Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 02-11-2018, 14:59   #1
Registered User
 
Cpt Pat's Avatar

Join Date: Feb 2012
Location: Half Moon Bay, CA, USA
Boat: 1963 Pearson Ariel, Hull 75
Posts: 898
Accelerated degradation of LiFePO4 batteries when stored fully charged

There's a common belief that storing LiFePO4 (LFP) batteries in a fully charged state is a poor practice. Linked below is a good thesis on factors that degrade the life of LiFePO4 batteries, with a detailed explanation of the chemistry involved.

Here's an excerpt from the abstract (emphasis is mine): Capacity loss in cells stored at high temperature and fully charged conditions resulted in faster degradation rates. Temperature had the most significant role in the degradation of the cell and then the cell’s SOC. Comparing capacity losses between cells stored at the same temperature, but with different SOCs, found that the cells with higher SOC experienced increased rates of degradation in comparison to their fully discharged counterparts. In addition, storage at high SOC and high temperatures promoted such severe losses that the cells in question were unable to recapture capacity that they had lost reversibly.

This calls for a storage regime that is the opposite of lead/acid batteries, which should be stored fully charged to prevent sulfation. It also indicates that simply "dropping in" an LFP to replace a lead/acid battery - without changing the storage regime - will result in degraded life.

I personally never charge my LFP battery above 80% SOC or discharge below 20% SOC, and I store the battery at 20% SOC; based on a combination of terminal voltage measurements and Coulomb counting (counting amp/hours in and out). I charge my battery on shore power just before going out to avoid storing it in a charged state between sails. Coulomb counting is especially important to prevent over charging: at very low charge currents, you can overcharge an LFP battery with a terminal voltage as low as 13.65 volts.

https://uwspace.uwaterloo.ca/bitstre...pdf?sequence=3
__________________

Cpt Pat is offline   Reply With Quote
Old 02-11-2018, 18:52   #2
Registered User

Join Date: Jan 2017
Posts: 12,742
Re: Accelerated degradation of LiFePO4 batteries when stored fully charged

I've never heard anyone claim it wasn't true.

That 80/20 idea is spurious IMO.

My zero SoC is 2.99Vpc, my 100% Full is 3.45Vpc, I do not even hold Absorb, no Float, just "charge to then Stop".

That gives me **over** the rated AH in most cases, never more than a few percent under with a new bank from a quality vendor,

like ​Winston/Thundersky/Voltronix, CALB, GBS, A123 & Sinopoly.

So, if you're getting the promised AH capacity while being so safe & gentle with your bank, why state you're "sacrificing" 40%?


Compared to a Full definition at 3.65Vpc, maybe lose 3-4%

Compared to defining 2.5V as zero, max "loss" is 10%, but you are risking major damage, certainly losing lots of lifetime cycles, so no one should really consider going that low, even for testing purposes.
__________________

john61ct is offline   Reply With Quote
Old 02-11-2018, 19:34   #3
Registered User
 
Cpt Pat's Avatar

Join Date: Feb 2012
Location: Half Moon Bay, CA, USA
Boat: 1963 Pearson Ariel, Hull 75
Posts: 898
Re: Accelerated degradation of LiFePO4 batteries when stored fully charged

Quote:
Originally Posted by john61ct View Post
.

So, if you're getting the promised AH capacity while being so safe & gentle with your bank, why state you're "sacrificing" 40%?
I don't recall ever saying that I'm "sacrificing" anything. I'm getting what I expect from my LFP, while keeping it "off its knees." I have no argument with the rest of your post. Yours sound like reasonably good practices to me. The rest is just semantics.


This may not apply to you, but watch out for charging over 13.65 volts (3.4125 volts per cell) at very low currents, such as you might get from a PV array at day's end. You could risk going over 100% SOC without Coulomb counting (counting amp/hours in and out).


The whole point of my post was to present a good study supporting the belief that storing LFPs at a high SOC can accelerate aging. I believe the thesis is well researched and may be of benefit to some readers. If you read an argumentative tone in my post, it wasn't intended by me.
Cpt Pat is offline   Reply With Quote
Old 02-11-2018, 19:59   #4
Registered User

Join Date: Dec 2009
Location: Australia
Boat: building Roberts Mauritius 43ft
Posts: 1,268
Re: Accelerated degradation of LiFePO4 batteries when stored fully charged

Maybe this is relevant

https://www.cycle9.com/wp-content/up...ery-manual.pdf

If you need to store the battery for long periods, start by fully charging it up, and then
make sure to charge it at least once a month to keep it topped up. These batteries will
discharge themselves a bit during storage, since the BMS draws a small amount of
power to maintain cell balance. If you don't occasionally charge them, one or more cells
may fall below the 2.0V per cell critical threshold, permanently damaging the battery
and voiding the warranty.

coopec43 is online now   Reply With Quote
Old 04-11-2018, 21:22   #5
Registered User

Join Date: Jan 2017
Posts: 12,742
Re: Accelerated degradation of LiFePO4 batteries when stored fully charged

Quote:
Originally Posted by Cpt Pat View Post
I don't recall ever saying that I'm "sacrificing" anything.
Someone tossed out the way they ensure longevity is to only cycle between 20% SoC and 80%. It might be "just semantics" but I hate for newbies to falsely interpret both the top and bottom 20% are being sacrificed from rated AH capacity.

> I have no argument with the rest of your post. Yours sound like reasonably good practices to me.

That's how I know you're a clever fellow 8-)

> This may not apply to you, but watch out for charging over 13.65 volts (3.4125 volts per cell) at very low currents, such as you might get from a PV array at day's end. You could risk going over 100% SOC without Coulomb counting (counting amp/hours in and out).

I can't see that being a problem charging **to** 3.45Vpc and then stopping without any Absorb.

But for me personally one of LFP's biggest advantages is eliminating any dependence on solar.

> If you read an argumentative tone in my post, it wasn't intended by me.

Same here. Getting hard evidence is A Good Thing, even of facts already universally accepted as beyond dispute.
john61ct is offline   Reply With Quote
Old 04-11-2018, 21:27   #6
Registered User

Join Date: Jan 2017
Posts: 12,742
Re: Accelerated degradation of LiFePO4 batteries when stored fully charged

Quote:
Originally Posted by coopec43 View Post
Maybe this is relevant
Not IRL for LFP in general, and in fact harmful advice 99.99% of the time.

As long as the cells are completely isolated, **including from any BMS circuitry**, and temps are cool, self discharge rates are very low.

If someone were to ask "how should I store my LFP bank disconnected for years without anyone looking at them",

IMO the only safe answer would be "don't do that".
__________________

john61ct is offline   Reply With Quote
Reply

Tags
lifepo4

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lifeline AGM's Fully Charged Voltage? frankson Electrical: Batteries, Generators & Solar 61 12-10-2018 13:54
Flashing "Charge light" when batteries fully charged gspeak Electrical: Batteries, Generators & Solar 3 17-06-2014 07:51
Carpeted Trailer / Cradle Pads = Accelerated Osmosis Geminidawn Construction, Maintenance & Refit 2 22-05-2010 07:29
12.5 Volts Fully Charged? Meck Electrical: Batteries, Generators & Solar 7 18-09-2009 09:12

Advertise Here


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 20:19.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×

ShowCase vBulletin Plugins by Drive Thru Online, Inc.