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  1. #1
    Newbie polarbear193's Avatar
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    Question Refurbishing battery packs

    Have plans to rebuild my 24V 10Ah battery packs from NiCd to Li-Ion . Can I use 6 or 7 UltraFire 18650 3.7V Lithium - Akku 3800mAh and just buy a new, intelligent charger, or are there more things I need to consider? Grateful for have other forum members experiences, knowledge and opinions.batteri.jpg
    Last edited by polarbear193; 04-26-15 at 01:36 PM.

  2. #2
    Senior Member long john's Avatar
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    Quote Originally Posted by polarbear193 View Post
    Have plans to rebuild my 24V 10Ah battery packs from NiCd to Li-Ion . Can I just use 6 or 7 UltraFire 18650 3.7V Lithium - Akku 3800mAh and just buy a new, intelligent charger, or are there more things I need to consider? Grateful for have other forum members experiences, knowledge and opinions.batteri.jpg
    Check out the site that rebuilds battery packs for cordless power tools. I don't remember it's
    name. It should be easy to find though. I believe they also replace a cap as standard rebuild.

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    I've heard that ultrafire batteries are way overstated as to capacity. Go to endless sphere and ask spinningmagnets about them.

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    We have a couple of still working Bionx PL-350 I2C units, circa, 2008. When Bionx switched to CANBUS they left us unsupported as far as batteries were concerned. We filled the void with rebuilds by electricrider.com. Real happy with the results.

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    Quote Originally Posted by 2old View Post
    I've heard that ultrafire batteries are way overstated as to capacity. Go to endless sphere and ask spinningmagnets about them.
    Bingo, don't buy 'ultrafire', it's BS. If you want to know what the capacity of a cell is, it's pretty easy to find out. Request a sample and do a discharge test. https://www.youtube.com/watch?v=usRE3gLFnOc This video will help illustrate some of the details on how to do a discharge test.

    You might consider 18650 29e cells.

    There is probably more to it than just swapping the cells, but I don't think I understand what you are dealing with. Different chemistries and such often have different high voltage cutoffs(HVC) and low voltage cutoffs(LVC). I am assuming you use a battery monitoring system(BMS) of some sort that prevents you from over charging and over discharging your cells, you'd need to be certain the voltage the BMS HVC and LVC matches up with the new cells you are using and that the charger you are going to use puts out the right voltage.

    Your pack also surely has more than 7 cells. I might guess your pack has at least 21 cells.

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    There is a guy selling tesla batteries on ES. Do a search for tesla battery and u can find him. Prices are decent and he welds the packs up and can make u what ever u want.

    PS dont buy any cell with fire in the name.... Well unless u want to start a fire

  7. #7
    Senior Member CliffordK's Avatar
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    Quote Originally Posted by polarbear193 View Post
    Have plans to rebuild my 24V 10Ah battery packs from NiCd to Li-Ion . Can I use 6 or 7 UltraFire 18650 3.7V Lithium - Akku 3800mAh and just buy a new, intelligent charger, or are there more things I need to consider? Grateful for have other forum members experiences, knowledge and opinions.batteri.jpg
    About 6 of those in series gives you about 3.8 AH, 24V.

    So, you would need about 6 in series, 3 in parallel to give you about 10 AH, 24V, or a total of about 18 batteries.

    Typically the battery packs are built with an internal charge controller. So, I think you would need something like a 6s charge controller.
    6S Li ion Lithium 21 6V 22 2V 25 2V 6 Cell Battery Protection Circuit Board PCB | eBay

    Perhaps get 3 of these controllers to wire in parallel to make 3 battery packs.

    I think the controllers are rated as xPyS for x batteries in parallel, and y batteries in series.

    I'm not sure about the charger. I think the protection board allows charging your batteries up to capacity, then cuts out, so you may just need a charger that will supply voltage in excess of 100% charged.

  8. #8
    Newbie polarbear193's Avatar
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    Thanks, this was useful. I will consider the warnings about Ultrafire batteries, check the costs of building my own battery pack and compare with the price of complete battery packs like Free shipping 24V 10Ah electric bike Battery Li ion Battery with PVC Case +BMS+charger-in Electric Bicycle Battery from Sports & Entertainment on Aliexpress.com | Alibaba Group
    Last edited by polarbear193; 05-03-15 at 10:27 AM.

  9. #9
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    There are a few small things to consider before slapping a few 18650 batteries together, depending on the charger you buy. Many chargers only handle a certain number of "lines out", if you want to think of them that way. Meaning, that they only charge cells in parallel, or in series. Charging in parallel is easy, because the charger can monitor each battery individually. Series is a little more difficult, and you would need to make sure the batteries are what they call "matched". All it really means is they have nearly identical charging profiles and total capacity. Li Ion are charged constant current, then constant voltage, then trickle. driving the constant current through batteries in series may give one battery a disproportionate amount of the load. In reality, it'll probably be fine. Just monitor the temp of the batteries if your charger doesn't have that capability.

  10. #10
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    Go to endless sphere and look up tesla batteries for sale. A guy on there is selling them for a decent price

  11. #11
    Newbie polarbear193's Avatar
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    Thanks

    Plenty of useful information.

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