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

[daddle]

As explained in the research paper posted about a week ago, it is not the overcharging, it is that the chemistry has a longer life at medium charge levels. The idea was to only charge the battery only enough to provide the power for the next discharge period.

So if you are in a cruising model where you are periodically running a generator to charge the batteries it would be best (from a cell health perspective) to let the state of charge fall to some lower level before recharging. Say 30%. And then not bother charging all the way to the top either. Same if you are imprisoned in a slip with shore power.

In an solar charging scenario where the solar conditions are variable I would tend to keep the charge level higher, but probably avoid the highest levels unless I knew bad charging conditions were imminent.

I would charge fully while offshore in a scenario where I was to save fuel, only sailing.

Helps to give up your beliefs from the painful years of living with LA chemistry.

[bill good]

diugo, HSF33 I am using them. Two points (1) you need a heat sink & fan to get the stated 80A. ok to expect 25A without. (2) there is a diode across the MOSFET which will pass current in the reverse.

[T1 Terry]

Wow, what was in the water over there :lol:
The reason for banding the cells is to prevent the plastic cases from bulging, they will bulge simply sitting on the shelf in warm to hot weather, we have warm to hot summers over here. When the cells bulge the plates in each pouch can move away from each other, there is no sea of electrolyte floating around in there, the pouches are evacuated and then the electrolyte allowed to draw itself in, it's virtually all absorbed into the material on the plates, bugger all extra there. If the plates separate, there is no contact of the electrolyte between the two plates (there is a micro thin separator between them) without electrolyte contact between the two plate there can be no ion exchange, capacity is lost, compress the cases so the plates and electrolyte is back in contact and the capacity returns.
Simply put, if you don't band them you will progressively loose capacity as they bulge, and they will bulge without a shadow of a doubt.

As far as mini cycling, my cells do it for around 6 hrs a day, they have been in service 24/7 for 2 yrs now, very early days for lithium ferrous batteries, but there are no signs of any problems. I think the issue with mini cycling is with people who don't understand that the battery is made up of individual cells, it's the voltage of those that must be monitored, the combined pack voltage will look after itself. Don't charge the cells past 3.6v, don't discharge them below 2.8v, and you have them for a very long time.
If you accidentally take them over 4v, say 4.2v, they will take longer between reaching the 3.6v and holding better than 3.5v, that absorption stage gets longer, the last part of the charge must be much slower. Discharges greater than 1C will result in voltage sag, the internal resistance has increased, probably a bad contact where the tabs bolt to the terminal blocks. Take the cells up to 4.6v or high and they are stuffed, the heat is like an oven, the cells develop bulges anywhere there is room for them to bulge. They don't just die, but they won't hold the 3.4v of fully charged, it gradually self discharges internally over days to weeks.
When I get a chance, I'll cut one of these tortured babies open and tell you what I find, not a happy camper, but accidents happen. At least it was only $600 worth of cells, not the whole pack.

T1 Terry

[ColdEH]

Thanks for the insight Terry. So it will be banding all the way , sorry to hear you have a few dead ones Ouch.

Regards

[deckofficer]

Good post Terry. You just have tortured cells, not any dying?

[mbianka]

Originally Posted by hellosailor

Heck, folks who make integrated circuits know that they're damaged by cosmic rays all the time. IBM used to say that the average server took four memory failures from cosmic rays every year. So, server, battery, same size box, but the battery is way up there and exposed to more radiation...Has anyone tried bombarding the battery with ionizing radiation, to see if that can cause a meltdown? Not that I've heard mentioned. A simple environmental factor, that isn't replicated on ground tests.

Good point.
Your post reminded me that I remember a number of years ago Sony's Broadcast Division stopped shipping there high end Broadcast TV cameras by air because of cosmic radiation. It was found because the cosmic rays where not filtered as much by the atmosphere at 30,000 feet compared to sea level their cameras occasionally arrived with pinholes in the camera's imaging CCD chips.

[mbianka]

Originally Posted by deckofficer

Capt Mike,

As I've said before, you and LiFePO4 are a good match. Electric propulsion at 48 volts, combined with a 48 volt inverter would be sweet. Your range without firing up the Honda would be at least 4 times what it is now, not to mention using a induction hot plate for cooking.

