan of lithium batteries. Dakota Lithium batteries also have a low self-discharge rate of <5% a month. This low self-discharge rate makes a battery maintainer for long term storage un-necessary (for more on battery storage see section below).

float

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Daniël Boekel (Victron Energy Staff) answered · Oct 20, 2022 at 02:17 PM

Hi @jpcirig

For lithium batteries you should see the 'float' stage as a 'not discharging' stage:

An lfp battery has a resting voltage of about 13.2-13.4 volt, by setting 'float' voltage to that level, if there is power use (for example in a boat or RV: lights, DC equipment, alarm), this power will come from the charger (if the load is not bigger than the charger can supply)

So: the battery is not really charging in the 'float' stage and won't damage the batteries.

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Answer 1 · 2022-10-20T02:02:16Z

klim8skeptic answered · Oct 20, 2022 at 02:02 AM

Dakota Lithium sell and recommend Victron SmartSolar mppt's.

Either the Lithium battery preset in the mppt is ok, or perhaps DL could be contacted for the recommended settings.

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Answer 2 · 2022-10-20T04:31:15Z

Alexandra answered · Oct 20, 2022 at 04:31 AM

@jpcirig

You have a few options.

One is to set reabsorption more often so the battery moves up and down between float (the rebulk offset lower) and absorption voltages.

The victron chargers dont really keep the system at kne voltage continuously unless they are in use or under load.

Or for longer periods to shutdown and disconnect the system.

But in any case the battery manufacturer needs to be contacted for clarification as klim8skeptic mentioned.

Float chargers are different though they may be referring to non intelligent older ones that are always on and trickling low amps into the battery? Again clarification may be needed there.

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Answer 3 · 2022-10-20T10:37:35Z

Wow - thank you for the fast and thorough replies. My experience with DL was not so good. They seemed to be resellers of batteries and directed technical questions to "a local marine electrician". The few marine electricians I've spoken with all responded with, "you shoulda used Brand X" and "just switch back to lead-acid". So, I'm stuck with $5k "drop-in lead acid replacement batteries" and little support on how to make them work. So again - thank you for your help!

With that said, I did find the following excerpt from the Phoenix manual. It indicated that when Li-ion mode is selected, the float feature is disabled. However, the Storage Mode is enabled at 13.5V. I couldn't find an explanation of storage mode vs float mode. Any thoughts?

From Phoenix manual:

6.1.1 Charge Voltage

By simply selecting the integrated charge mode appropriate for the battery type being charged, (refer to the battery manufacturer’s recommendations) the voltage settings for each charge stage will be altered according to the table below:

Mode	Absorption		Float		Storage		Recondition
Mode	12V	24V	12V	24V	12V	24V	12V	24V
Normal	14.4V	28.8V	13.8V	27.6V	13.2V	26.4V	Disabled
Normal + Recondition	14.4V	28.8V	13.8V	27.6V	13.2V	26.4V	16.2V	32.4V
High	14.7V	29.4V	13.8V	27.6V	13.2V	26.4V	Disabled
High + Recondition	14.7V	29.4V	13.8V	27.6V	13.2V	26.4V	16.5V	33.0V
Li-ion	14.2V	28.4V	Disabled		13.5V	27.0V	Disabled

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