Possible Group Buy - Check Interest - Lithium Titanate cells

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

  1. OP
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    rainwulf

    rainwulf Member

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    No, so im on a journey of discovery. On paper, they seem to be too good to be true. Their only downside is the energy density compared to Lipo, but when these things last at least 20 times longer, who cares.

    Building a monitoring system now, was going to drive to Jaycar to pick up some resistor ladders, but needed fuel in the car. Price is so high right now i think im going to stay at home and code.
     
  2. OP
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    rainwulf

    rainwulf Member

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    First module done.

    Run out of printer filament, so have to get more. These things will do 400-700amps short circuit without even blinking, so im making sure i can mount them solidly in any orientation and not have a huge short circuit.

    btw, this battery sits at 6.8kg, 40a/h, 12 volts. If you treat lead acid storage at a 25 percent depth of discharge, that means 40a/h is one quarter of an equivalent lead acid battery. That makes this here equivalent to a 160a/h AGM.

    160a/h agm does NOT weight 6.8kg. It also does NOT have a 20 thousand cycle life.

    To be conservative, i will treat this pack as a 120ah AGM. A 120ah agm weighs around 30kilos.



    [​IMG]
     
    Last edited: Sep 9, 2018
  3. Mathuisella

    Mathuisella Member

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    in your gearbox...grindin
    Can you start a diesel car with it :D ?
     
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    rainwulf

    rainwulf Member

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    i wouldn't even hesitate. They are rated for 10-15c discharge.

    Leaving it on the alternator would be a disaster though. These things max at 13.6 volts. Charge them above that and i wouldn't want to see what would happen.
     
  5. mAJORD

    mAJORD Member

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    Curious What did the individual cell weight come in at And why not 6 cell? Is the nominal and cutoff voltages closer to LA with 5?
     
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    rainwulf

    rainwulf Member

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    around 1.2 kg a cell.

    LTOs run in groups of 5 due so they can be charged effectively. Their max full voltage is around 2.7 volts, so if they were in a group of 6, they would be sitting at 16.2 volts. They would never get a full charge.
     
  7. mAJORD

    mAJORD Member

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    Is that problematic though if they don't get full charge, say for a car battery placement? All it would mean is an effective lowering of AH of the pack otherwise
     
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    rainwulf

    rainwulf Member

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    Not really no, but then you would have to oversize the pack significantly to keep the AH decent, and you run the risk of flattening them to dangerous levels. It would work though, but yea you might lose 30-40 percent of your capacity.

    They are effectively "Flat" at 2.1 volts, which is still around 12.6 volts. That's above standard cut off voltage for all 12 volt devices, and they will continue to draw current past the "Flat" level possibly causing damage and shortening their life.

    edit: the specific cells im getting are 2.1 volts, apparently there are slightly different chemicals used by different manufacturers which can bring that down to around 1.8 volts which would fit well in a 6 cell pack.
     
    Last edited: Sep 9, 2018
  9. Privatteer

    Privatteer Member

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    Any capacity test done yet?
     
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    rainwulf

    rainwulf Member

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    Not yet, im still building the backs and mounting them safely. I do NOT want them to be knocked or fall over or have something conductive fall on them.
     
  11. Sunder

    Sunder Member

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    Haha. I had them mounted/connected like you do. I needed to remove one cell to install a balancer... Didn't think it through too well, and undid a bolt, and the other bolt was not torqued up. As metal plates which are installed on bolts are wont to do, it pivoted on the remaining bolt, and hit the terminal below it causing a short.

    But even at 2.7v, the available current was so high, the force of the spark pushed the connector back up - then the force of gravity made it pivot back down, shorting it, and the force of the spark... You get the idea. Totally frightening, but no damage to the cells. (large chunks taken out of the connector though.)

    These things are bulletproof!
     
  12. OP
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    rainwulf

    rainwulf Member

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    Yep, i did something similar, but with spacing my 3d printed mounts. I was spacing the copper link between two terminals to make sure my cradle wasn't too thick, and forgot the other ends of the cells where already joined.

    DAMN. My cells aren't even fully charged, sitting at about 2.1 volts atm, even so the current they put out is fucking ridiculous. Btw, check the data sheet, you can charge each one at 400 amps. safely. 4 bloody hundred amps.

    Btw, what balancers are you using? I have a bunch coming from ebay now.
     
  13. Sunder

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    Not so much balancer, as a HVC safety:

    [​IMG]
    https://www.ebay.com/itm/Hot-Sale-2...964?_trksid=p2349526.m4383.l4275.c10#viTabs_0

    These are super cap balancers. Supposedly burn off 1A once it reaches 2.8V in reality, at 2.85v it only burns off about 200ma. At 3.2v (Simulated without a battery), it I get it to 700ma, but didn't want to go over that, because if the battery is over 3.2v, I'm up shit creek anyway.

    It's "good enough" for a holiday home off grid solar array, because I only trickle in for like 1-10A (Theoretical 540w system, 24v bank - in reality I get nothing near that) a few hours a day and a solar charger "should" provide a secondary high voltage cut off, and it has plenty of time for the rest of the day to balance, so unless one completely fails, then it'll never get that far out of whack. I'm not sure I could recommend them with a big system though.

    For my motorbike, which I'll be charging at either 2400W or 4800W (depending on home charger or public electric car charger), I'm thinking of using a proper one like this:

    https://www.aliexpress.com/item/35S...4cb5-47af-bff8-48007d7fac95&priceBeautifyAB=0
     
  14. OP
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    rainwulf

    rainwulf Member

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    hahaha, thats exactly what im going to be using for the solar storage array, as its charge/discharge voltages i can control exactly.

    And yea, its more of a last ditch protect each cell on its own kinda thing.
     
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    rainwulf

    rainwulf Member

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    Well, got the bank running today on Solar. Was sucking down 60 amps at 24 volts nicely until i started to measure individual cells. Definitely need balancing before anymore charging is done, probably a long slow balance charge before putting them into production.
     

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