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Thread: BMS grades / types / categories

              
   
   
  1. #1
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    BMS grades / types / categories

    This thread will try to categorize the types of BMS's, their overall approach to battery management and differentiating features. It's a high-level description and I welcome discussion drilling down into the gory details. This is meant for others as much as myself to keep things straight in my head. And to keep me honest in exposing how little I know
    I will endeavor to update this post with additions and corrections.

    I'm assigning a grade level for each major category. Some ElMoto'ers have used it and I've seen it referenced on other boards, though there doesn't seem to be industry standard terminology yet. Each level includes the features of the previous levels (for instance, Level 2 has all the features of Level 1 & 0).

    Terminology --
    BMS: Battery Management System
    HVC: High Voltage Cutoff
    LVC: Low Voltage Cutoff

    Level 0: Pack voltage monitoring only. Pack HVC & LVC are usually included. It could be argued that this is not a BMS, though technically a battery is a collection of cells and pack monitoring is a rudimentary way of managing the battery. Some consider this equivalent to not having a BMS. Others believe that this is all that is needed if the pack is bottom-balanced before installation and drift is negligible.

    Level 1: Cell-level voltage monitoring with cell-level HVC & LVC. No balancing, just monitoring of voltage on every cell. Charge is stopped when any cell hits HVC. During discharge, limp mode or shutoff is engaged when a cell hits LVC. The BMS must be able to shut off the charger (HVC) or signal the controller to reduce load (LVC).
    Voltage data logging is an additional feature provided by some L1 BMS's.
    Cell temperature readings and logging are provided by some L1 BMS's, though this tends to be more common in L2 BMS's.
    These types of BMS's typically require pre-balancing the cells before installation (top-, mid- or bottom-balanced).

    Level 2: Automatic top-balancing* through individual cell shunts, charge shuttling and/or charge bypass. The BMS's goal is to bring each cell up to its maximum capacity. There are a number of approaches, but in all cases a circuit attaches to each cell to direct the charge.
    • Shunt balancing shuts off the charger when a cell hits HVC. The cell is bled down with a shunt. Charging resumes after some time. This repeats until all of the cells are topped off.
      Proper bleeding of the cells is crucial to prevent overcharging. Unfortunately it can be difficult to determine which BMS's do this properly before purchasing.
    • Charge shuttling is similar to (i) but the cell's charge is transferred to another cell instead of being shunted. Additionally, charge may be transferred during discharge for continuous balancing. Less energy is wasted but the circuitry is more complex.
    • Charge bypass on an individual cell level. The charger remains on and the circuitry routes around the full cell. Challenges are high current handling and/or granular control of the charger. This feature might belong under L3.

    [*It's theoretically possible for a BMS to do mid or bottom balancing, though I've not seen such on the market yet.]

    Level 3: Cell-level bypass during charge and discharge. This is functionally equivalent to removing a depleted cell and placing a short in its place during discharge. The pack continues to operate using the cells which have charge remaining. Pack voltage is reduced for each cell that drops off until it hits pack LVC. This is no simple feat as the current bypassed can be in the hundreds of amps.
    Last edited by chef; 21 March 2011 at 2328.

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    This post is a placeholder for links to BMS's on the market and will be updated periodically. It's unlikely to ever be complete as the number of BMS's seems to grow exponentially. Please PM me or post a reply with information about a BMS not on this list.

    Level 1
    Mini BMS by Clean Power Auto
    ThunderStruck BMS-II
    CellLog 8s [Review] (really more of a data logger than BMS, though its alarms can be adapted for HVC & LVC. See Bruce's circuit)
    Chargery BM6
    Chargery BS6
    Signalab BMS (link?)

    Level 2
    Mini BMS with optional shunt balancing (see link under L1)
    Modalis BMS sold by Electric Motorsport (known to excessively overcharge cells)
    Elithion Lithiumate
    Wicom Auto EMS
    Elite Power Solutions BMS (only available for GBS cells)
    Manzanita Micro MK3x8

    Level 3
    [Haven't been able to dig this up. Searching the TS group is... difficult]


    ---------------------------------------------------------------------------------------------
    Handy BMS selector
    http://liionbms.com/php/bms-selector.php

    ---------------------------------------------------------------------------------------------
    Other BMS lists:
    http://liionbms.com/php/bms_options.php
    Last edited by chef; 15 June 2011 at 1326.

  3. #3
    Not to be taken seriously DaveAK's Avatar
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    Mini BMS can also be bought as a balancing BMS, i.e. Level 2.

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    Thanks for the heads up about the MiniBMS. Didn't see it at first but their PDF mentions "Optional shunt balancing"
    Last edited by chef; 12 March 2011 at 2028.

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    Moderator Nuts & Volts's Avatar
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    Sweet thread. I am glad this topic was posted. I'll add a sticky to this.

    You can add Elite Power Solutions BMS to level 2. It offers programmable balancing, programmable cell level HVC and LVC, cell temp readings and cutoff temp. It can display pack level instantaneous voltage and instantaneous current. It also determines SOC using the instantaneous current and voltage measurements. It can be noted that the Elite BMS can only be purchased with GBS battery cells.

    Maybe you can add Cell-loggers (with modifications, ie a charger disable circuit) as a Level 1 option.

    Just as reference the charge shuttling can be accomplished with capacitors or inductors. Inductors offer the most efficient and quickest balancing from what i remember, but like chef statemented these are complicated and almost no one is trying to design these BMSs
    Last edited by Nuts & Volts; 12 March 2011 at 2050.
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    Not to be taken seriously DaveAK's Avatar
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    Quote Originally Posted by Nuts & Volts View Post
    Just as reference the charge shuttling can be accomplished with capacitors or inductors. Inductors offer the most efficient and quickest balancing from what i remember, but like chef statemented these are complicated and almost no one is trying to design these BMSs
    I have one on my desk.

    At least I have a TI evaluation board that does just that.

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    Moderator Nuts & Volts's Avatar
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    Quote Originally Posted by DaveAK View Post
    I have one on my desk.

    At least I have a TI evaluation board that does just that.
    Well of course and El Moto'er is doin it. We straight up BAMFs.

    Is it capacitor based? I grand ideas once to do a inductor based setup, i don remember why i picked inductor over cap except for the reasons i stated above
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

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    Ah yes, need to shoehorn cell temps in one of the levels. Thanks for the info on Elite Power Solutions and the CellLog 8s.

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    Not to be taken seriously DaveAK's Avatar
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    Quote Originally Posted by Nuts & Volts View Post
    Well of course and El Moto'er is doin it. We straight up BAMFs.

    Is it capacitor based? I grand ideas once to do a inductor based setup, i don remember why i picked inductor over cap except for the reasons i stated above
    It uses inductors. And also monitors cell temps. I haven't played with it much yet, but I want to see what it takes to scale it up to the size we need.

  10. #10
    Moderator Nuts & Volts's Avatar
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    Quote Originally Posted by DaveAK View Post
    It uses inductors. And also monitors cell temps. I haven't played with it much yet, but I want to see what it takes to scale it up to the size we need.
    Dave you have all the cool toys! That was my dream BMS, but now I would rather save my money and rather save up and use cells that only require a Level 1 system.

    By the way this level system could be awesome. If any new members come on we can point them to this thread and they can tell them to go for a level 11 BMS someday. Level 11 will work like a microwave, but instead of pushing the popcorn button you push the LiPo quick charge option or the max energy charge buttons.

    Also I would suggest making the charge shuttling and bleed resistors should be on two different levels. The availability, complexity and cost between the two is pretty significant IMHO.
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

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