Deckofficer:

You know I want this technology to succeed and hope to put it in my boat when it comes time to replace my 48 volt AGM bank. I'm just waiting for you guys to get the charging issues down to where I can plug and play. I also don't want to spend a lot of time being a nurse maid to the batteries either. Because if you are doing it with 12 volt packs it will be a lot more time consuming with my 48 volt one from what I'm reading so far. Just sayin'

[deckofficer]

Capt. Mike,

My feeling is they are ready for prime time. Just hook up a cell logger, set your charge profiles on solar, engine alternator, and charger's regulators and your done. But I'm with you, get all the life out of your AGMs, it would be wasteful otherwise.

[T1 Terry]

Originally Posted by deckofficer

Good post Terry. You just have tortured cells, not any dying?

2 of the 4 are dying, the other 2 are tortured, the centre 2 in a pack of 4 suffered the worst, heat is the killer, over charging creates the heat. I thought I had turned the charger off when I walked away from the cells as guests had arrived, as I was personally monitoring them, I didn't have a cell logger or alarm attached. It was 4 cells in parallel, doing the initial 4v conditioning charge, a switch mode 12v charger capable of 40 amps. when i realised there was a problem I immediately grabbed the charger leads off the battery, grabbed the multimeter, they read 4.65v at that stage, hot as, undid the terminal bolts with the battery drill and 13mm socket, the terminal bolts burnt my fingers lifting them off, that much heat. The pressure buckled 3mm x 50mm strapping that made up the battery cradle, actually tore a 6mm threaded stud from where it was welded into the strap, this was the noise that alerted me there was a problem.
Mistakes happen, the gassing wasn't visible but the smell was a definite, nothing exploded, no flames or fire, except $600 out of the wallet going up in smoke, it wouldn't have hurt as bad if they hadn't been brand new cells and the last in the country for a while... possibly quite a while with Winston going to the wall.
Wonder if he will open up as another entity?

T1 Terry

[deckofficer]

That hurts Terry! For the cost of $600, you are the forum expert on what happens when these cells are over charged, and with you being candid, you have made all of us aware that over charging is a big no-no. Thank you for sharing.

[durundal]

Can you post any photos Terry? I am curious to see how the strapping held up.

[T1 Terry]

Unfortunately it doesn't appear that I took any photos while the cells were in the battery cradle to show how much it was buckled, this photo sort of shows a bit, you can see how the ends have been spread and the rear steel straps are bent compared to the angle iron base. The cells themselves actually swelled that much the ribs near flattened, and they have love handles now :lol: It's a bit hard to see, but the bottoms and tops are also ballooned, yet the cases didn't rupture anywhere.

[Lagoon4us]

That damage look's like pure heat has put the case into a quite soft state.

Steel straps are not the best way to give some structural strength to the pack of cells, a containment box with some ribs in the appropriate mid areas, on the outside, would be smarter.

But if you stopped bulging of the faces wouldn't the expanding energy go upwards pushing the top of the cell out?

Or does the venting cap assist?

[Lagoon4us]

Originally Posted by T1 Terry

2 of the 4 are dying, the other 2 are tortured, the centre 2 in a pack of 4 suffered the worst, heat is the killer, over charging creates the heat. I thought I had turned the charger off when I walked away from the cells as guests had arrived, as I was personally monitoring them, I didn't have a cell logger or alarm attached. It was 4 cells in parallel, doing the initial 4v conditioning charge, a switch mode 12v charger capable of 40 amps. when i realised there was a problem I immediately grabbed the charger leads off the battery, grabbed the multimeter, they read 4.65v at that stage, hot as, undid the terminal bolts with the battery drill and 13mm socket, the terminal bolts burnt my fingers lifting them off, that much heat. The pressure buckled 3mm x 50mm strapping that made up the battery cradle, actually tore a 6mm threaded stud from where it was welded into the strap, this was the noise that alerted me there was a problem.
Mistakes happen, the gassing wasn't visible but the smell was a definite, nothing exploded, no flames or fire, except $600 out of the wallet going up in smoke, it wouldn't have hurt as bad if they hadn't been brand new cells and the last in the country for a while... possibly quite a while with Winston going to the wall.
Wonder if he will open up as another entity?

T1 Terry

Terry i'm buying mine direct from China

ES-Keith Lau <keith-lau@everspring.net>

Keith Lau is his name.

[bill good]

T1 congrads you have done a B1!! Someone will I am sure post their latest pictures of the new fire proof containment box & externals. I am guilty of killing 2 small headways @ $28 each but suspect loss of performance in the other cells. Will test at a later date. It will be of interest to weigh them to see how much has been expelled.