I was thinking of an op amp comparator.
On Thu, Apr 17, 2014 at 10:01 PM, Lee Hart <[email protected]> wrote: > Michael Ross wrote: > >> EBikes and such often (always?) have a pack assembled with an >> interface-less BMS. The low warning is it shuts off. >> > > I have an Ebike with a lithium pack, and that's how it works. Its "fuel > gauge" isn't very accurate; but at least it shuts off the pack when it > reaches "empty". I don't really know what its criteria is for this, or > whether the pack really is empty or not. But that's OK. I can always pedal > to get where I'm going. :-) > > > Bottom balancing does obviate the need to worry about this somewhat, >> though >> you still want to find your lowest capacity cell and stop charging soon >> enough to pamper that one. >> > > With the BMS built into the pack, you don't really know (and aren't > allowed to find out) whether the cells are bottom balanced, or top > balanced. You can't really do anything about it, anyway; it's a sealed > unit, with no access to individual cells. If it works right, the internal > BMS prevents overcharging, and over-discharging. > > The drawback is that as soon as one cell fails, the whole pack fails. I've > cut open laptop packs that quit like this, only to find that exactly one > cell had failed, rendering the whole pack "bad". If I cut it open and > replace the bad cell, in works again. Maybe $10 for a cell instead of $100 > to replace the whole pack. :-) > > These internal BMS often aren't very good. They do the minimum necessary > to prevent fires and other catastrophic failures, but don't do much to > extend the life of the pack. > > > Lee, I really like your website which I had not seen before. Thanks for >> doing that. I hope you get payback from it. >> > > Thanks! But it's mostly a labor of love. No flash and no glamor means only > a few sales a month... > > See, I have a problem. I favor simple, cheap solutions. So simple and > cheap in fact, that no one will buy them! They either don't believe it will > work and so buy something expensive and complicated that has extravagant > advertising claims. Or, they see that it works, and so build it themselves! > Either way, I get nothing... > > > How much use would a Batt-Bridge that is adjustable be? As in set the >> allowable difference between pack halves that send the warning? I don't >> instantly see where any hysteresis comes from. Is it the difference in >> drop between the green and red LEDs? Are there any disadvantages to the >> Batt Bridge? >> > > It's an analog device; not digital. The more the imbalance, the brighter > the LED lights. The two divider resistors determine how bright it can get. > With modern superbright LEDs, even 10ma is enough to see in sunlight. > > The threshold at which it first begins to glow is set by the difference in > forward voltage drop between the green and red LEDs. You could make it > adjustable by using something like a TLV431 "adjustable zener" with a > trimpot in place of the green LED. > > > On Thu, Apr 17, 2014 at 7:50 PM, Lee Hart<[email protected]> wrote: >> >> Peakfoto Digital Photo Still n Video wrote: >>> >>> I have a an ev scooter, with 22 lfp cells. I'm using min bms board >>>> and evpower cell moduals and an aq Cycle anlyist. >>>> >>>> BUT it'd be nice to have a some kind of an setable audble alarm , >>>> while driving if a/any cells get below a set point. so I can know >>>> "the end getting close " not " you better stop NOW!" . >>>> >>>> I kinda know about CELL logs , but sound s a alttle messy. I don't >>>> need a screen on the dash. any reasobale ideas? >>>> >>>> >>> If you already have a BMS, doesn't it have an undervoltage alarm? >>> >>> You don't *have* to monitor every cell to know if one is undervoltage. If >>> you want something very cheap and simple, try my Batt-Bridge. It splits >>> the >>> pack into two halves, and compares the voltage of each half. If they are >>> different, some cell has just went dead, and is at a lower voltage. >>> >>> The Batt-Bridge normally lights an LED. But you can use the LED of an >>> optocoupler, and have the output of the optocoupler turn on a buzzer or >>> other more noticeable indicator. >>> >>> The Batt-Bridge is described more fully at: >>> http://www.sunrise-ev.com/LeesEVs.htm#battbridge >>> >> > -- > If you're not stubborn, you'll give up on experiments too soon. > And if you're not flexible, you'll pound your head against the wall > and you won't see a different solution to a problem you're trying > to solve. -- Jeff Bezos > -- > Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/ > group/NEDRA) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do With your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140418/0b410956/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
