That is Brilliant! I love living in the future :) And I love that my pack will cost somewhat less for the same KVA.
On Thu, Jun 18, 2015 at 5:29 PM, Cor van de Water via EV <ev@lists.evdl.org> wrote: > The Lee Hart alternative of this solution is to have only a single pack, > add a (very low current) tap in the center of the pack, connected to two > super-bright LEDs mounted in a very visible place (on the dash right in > front of you). Connect the two LEDs in anti-parallel so whichever direction > there is more than about 2V difference, one of these LEDs will light up. > Connect the other side of the 2 LEDs to a voltage divider that goes from > pack+ to pack- and which in rest outputs the same voltage as at the tap. > If you have an even number of cells/modules then this voltage divider is > simply two identical resistors in series across the pack so the center > point > is at exactly half pack voltage. If you have an odd number, one of the two > resistors needs to be a little bigger than the other (or use 2 in series or > use a potmeter in between the two resistors so you can fine-tune the > divider > to be equal to the tap. > Alternative could be a simple cheap zero-centered meter as often used in > the > current meters (can measure positive and negative) and place that instead > of > the two LEDs. Any imbalance between the two pack halves is indicated by the > LEDs or this meter. > Size the resistors so they allow for a small current, enough to light the > LEDs > or move the meter - you can easily test this by deliberately tapping the > pack > one cell too high/low and watching the result. > for example, if you have a 120V pack then you will tap this at the 60V > point > and to get a 1mA through one of two red LEDs at that voltage when you have > an > (arbitrarily) 6V deviation between tap and the average of the pack, then > you > need a resistance divider of 10k + 10k Ohm. Note that this put a constant > drain of 6mA > on the pack - not a whole lot since it needs almost a week before it > drains 1Ah, > so even a moderate 100Ah pack would last almost 2 years from full to dead. > But it is something to be aware of and disconnect when you store an EV. > The approach with the needle meter is more sensitive since those typically > have > 100uA full scale so you would use at least 10 times bigger resistance value > and this leads to 1/10th of the drain. > Regards, > > Cor van de Water > Chief Scientist > Proxim Wireless > > office +1 408 383 7626 Skype: cor_van_de_water > XoIP +31 87 784 1130 private: cvandewater.info > www.proxim.com > > > This email message (including any attachments) contains confidential and > proprietary information of Proxim Wireless Corporation. If you received > this message in error, please delete it and notify the sender. Any > unauthorized use, disclosure, distribution, or copying of any part of this > message is prohibited. > > -----Original Message----- > From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Sean Korb via EV > Sent: Thursday, June 18, 2015 1:41 PM > To: Electric Vehicle Discussion List > Subject: Re: [EVDL] Bicycle battery > > This sub-subject gets done to death pretty regularly but I like gathering > what I hear from both camps. Definitely going to use a BMS but I really > like the non-BMS workaround of getting *two* expensive battery packs and > using a really simple gauge that shows their comparative voltage. If one > is sagging more than the other, pull over and find out what is wrong. If > you have a smart BMS... it takes care of it for you until you can get home > ;) > > sean > > On Thu, Jun 18, 2015 at 3:58 PM, Cor van de Water via EV < > ev@lists.evdl.org> > wrote: > > > Paul, > > In your case, *you* were the BMS. > > But you were lucky that you noticed the lower end voltage and knew > > something was off. > > You were lucky that the charger finished charging without cooking the > > other cells to death You were lucky that the bad cell was a short and > > not a partial failure or you might not have detected it in time or > > faced a much more severe situation than a shorted cell. > > Anyone less knowledgeable than you about your EV (and that would be > > 99+ percent of all drivers) would not have caught this failure and > > continued until disaster, so your vehicle can be used by you alone, > > because you are an essential part of that vehicle! (namely, the BMS) > > It looks like you just confirmed the thing that you tried to disprove... > > > > Cor van de Water > > Chief Scientist > > Proxim Wireless > > > > office +1 408 383 7626 Skype: cor_van_de_water > > XoIP +31 87 784 1130 private: cvandewater.info > > www.proxim.com > > > > > > This email message (including any attachments) contains confidential > > and proprietary information of Proxim Wireless Corporation. If you > > received this message in error, please delete it and notify the > > sender. Any unauthorized use, disclosure, distribution, or copying of > > any part of this message is prohibited. > > > > > > -----Original Message----- > > From: Paul Dove [mailto:dov...