Lithium facts in practice

[nut17]

I could not resist the temptation and got a little carried away in a bidding war on Trademe - winning the auction on this 400 AH LiFePO4 battery bank. I paid NZ$855.00


12V 400AH LiFePo4 battery bank and 40A MPPT charge controller, in good condition. Perfect for an entry-level off grid solar installation. Controller and batteries are already wired and packaged in a sturdy wooden box. Just hook up your panels and away you go. Also includes 300W inverter for powering small loads.

THE BATTERIES:
16x HiPower 3.2V 100AH cells, connected as 4S4P to make 12V 400AH. These cells were manufactured in 2010 and used for a research project, then placed in storage for years unused. Although they are old and some show signs of swelling, they have hardly been used and have done maybe 10 cycles in their entire life. These cells are rated for 2000 cycles so there should be plenty of life left in them. All cells have been stored balanced, and currently sit at 3.29V. Will be supplied with 11x charge balance boards (4 shown in pictures).

Battery datasheet here:
http://www.litrade.de/pub/Hipowerdifferent.pdf

THE CHARGE CONTROLLER:
Tracer 4210RN MPPT solar charge controller. Supports 12V or 24V batteries. 40A charge current, 20A discharge current. 100V max PV input. Comes with MT-5 remote monitoring display, and all instruction manuals. With a 24V battery (just re-wire the cells!) you can run 1000W of PV into this controller, or 500W with the current 12V setup.

[BruceS]

Got a good buy there I think but might pay to put some decent sized links on it before you use it in anger.
May be pull it all out & charge each cell up as per T1's advice & reassemble again. At least you'll know it's good to go?

[T1 Terry]

I think you will need to compress the cells and add end plates and stainless straps. "The cells show some signs of swelling" means the wooden box did not hold the cells compressed enough allowing them to swell. When they swell there is more room inside the cell case and this allows the plates to separate and there is not enough electrolyte in there to keep both plates flooded between them to allow an electron flow through the separator material ....... basically they loos capacity. Once you compress them back together, most of the lost capacity returns, but you might have to remove the vent caps to allow the built up gas to escape. Best to do this when it's really cold, the electrolyte will vaporise at around 15*C and once it's gone you can't get any to replace it.

T1 Terry

[nut17]

Thanks Bruce and Terry. The plan is to re configure them into two 200 AH packs. I have someone interested in one already. I will use alloy end plates and threaded rods to provide compression cases and make up new connection straps using flattened copper tube. Subject to successful capacity tests I am hoping to get around $850 for each 200 AH pack.

Cheers
Chris

[Grandad]

Loved your description of a possible future Terry. You obviously try to keep yourself up to date in these matters.
And, that's the first time I'd heard a simple explanation of 'why' the cells need to be held so securely, Thank you

Chris, is it safe to assume shipping to Australia of a pack is out of the question?

Jim

[T1 Terry]

Loved your description of a possible future Terry. You obviously try to keep yourself up to date in these matters.
And, that's the first time I'd heard a simple explanation of 'why' the cells need to be held so securely, Thank you

Chris, is it safe to assume shipping to Australia of a pack is out of the question?

Jim

There is an insane shipping restriction that arose from the aircraft battery fires a while back. It is in reality just a method of increasing revenue, but there is a whole wad of dangerous goods paperwork involved in moving lithium battery cells and a complete ban on moving any assembled as batteries. Somehow Evilbay has worked out a way around this, maybe because the batteries sold there are inside black plastic cases and so how that makes them safer
As a result, it is very difficult to ship lithium batteries cost effectively and in a timely manner, unless you tell fibs, a method one company that resells lithium batteries appears to do.
So, if you can find a shipping company that will actually move them from NZ to a location close to you at a price you can afford, then it would be possible

T1 Terry

[Grandad]

I thought that might be the case. Thanks Terry.

[nut17]

Your price on new cells is substantially cheaper in Australia than we suffer here in Kiwiland Jim. It will be another couple of weeks before I get my hands on these cells and it could well be another month after that before I have them tested and ready to sell on. I have spent some time investigating importing some cells from China, but the risk in all cases seemed to outweigh the potential savings. As Terry said, there seems to be total paranoia about the unfounded potential risk with shipping of lithium cells.

Cheers
Chris

[native pepper]

I think you will need to compress the cells and add end plates and stainless straps. "The cells show some signs of swelling" means the wooden box did not hold the cells compressed enough allowing them to swell. When they swell there is more room inside the cell case and this allows the plates to separate and there is not enough electrolyte in there to keep both plates flooded between them to allow an electron flow through the separator material ....... basically they loos capacity. Once you compress them back together, most of the lost capacity returns, but you might have to remove the vent caps to allow the built up gas to escape. Best to do this when it's really cold, the electrolyte will vaporise at around 15*C and once it's gone you can't get any to replace it.

T1 Terry

Do you reckon all lifepo4 cells swell during their life, my house and bus are over 10 years old and portable getting on for 12 years, none have swelled at all and they are not packed into their containers, you can put a finger between the container and cells. Could it be the DOD and SOC parameters have an influence in swelling, as I've mentioned, mine never go over 13.8v settled (3.45v per cell), and so far have never gone below 13v (3.25v per cell), yet they are set to go down to 12v (3v per cell). Or are you referring to cells housed in plastic.

Could be wrong but most of the sites I've read seem to claim they can be charged to 14.4v (3.6v per cell) and discharged to 11.8v (2.95V per cell) in a 12v pack. Sadly the tech stuff is beyond my understanding so not sure, just using the parameters my mate used and they seem to work pretty well.

[T1 Terry]

Yes NP, the plastic case cells. They will even bulge sitting on the shelf unused, but they certainly bulge during use. Maybe the aluminium cased cells are better as far as bulging, but the stray voltage and capacitance between the cell aluminium cases causes problems all of its own. Some come with a plastic cradle around them to hold them apart, this causes issues of its own due to size restrictions. I've seen them in EV's with that plastic BBQ cooking sheet between them to act as an insulator and that seems to work to get around the stray capacitance test an EV is subject to when being engineered.

T1 Terry