LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[daddle]

Originally Posted by noelex 77

Gentlemen it's time to stop the person attacks.

Thanks. Folks, you are not obligated to respond or defend yourself here. Avid readers know the posters here and easily filter the odd trolls. Ignore what you consider to be noise and stay on the very interesting topic.

[Barra]

Originally Posted by mcarling

Sounds good Barra. 400AH of LiFePO4 will give you more usable capacity than 540AH of AGM.

However, I agree with the point above that 600W of solar will be a lot for this size battery bank. Even the 300W you have now is large for this size battery bank.

Yeah it probably does seem pretty high on the surface but its mounted on the hard bimini and sees a fair bit of shade from boom or sails so probably be closer to 400 watts equivalent im expecting.

Still if im wrong the overcharging issue could come into play around midday so decent solar reg will be important

[diugo]

Originally Posted by Barra

mastervolt inverter charger combo which im pretty sure can be set to bulk and maintenance volts ok as per Terry says

Terry's great contributions and good preliminary findings notwithstanding, I would be extremely apprehensive about setting float to 13.8 volts---as I believe it would promote a slow plating of the anode over time.

While the LiFePO4 cathode may be stable, we often lose sight of the fact that the LFP shares the same anode material as all other lithium-ion chemistries, and few (if any) manufacturers recommend trickle charging---the net effect of a high float voltage. The graphite anode can undergo plating through various mechanisms, resulting in permanent loss of capacity and premature aging.

[Hyprdrv]

This string is closing in on 1500 posts. Is there a way someone could create a Sticky up front with drawn conclusions as well as a possible "How to" on the following.
Selection
Balancing
Installation
BMS (Both Monitoring and Management)
Safety
Wiring

It would be a great help.
Steve in Solomons MD

[NahanniV]

I finally seem to be getting somewhere with charging my 4*400AHA cells in parallel (see attached).

My power supply was only able to produce 7A max.

I will bring them up to 3.8V and let them sit for a while.
Then on to doing a load test.

[downunder]

Originally Posted by NahanniV

I finally seem to be getting somewhere with charging my 4*400AHA cells in parallel (see attached).

My power supply was only able to produce 7A max.

I will bring them up to 3.8V and let them sit for a while.
Then on to doing a load test.

What did you do the chart with? Thanks

[ebaugh]

Originally Posted by diugo

Terry's great contributions and good preliminary findings notwithstanding, I would be extremely apprehensive about setting float to 13.8 volts---as I believe it would promote a slow plating of the anode over time.

While the LiFePO4 cathode may be stable, we often lose sight of the fact that the LFP shares the same anode material as all other lithium-ion chemistries, and few (if any) manufacturers recommend trickle charging---the net effect of a high float voltage. The graphite anode can undergo plating through various mechanisms, resulting in permanent loss of capacity and premature aging.

I think that's too high too, but we really don't have the answer to this yet. Just opinions. I keep my float below 13.4V. This will be real important for those in marinas with a constant charge source available. At some point, where no charge occurs and the charger is essentially a power supply for house loads, I don't see a problem. To the battery, its little different than disconnected. But if it's a huge concern you could keep a small traditional battery on-line and turn off the LiFePO4 bank.

[ebaugh]

Originally Posted by Hyprdrv

This string is closing in on 1500 posts. Is there a way someone could create a Sticky up front with drawn conclusions as well as a possible "How to" on the following.
Selection
Balancing
Installation
BMS (Both Monitoring and Management)
Safety
Wiring

It would be a great help.
Steve in Solomons MD

There is a 12-13 page PDF file on our blog site at:

http://www.ebaugh.net

Poke around, you will find it, it is a recent posting. It is not a consensus, it's my opinion on all of the topics you mentioned. Largely reviewed by Terry, but any flaws are mine.

[deckofficer]

Originally Posted by diugo

Terry's great contributions and good preliminary findings notwithstanding, I would be extremely apprehensive about setting float to 13.8 volts---as I believe it would promote a slow plating of the anode over time.

