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  1. #1
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    Can anyone help me...think I have a battery problem...

    this is either a battery problem..BMS problem or charger problem...

    all of the above items are brand new....

    my lifepo4 battery is 48 volt /20 A/h ....

    I just got my new 6 A/h fast charger....

    I plugged the charger up to the battery and then I connected a multimeter to the batteyr to monitor the voltage...

    right before the charger automatically kicks off the battery reads 57.6 volts....

    then once the charger turns off...I check the battery again about 5 minutes later and it goes down to 53.5 volts....

    arent these 48 volt batterys suppose to hold a full charge at around 58.4 volts when they are taken off charge ?
    Last edited by sunnyday; 01-18-11 at 04:20 PM.

  2. #2
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    so im only getting each cell to hold about a 3.34 volt charge after the charger kicks off...

    would a faulty BMS cause this to happen...by shutting down the charger to soon, before it has fully charged each cell to 3.65 volts ?

    would it be safe for me to not use the charging adapter end of the battery , that is hooked up to the BMS...and instead hook my charger up to the other battery connector that connects to the hub motor ? If I can do that, and it wouldnt damage anything , I could then bypass the BMS totally, and then see if the charger charges the battery to a higher voltage and see if the batteyr then holds a higher charge...the charger has a built in cutoff, so it wouldnt overcharge the lifepo4....is it safe to try this and bypass the BMS just once, and charge the battery thru the wires used to connect the battery to the hub motor to see if this is a BmS problem ? I dont want to short anyhting out or damage anyhting..

  3. #3
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    Sounds pretty normal. These cells will almost immediately drop down to around 3.2V once you start using them, so the difference in energy available between a cell originally charged up to 3.7V and one only charged to 3.3V is almost negligible. Based on the 57.6V at cutoff, you're charging them to 3.6V/cell. That's at the lower end of the accepted range - so you might be reducing your potential range by an insignificant amount but playing it safe with regard to not damaging the cells.

  4. #4
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    Quote Originally Posted by prathmann View Post
    Sounds pretty normal. These cells will almost immediately drop down to around 3.2V once you start using them, so the difference in energy available between a cell originally charged up to 3.7V and one only charged to 3.3V is almost negligible. Based on the 57.6V at cutoff, you're charging them to 3.6V/cell. That's at the lower end of the accepted range - so you might be reducing your potential range by an insignificant amount but playing it safe with regard to not damaging the cells.


    the battery seems to be holding at 53.3 volts now....

    is it safe for me to bypass the BMS..and hook the charger up to the batterys connector that would usually get connected to the hub motor ?

  5. #5
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    My charger is putting out 57.9 volts when I put a multimeter on the end of the chargers plug. ...no load on charger ..just the multimeter hooked up

  6. #6
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    Quote Originally Posted by prathmann View Post
    Sounds pretty normal. These cells will almost immediately drop down to around 3.2V once you start using them, so the difference in energy available between a cell originally charged up to 3.7V and one only charged to 3.3V is almost negligible. Based on the 57.6V at cutoff, you're charging them to 3.6V/cell. That's at the lower end of the accepted range - so you might be reducing your potential range by an insignificant amount but playing it safe with regard to not damaging the cells.

    I was told by a lifepo4 company, that when fully charged, the 48 volt lifepo4 pack should hold at about 58 volts no load for at least 1 day ....if true , im only getting 53.3 volts fully charged...so thats about a full 5 volts difference...you dont think that is a signinifcant loss of performance ? I would think a 58.4 volt pack compared to a 53.3 volt pack is gonna be a noticeable difference in useable battery power to go longer distances.

  7. #7
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    Quote Originally Posted by sunnyday View Post
    the battery seems to be holding at 53.3 volts now....

    is it safe for me to bypass the BMS..and hook the charger up to the batterys connector that would usually get connected to the hub motor ?
    Wouldn't advise it. You could easily end up overcharging some cells and undercharging others therefore damaging your battery pack.

