LiFePo4 small battery - anyone tried one?

[GHA]

2,000 cycles to fully discharged for the little one! Should last forever with cycling less. Can't wait to do some testing on it, little lead acid one on charge at the moment, capacity test on that would be interesting, if rather time consuming.

 

[Refueler]

I still reckon a trip to local breakers / car scrap yard is worth it ...

I've used 2nd hand car batterys for donkeys years ... average life I've got from each 5yrs .... at a cost that is just peanuts.

Just because its from a scrap yard does not mean its no good ... remember most come from cars that have been accidents and written of. The battery was fine ... and the yards usually have load testers to weed out the rubbish ones.

Unfortunately over here in Latvia - not same availability as I had in UK.

 

[Poey50]

Just to clear up something that seems to be creeping in ...

LiFePo is max charged at 3.6V per cell. This is a fixed figure regardless of capacity.

To charge to this requires a slight over-voltage of 3.65V per cell. If you charge at 3.4V as per a previous post - the LiFe will never reach full charge and in fact will be barely over nominal level of 3.3V.

It's worth reading this: LiFePO4 Batteries On Boats

He writes, for example, "If the constant voltage stage of the charger is held long enough an LFP cell can be fully charged at voltages as low as 3.42VPC."

HIs overall point is that all three factors - of charging rate, target charge voltage, and duration of charge - have to be considered together for LFP batteries. My main point is not (simply) to argue with you but to caution anyone against using lead acid charging systems with so called 'drop-in' LFPs without considering how different the charging needs of LFP batteries are.

 

[GHA]

It's worth reading this: LiFePO4 Batteries On Boats

He writes, for example, "If the constant voltage stage of the charger is held long enough an LFP cell can be fully charged at voltages as low as 3.42VPC."

HIs overall point is that all three factors - of charging rate, target charge voltage, and duration of charge - have to be considered together for LFP batteries. My main point is not (simply) to argue with you but to caution anyone against using lead acid charging systems with so called 'drop-in' LFPs without considering how different the charging needs of LFP batteries are.

Looking at test data seems very little difference to state of charge between charging at 3.4v - 4.2v but massive difference between 3.3v - 3.4v.

 

[Poey50]

Just to underline the point on differences. This from the excellent Nordkyn Design site.

Benefits and challenges with using lithium batteries on board

Lead-Acid Batteries	Lithium Batteries
Must be kept fully charged as much as possible	Deteriorate if left fully charged and must generally be kept in a partial state of charge
Deteriorate quickly if left in a partial state of charge	Can be stored for years in a partial state of charge with little or no adverse effects
Are kept balanced and topped up by trickle-charging and maintaining an elevated floating voltage	Are quickly and irreversibly damaged by trickle-charging
Can be equalised by controlled overcharging	Are destroyed by overcharging
Can be recovered after an excessive discharge	Are destroyed by excessive discharge
Require temperature compensation for charging	Are quickly damaged by charge temperature compensation schemes
Require higher voltage to charge in low temperatures	Can be damaged if charged at very low temperatures
Can be charged continuously if the voltage is not excessive	Must use charge termination once full
Are reasonably immune to elevated ambient temperatures	Age and degrade much more rapidly at higher temperatures

 

[Refueler]

Marinehowto does NOT say he reaches full charge at 3.4VPC ...... what he says is that because Lithium based deliver a relatively flat voltage line until near discharged - he does not need to charge to higher than 3.4VPC and then claims that charging to full 3.65V 100% SoC can be detrimental ... (I agree with that because LiFe is designed for 3.6V not 3.65V)

Well ... a) He admits that Lithium batterys are relatively new to him and they conducted tests, but his main info given is based in his use of them, b) millions of RC hobbyists are using LiFe batterys and charging to 100 SoC and getting years use out of them and in majority of cases pushing them hard with high discharge loads etc.

RC Hobbyists invest a lot of hard earned money and effort into their models and they would never commit such investment in the air with part charged batterys ... if their battery dies on them - that's a crash ... they cannot just float around ...

Simply put : LiFe cells are 3.6V at 100% SoC .... it is impossible for any charger set at 3.4V to charge to full 3.6V level. EVERY charger regardless of format it is charging HAS to have a slightly higher voltage than the battery that is resisting the charge. It makes no difference CV or CC mode ... You cannot change physical fact.

 

[Poey50]

Marinehowto does NOT say he reaches full charge at 3.4VPC ...... etc

Yes he does, but thanks for playing. I'm out, but I suggest anyone interested reads-up for themselves

 

[Richard10002]

Before using them, I charged each of my 4 Valence batteries using 14.6V, (3.65V per cell).

Once they reached the voltage, and the Amps dropped to C/20, (7A or so), I considered them full, and terminated the charge.

Apropos of nothing: Over a relatively short period, they all fell to 13.4V, (3.35V per cell), and settled there until I started using them. It seems that this is normal for the Valence... so they reach 13.6V, (14.4V for a 4 cell battery), but they dont settle there.

 

[Refueler]

Just to show that some do NOT read the very articles they link to ....

1. Marinehowto states clearly LiFe voltages :

"4S just means four 3.2V cells in series to make a 12V nominal pack. The pack/bank is really closer to a 13.3V pack as the resting & nominally loaded cruising voltage of these cells is around 13.2V – 13.35V. "

A little bit of maths shows that 3.34V per cell NOMINAL ...... Nominal is NOT full charge,

2. Marinehowto states clearly a charge voltage of 3.6V - showing he is well aware of the full charge voltage requirement :

" With LFP the current limiting or acceptance taper is very, very short in duration, even at relatively low 12V nominal pack charging voltages of 13.8V – 14.0V (3.45VPC to 3.5VPC) this duration can be as short as 10-30 minutes depending upon charge rate. If you increase the voltage of the pack towards 3.6VPC the CV duration almost entirely vanishes. "

3. Marinehowto even talks about his own boat system ... which he only maintains to 13.8V :

"On my own boat I charge the 400Ah LFP bank at approx 145A to 13.8V and the current taper lasts only 30-35 minutes. Compare that to hours and hours of current limited charging using a 145A charge source on 400Ah of lead acid batteries. With a small charge current source, like a small PV system or wind, you can hit 99%+ SOC before the constant voltage (CV) stage is attained or before any current limiting can even occur. This means a 100% acceptance rate all the way to 99% + SOC. My 400Ah bank literally has to be chock full before the solar array can even get it to 13.8V. These batteries can take immense current, and charge extremely fast, but really tend to do extremely well with .3C to .5C in charge current. "

I could go on pasting ... so I would suggest to 'Sadler' - if you want to use a site then read it fully.

As regards Lithium batterys ... there are actual manufacturers and Specialist online sites that describe them far better.

I applaud Marinehowto and his testing .. he is obviously FROM the text he's written - using battery packs designed to replace Lead Acid and with suitable setup able to live with marine BMS ... BUT NOTE - he also strongly suggests NOT to DIY with these batterys.

I will say it again :

LiFePo batterys are full charged at 3.6V per cell. They are in nominal float state at 3.3 - 3.45V per cell. That is fact.