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Open Roads Forum  >  Tech Issues

 > Lifepo4 float setting?

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jaycocreek

Idaho

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Posted: 05/13/22 05:46am Link  |  Quote  |  Print  |  Notify Moderator

I'm still confused about float with LFP batteries..Is it better to be in float or bulk the majority of the time?

Off-Grid Garage say's one should set float and bulk the same therefor it is in bulk mode charging when the sun is out vs floating or using battery capacity..

I have been experimenting in different modes to see which is the best way but yesterday was the first day I used more power than I made because it was in float 67% of the time...

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BFL13

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Posted: 05/13/22 07:07am Link  |  Quote  |  Print  |  Notify Moderator

"I'm still confused about float with LFP batteries..Is it better to be in float or bulk the majority of the time?

Off-Grid Garage say's one should set float and bulk the same therefor it is in bulk mode charging when the sun is out vs floating or using battery capacity."

Seems to be mixing two different things. Float voltage setting for the controller vs Float Stage for the battery.

You don't want the controller to be in Float voltage until after the battery is full. Now the battery can go to Float Stage while solar now in Float (after Bulk) can run loads.

Running loads while the controller is in Bulk voltage will reduce the amps going towards charging the battery so best to wait until after the battery is full (except LFP does not have to be full--so running loads might take priority in some scenarios )

Meanwhile if the question is about the LFP Float Stage, you do want that to be at the lower voltage per battery spec.

Also just to confuse things-- your Victron monitor wants the charging parameter voltage used to decide when the battery is full (along with tail current and a time for that) to be related to the battery's Float voltage.


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jaycocreek

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Posted: 05/13/22 07:19am Link  |  Quote  |  Print  |  Notify Moderator

If it was so simple..

There are so many opinions and recommendations on LFP settings,it is hard to distinguish which may apply to my use..I have set to the Victron defaults several times but before I just leave it there,I change some numbers based on others recommendations as in lower than 14.2 and less than 2hrs absorption and of course,float which I don't understand because LFP do not float they say ..

Seems maybe I just otta leave it on Victron settings period and try that as they are Victron...Maybe I am just over thinking it and worrying about it when it doesn't matter that much..

Thanks for the responses..

BFL13

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Posted: 05/13/22 07:42am Link  |  Quote  |  Print  |  Notify Moderator

The Garage guy is just saying what I had to do when on solar with the controller I used that would get the batt to Vabs set at 14.8 in my case, then drop to Float (which was adjustable) with no time at all in Absorb.

That happened before the battery was full and would leave the rest of the day in Float at low amps. So I had to set Float to the same as Bulk to keep the amps up till the battery was Full and could now drop to a lower Float voltage.

EP solar controller uses a standard charging profile where it stays in Bulk voltage 14.x for two hours (Absorb time) after getting the batt to that voltage, then it drops to Float 13.x automatically. If the battery is not yet full after the two hours, too bad.

So it is good to have Float voltage adjustable on the controller and also good if you can pick your Absorb time.

Same for any type of battery, not just LFP.

You need the monitor to know the battery SOC because the controller only knows what amps it is sending along, not where they are going-loads or battery or some to each. The monitor not the controller tells you when the batt is full so you know it is ok to have the controller at the lower Float voltage and so at lower amps.

time2roll

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Posted: 05/13/22 07:50am Link  |  Quote  |  Print  |  Notify Moderator

jaycocreek wrote:

I'm still confused about float with LFP batteries..Is it better to be in float or bulk the majority of the time?

Off-Grid Garage say's one should set float and bulk the same therefor it is in bulk mode charging when the sun is out vs floating or using battery capacity..
Depends on the purpose. If there is several days battery capacity there is no reason to keep the float close to bulk voltage. Certainly don't want to go into the evening with a low battery and not make it through the night.

Also if charging at 14.2+ a lower float voltage will be lower stress on the battery. I believe off grid garage is solar charging at 13.8 bulk so dropping the float is less important. Although once charged 13.4 to 13.6 will keep the LFP fully charged. Anything above resting voltage will be fine.


