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

[newhaul]

Originally Posted by john61ct

The key is maintaining the constant current all the way from 100% Full voltage down to 0%.

Rig something like a dimmer switch, watch your ammeter.
.

stop thinking lead based batteries.
Any relatively high load and a columb counter along with an a meter to monitor for lvc. Is all you need to test Lfp.

[john61ct]

Originally Posted by mike_kelly

If the bags are punctured they catch on fire.

Not LFP though, again, completely different level of safety from the other LI chemistries.

And LiPo is just a packaging technique to save weight, that name does not specify the chemistry.

Most are LCO these days.

[newhaul]

Originally Posted by mike_kelly

Lithium burns when exposed to air. All li-po chemistry are in vacuum sealed bags. IF they are over charged and produce gas, that is why they "puff". If the bags are punctured they catch on fire.

well not necessarily. Lfp is a different chemistry no more chance of fire from it than from Fla

[john61ct]

Originally Posted by mike_kelly

I would think this depends on how fast you want the battery equalized.

That last term has a specific high-voltage meaning in deep-cycling storage world from lead, best for clarity to just use "balancing" for this functionality.

The mainstream approach is always-on "live" balancing, using the BMS but only activated at the end of charge cycle at top level voltages.

> you can't have the battery charging with a balancer active

That makes no sense, that's the only time most systems are balancing. The ones that let you balance at say 3.4xVpc are vanishingly rare, most require holding charge much higher, and since they're very slow, for a long time.

That is normal in this world. In fact you don't need to explicitly disable balancing, most BMS you just stop charging before you hit their threshold.

> Maybe LiFePo4 are very tolerant but I can't get my head around charging and then leaving a bunch of balancers turned on continuously to equalize. You are never going to get a full charge that way.

That's RC world stuff. Again, pushing the last couple minutes' range / runtime is not even a valid goal.

The balancing is only taking place while charging, at the very end, not after charging stops.

And House storage cells aren't getting that unbalanced anyway, returning to "perfect" every charge cycle does not take long even at low current.

And in fact they do get to Full.


> So does anybody make a system with the balancers on the batteries networked to a charger that coordinates with the balancers?

No, and not needed. The balancers just bleed or shunt the higher cells while waiting for the lower ones to catch up, charge buss keeps pumping the current in oblivious.

The Deligreen style are an exception, but very rarely used in these circles, more of a propulsion concept, and as I said, for me would not want hooked up all the time, just adds more points of failure afaic.

[john61ct]

Originally Posted by newhaul

Any relatively high load and a columb counter along with an a meter to monitor for lvc. Is all you need to test Lfp.

Yes, can be done that way if precision is not required.

[newhaul]

Originally Posted by john61ct

Yes, can be done that way if precision is not required.

john you don't need accuracy wrt capacity to the 10th of an ah .

Try testing your own bank and let me know what the difference was between the two tests.

That is when you actually buy a bank of Lfp to run the tests on.

[john61ct]

Yes no precision is required for a rough yes/no decision.

If the goal is to detect loss of a given bank's capacity over the years, and a well-treated bank seems to be maintaining exactly the same SoH using a rough measure,

is only losing a small fraction of a percent per year,

that is when more precision is required.

Even more so

if testing the effects on longevity of different cycling patterns, when you want data from actual real-time cycling at low C rates.

Otherwise will take many years before coming to any definitive conclusions.

[john61ct]

Originally Posted by mike_kelly

So does anybody make a system with the balancers on the batteries networked to a charger that coordinates with the balancers?

From the propulsion world, ebikes scooters skateboards etc, some BMS to check out.

https://endless-sphere.com/forums/vi...67051#p1467051

If anyone has experience with any of the better ones listed here, feedback would be appreciated.

[newhaul]

Originally Posted by john61ct

Yes no precision is required for a rough yes/no decision.

If the goal is to detect loss of a given bank's capacity over the years, and a well-treated bank seems to be maintaining exactly the same SoH using a rough measure,

is only losing a small fraction of a percent per year,

that is when more precision is required.

Even more so

if testing the effects on longevity of different cycling patterns, when you want data from actual real-time cycling at low C rates.