@bellsouth.net] > > Sent: Thursday, June 18, 2015 11:13 AM > > To: Cor van de Water; Electric Vehicle Discussion List > > Subject: Re: [EVDL] Bicycle battery > > > > I had this issue early on in my vehicle and at the end of charge my > > pack voltage reflected this and I removed the bad cell. The cell was > > shorted but the rest of the pack was fine. I have no cell monitoring. > > > > Pretty sure it was caused by a loose connection. That said, apart from > > expense I have no problem with a BAttery Monitor that looks at every > > cell but prismatic cells have multiple cells in them in parallel so > > you can't monitor them individually. > > > > Still of the opinion it is an unnecessary expense. > > > > You haven't convinced me that cell discharge or drift between SOC is a > > real issue. I cat see it ever being an issue. > > > > Sent from my iPhone > > > > > On Jun 18, 2015, at 12:44 PM, Cor van de Water via EV > > > <ev@lists.evdl.org> > > wrote: > > > > > > Paul, > > > It is true that in series string the same *load* current goes > > > through all cells, but the principle of self-discharge is that it > > > occurs internal to the cell, so it is invisible to the outside world > > > except when you measure each cell (or blow them up due to overcharge > > > or > > under-discharge). > > > I have actually measured cells and seen the self-discharge. > > > As you say, it is a small effect in good cells. > > > But still, there is about 1:2 difference in self-discharge between > > > the cells I monitor and the differences add up over time. > > > It might not be a problem in the first year or even in the second. > > > Then in the 3rd year you try to squeeze an 85 or 90% discharge from > > > the cells and boom - one reverses (or more) and it is destroyed and > > > you might only find out from the fireworks when you try to charge it > > > the > > next cycle or when you drive it. > > > Oh BTW - one reason to monitor *all* and *every* cell is exactly the > > > issue with the infamous bottom-balancing without BMS approach: > > > Some of the cells that I have were abused and too deeply discharged. > > > Guess what happens? They become a resistor. > > > Some are "low" resistance which is OK when they resemble a wire, > > > others are still "in doubt" whether they want to become a piece of > > > wire > > or rather a heating element. > > > This has at least 2 disastrous effects if you do not detect this > > immediately: > > > > > > 1. The pack voltage has dropped and each cell now gets a much higher > > > finish charging so you might have been charging conservatively with > > > all cells in the string, but with some cells "removed", all the rest > > > is dividing up the difference and may easily be charged to > > > destruction > > now! > > > > > > 2. If charging does not harm the pack, what about discharging > > > hundreds of Amps through a resistor that is nicely embedded in the > > > pack, insulated from the outside by the cells around it? If it even > > > drops 10V across it at hundreds of Amps, you now have a > > > multi-kiloWatt heater > > inside your pack without much cooling. What do you think will happen? > > > > > > Just some easy illustration of the *need* for a cell-level BMS, from > > > practice by measuring what happened to a used set of Lithiums (that > > > indeed was run without BMS) and I have been monitoring since taking > > > it > > out of service. Learn from it or get your own experience, your choice. > > > > > > Cor van de Water > > > Chief Scientist > > > Proxim Wireless > > > > > > office +1 408 383 7626 Skype: cor_van_de_water > > > XoIP +31 87 784 1130 private: cvandewater.info > > > www.proxim.com > > > > > > > > > This email message (including any attachments) contains confidential > > > and > > proprietary information of Proxim Wireless Corporation. If you > > received this message in error, please delete it and notify the > > sender. Any unauthorized use, disclosure, distribution, or copying of > > any part of this message is prohibited. > > > > > > > > > -----Original Message----- > > > From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of paul dove > > > via EV > > > Sent: Thursday, June 18, 2015 9:57 AM > > > To: Lee Hart; Electric Vehicle Discussion List > > > Subject: Re: [EVDL] Bicycle battery > > > > > > Excerpt:In theory, all batteries are identical. If wired in series, > > > you > > would therefore expect them all to charge and discharge equally. But > > in practice, there are differences. New batteries that are all the > > same brand, same model, same