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LTO Lithium Titanate Batteries For Solar? (Read 481 times)
electron
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Re: LTO Lithium Titanate Batteries For Solar?
Reply #1 - Feb 3rd, 2018 at 5:36am
 
If you get the flat pack cells made by Kokam, the tabs/terminals at the top are a very soft aluminum and are long and straight.

For my test pack I used a Leather Punch Tool that you can get at Walmart in the craft section. I think the biggest hole size is 3/16" or .188" on the tool.

I punched two holes to match a metal piece from Home Depot in the cabinet hardware section called "Mending Plates" the 2 in. long ones with two holes are perfect for this, zinc plated, I used 2 plates per terminal.

I used short 10-24 3/8" phillips pan head screws and nuts with lock washers, internal style. Longer ones were put on the end plates for connection to wire lugs.

I had to hold the plate with my thumb, then used a scribe tool inside the holes to make a mark, then used those marks to punch.

While punching I squeezed hard and then gently twisted sideways only slightly back and forth and I could feel when the hole was done. After one hole was done through TWO terminals, I would insert a screw and nut temporarily and check everything else for alignment, then punched the other hole.

I think the punch is better than trying to drill holes.

I had to be SUPER CAREFUL to insulate the terminals and operated on only 2 cells at a time basically. I worked backwards and numbered the cells as I went making sure they are aligned on top of each other for each one, then putting them aside in a safe way so the terminals don't touch anything. 2 cells at a time slowly and carefully, put one aside and move to the next one in order.

If the punch tool ever shorted, these batteries will put out a lot of power really fast and so I was super careful and used cardboard to insulate other terminals and made sure I could concentrate the whole time and not be interrupted. No distractions.

As I added in the screws to finish the stack after all the cells were correctly punched 2 at a time, I also put on a piece of black tubing used for "drip irrigation" with a slice down the length on one half, covering the entire terminal and screws, it just slips on from the side and that insulates the terminals and is cheap. This helps when using tools so I put them on as each connection was finished. I taped the cells together as a stack using some strong packaging tape when done because they will slip around and they are very heavy once assembled. I used them stacked on top of each other, they could probably be used sideways or with the terminals at the top with the proper container.

Well, that's what I did and it worked. I don't think this is something just anyone can do, especially the - impatient in a hurry types. One "24V" 10S stack took probably 2 or 3 hours of total concentration.
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electron
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LTO Lithium Titanate Batteries For Solar?
Feb 3rd, 2018 at 5:03am
 
A Lithium Titanate or Lithium Titanium Oxide battery is a modified Lithium Ion battery that uses Lithium Titanate nanocrystals on the surface of its anode instead of carbon. This gives the anode a surface area of about 100 square meters per gram, compared with 3 square meters per gram for carbon, allowing electrons to enter and leave the anode quickly. This makes fast recharging possible and provides high currents when needed. (from wikipedia)

The fast charging features are not a big deal for solar systems.

But, they perform very well at low temperatures and extreme temperature tolerance from -22 degrees F to +131 F. Most other lithium's will either not perform or quickly degrade if operated in these temperatures .

They are very stable and considered one of , if not the, safest of all lithium's. There is test data showing them charged to TWICE their normal voltages with no thermal runaway , and they continued to function properly.

25+ year shelf life

20,000+ life cycles (charged and discharged TWICE a day would be 27 years!)

LTOs can be stored at 0 volts. There is a test online were they stored them over one year at zero volts and after 1 year there was no loss of capacity so if you have an application were there is a deep discharge or storage without the ability to keep on a charger these will work great. Other lithium's will be permanently ruined if they were to go below there minimum voltages.

Nominal voltage is 2.4v
Max recommended 2.8v
Minimum recommended 1.5v
About 95% of the power is between 2.4v - 1.9v
2.65V is recommended to get a full charge

One manufacturer is Kokam Co. LTD

Some charts:
http://gwl-power.tumblr.com/tagged/LTO
https://www.ev-power.eu/LTO-Tech/

Test videos showing crushing, penetration, overcharge
http://www.scib.jp/en/about/index.htm#con1

Another unusual thing about these cells is that you can overcharge them without damage. Generally, 2.65V is recommended to get a full charge but you can push them to 2.8V without damage. This may work well with some low cost charge controllers that do not have remote battery sense. The older Lead Acid batteries could be overcharged a little without damage and some charge controllers were designed without remote sense for that reason, it didn't matter if the charge controller was reading 15.5V when the battery was really at 14.5V, it would still get a good charge while allowing the high charge cut off setting to be at 15.5V, and if the battery ever actually went to 15.5V eventually, it would not be critically damaged unlike a typical Li-Ion with a hard upper limit of 4.2V per cell. (the remote sense feature is needed due to wire loss during high amp charging, if you want a accurate battery volt reading during charge)

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