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Thread: I see a Lithium battery dead end looming -- have you figured out the workarounds?

              
   
   
  1. #11
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    Quote Originally Posted by NonPolluter View Post
    LIFEPO4, like the Electric Motor Sports GPR-S and Native Z6000 scooter, look good on paper. Real world experience is a nightmare, compared to just buying even a cheap 50cc Chinese scooter, like the one I had two years ago.

    Here is the real-world experience with Thundersky batteries, and the extremely time consuming data-logging, repairs, drilling bloated cells, hacksawing into battery trays, etc. necessary simply because consumers can't buy a cell-level battery analyzer:
    You've taken one manufacturer's faulty implementation of LFP and generalized it to all LFPs. This in spite of the information presented to you here. No offense but if you've already made up your mind and won't accept any information contrary, why bother asking? It's turning into a Rickard fest.

    If you're not going to be convinced by anyone else's experience, build both lead and LFP bikes (with properly configured packs of course). Run on leads for 1000 cycles... oh wait you'll get 500 or fewer full cycles. Run on LFP for 1000 cycles and you'll still have another 1000 to go.

  2. #12
    SMPS Engineer BaldBruce's Avatar
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    The battery analyzer you are talking about is for a 12V lead acid battery ONLY. They rely on the linear relationship between voltage and state of charge in lead acid batteries ONLY. A load is applied and the resultant loaded voltage is measured over the period of the test to determine capacity/health. This method has no bearing whatsover on lithium batteries. Their load curve is almost flat and it is the knees of the curve we are looking for. We want to operate on the flat part of the curve and stay away from where the voltage rises like crazy or falls of the cliff. Damage to your cells is right around the corner if you allow them to see either area outside the flat part of the curve. Thus most people who are SUCCESSFULLY operating lithium systems are using a BMS to at least make sure the cells are always in their "safe " operating range. Whether or not a BMS should do cell balancing, logging, reporting, temperature sensing, etc is a whole nother discussion. (A whole raging debate on another forum if you really want to get bored quickly.)
    (Also a whole seperate argument is also flying around concerning the definiition of BMS in terms of which function this term implies even. Clogging my inbox lately it's so bad......)
    I have not failed. I've just found 10,000 ways that won't work.
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  3. #13
    Not to be taken seriously DaveAK's Avatar
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    Pretty much what Bruce said. Start with LVC and HVC and go from there depending on your needs and desires. I want the full gamut of what can be done, and will have it all when I'm finished. My MiniBMS will give me LVC and HVC to start with, and that's all I really need. I'll do the rest just 'cause I can.

  4. #14
    Senior Member larryrose11's Avatar
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    Quote Originally Posted by BaldBruce View Post
    The battery analyzer you are talking about is for a 12V lead acid battery ONLY. They rely on the linear relationship between voltage and state of charge in lead acid batteries ONLY. A load is applied and the resultant loaded voltage is measured over the period of the test to determine capacity/health.
    I totally agree with Bruce. Further, different SLA have different pukert effect's, so the load applied from the analyzer has a direct effect in its measurements. If the analyze ran different loads, the it will also have different results.

    Quote Originally Posted by chef View Post
    There are ways to get by without a BMS on LFPs if you're intimately familiar with the specific manufacturer's chemistry. That entails sacrificing capacity and operating in the 20-90% range and periodic manual checkups. It's tough to sacrifice capacity on space-constrained 2-wheelers, but if I had to do it over again I'd gladly make that compromise and still have healthy cells.
    I have been saying this for years. I have gotten some good responses from some BMS manufactures that will let me program the HVC, LVC myself for each cell to stay in the healthy range


    Quote Originally Posted by BaldBruce View Post
    This method has no bearing whatsover on lithium batteries. Their load curve is almost flat and it is the knees of the curve we are looking for. We want to operate on the flat part of the curve and stay away from where the voltage rises like crazy or falls of the cliff. Damage to your cells is right around the corner if you allow them to see either area outside the flat part of the curve. Thus most people who are SUCCESSFULLY operating lithium systems are using a BMS to at least make sure the cells are always in their "safe " operating range.
    Exactly. ALL the major OEMs that will warranty their packs, be it car or bike, will do this. The VOLT, has a 16 kW-hr pack, but limits the avalable to 8-10 kW-hrs for durability. The HEV packs in the Ford's limit the (small, 6Ah or so) pack usage to the 40-60% range, and last over 300K miles.