date code (and without "lemons" or > > quality control > > defects) will still have small differences. Each cell 's > > self-discharge rate, amphour capacity, internal resistance, and > > charge/discharge efficiency will be slightly different. This makes > > them drift to different states of charge. For example, cells with a > > higher self-discharge rate run down faster just from sitting. Cells > > with a lower amphour capacity get more deeply discharged on each > > cycle, which lowers their efficiency (so they need a bit more current > > to fully recharge). Cells with a higher internal resistance run a > > little hotter, which affects their efficiency and self-discharge rate. > > These differences tend to get larger over time. If not corrected, you > > can have a pack with some cells almost full, and some almost empty! > > > Ok, here's the deal this is fiction. Self discharge is so low > > > (milivolts > > over years) as to be non-existant.Secondly, if they are in series then > > all current passing through cells is equal. It is impossible to draw > > more current from one cell than another in a series pack. It can > > short and pass all current or it can open and pass no current but it > > cannot discharge faster or slower. > > > If it has higher resistance then it will cause cells to heat faster > > > that > > is all. > > > Please show evidence that your theory is possible. > > > The only person I spoke with having issues with new cells is when > > > they > > were placed in parallel with old cells. In that case the wires melted > > because the new cell was handling more of the current. You may damage > > cells if there is a big difference in resistance only if you exceed > > the max current draw from the cell. If one never approaches the max > > current draw this will not be an issue. > > > > > > > > > From: Lee Hart via EV <ev@lists.evdl.org> > > > To: Electric Vehicle Discussion List <ev@lists.evdl.org> > > > Sent: Thursday, June 18, 2015 10:53 AM > > > Subject: Re: [EVDL] Bicycle battery > > > > > > Paul Dove via EV wrote: > > >> That was a very good summary. Cell balancing is something that was > > >> done with other chemistry a and many have tried to apply it to Li > > >> Ion chemistries but it doesn't work with Lithium since cells do > > >> self discharge or drift. > > >> > > >> If one wanted to balance them it has to be done below 3.38 volts > > >> otherwise you are still charging the cell. Thanks for your input. > > > > > > Lithiums need balancing even more than other chemistries! You can > > > only get by without a BMS if the cells are so well matched that they > > > accidentally stay in balance. (Do you feel lucky?) > > > > > > Look at my own balancer at http://www.sunrise-ev.com/balancer.htm > > > I built it to *use*, not to sell. It doesn't load the cells, or > > > clamp > > the voltage at some arbitrary level, and doesn't have failure modes > > that murder cells. > > > > > > It basically does what you would do yourself, if you had the time > > > and > > inclination. It measures the voltage of every cell, and charges the > > ones that are low. > > > -- > > > The greatest pleasure in life is to create something that wasn't > > > there before. -- Roy Spence > > > -- > > > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com > > > _______________________________________________ > > > 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) > > > > > > > > > > > > > > > -------------- next part -------------- An HTML attachment was > > > scrubbed... > > > URL: > > > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150618/ > > > dc 23c230/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) > > > > > > _______________________________________________ > > > 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) > > > > > _______________________________________________ > > 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) > > > > > > > -- > Sean Korb spk...@spkorb.org http://www.spkorb.org > '65,'68 Mustangs,'68 Cougar,'78 R100/7,'60 Metro,'59 A35,'71 Pantera #1382 > "The more you drive, the less intelligent you get" --Miller "Computers are > useless. They can only give you answers." -P. Picasso > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150618/5175d1ba/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) > > _______________________________________________ > 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) > > -- Sean Korb spk...@spkorb.org http://www.spkorb.org '65,'68 Mustangs,'68 Cougar,'78 R100/7,'60 Metro,'59 A35,'71 Pantera #1382 "The more you drive, the less intelligent you get" --Miller "Computers are useless. They can only give you answers." -P. Picasso -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150618/b26026d5/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)