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jaycocreek

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Posted: 05/13/22 08:14am Link  |  Quote  |  Print  |  Notify Moderator

Time2

I guess that is what makes it so confusing to this old hillbilly..Charging to 14.4 etc seems is just a surface charge because it quickly drops after taking it off the charger to 13.3/13.4 where it sits at 100% charge..So the purpose of all the settings above that number really don't makes sense to me...

All activity and power usage happens below the settled voltage for the most part...So why the higher numbers except to balance...

Seems a charge to say 13.5/13.6 would be enough and a float at around 12.8/12.9 would be around the 20% mark?

3 tons

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Posted: 05/13/22 08:32am Link  |  Quote  |  Print  |  Notify Moderator

I agree with Time2roll…

IMO (Sad as it is…), Since earnest LiFePO4 post here have a tendency to get corrupted by ‘slight of hand’ theorist (SiO2 battery spin-masters busy at their crusade…), one need be wary of their long run at anti-LFP mischief - ‘Caution, extreme discernment required’, comes to mind!!…

Thus, I would recommend a solid information source, free of the imputed confusion - here’s what Solacity states - info here is uncorrupted and based in reality:

https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

“Lithium-ion batteries are charged in two stages: First the current is kept constant, or with solar PV that generally means that we try and send as much current into the batteries as available from the sun. The Voltage will slowly rise during this time, until it reaches the ‘absorb’ Voltage, 14.6V in the graph above. Once absorb is reached the battery is about 90% full, and to fill it the rest of the way the Voltage is kept constant while the current slowly tapers off. Once the current drops to around 5% – 10% of the Ah rating of the battery it is at 100% State-Of-Charge.”

And then there’s BattleBorn (on charging):

https://battlebornbatteries.com/how-do-i-charge-my-rv-battery/

FWIW, In my case, using a single stage MPPT controller set at 13.x volts, and short of occasional cell-balancing, I seldom find a need for a higher voltage, this since LFP seldom require a 100% recharge, so this works well for me (Be advised, I have two parallel systems, another with a PMW controller set at 14.x volts )…Therefore, to some degree, individual preference, technique and charge equip all plays a roll - with a bit hands-on experience, I believe you’ll find your battery to be most forgiving and highly receptive to receiving a charge pretty much regardless of settings…Again, JM hands-on based opinion…

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BFL13

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Posted: 05/13/22 08:41am Link  |  Quote  |  Print  |  Notify Moderator

You need 14.x to get those ions moving better. Once there you can lower the voltage

Lower charging voltage than 14.6 needs more time so keep
Float voltage same as Bulk longer too till desired SOC is reached

otrfun

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Posted: 05/13/22 08:51am Link  |  Quote  |  Print  |  Notify Moderator

jaycocreek wrote:

I'm still confused about float with LFP batteries..Is it better to be in float or bulk the majority of the time?

Off-Grid Garage say's one should set float and bulk the same therefor it is in bulk mode charging when the sun is out vs floating or using battery capacity..
What are you striving for? Absolute max cell longevity? Max usability/ah capacity? Or, somewhere in-between?

If you want absolute max cell longevity float a 12v lifepo4 at ~13.15V (~50% SOC). Downside, minimal usability/ah capacity.

If you want max usability/ah capacity, float the battery between 13.6 - 14.4v (~99 SOC). Downside, some reduction in cycle life. More so as you approach 14.4v. Floating at 14.6v is not recommended.

Can't have your cake and eat it, too. Pick your poison.

3 tons

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Posted: 05/13/22 08:58am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

You need 14.x to get those ions moving better. Once there you can lower the voltage

Lower charging voltage than 14.6 needs more time so keep
Float voltage same as Bulk longer too till desired SOC is reached


BFL, In the interest of discouraging added confusion, consider clarifying this statement as either ‘opinion’ or ‘fact’…If opinion (denoted by ‘IMO’ or ‘JMO’), feel free to state how you arrived at your conclusion…

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