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

[neelie]

Mini drift here..

How best to store the four cells for 4 months?

They came from the factory at 2.95V. So I guess this is a good voltage for storage?

Should I connect them in parallel to ensure balance when I unpack them and reconnect in series? Or leave them as 4 individual cells?

[hellosailor]

Zil, I don't think the chemistry or the term "cell" is a problem. Rather, some genius decided to use the oxymoron "prismatic battery cell" which is simply bad grammar, bad YnGlitch, and not a "cell" at all, while others grabbed onto this and probably out of ignorance shortened that to "cell" assuming it as a "prismatic battery's single cell".

It is a battery, not a cell. Call it a "bi-cell" or "di-cell" or something like that, which follows traditional construction to indicate it is two of something rolled up in one, and the problem goes away, without requiring any fuss. Or just call it a "prismatic battery", which it IS. Two cells joined up, is a battery. Regardless of whether they are serial or parallel, as far as I know.

Although I'd bet there's a special word in German for each configuration.<G>

[deckofficer]

Originally Posted by neelie

Mini drift here..

How best to store the four cells for 4 months?

They came from the factory at 2.95V. So I guess this is a good voltage for storage?

Should I connect them in parallel to ensure balance when I unpack them and reconnect in series? Or leave them as 4 individual cells?

I would not store for extended time at 2.95 volts. Make them happy, give them a charge, then store.

[Zil]

HelloSailor, Ja. That's my understanding. I bet it could be a very long word.

[daddle]

Originally Posted by deckofficer

I would not store for extended time at 2.95 volts. Make them happy, give them a charge, then store.

From the research I have seen they are best stored at half charge. The chemistry is at its least reactive at half charge. Posters here have indicated that cells arrive from the supplier at around half charge. This is typical for rechargeable electronic devices too. That's the research. Link posted somewhere above.

There is no health benefit, only negatives, to LFP sitting around at full charge. That is an old LA practice which does not apply here in any way.

[goboatingnow]

Originally Posted by hellosailor

Zil, I don't think the chemistry or the term "cell" is a problem. Rather, some genius decided to use the oxymoron "prismatic battery cell" which is simply bad grammar, bad YnGlitch, and not a "cell" at all, while others grabbed onto this and probably out of ignorance shortened that to "cell" assuming it as a "prismatic battery's single cell".

It is a battery, not a cell. Call it a "bi-cell" or "di-cell" or something like that, which follows traditional construction to indicate it is two of something rolled up in one, and the problem goes away, without requiring any fuss. Or just call it a "prismatic battery", which it IS. Two cells joined up, is a battery. Regardless of whether they are serial or parallel, as far as I know.

Although I'd bet there's a special word in German for each configuration.<G>

I've always treated the entity at the cell nominal voltage as the " cell" irrespective of its internal construction. Hence I see no issue with using the term cell. Many cells are in effect parallel micro cells inside. When we get higher voltages at then the basic cell voltage we tend to use the generic term "battery" , usually meaning cells in series.

Prismatic in this context just means having flat right angled sides , as opposed to cylindrical form factors.

Hence prismatic cell is a completely acceptable terminology to describe the individual units we are dealing with here.

Dave

[roetter]

Spoofing or what?

There have been at least two posts around the 25 March under my name that did not come from me.

This post is NOT from me.
Originally Posted by roetter
This thread is great but hard to weed through a lot of the crap people want to stir up.

I can only hope that this is a database glitch.

[Zil]

That is actually #2489 Rainmaker attached from your post #2447
Agreed it gets confusing. Something similar happened to me a while ago back.

[diugo]

If it puts out ~3.3V it is unequivocally an LFP cell---regardless of the internal construction.

Even though there are multiple foil connections tied to a single terminal, doesn't necessarily mean individual pouches wired in parallel. Foils can have cathode/anode material on both sides---with an electrolyte separator tightly sandwiched in between---making it virtually impossible to replace any defective "subcells".

[Zil]

Will it ever end

[diugo]

I am pleased to report a dramatic reduction in my LFP internal resistance. When I acquired the cells in January, battery sag under 60A load was a whopping 0.5V, suggesting a resistance in excess of 2 millohms per cell.

Lately, however, I have been noticing voltage consistently staying above 13V, sometimes even 13.1V---which means resistance has fallen to only 0.8 millohm per cell. This is much more in line with the 0.4 millohm advertised by Winston for their 260Ah cells.

Average cell temperature has increased from 60F to 75F thanks to the warmer weather. Would you think 15F would make such a big difference? Or the fact the cells now have 25 charge cycles behind them?

[Maine Sail]

Fusing update from a few pages back. A member, Ebaugh, took me up on my offer and graciously sent me 10 ANL (inexpensive car stereo quality) fuses to have fun blowing. Below is basically what I sent to him last night (I added a bit more detail for here).. The bank was four Winston 400Ah cells in a 12V nominal bank configuration. This was done more for curiosity about "AIC" and fuse failing "safely" under the high currents of LFP banks than anything else.


"Sorry for the delay. I blew 8 of those fuses tonight.

Three were blown in a dead short situation and five were in a "load" situation using my 500A carbon pile load.

Short:
Two of the three fuses failed unsafely and blew the window out of the fuse. These pops were LOUD, like fire cracker loud.. None failed to "open" and none damaged the plastic case, though I did not "closely" examine them.. In a dead short they all blew at below 75A as measured with a Fluke 376 meter using the "inrush" capture feature. In contrast I blew a 60A Blue Sea/Bussmann ANL and it failed at 136.5A which is more than double its rating into a dead short (this is to be expected). A 300A Blue Sea MRBF over loaded "OL" my 1000A Fluke meter. The third cheap ANL fuse did not blow the window, that I can tell visually without my reading glasses, but I am certain based on the other two that it would meet "ignition protection" requirements.

Load:
Using my carbon pile load tester I had these 100A fuses blowing at 200A instantly with no delay, just POP.. The "pops" under a 200A load were barely audible and not anywhere near the viciousness of the fire cracker sound of a dead short. I found this interesting.

I suspect blowing instantly at 200A for a 100A fuse means these are probably not true ANL fuses and are likely closer to an ANN fuse. This makes them not well suited to motor starting loads like an engine, windlass or thruster where a Cooper Bussmann/Blue Sea ANL preforms extremely well... A Blue Sea fuse can handle 200% for about 5-8 seconds and not pop instantly, and they do.

In short the "car stereo grade" ANL's are far from the quality of Blue Sea/Cooper Bussmann ANL. While they do tend to fail "safely" (n=5) in a "load" blow, they do NOT fail safely in a dead short (n=3).

None of these ANL's failed to open but two out of three in a dead short failed unsafely blowing the window open. The Blue Sea 60A ANL failed completely safely.

I did capture some video and will try to figure out how to edit the blows together if I can...

-RC Collins"

[Lagoon4us]

Fresh from CHINA to Croatia, arrived today serial numbers Y11692 Y11691 Y11690 and Y116989. Build date is 8th March 2013....

We sail for Corfu on Saturday and there i'll start charging the cells. They are 400amp.

[Lagoon4us]

All were shipped at 3.30 volts precisely....

[hellosailor]

Maine, when you say three of them blew unsafely, what's unsafe about how they blew? Body stayed intact, what's left that would cause a safety problem?