More LifePo4 - Float/Full Charge

[ssurabus]

I've been preparing to swap out my old house bank with LifePo4 and am pretty comfortable that I'm about ready to make the switch. I have a couple of usage questions though that I want to understand before I move forwards:

1) Float
I've come to understand that LifePo4 does not need float. BattleBorn says you can float them at 13.6V or below. My charger can be set to 2-stage (i.e., remove the float stage completely). So I can choose between 'no float' or 'low float (13.6-)'. Given that choice are there advantages to using a low-float charging profile? Does leaving the charger on float at the appropriate level have the advantage of basically supplying power if there is any draw while not actually harming the battery as the float voltage is so low? What do you recommend, no float or low float?

1b) With 'no float', if the battery had a draw on it and got down to a certain level, I assume that a typical 'smart charger' would kick back on at some point and bring it back up. Seems like an obvious 'yes' on this one. True?

2) Full Charge
When out on the boat and there will be constant discharge (refrigerator, etc), I clearly want to charge the batteries to 'full' (they are being 'used', not 'stored'). On the other hand, I've read that LifePo4 should not be 'stored' at 100 percent charge. Historically, I come back from a trip, flip the charger on and leave. Obviously, I don't want to hang around waiting until the batteries get to 80 percent and shut the charger off before I go. So, float charge or not, do I really need to make sure the batteries don't get to full charge before I leave for a couple of days or a couple of weeks? I'd be happy to do that prior to winter layup when they are being stored for months, but not each time I use the boat.

Thanks!

 

[twistedtree]

Float between 13.4 and 13.6V. Float will allow the charger/shore to carry your DC loads when plugged in. Otherwise you are cycling the batteries over and over again drawing down recharging, drawing down, etc.

The float voltage will hold the batteries between 80-100% depending on the voltage. 13.4v will get you around 70-80%. When you arrive at the dock with batteries full from being underway, then plug in, the batteries will draw down for a while until they hit the float voltage, then settle it with the charger carrying loads.

 

[Don L]

I would, and am, float at 13.4V. But I am acturally only letting my batteries operate off solar while at the dock and have not turned on the battery charger.

Floating at 13.6V is basically just maintaining the LFP fully charged just like leaving your cell phone plugged in all the time and isn't good for the batteries.

 

[Delfin]

I've been preparing to swap out my old house bank with LifePo4 and am pretty comfortable that I'm about ready to make the switch. I have a couple of usage questions though that I want to understand before I move forwards:

1) Float
I've come to understand that LifePo4 does not need float. BattleBorn says you can float them at 13.6V or below. My charger can be set to 2-stage (i.e., remove the float stage completely). So I can choose between 'no float' or 'low float (13.6-)'. Given that choice are there advantages to using a low-float charging profile? Does leaving the charger on float at the appropriate level have the advantage of basically supplying power if there is any draw while not actually harming the battery as the float voltage is so low? What do you recommend, no float or low float?

1b) With 'no float', if the battery had a draw on it and got down to a certain level, I assume that a typical 'smart charger' would kick back on at some point and bring it back up. Seems like an obvious 'yes' on this one. True?

2) Full Charge
When out on the boat and there will be constant discharge (refrigerator, etc), I clearly want to charge the batteries to 'full' (they are being 'used', not 'stored'). On the other hand, I've read that LifePo4 should not be 'stored' at 100 percent charge. Historically, I come back from a trip, flip the charger on and leave. Obviously, I don't want to hang around waiting until the batteries get to 80 percent and shut the charger off before I go. So, float charge or not, do I really need to make sure the batteries don't get to full charge before I leave for a couple of days or a couple of weeks? I'd be happy to do that prior to winter layup when they are being stored for months, but not each time I use the boat.

Thanks!

You identify the conflict between floating LFP, which will result in them likely being fully charged, and LFP's preference for not being fully charged in 'storage'. For that reason, I don't ever float mine, using a LA starter bank as the destination for charge current at the dock, or alternator output when underway. I use the LFP when at anchor, or a dock w/o power, recharging as needed. If not being used for house power, I leave them offline.

 

[CharlieJ]

@TwistedTree #2: +1

 

[motion30]

In my reading everything I have seen recommends no float charge on lithium. There is a phenomenal called low voltage overcharge. I wish I could remember the article but I don't

 

[SteveK]

In my readings on lithium.
When given a choice to set charger to float or no float, choose no float is recommended.
As others said that would cause a discharge/recharge and float would maintain low draws.
On my magnasine inverter/charger float setting says managed by LFP, no choices.

 

[motion30]

In my readings on lithium.
When given a choice to set charger to float or no float, choose no float is recommended.
As others said that would cause a discharge/recharge and float would maintain low draws.
On my magnasine inverter/charger float setting says managed by LFP, no choices.

I have a magnum inverter as well. You don't have a problem. Just set your float voltage below the resting voltage of your batteries I believe I'm using 13.1 volts

 

[twistedtree]

A lot of the float confusion, ironically, came from some early material from Rod Collins. He has been an enormously generous wealth of information on LFP, and all other things electrical on boats, and I don't intend to detract from his contribution - just want to clarify. He had an LFP charging Mantra that went something like "charge until full then STOP charging", aka, do NOT float. But that actually created a lot of confusion, depending on what you consider "float" to be.


With lead, a float charge is
1) an ELEVATED voltage, resulting in
2) ONGOING charge current.


This is great for lead, but death for LFP. Rod's Mantra says don't do this, and he is absolutely correct.


But this DOES NOT mean you can't or shouldn't use the float function in your charger. You just need to program it correctly. With LFP, a float charge should be

1) a voltage that is NOT ELEVATED above the battery's resting voltage, resulting in

2) ZERO ongoing charge current into the battery.


