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Thread: What replacement battery for H8.5" L8" W4.5" SLA or LIFEPO4 batteries fried by BMS

              
   
   
  1. #1
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    What replacement battery for H8.5" L8" W4.5" SLA or LIFEPO4 batteries fried by BMS

    The Thundersky LIFEPO4 batteries on our EMS Z-6 electric scooter (model changed to Z6000 for 2011) was totally discharged by the Modalis BMS.

    We didn't realize that the Modalis BMS draws enough energy to deplete the State of Charge in a month or less.

    Upon charging, the cells expanded, breaking many of the battery straps that act as a cage to keep the cells from expanding (apparently an important function.) Those straps aren't welded that well, or at least not strong enough. Now, there are gaps between the cells, as the cell casings have expanded and/or warped.

    The pack voltage is nearly 14V and the total system voltage is 55V (on this 48V bike) but when we try to run the motor, the motor just chugs, not moving, and the fuel gauge sits at 1/4 power.

    We're guessing that the cells got overcharged somehow. When the battery capacity is diminished, the charger needs to charge less, apparently. Either that, or the fully discharged battery went into thermal runaway under charge.

    The BMS is unable to balance the cells now (they used to be within .001V of each other).

    We're sick and tired of the LIFEPO4, charger, BMS issues and would like to replace these TS cells with SLA's. (lead acid)

    The battery tray will only fit a 16AH Hawker Genesis Pure Lead or 20AH B&B SLA's.

    On a side note, the manufacturer Electric Motorsport imho should have pasted a warning label on the bike about the need to charge this scooter weekly. And provided a user guide, even online, with a warning that the expensive batteries can get depleted by the 'stupid' BMS.

    Another reason we want to go to lead acid is that the LIFEPO4 acts like a capacitor -- the scooter had good performance only immediately after a charge; wait a day, and some of the horsepower seems to be missing.
    Last edited by NonPolluter; 06 February 2011 at 1653.

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    Additional information: The SLA batteries would be 13V vs 14V for the Lithium.

    Under full throttle, the LIFEPO4 exhibits voltage sag. The TS LIFEPO4 obviously cannot sustain the Z6 current draw (said to be 6000 watts).

    The Hawker Genesis Pure Lead batteries have NO HIGH CURRENT LIMIT, either charge or discharge.

    Perhaps I should find a way to fit two Hawkers sideways for every 12V pack?

    http://www.enersysreservepower.com/d...S-001_0406.pdf

  3. #3
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    I'm not sure I would blame the LiFePO4 chemistry, as much as it is now pretty clear that TS batteries aren't the best performing batteries out there. I wouldn't recommend SLA but for an interim fix. From what I have read the Headway LiFePO4 batteries perform at a much higher level, but I have no personal experience. Also, LiPo could be an option, as I am sure some will mention. Hopefully other will chime in soon. I'd also get the BMS sorted as well. It sounds like the batteries were over charged.

    Hope that's helpful in some way,
    Rich

  4. #4
    Old EV Racer EVcycle's Avatar
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    I agree with Rich. Many BMS units have been the downfall of the Lipo/Lifepo4 battery issue.

    That is why I do not use one. (until I see a good one that is fool proof)
    I love the headway's. But that is just one persons opinion.

    Do not give up on the non-lead option just yet.
    EV Ed
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  5. #5
    teddillard
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    Interesting information, and good point on the BMS discharge issue. You may want to look at Staab for the SLA source, I had really good luck with them. http://www.staabbattery.com/

    I think, from my experience, some good lead batteries are always good for a fix, short term or long, and they always come in handy in one form or another. ( I have some ex-scooter batteries powering my lawnmower at the moment )

    Ed's so coy... read about his non-BMS BMS idea here: http://www.elmoto.net/showthread.php...BMS-Conversion

    For some more info on the challenges of Headway packs in particular, see this thread on ES:
    http://endless-sphere.com/forums/vie...p?f=14&t=12320


    On the TS, I think although the performance of those cells isn't cutting edge, they certainly have had a huge following, and in a scooter they may be a great solution with a good BMS. I'd ditto Ed, and encourage you to look for a good solution to the BMS issue. Other chemistry is going to have the same issues, and as far as LiPo goes, I'd caution you against considering it if you're looking for a hassle-free solution. It's small, light and has a high discharge rate, but they're catastrophically touchy about charge and discharge conditions...
    Last edited by teddillard; 07 February 2011 at 0559.

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    Misery loves company. That is what happened to my Hi Power batteries. I am not sure if you can blame the batteries. My blame was first focused on the Modalis BMS. It was eating my batteries as fast as I could install new ones - before I finally figured out what was happening. It seemed to be something about the "master" board, rather than the slave boards on top of the other battery packs. All of those batteries are still in reasonably good condition (although I have replaced the Modalis BMS with a mini-BMS).

    However, I am still having problems with the last two batteries in my pack. I had two swell up last week, but they were numbers 23 and 24 of the pack. When just sitting around for a week, they dropped from 3.3 volts to .4 volt and swelled up - after having ridden the bike for a few miles and not recharging it. However all of the other batteries were just fine and kept their charge, including the other two batteries in the 4-cell group. I have no idea what is going on, but maybe the LiFePo4 prismatic batteries can only deal with a limited amount of voltage or current passing through the batteries. I really have no idea, but that is my latest theory.

  7. #7
    teddillard
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    Quote Originally Posted by Richard230 View Post
    ... but maybe the LiFePo4 prismatic batteries can only deal with a limited amount of voltage or current passing through the batteries.
    Exactly. That's true of any battery, even lead. Running the pack with the cell at .4V is what fried it and made it swell. If that's what you're saying... not entirely sure. If you'd done that with LiPo it woulda gone boom.

    Last edited by teddillard; 07 February 2011 at 0854.

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    Ted, the two cells that went bad apparently did so while the bike was just sitting around for a week. We had ridden it for several miles trying to fix the stalling problem and checked the voltage on the batteries after our ride. Each cell was showing 3.3 volts and we did not put the pack on the charger after our ride. We didn't check them again when I rode the bike 7 days later, but I immediately knew there was something wrong as I rode down to the end of the block, as the pack voltage went from 80 volts to 74 volts with a few hundred yards. Returning to the shop, we discovered the two fat batteries and replaced them with good ones. But then the stalling returned again. We have no idea what happened to those batteries while the bike sat around the shop for a week. It is all getting very distressing, especially as the BMS was hooked up at the time. The controller is showing a couple of fault codes and my friend plans to call the Sevcon expert this week to try and find out what they mean. Frankly, I would really prefer riding to fiddling. I just hope I can learn something from all this hassle.

  9. #9
    teddillard
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    ...got it. But for whatever reason they were at low voltage, the cells being at the low voltage and getting tapped is what made them fat. Maybe.

  10. #10
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    Quote Originally Posted by teddillard View Post
    ...got it. But for whatever reason they were at low voltage, the cells being at the low voltage and getting tapped is what made them fat. Maybe.
    I agree. Fat cells are unhappy cells and every fat cell that I have seen has had voltage below 1/2 volt. The odd thing is that you can squeeze them thin again and charge them back up to 3.3 volts. What happens to the Ah capacity when you do that, I have no idea.

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