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Thread: A123 piggyback packs

              
   
   
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    Seņor Member podolefsky's Avatar
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    A123 piggyback packs

    I have a opportunity to get a bunch of A123 26650 cells...enough to make a 24s3p pack.

    This would only be about 0.5 kWh, but it would be capable of over 300A peak.

    My pack right now is 72V, 60Ah GBS prismatics.

    Question: has anyone used A123's (or something similar) as a "booster pack" to increase the current output of a prismatic pack?

    One idea I had was to build 24 little 1s3p piggyback packs that parallel with each GBS cell, thus using the same BMS and charger.
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    Senior Member Coninsan's Avatar
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    Never heard about anyone using A123 cells, but I have seen a few youtube videos made by a guy in central europe building a motorized Velomobile of sorts. He used supercaps in conjunction with Lipo cells. I don't remember the details or whether it's even particularly relevant for your uses. So I apologize if this is useless.
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    Not to be taken seriously DaveAK's Avatar
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    I believe that Mark from Enertrac did a LiPo/LiFePO4 hybrid pack. The A123 cells would have the advantage of being the same chemistry.

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    Senior Member DRZ400's Avatar
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    i've been waiting for the a123 15ah prismatics to come down in price, like to put 24 of them between my 24 calbs and share each bms module.
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    Old EV Racer EVcycle's Avatar
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    What do you use for your 12V setup? This could make up alight powerful 12V package.....
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    Senior Member larryrose11's Avatar
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    Sounds like it could work. Can you get access to 3 cells, for testing purposes? I would run a load test where you put them in parallel, and use 2 current meters, on for the gbs and for the A123. sinking to the same dump load. How is the current shared?

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    Seņor Member podolefsky's Avatar
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    I abandoned this idea after talking to markcycle. He pointed me to his booster pack, using lipo. It only works because the prismatics sit at a slightly higher no load voltage than the lipo. There's a clever diode in there to keep the lipo from kicking in until the prismatics sag enough to let the lipo take over.

    http://enertracrawfeed.blogspot.com/...Battery%20pack

    With A123 paralleled with each calb, you might have a problem. Since they have a lower IR, the A123s will completely discharge before the calbs do much of anything. Possibly to the point that they hit LVC and destroy themselves.

    Could be wrong, but that's basically why I gave up on the idea.
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    Senior Member seanece's Avatar
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    Noah or MarkCycle,

    Do either of you have the data (or an updated blog post) from the Dual Chemistry Booster Pack setup? The idea and application sound like a very interesting, cost-effective and practical solution.
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    Probably a dumb question, but I was wondering -- if a typical controller can cut off the juice when the total voltage of the batteries gets too low, how hard would it be to instead make the controller switch over and start sucking juice out of a spare pack in some kind of optimal way? For instance when I go up the long steep road to my house. The TS batteries, for a very short time, will get down to the 2.5 volt level. It is quick enough so that I can't actually see it on the cycle analyst display while riding, but after the ride I can see from looking at the cycle analyst vmin register that the pack of 24 batteries (probably momentarily) got down to 59 volts.
    Wonder if somebody could make a controller that, instead of just cutting off voltage at a certain low point, would instead switch over to a spare pack momentarily, and maybe even switch back and forth between the main pack and the spare pack for a brief time in case the problem is just a sudden heavy load rather than batteries that have simply used up too many amp hours?

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    Senior Member larryrose11's Avatar
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    Quote Originally Posted by podolefsky View Post
    With A123 paralleled with each calb, you might have a problem. Since they have a lower IR, the A123s will completely discharge before the calbs do much of anything. Possibly to the point that they hit LVC and destroy themselves.
    Could be wrong, but that's basically why I gave up on the idea.
    chime in here if my logic (on this post) is screwy, especially LiveForPhysics, as he may have some experience like this to share.

    Since these 2 different cells have the same chemistry, they would have some of the same voltage characteristic's, such as HVC, LVC, and SOC as a function of rest voltage. If they are significantly different in these key parameters, then my logic falls apart.

    I would think that there would be a dynamic current balance between the A123 and the prismatic, assuming that the peak discharge event was only 5-10 seconds or so.
    If they were parallel at the cell level, then their voltage would be the same for each pair. They would hit the LVC together. I would think that under a heavy discharge, the A123 would sag less, would carry the load for the first few seconds of the discharge, until the SOC adjusted V of the A123 is lower than the prismatics. At this point, the prismatics would carry more load, which would make the prismatic cell sag, and repeating the cycle.

    When the load disappears or is reduced, the opposite would happen. the SOC adjusted voltage of the A123 cells would be lower than the prismatics. The prismatics would then charge the A 123 cells back to a matching voltage.

    Under a regen event, the A123 cells would absorb more of the current, as they would rise less under a hard charge, then slowly releasing it to the prismatics as their voltage self adjusts.

    Am I out of whack here?
    I know Im out of whack in general, or so my wife tells me. I think that's on par around here.

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