While the LiFePO4 cathode may be stable, we often lose sight of the fact that the LFP shares the same anode material as all other lithium-ion chemistries, and few (if any) manufacturers recommend trickle charging---the net effect of a high float voltage. The graphite anode can undergo plating through various mechanisms, resulting in permanent loss of capacity and premature aging.

Doug,

Can you give a link about the evils of trickle charging? Using my adjustable power supply to balance my cells in parallel is like trickle charging, 3.7 volts @ 2 amps for around 200 hours.

[diugo]

Sorry Bob, my use of the phrase "trickle charging" refers to leaving the batteries at a constant voltage after they are fully charged. It's quite a misnomer for LFP, as actual charge current can fall very close to zero. But even at truly zero charge current, there is still a strong electric field present, under which the intercalated lithium could permanently plate onto the graphite.

Nothing wrong with your low current charging method---as long as you disconnect the charger after 3.7V is reached. (And even at 3.7V, you can safely continue charging until the charge current drops to C/33---but no less.)

Here's one link for ya: Charging Lithium-Ion Batteries

[deckofficer]

PS will go to 0 amps when average of all cells (and I hope each cell) is 3.7 volts.

[mrm]

downunder, once you have data in a tabular form, (almost?) any spreadsheet will offer a way to create graphs, pie charts and whatnot. There is also a very good free program called Gnuplot gnuplot homepage which creates beautiful plots (see their web demo section). I attach an example too.

[Lagoon4us]

Asked our supplier who strongly recommends a BMS for the installation if the BMS cards themselves should be fused and if so what size to prevent any fire from card failure.

His reply has got me considering that the actual containment of the battery pack could/should be lined with non-flammable board, after all we don't need liquid containment as we have on LA's.

Here is his reply:-


Regarding fire caution and prevention, when considering LiFePO4 you are on the quite safe spot.

Fuse on each wire from BMS is not nessesary mainly since even during BMS malfunction where no balancing would happen and batteries would be charged over maximum the fuse wouldn't be able to catch any extreme currents. Basically the charging would continue as before with the side effect of likely damaging the cell due over charge.

The over-charge effects on its own is not fire, actually even direct and extreme abuse of cell/battery like shortcutting and similiar will not directly means fire.

The cell will melt (the case) and will create high temperatures that could set a flameable surroundings to fire indeed. But the most you will get from cell alone is melted case with pressure gas leak through ventile (and smoke caused by the melting). I would rather recommend to put the cells to properly maintaned place, where is no paper or similiar parts around.

When connecting the parts, you should have strong fuse/relay between the battery pack and your load to prevent any issues raising. The fuse in this place must be strong enought to hold standard work currents of the device you power up or its peak currents but it would provide safety measurements towards possible shortcut and other situations of massive current flow.


Cheers

[goboatingnow]

Sorry Bob, my use of the phrase "trickle charging" refers to leaving the batteries at a constant voltage after they are fully charged. It's quite a misnomer for LFP, as actual charge current can fall very close to zero. But even at truly zero charge current, there is still a strong electric field present, under which the intercalated lithium could permanently plate onto the graphite.

Nothing wrong with your low current charging method---as long as you disconnect the charger after 3.7V is reached. (And even at 3.7V, you can safely continue charging until the charge current drops to C/33---but no less.)

CORRECT, and I made this point ( before the trolling), You should not Float charge LIs. the charger should be disconnected from the battery and reconnected at a point where recharging is neccessary.

Constant float charges , even if no current is flowing damages Li.

This is the feedback I have from all the solutions to charging Li

Dave

[deckofficer]

I'm just letting voltage differential determine charging current when the cells are in parallel for balancing. I set the PS at 3.7 volts on a 80~90% DOD cells and it starts out charging at about 4.5 amps. 3 days later as cell voltage is coming up, it now is only putting 1.8 amps into the cells.