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Thread: What You Shouldnt Do When Building a EV

              
   
   
  1. #31
    Old EV Racer EVcycle's Avatar
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    Just so everyone understands my position on a BMS. (please read it completely)

    Some BMS units are good and some, not so much. Not too many I have seen out there work perfect as you have heard from some of our other members.

    On a motorcycle they can corrode and the extra wiring can be a nightmare. On a sealed vehicle (car or bike) you have a much better chance of success.

    AT THIS TIME, the really good BMS units are relativity expensive. Now you see why we have the two camps of BMS and non-BMS folks.

    I am in the middle.

    Each project and designer (that is you) requires a different look at the battery systems and what is best for that project.

    There is more than one way to monitor batteries and different setups NEED a BMS. I have run the Headway's long enough to understand what
    they need and how well they stay balanced when charged the way I do it. 26 chargers is not for everyone, but I do get a full balanced charge every time.

    I have also killed more batteries than most of you..... and that was with a (crappy) BMS.

    I have not killed one since.

    If you need one, get it.

    Crazy Ed .
    Last edited by EVcycle; 16 November 2012 at 1627.
    EV Ed
    Never let being a responsible adult get in the way of passion and curiosity.
    Motenergy.com
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  2. #32
    Senior Member larryrose11's Avatar
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    Ed, I talked to you on the phone about this idea back in elmoto_v1. I cant say it was my idea. Glad it has worked out so well for ya.

  3. #33
    Old EV Racer EVcycle's Avatar
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    Quote Originally Posted by larryrose11 View Post
    Ed, I talked to you on the phone about this idea back in elmoto_v1. I cant say it was my idea. Glad it has worked out so well for ya.
    Yes we did! See...... I do listen ..... sometimes!
    EV Ed
    Never let being a responsible adult get in the way of passion and curiosity.
    Motenergy.com
    Ev album 2456, 2458, 2457, 2681, 3456, 3630, 5511, 5512

  4. #34
    SMPS Engineer BaldBruce's Avatar
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    Just the accronym "BMS" causes confusion! Jack R gets on his soapbox real quick about the word, when what he abhores is actually a Battery MANAGEMENT System. He still manually monitors and balances his cells himself! The bare minum, as Travis points out, is a Battery MONITORING System. I use two of RWaudios cell log holder boards on my 144V car system. (We both have 944 conversions so we chat once in awhile..) His boards each hold 4 cell log 8s. Link to his blog is here: http://electricporsche.ca/ He has a store front on his blog to sell his designs and also other commercial conversion parts.
    I have not failed. I've just found 10,000 ways that won't work.
    Thomas A. Edison

  5. #35
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    Quote Originally Posted by EVcycle View Post
    Some BMS units are good and some, not so much.
    On the not-so-much ones (which seem to vastly be population dominate), the BMS acronym is battery MURDERING system.

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  7. #36
    Senior Member moon's Avatar
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    If having a proper BMS means more cool gauges, readouts, blinking lights, datalogging, and HUDs to cram on the dashboard consider me in the pro-BMS camp.

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  9. #37
    Senior Member Hugues's Avatar
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    i wish we have more neutral and fact based statistics here so we can better judge the risks and benefits of BMS vs non-BMS.

    Confirmation Bias makes it that we remember and talk more about a story where a BMS damaged the cells than another one where cells were damaged due to lack of BMS.

    So, to re-establish a bit the odds, i link to a recent LiPo fire, caused by charging cells without any kind of balancing or monitoring:
    http://endless-sphere.com/forums/vie...p?f=14&t=45561
    i read stories like this on weekly basis.

    my two cents,
    Regards from Switzerland
    My 2.5 Upgrade Thread

  10. #38
    Senior Member jonescg's Avatar
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    There are scores of threads filling the interwebs of the benefits or otherwise of a BMS. I see it as a trade-off between complexity and convenience, safety and simplicity. I see benefits and drawbacks of many BMS options, including none at all. So you eventually have to ask yourself,

    1. Do you lend your e-moto out to others?
    2. Could a numpty get on your bike and ride it till it's dead flat, then overcharge it with the wrong charger?
    3. Would the systems in place prevent the bike and house from catching on fire, or even protect the bike from damage?

    If the answer to 1 is yes, then you had better come up with solutions for 2 in order to prevent either option in 3.
    If the answer to 1 is no, then you have assumed responsibility for the monitoring of your battery. And this is cool; I happen to like this option, but it needs more vigilance.

    I recently saw a case where the BMS didn't prevent damage to the bike, and somehow managed to flatten every cell in the pack to 0.5 volts. Shouldn't the BMS have prevented this? Turns out the BMS was turned off to save power and the user thought that charger was charging very quietly (it wasn't working at all).

    I would tend to agree that most BMS problems are human inspired, and only a few options out there really make human incompetence difficult, but these are way more expensive and complex.

    Maybe like riding bikes without helmets, or driving with a 100 mm blade embedded in the steering wheel, forced vigilance is a good thing? Food for thought.

  11. #39
    Ghost Rider Allen_okc's Avatar
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    Quote Originally Posted by liveforphysics View Post
    On the not-so-much ones (which seem to vastly be population dominate), the BMS acronym is battery MURDERING system.
    you know once in while, you really make my day...
    The Greatest thing about a EV, is the Song of the Terrain...

  12. #40
    teddillard
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    I think a few things are pretty obvious. First, a BMS would be a lot less necessary on a bike with a transmission. ().

    Second, Jack Rickard or however you spell it talks too much.

    Third, we're all using lithium batteries with a BMS in two of the most ubiquitous products on the planet today - cell phones and laptops, so the challenge is to scale those up to the size needed for an EV at a reasonable cost, which, to my eyes, hasn't been done yet, thus my use of a similar charging system to Ed's - individual balance chargers on my RC lipo (which work really well, my neglectfully leaving my controller on for a few days notwithstanding). So, kidding aside, I get right back to my conclusions on transmissions... when I can get one that works, and I can afford, maybe I'll give it a shot.

    Fourth, I don't like gauges and lights... and that's really the reason I don't believe in BMS's.

    Fifth, Confirmation Bias is an awesome concept. Cognitive Dissonance is equally awesome. "Dissonance is aroused when people are confronted with information that is inconsistent with their beliefs. If the dissonance is not reduced by changing one's belief, the dissonance can result in restoring consonance through misperception or rejection or refutation of the information, seeking support from others who share the beliefs, and attempting to persuade others".

    Sixth? NonPolluter must be sleeping late, what with him not joining the "BMSs destroy Batteries" fray and all...
    Last edited by teddillard; 17 November 2012 at 0602.

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