I wonder, were the four batteries manufactured in the same batch? or even built the same day? or not? The description indicates measurement almost immediately upon stopping the charging, usually we wait two hours for temperature internally to stabilize, and the voltage difference from a 13 volt stack in one package is only 0.03% different from the 13 volt stack in another package. That seems very acceptable in a series string of four packaged where only a few degrees difference in internal package temperature can result in that much variation. and on the initial charge where you have no history or obviously no bottom balancing because that is not in favor with newer chemistries. If you were using four different digital meters to measure them simultaneously, I would suspect the meter accuracy at +/- 0.03% (in addition to one digit +/- in the rightmost place due to "aliasing") to be the reason for the variation. But, using the same meter, the readings normally show the variation validly. The accuracy of a meter is from a "standard," not from reading to reading in the same scale or range, in normal usage...
*Dennis Lee Miles * *Founder**/**Director/CEO:* *E.V.T.I. Inc. **[dba]* *Electric Car Service Shop, * *Director/Chief Technology Officer:* * EV-Solar-Hybrid Systems Innovation Center * *E-Mail:* *[email protected]* <[email protected]> *Phone #* *(863) 944-9913* *Temporary Office:* 33408 Trilby Road, Dade City, Florida 33523-6435 USA *This electronic message and any attachments are for the sole use of the intended recipient(s). They may contain confidential and/or privileged information or other information subject to legal restrictions regarding disclosure and/or dissemination. If you are not an intended recipient of this message, any review, re-transmission copying, use, disclosure, or dissemination of this message or its attachments is prohibited. If you received this message in error please notify the sender by replying to this message and deleting or destroying all copies of this message and any attachments. * On Mon, Feb 3, 2014 at 12:42 PM, Cor van de Water <[email protected]> wrote: > Michael, > One reason that batteries differ in their charging voltage in series > charging is that one battery may reach full a little before others, so you > need to continue charging at a much reduced charging rate (less than 0.03C) > to avoid gassing out sealed batteries (losing water) to equalize them. > Since this was the first charge, you can find they are aat slightly > different SoC, so they need to be pulled together more. > A battery Balanced can help there too. > Then there is the issue of temperature: > If one battery finishes charging a little earlier than another, > that battery will start warming up (the equalization produces gas and heat > - as long as the charging is below the limit where the battery can > recombine the gasses, all charging energy will be converted to heat. When a > battery is warmer, it has lower internal resistance and the charging > voltage goes down. > This can even lead to thermal runaway if you charge a battery to a fixed > voltage. > There probably are other reasons, such as slight differences in the > concentration of the electrolyte, but I am no expert there. > > I have found that batteries can show different voltages while charging and > still behave pretty much the same, you just need to keep an eye on pushing > them closer together with every charge to avoid one drifting away from the > herd and getting killed early. > > Success, > > Cor van de Water > Chief Scientist > Proxim Wireless Corporation http://www.proxim.com > Email: [email protected] Private: http://www.cvandewater.info > Skype: cor_van_de_water Tel: +1 408 383 7626 > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Michael K Johnson > Sent: Monday, February 03, 2014 3:25 AM > To: Electric Vehicle Discussion List > Subject: Re: [EVDL] dissimilar voltages charging series string of > AGMbatteries > > On Sun, Feb 2, 2014 at 7:36 PM, Michael Ross <[email protected]> > wrote: > > Just brainstorming, your meter is probably not better than ±0.01. You > can't > > be sure that 13.32 in't 13.33, and 13.36 isn't 13.35. If you are going > to > > make money and time decisions based on this you should take multiple > > readings and be convinced of a stable state. > > The readings were relatively consistent (the same across multiple > readings), > though I know not absolutely accurate (adding up the four battery voltage > measurements is consistently off by .1-.2% from measuring the chain > all together in a single reading, and I have not tested the multimeter > against > a reference voltage to know how close it is). > > > Anyway it sounds like a tiny difference to me. > > To me too. It was the larger difference while charging that made me > curious and thus seek the wisdom of the crowd regarding a physical > model for that difference. > > > On Sun, Feb 2, 2014 at 9:38 PM, Lee Hart <[email protected]> wrote: > > That's why I generally keep these parts in stock. See > > http://www.sunrise-ev.com/LeesEVs.htm#zenerlamp > > I wish the EVDL page on them linked to your page so I would > have seen that before ordering. Oh, well. :( > > > On Sun, Feb 2, 2014 at 5:05 PM, EVDL Administrator <[email protected]> > wrote: > > Connect the 4 batteries in parallel and leave them that way for as long > as > > you can - at least a week or two. This may not totally equalize the > state > > of charge among them, but it will at least tend to equalize the VOLTAGE. > > There might be just enough time for me to do that before mowing season, > at which point I should be able to put the charging regulators on. ☺ > > > Thanks everyone! > _______________________________________________ > 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) > > -------------- next part -------------- An HTML attachment was scrubbed... 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