Possible Group Buy - Check Interest - Lithium Titanate cells

Discussion in 'Hobby Engineering' started by rainwulf, Jul 15, 2018.

  1. vk2fro

    vk2fro Member

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    has anyone tried the GTK LTO batteries all over AliExpress? They come in capacities ranging from 25aH to 40aH, voltages, weight and stupidly high cycle count seem to fit the LTO specs, obviously the more you buy, the less they cost per piece.

    for example, you can get 20 of the things for around $1200 (30Ah). Bear in mind the shipping is free, others had to pay oodles for shipping just a few of these. if you factor that in, lets assume I chose the $1302 20 piece option @ 40Ah, with a cost of $65 per cell, shipped via UPS express saver (they're not known to be a cheap courier), you'll get them in 10-20 days. Another merchant wants $175 odd to ship 6 of them. So 175x3 (18 cells, close enough to 20) equates to $525. So the cells are really around the ballpark of $37 a cell or there abouts.

    I'd be willing to try a 6 pack of them and test them out for the forum, being at around $450 landed a set of 6 (still gotta factor in that stupidly high shipping which has been built into the per piece price), one could build a battery slowly, depending on what capacity they want, and at what volage. If they work out, I'll get the 20 cell lot and build up a 48v battery from there.

    I already have some heavy 0 cables with terminals on them which I can temporarily wire a 12V pack together, and nice battery terminal covers, which means all I need to do is make a wine rack type set of holders, for which I already have the mdf and a set of hole saws.

    Do you guys think they are reasonably priced, considering the shipping cost is built into the per piece price? Could lead to a less painful way of getting these things instead of haggling with vendors and stuff.

    Link to 20 piece listing: https://www.aliexpress.com/item/20p...0d-486c-a89c-1ac675037994&transAbTest=ae803_3

    Link to 6 piece listing ($65 DHL shipping): https://www.aliexpress.com/item/6pc...0d-486c-a89c-1ac675037994&transAbTest=ae803_3
     
    Last edited: May 13, 2019
  2. Sunder

    Sunder Member

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    Mine aren't branded GTK, but they are the same type.

    These are really solid cells. Almost indestructible (as in my battery was 3" under water, draining some cells flat, and charging others to 5.0v and they still kept going, even through 55*C shed temps), and they pack one hell of punch in terms of current. I accidentally shorted one, and it turned a copper bar (not wire, bar) glowing red hot.

    Be careful of Shenzen Foxell Technologies as one of their resellers. They are one of the cheapest, but I had a bad experience with them around dishonesty, and their low (94%) feedback rating indicates that they are substantially below their peers in satisfaction.
     
  3. vk2fro

    vk2fro Member

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    I read about foxell, and am avoiding them. I'll probably get mine from that "hybrid" or "Shenzen GTKPower" mob, they seem to have good rep.

    Edit: hybrid store 2 seems to be the go - slightly more expensive, but 97.4% positive feedback.

    with regards to the cell you shorted, how in heck did you manage that, their terminals are at either end. You would have had to bend the bar into a u shape to short it out :p
     
    Last edited: May 13, 2019
  4. bryn

    bryn Member

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    US$280 shipped for 6 is very tempting as a test 12v pack... just need to find a decent BMS board for it.
     
  5. vk2fro

    vk2fro Member

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    The chargery ones are about $171 (australian), come with 2 parts, the bms itself, and the screen unit which connects via a curly telephone cord. The screen unit has a gas guage, which is handy for looking at the remaining capacity at a glance, and also can display individual cell voltages. 1.1A balancing current. The smaller 8S one is even cheaper. I'd be getting the 24S one as I'll be building a 48V pack in the end.
     
  6. Sunder

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    More correctly, I shorted a battery.

    I built them using solid copper bars between each cell to lower "internal" resistance. Anyway, two rows tall, loosened all nuts without taking any off (habit from working on cars).

    Anyway, started from the top, removed the first nut. Did not really think ahead, but a copper bar mounted on a loose nut will pivot, and pivot it did. Down onto the lower row of cells. Massive sparks, molten metal, bounced up couple times, before it fused to the end and just started heating up. Thankfully my socket had a rubber handle, so I just knocked it upwards and held it there and called my wife to get some water to cool it.