Otherwise will take many years before coming to any definitive conclusions.

as has been discussed by those of us actually using them with several thousand cycles on some nobody has yet noticed and appreciable reduction in capacity .
My bank only a year old and a mere 200 cycles is still factory over clocked. I get about 110ah out of my 100ah bank. I fully expect 10k cycles life out of them . So realistically unless you are building them to sell there is imo no need for precision to the 1/10th of an ah capacity. Don't discharge below approx 20% dod and charge to between 80%and 90% you can expect many thousands of cycles .

Get a bank john and run some of these real world tests you will come to realise the white paper is just an estimate.

[john61ct]

All you're saying is that you do not have a need / desire to load test with precision. That is fine, no worries. . .

There is no harm in having the information out there, discussing other options for those that do want that. Live and let live dude

[CatNewBee]

Originally Posted by mike_kelly

CatNewBee

"You do not need high current balancers. 1..3 A are sufficient even for 1000Ah cells. The balancer have all the time t9 keep the cells in sync."


I would think this depends on how fast you want the battery equalized.



So does anybody make a system with the balancers on the batteries networked to a charger that coordinates with the balancers? Otherwise you would have to control it manually since you can't have the battery charging with a balancer active.


Maybe LiFePo4 are very tolerant but I can't get my head around charging and then leaving a bunch of balancers turned on continuously to equalize. You are never going to get a full charge that way.



Anyone using Hall sensors instead of shunts?

This is exactly how balancers work. While charging they either burn some energy on one cell to slow it down. Assume the charger delivers 10A, all cells are charged with 10A, while the fuller cell is charged by 8A, because the balancer burns 2A at the same time.

The balancers kick in at a programmed voltage, e.g at 3.55V, the cells reach this voltage only when charged, full cells with no charge currentbreside at lower cell voltages around 3.4V.

[newhaul]

Originally Posted by john61ct

All you're saying is that you do not have a need / desire to load test with precision. That is fine, no worries. . .

There is no harm in having the information out there, discussing other options for those that do want that. Live and let live dude

your correct about having other options but you would carry more weight here if you actually were using Lfp for a house bank like the title of the thread implies .

[mike_kelly]

Originally Posted by CatNewBee

This is exactly how balancers work. While charging they either burn some energy on one cell to slow it down. Assume the charger delivers 10A, all cells are charged with 10A, while the fuller cell is charged by 8A, because the balancer burns 2A at the same time.

The balancers kick in at a programmed voltage, e.g at 3.55V, the cells reach this voltage only when charged, full cells with no charge currentbreside at lower cell voltages around 3.4V.

Yours may work that way and if so it would be very inefficient. Mine charge, balance by transferring charge and then charge again.

[Checkswrecks]

To be upfront, I'm an accident investigator and have been looking at various battery systems for a long time, with a focus on various lithiums since 2013. Since I am still working cases (retire in 3 months) I'm not going to name any companies. I don't have lithium on my Ericson 32 at this point, mostly because I'm currently using those dollars to refit the rest of the boat while the FLA are still functional.

Mike Kelly - Lithium in the terms of this thread only have lithium ions to move charged electrons between anode and cathode. These do not contain lithium metal, so a lithium fire is not a factor. These also do not contain cobalt, which is much more efficient but would increase flammability. (Not directly due to the cobalt, but from the mixtures which cobalt is part of. Example: Tesla cars) The potentially flammable part of the batteries under discussion is the electrolyte and possibly some plastic.

A little inflating/puffing of cells is normal charge/discharge but beyond that it's an electrolyte breakdown process which deposits the lithium ions and massively reduces the charge capability of the cell. The gas is mostly CO2, O, and some light petroleums so it's usually flammable but not always. The damage will also reduce the resistance across a cell due to the lithium deposition, so after a cell starts to swell the charge and discharge profile is no longer the same as the other cells in a pack. That initial one can quickly degrade the additional cells.

With LiFePo4 and as long as you watch your max and min charging limits, the risk is more of killing your investment than of starting a fire. Newhaul's 20%-80% SOC or even John61ct's 12%-90% go a long way toward keeping the investment in good shape.

A BMS which can monitor and balance at the cell level is best by far. If not equipped with that level of BMS, then restacking the cells periodically because the end cells tend to age faster.



Cat - There are some BMS which do not regulate by "burn some energy" with shunts, resistance and heat, but work thru PWM for each cell. Much more efficient. Probably too expensive for the retail crowd but I've not looked into who is selling what.

[john61ct]

Originally Posted by mike_kelly

Mine charge, balance by transferring charge and then charge again.

Sorry but your what? Could you link to them?