Frequency of getting LFP batteries fully charged

[sailorboy1]

I have had my 400aH LFP bank almost a month with no issues. In that time I think they have only gotten 100% SOC, based on being 0aH out per the battery monitor, once. I don't think they have gotten to the 14.4V and stayed there to do this mysterious balancing act (except on day 2 of installation that I went to pains to do) at all.

So how long are people going without getting their LFP to "fully" charged?


Yes I know it isn"t needed to fully charge. But FireFly told me the same thing and I still have lingering lead acid knowledge to overcome.

Vote on poll so when the drift starts the original question gets answered please.

[wholybee]

I have gone many months. Never kept track. During a recent incident when my batteries went to zero and the BMS cut out, I used that opportunity to do a capacity check. After several years I still get 330Ah out of my 300Ah bank.

The only reason to charge to 100% is to fully reset and calibrate your SOC meter, which will drift off over time, but not as badly as with lead acid. Or, I make sure to get to 100% if inclement weather is coming and I don't expect as much solar for a few days.

[Chotu]

I don’t try. But every single day they get filled all the way up.

Thank you, OP, for solving my issue of an unbalanced bank in the other thread.

[hjohnson]

I make sure mine are fully charged before we leave the dock. While in "storage" mode, I let the battery sit at 60%. Day before heading out, I'll log into VRM, remove the limit, and let the system charge up using shore power.

The joys of the Victron system.

[sailorboy1]

well I google searched the question and there doesn"t appear to be an answer agreed on

then again so much of the "info" out there doesn't match how a cruiser uses their batteries at all

[rslifkin]

From a technical perspective, as long as you aren't having issues with cells getting out of balance, I can't see a reason why it matters how often they do or don't get topped off.

[sailorboy1]

I wouldn't know really if they are out of balance

[maine-cruiser]

Originally Posted by hjohnson

I make sure mine are fully charged before we leave the dock. While in "storage" mode, I let the battery sit at 60%. Day before heading out, I'll log into VRM, remove the limit, and let the system charge up using shore power.

The joys of the Victron system.

Where in the VRM system can you set the charge limit?

Thanks,
Bill

[Networker]

Originally Posted by hjohnson

I make sure mine are fully charged before we leave the dock. While in "storage" mode, I let the battery sit at 60%. Day before heading out, I'll log into VRM, remove the limit, and let the system charge up using shore power.

The joys of the Victron system.

From what I understand, you should turn off Storage mode on the Victron charger if using LiFePO4.

[Simi 60]

Ours never get below 30% and rarely get above 80%
But in the 12 mths we have had them we have seen them at 100% so sayeth the BMS 3 times

[hjohnson]

Originally Posted by maine-cruiser

Where in the VRM system can you set the charge limit?

Thanks,
Bill

I log into the Cerbo, and configure a DVCC override, dropping the voltage limit to 13.2V. This translates to roughly 60% SoC. Then, the day before a planned overnight trip, I’ll remote in and remove the override. This lets the inverter/charger bring it back up to 100% and do any balancing that the BMS might want to do.

[hjohnson]

Originally Posted by Networker

From what I understand, you should turn off Storage mode on the Victron charger if using LiFePO4.

It’s Just what I call it, not an official “storage mode” i just tell the system to hold the DC bus at 13.2v rather than where the BMS wants the voltage.

[maine-cruiser]

Thanks. I don't have a Cerbo but do have a raspberry pi running Venus OS. I'll poke around with it to see if I can do it from there.

Bill

[PaulCrawhorn]

From the POV of cell health it is better if they never get even near Full, that reduces longevity nearly as much as getting near Empty.

The ideal is cycling a narrowish capacity band around the midpoint.

Now, if you want your SoC meter to be accurate

or you want to utilise most of the bank's potential capacity

or your balancer only works at high SoC levels

then those factors require you to go there.

But the actual LI cells themselves prefer to stay in the middle ranges for 100% of their lifespan.

If longevity is important to you, define Full and Empty accordingly, buy more capacity than you need, use a balancer that works at any voltage point you like and never mind about extreme SoC accuracy use it as a ballpark measure and use V at rest for protection measures instead.

[wholybee]

Originally Posted by PaulCrawhorn

From the POV of cell health it is better if they never get even near Full, that reduces longevity nearly as much as getting near Empty.

The ideal is cycling a narrowish capacity band around the midpoint.

Now, if you want your SoC meter to be accurate

or you want to utilise most of the bank's potential capacity

or your balancer only works at high SoC levels

then those factors require you to go there.

But the actual LI cells themselves prefer to stay in the middle ranges for 100% of their lifespan.

If longevity is important to you, define Full and Empty accordingly, buy more capacity than you need, use a balancer that works at any voltage point you like and never mind about extreme SoC accuracy use it as a ballpark measure and use V at rest for protection measures instead.

I disagree with this. Higher voltages are bad, mostly in combination with higher heat. And i don't believe lower voltages are bad at all, unless you go below 2.5v. Higher SoC, when not associated with higher voltage, higher heat, and when not stored there but charging is stopped and immediately begun to discharge, is not bad

I am sure we have all read Rod Collins lengthy articles. How many years old are his batteries? 15+, and over 2000 cycles and he still gets full capacity. Its difficult to argue he is doing it wrong. He charges at a lower voltage, but still nearly 100%.(his article is long and rambles, but what i make of it is 3.55Vpc) He discharges to 80% DoD (20% Soc). Personally i think he could go lower SoC but thats the SoC he uses. He discusses the danger of low Soc as a polarity reversal at 0V, which LA will survive, and LFP will not. The main thing, is that his batteries are in a temperature controlled environment.

Also, an active balancer will not balance cells at a lower voltage. You can only balance cells at a higher voltage, in the upper knee. Period. Attempting to balance lower might actually unbalance them. If you want to cycle in the middle of the operating range, do not use active balancers. Turn off all balancing in the BMS, and occasionally charge to 100% and go through a balancing proceedure.

https://marinehowto.com/lifepo4-batteries-on-boats/