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Thread: Using a BMS for charge balancing only?

              
   
   
  1. #1
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    Using a BMS for charge balancing only?

    A question for all you battery wizards...

    I have an 18S1P LifePO4 lifetech 15ah pack. I have a BMS but the BMS can't support the 100A load that the battery has on it when in use. Thus I only used the BMS when I hook the auto charger up to the BMS, and discharge via the Pos and Neg port on the battery. It’s a shunting BMS that I run the 18S charger through, I don't seem to have any dramas with voltage, the shunts seem to be working (warm), and the charger still auto cuts when it reaches its voltage plateau.

    BMS here
    http://bestechpower.com/576v18spcmbm.../PCM-D107.html

    Does anyone see any problems arising from operating the cells this way? I monitor the battery through a victron 600s and never draw more than 12Ah from the pack.

    Cheers

  2. #2
    Ghost Rider Allen_okc's Avatar
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    Thats the only thing i would use a Battery Murdering System for "BMS", otherwise get a PCM for balance charging only. just my opinion... use cell logs for your discharge shut down warning...
    The Greatest thing about a EV, is the Song of the Terrain...

  3. #3
    Señor Member podolefsky's Avatar
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    That should be fine. If you have some other way to monitor discharge, then you can just use the BMS during charging. Most high current drive systems (>35A) are connected directly to Pos and Neg of the battery.

    As long as it looks like the BMS is balancing the cells, and keeping them from overcharging, then it's doing it's job.
    - Noah Podolefsky -
    The GSX-E

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    Quote Originally Posted by bodie View Post
    Question back for you. Where do you buy the product? How much do they cost?

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    Empulse R #24 frodus's Avatar
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    Re: Using a BMS for charge balancing only?

    There's still nothing to prevent over discharge or over current. Just be careful.
    Travis

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    Quote Originally Posted by lugnut View Post
    Question back for you. Where do you buy the product? How much do they cost?
    Purchased direct from the manufacturer, $60 USD.

  7. #7
    Señor Member podolefsky's Avatar
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    Quote Originally Posted by frodus View Post
    There's still nothing to prevent over discharge or over current. Just be careful.
    Good point. As long as the cells are balanced and healthy, and you are only discharging to 80% DOD (12 Ah), you'll probably be OK at the cell level. But you never know.

    Using cell logs to monitor cell level voltage like Allen said is a good idea.

    Can you still use the 18s BMS you have for monitoring voltage without current through it? Since you have the Victron Ah meter, you've got SOC, so all the BMS needs to do is monitor voltage.
    - Noah Podolefsky -
    The GSX-E

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    I think I may have confused myself a bit here. The unit I'm using is a pcm not a bms as I wrote earlier. I have to admit I'm still perplexed what the difference is. Is a pcm just a charging/balance aid that doesn't draw power when not in use while a bms is always monitoring and drawing power?

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    Quote Originally Posted by bodie View Post
    Purchased direct from the manufacturer, $60 USD.
    I tried that. I got an email from Henry. Requested price and order info (twice) and get nothing.

  10. #10
    Señor Member podolefsky's Avatar
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    Quote Originally Posted by bodie View Post
    I think I may have confused myself a bit here. The unit I'm using is a pcm not a bms as I wrote earlier. I have to admit I'm still perplexed what the difference is. Is a pcm just a charging/balance aid that doesn't draw power when not in use while a bms is always monitoring and drawing power?
    I hadn't seen "PCM" before, but from what I can tell it's semantics. BMS stands for "Battery Management System" - they can be all sorts of configurations. It looks like the unit you got does the basics: high and low voltage warnings as well as top balancing during charging. It's a simple BMS that will protect and maintain your pack without any bells and whistles.
    - Noah Podolefsky -
    The GSX-E

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