Electrically, this is equivalent to the battery being disconnected, yet the charger (including solar) can and will carry varying house loads. You can further match the float voltage to a battery resting voltage that is BELOW 100% SOC, and thereby maintain the batteries at a reduced SOC when plugged in for an extended period of time.

 

[SteveK]

I have a magnum inverter as well. You don't have a problem. Just set your float voltage below the resting voltage of your batteries I believe I'm using 13.1 volts

You need to read my post again

 

[CMS]

Victron IP series Chargers can be programmed for a "storage voltage" after float has completed and you can set this at a voltage that corresponds to approx 30-50% SoC. The IP22 30A chargers are very affordable and can be run in parallel..

 

[Wdeertz]

I have a battleborn LFP house bank and after consulting with their technical support came to the conclusion that it’s preferable not to float. My charge profile is bulk to 28.8v which is held at this voltage for 2 hours (12 batteries in parallel, this allows top end cell balancing) and then the charger turns off. While on shore power my house bank runs my DC loads and after about 4 days it hits the recharge voltage of about 25.6v which equates to about 20% SOC. While on shore power my house bank cycles between 100% SOC to 20% SOC every 4 days. So if on shore power for a full year I’d be going through say 90 charge cycles but with a claimed 3000-5000 cycles I’m not too concerned. While on anchor I cycle every day. After 2 years in I have about 600 cycles and the battery bank still delivers 100% rated capacity.

 

[motion30]

You need to read my post again

I guess I am mistaken, you do not have a magnum inverter charger?

 

[SteveK]

I guess I am mistaken, you do not have a magnum inverter charger?

No, you are mistaken, I have a Magnum 2012. But since I am relating something to the thread you assumed I was having a problem. Let me help you. On my control panel when choosing battery type as LFP the float setting said managed by LFP, so no choices.

In my readings on lithium.
When given a choice to set charger to float or no float, choose no float is recommended.
As others said that would cause a discharge/recharge and float would maintain low draws.
On my magnasine inverter/charger float setting says managed by LFP, no choices.

 

[motion30]

No, you are mistaken, I have a Magnum 2012. But since I am relating something to the thread you assumed I was having a problem. Let me help you. On my control panel when choosing battery type as LFP the float setting said managed by LFP, so no choices.

We must have different controllers as mine gives me more choices

 

[motion30]

No, you are mistaken, I have a Magnum 2012. But since I am relating something to the thread you assumed I was having a problem. Let me help you. On my control panel when choosing battery type as LFP the float setting said managed by LFP, so no choices.

It's been a little while so I don't remember having an aged addled brain. But for the battery profile I think I selected custom profile which allows you to program the parameters you wish

 

[Delta Riverat]

Good thread, I'm on the LiFePO4 path too. Going to use a Xantrex which has this setting, but also defaults to 13.6.

But there is a custom setting and I will use this. Set charge to 14.5 (avoid max) and float to 13.2 (dump em half way before reset)

 

[SteveK]

It's been a little while so I don't remember having an aged addled brain. But for the battery profile I think I selected custom profile which allows you to program the parameters you wish

There you go, the custom profile will let you overrule the set parameters

 

[J.T kearney]

Good morning. Not to hijack this thread but trying to figure out how to maintain a charge on my flooded lead acid battery(start battery) while connected to shore power. My xantrex 2000 xc/pro is set for a lithium profile for house batteries(LFP).Any suggestions? Tried contacting xantrex but no reply. Any help would be appreciated

 

[SteveK]

Good morning. Not to hijack this thread but trying to figure out how to maintain a charge on my flooded lead acid battery(start battery) while connected to shore power. My xantrex 2000 xc/pro is set for a lithium profile for house batteries(LFP).Any suggestions? Tried contacting xantrex but no reply. Any help would be appreciated

DC2DC charger? From LFP to FLA

 

[J.T kearney]

charging FLA start battery while on shore power

Hi Steve,
I have a lithium house bank that is charged while on shore power and by a 30 amp DC/to DC charger from my start battery which is charged by my alternator. I need a float charge on my start battery but not my lithium house bank. My 30 amp DC to DC wont charge up my lithium on the short runs I take between mooring . I have a 400 amp hour house bank . Any ideas on float charging my start while on shore power?
cheers
J.T.

 

[jeremy.st]

I set the AC charger float at 13.4 and alternator float at 13.5 or 13.6.

I have some small DC loads at the dock so floating at 13.4 maintains about 80% the majority of the time. When underway I don't want to arrive at the anchorage at 80% so I float higher to keep the batteries full.

 

[BILL GOOD1]

float charge

In my reading everything I have seen recommends no float charge on lithium. There is a phenomenal called low voltage overcharge. I wish I could remember the article but I don't

I also wish I kept more notes!! When the li cells first started to appear there was a lot of uni papers about. I recall one which showed the effect of a "static voltage" being applied for 48hrs & the growth rate of the denrites continuing to grow even with no current flowing shown under a electron microscope. I assumed that was at 3.65V at the time. Not sure if still applies to LIFEPO4. Currently using a 123smartbms & they recommends (1) de-rate capacity by .8% to allow for aging etc. (2) this then becomes the new 100% SOC & the default setting for charge on/off is this 95% SOC on/ this new 100% SOC off. This for me means as the sun sinks in the west, the battery is approx 95% SOC for night. i.e. keeps almost "fully charged" all day. When on shore power 95% min day & night. Balance is good & temps are very low.
Regards Bill

 

[twistedtree]

I set the AC charger float at 13.4 and alternator float at 13.5 or 13.6.

I have some small DC loads at the dock so floating at 13.4 maintains about 80% the majority of the time. When underway I don't want to arrive at the anchorage at 80% so I float higher to keep the batteries full.

I do exactly the same. It works really well, at least fro how we use our boat.