    Anyone spotting the trend here? This horse AINT DEAD YET?!?
    If you want good durability out of your expensive Li based batteries, stay in the 80-20% or so range of battery operation.

    Minimally, have some sort of warning that lets you knw when you hit the LVC / HVC for the healthy range.
    Better still, find a BMS that will do this for you, one that will communicate with your motor controller that will throttle back the current (either direction) when it hits these voltage ranges under operation, and will talk to the charger as well and keep this cells in this region

  5. #15
    Senior Member Skeezmour's Avatar
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    Geez I wish I know of a BMS that did all this....oh wait

    Have some updates on the site about the new items in the line up. More to come very very soon.

    Gene

  6. #16
    Only2Jakes
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    Nice Gene, I'm definately getting that and your BMS if I ever do an electric car.

    I recently oredered some of the 2 headway cell mounts/brackets and bus bars, waiting on an email invoice Jake
    Last edited by Only2Jakes; 12 February 2011 at 1630.

  7. #17
    Old EV Racer EVcycle's Avatar
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    Questions for people in this forum:

    1) How many miles have you gotten out of your Lithium pack, and please specify brand and model.

    Over a 1000.

    2) Are you running with/without a cell-level battery bank equalizer? What are your conclusions?

    Individual changers to each paralleled bank. (I.E 26 chargers to 26 packs of 4 Lifepo4 batteries) plus Celllog 8 devices.

    Works great!
    Last edited by EVcycle; 12 February 2011 at 1701.
    EV Ed
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  8. #18
    Senior Member SplinterOz's Avatar
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    I am building a headway pack for my bike and I am going to use Celllog 8 devices to keep track of my cells.
    With these I am going to create a circuit from the alarm output to ensure that I avoid HVC and LVC problems.
    Working from this thread on Endless-Sphere I should be able to kill my bulk charger if any cell is HV. I plan to run a balancing charger across the pack every weekend to ensure the cells are balanced. When the bike is operating the alarm circuit will either sound an alarm or drag the throttle down to reduce my total power drain.

  9. #19
    Old EV Racer EVcycle's Avatar
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    Quote Originally Posted by SplinterOz View Post
    I am building a headway pack for my bike and I am going to use Celllog 8 devices to keep track of my cells.
    With these I am going to create a circuit from the alarm output to ensure that I avoid HVC and LVC problems.
    Working from this thread on Endless-Sphere I should be able to kill my bulk charger if any cell is HV. I plan to run a balancing charger across the pack every weekend to ensure the cells are balanced. When the bike is operating the alarm circuit will either sound an alarm or drag the throttle down to reduce my total power drain.
    Sounds like a good plan.
    EV Ed
    Never let being a responsible adult get in the way of passion and curiosity.
    Motenergy.com
    Ev album 2456, 2458, 2457, 2681, 3456, 3630

  10. #20
    SMPS Engineer BaldBruce's Avatar
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    Quote Originally Posted by SplinterOz View Post
    I am building a headway pack for my bike and I am going to use Celllog 8 devices to keep track of my cells.
    With these I am going to create a circuit from the alarm output to ensure that I avoid HVC and LVC problems.
    Working from this thread on Endless-Sphere I should be able to kill my bulk charger if any cell is HV. I plan to run a balancing charger across the pack every weekend to ensure the cells are balanced. When the bike is operating the alarm circuit will either sound an alarm or drag the throttle down to reduce my total power drain.
    I know you are aware of it, but want to make it clear for others who are interested in those great little cell loogers. If you want to use the alarm output of more than one, you MUST isolate the outputs. Smoke will ensue if you try to tie more than one of these outputs together. And also remeber they have a cool USB port to dump data from, but the same caveat applies. Do not tie more than one port together at the same time or you let the smoke out.

    P.S. I built such an interface PCB for my own bike if someone wants a DIY project or advice on how to do it.....
    I have not failed. I've just found 10,000 ways that won't work.
    Thomas A. Edison

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