    Scary!
     
  7. vk2fro

    vk2fro Member

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    Yep sounds like a bit of a scary oops moment :)
     
  8. Sorenad

    Sorenad Member

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    I believe we should be ok.
    The largest difference in dimensions on my battery (10 cells) flat at ~5V and fully charged at 14.2V was < 0.2mm across the centre. This may possibly be because I'm using some fairly substantial pieces of polycarbonate.
    I also intend to tig weld a bracket/car boot mount from 40 x 3mm aluminium that should hopefully further limit any expansion.
     
    Last edited: May 18, 2019
  9. Sunder

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    Thanks mate. Gives me a bit more confidence.

    I'm still a bit wary though, because charging and discharging in controlled conditions, might be a bit different from hard regen and hard use.

    Probably not going to be a big issue though
     
  10. Mathuisella

    Mathuisella Member

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    in your gearbox...grindin

    What about a leather or rubber strip around the cells, something that will absorb any expansion ?
     
  11. Sunder

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    Got an updated quote for my dad, who decided not to go through with it, so not the start of a group buy:

    LTO 30AH ---US$22.8/PC 30PCs cost US$684
    Shipping cost is US$320
    Total amount is US$1004

    LTO 40AH ---US$33.4/PC 20PCs cost US$668
    Shipping cost is US$220
    Total amount is US$888

    So it seems the price is now 84c/Ah for 40Ah, and 76c/Ah for 30Ah (make sense, you pay more for higher energy density)

    Shipping appears to be $10/unit, + a $20 non scaling handling fee. Add about 15% for GST and Duty.

    All figures in USD.
     
  12. dakiller

    dakiller (Oscillating & Impeding)

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  13. Sunder

    Sunder Member

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  14. bryn

    bryn Member

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    I really want to build a pair of 5kw plus packs, if I can get the project go ahead- perfect batteries for UPS' due to high discharge current and long life.
     
  15. Sunder

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    So each of the 30Ah cells has 69Wh.

    A 5kwh pack would need at least 72 cells, so you're looking around $2400USD ex-works.

    Add in customs and GST, and some handling fees, and you won't get much change from $3000USD. It'll be around $4k AUD.

    That's one hell of a UPS. What are you powering, an entire data centre?
     
  16. bryn

    bryn Member

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    a very small one, yes.
     
  17. Sunder

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    Haha, I shouldn't have asked. Good on you. :) I ran a single 2kw UPS on LTO for a while, mostly to test it was working. Bought one to run an electric motorcycle, but haven't gotten around to putting it in yet.

    It supplies current without complaint from full charge to 95% DOD, then suddenly just dies, no warning. The voltage meters in UPSes are not designed LTO, so low voltage cutoff gives you no warning. Expect no graceful shutdown, if your UPS normally supports that.
     
  18. Sorenad

    Sorenad Member

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    For larger packs, I've been keeping an eye on the prices on a few different form factors (the >60Ah pouch cells are becoming scarce);

    This one is ~AUS$30 to buy in China.....

    [​IMG]

    This one is ~$AUS30....

    [​IMG]

    This one ~AUS$55...

    [​IMG]


    Unfortunately I have to wait until after a full kitchen + bathroom teardown and rebuild reno to buy enough to go completely off-grid.
     
  19. Sunder

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    Do you have links to suppliers for those?

    Curious what shipping would add, given they are flat and therefore can be packed tighter.
     
  20. Sorenad

    Sorenad Member

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    Sure have;

    https://item.taobao.com/item.htm?sp...rnmVK&id=587086636616&ns=1&abbucket=10#detail

    https://item.taobao.com/item.htm?sp...rnmVK&id=596916729763&ns=1&abbucket=10#detail

    https://item.taobao.com/item.htm?sp...rnmVK&id=596680240677&ns=1&abbucket=10#detail

    Don't worry too much about the prices on those pages as it's easy to phone/chat with them and haggle a bit.
    I just told them I was looking at buying 20 cells. I'm fairly certain the pricing could be brought down further.

    Unfortunately they'll only send to a Chinese address.

    If you go to Taobao and do a search for ι’›ι…Έι”‚ there are a lot more options
     
    Last edited: Jun 28, 2019

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