  8. #8
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    Quote Originally Posted by sunnyday View Post
    I was told by a lifepo4 company, that when fully charged, the 48 volt lifepo4 pack should hold at about 58 volts no load for at least 1 day ....if true , im only getting 53.3 volts fully charged...so thats about a full 5 volts difference...you dont think that is a signinifcant loss of performance ? I would think a 58.4 volt pack compared to a 53.3 volt pack is gonna be a noticeable difference in useable battery power to go longer distances.
    No, I don't think it's a significant loss of performance. Once you start running the bike for a minute or two the voltage of both battery packs will be down around 52V.

  9. #9
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    My Ping charges to 58.4 volts and then all the LEDs for the 16 cells are lit up, after they are all in balance, and the voltage stays at 58.4 with the charger still connected. It won't drop to its operating full voltage of around 53.4 until after the charger is disconnected, and a load is placed on the battery. So it is unusual for your battery to drop, with no load on it, if the charger is still connected, unless the controller is on, which which could pull enough current to dissipate the surface charge, or if you have cycleanalyst connected say - that is if the battery is left connected, on the bike, while charging. I fully remove my battery from the controller, move it to my bench, plug in the charger, wait till the BMS is lit up, disconnect from the charger then back to the bike, and THEN it still reads 58.4 volts until the first load of any sort rapidly uses the surface charge, dropping to its "operating full charge" level of 53.4. The 5 volts of surface charge is not a meaningful amount of energy. Energy stored is NOT LINEAR with battery voltage, when there is any surface charge.
    Last edited by chvid; 01-18-11 at 05:54 PM.

  10. #10
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    Quote Originally Posted by chvid View Post
    My Ping charges to 58.4 volts and then all the LEDs for the 16 cells are lit up, after they are all in balance, and the voltage stays at 58.4 with the charger still connected. It won't drop to its operating full voltage of around 53.4 until after the charger is disconnected, and a load is placed on the battery. So it is unusual for your battery to drop, with no load on it, if the charger is still connected, unless the controller is on, which which could pull enough current to dissipate the surface charge, or if you have cycleanalyst connected say - that is if the battery is left connected, on the bike, while charging. I fully remove my battery from the controller, move it to my bench, plug in the charger, wait till the BMS is lit up, disconnect from the charger then back to the bike, and THEN it still reads 58.4 volts until the first load of any sort rapidly uses the surface charge, dropping to its "operating full charge" level of 53.4.
    yeah...something sounds wrong with my situation...my battery drops to 53.3 volts without a load.....

    so I either have some bad cells in my lifepo4 pack...or my BMS is malfunctioning...or this brand new charger is incapable of chargin the lifepo4 pack up to a full 58.4 volts..

  11. #11
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    Quote Originally Posted by prathmann View Post
    No, I don't think it's a significant loss of performance. Once you start running the bike for a minute or two the voltage of both battery packs will be down around 52V.
    shouldnt I be concerned that my pack has 1 or more bad cells or low charged cells ?

    I dont want to damage the pack ....and if I can figure out whats wrong now, I may be able to balance any cells that are out of order....

  12. #12
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    once again...this is a brand new battery..new BMS and new lifepo4 charger.,...

    is it possible that the battery needs to be used a few times , to bring it up to its peak perfomance and charge capabilities ?

  13. #13
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    Quote Originally Posted by prathmann View Post
    No, I don't think it's a significant loss of performance. Once you start running the bike for a minute or two the voltage of both battery packs will be down around 52V.

    you may be correct afterall..

    I found this on another forum ;

    quote :

    Thanks for sharing that info. I've just been studying the discharge curves for these LiFePO4 battery cells and your explanation just clarifys and confirms my understanding now. A major desireable benefit of thes LiFePO4 is their ability to hold a relatively constant voltage (discharge plateau) over their discharge cycle. The specs on these cells show that the discharge plateau occurs between 3.2 and 3.3volts. This roughly translates to about 51 to 53 volts. So any stored charge higher than 53 volts is gonna get used up quickly (just like you explained).

    Sacman 1 kW
    Posts: 409 Joined: Tue May 27, 2008 3:42 am Location: Corona & Irvine, California, USA

  14. #14
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    SANGESF,,, whats your advice??

  15. #15
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    How Many threads are you going to ask the same question? LOL
    Without a load, they should stay at 3.65 per for at least 20min or so.

  16. #16
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    Quote Originally Posted by Sangesf View Post
    How Many threads are you going to ask the same question? LOL

    you think I have a bad cell/s ? //

    and that 53.3 volts is deifnitely a sign of a problem ?

  17. #17
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    if I had a cell that was charged to low, my BMS and automatic charger should take care of it...correct ?

  18. #18
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    Yes after a time, some times it's a couple of minutes, some times hours, sometimes a day.
    I won't go into the exact reason why. But they should stay close to the 3.6 per cell for at least 20mins.

  19. #19
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    Quote Originally Posted by Sangesf View Post
    Yes after a time, some times it's a couple of minutes, some times hours, sometimes a day.
    I won't go into the exact reason why. But they should stay close to the 3.6 per cell for at least 20mins.
    interesting...

    some people tell me that it sounds like a unbalanced cell/s...

    and other people tell me that 53.3 volts is fine...and normal...

    the voltage drops quickly after taking it off the charger...but it does stabilize at 53.3 volts....

    maybe a few dishcharge and charge cycles will improve it.

  20. #20
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    im just concerned that 1 or 2 cells may only be chargind to 3 volts or so...but if my BMS is working properly..that shouldnt be the problem.

  21. #21
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    Correct..
    Just try this.
    Plug in the charger and leave it plugged in for 24hrs and tell me what happens.

  22. #22
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    I wouldn't get too excited if the cells are 3.2-3.4v. They will settle back down there off the charger. Get a watt meter to measure the capacity and see how many amp hours or watt hours you get out of it before the voltage drops below 3v per cell.

    How accurate is your volt meter? If it's off by 0.1 or 0.2 Volts it can make a big difference on how you view things.

    Hobby king has a cheap watt meter. Or you could go for a cycle analyst.

  23. #23
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    Quote Originally Posted by Sangesf View Post
    Correct..
    Just try this.
    Plug in the charger and leave it plugged in for 24hrs and tell me what happens.
    okay...will do that now...

    the thing is...my charger is unique in that it doesnt shut totally off....once the charger reads the battery as having a full charge, the charger goes in standby mode and then kicks back on continously as it reads the battery voltage drops below about 58 volts...

    I had the charger hooked up to the batteyr for about 3 hours today...and at about 2- 1/2 hours into the charge, the charger started kicking on and off...every 15 seconds or so.....and it did that for about 20 -30 minutes...but the battery still came immediately down to 53.3 volts after I disconnected it from the charger.

  24. #24
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    Quote Originally Posted by yopappamon View Post
    I wouldn't get too excited if the cells are 3.2-3.4v. They will settle back down there off the charger. Get a watt meter to measure the capacity and see how many amp hours or watt hours you get out of it before the voltage drops below 3v per cell.

    How accurate is your volt meter? If it's off by 0.1 or 0.2 Volts it can make a big difference on how you view things.

    Hobby king has a cheap watt meter. Or you could go for a cycle analyst.
    my main concern is a bad cell/s in the battery....

    whats the procedure for me to check each cell , if I dissconnect the two clips from the BMS?

    my digital multimeter is pretty accurate....and I can clearly see the battery drop from 58 volts to 53.3 volts in about 20 minutes, without a load, when I take it off the charger

  25. #25
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    does anyone know, if I can safely plug my charger into the battery connector that is supposed to be used to hook up to the hub motor ? ...that battery connector does not have the BMS unit connected..perhaps that will tell me if the BMS is bad..if I hook up to that battery connector with out the BMS..and the battery takes and holds a full charge ?

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