Steve On 13/03/2019 17:39, Jay Summet via EV wrote:
I would recommend buying an inexpensive amp hour / voltage / watt hour meter and using that to monitor the battery. (The one I use records the data it has logged when power is removed, so that when you apply power again the AH counter keeps the last reading. You can also buy them with relay outputs that allow you to program a "low voltage disconnect" to act like a very basic BMS protection circuit...but the low voltages is based off of the entrie pack, not the individual cells....)This is the one I used on my last project:https://www.amazon.com/gp/product/B07B4CWKRJ/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1(It does not have relay outputs, but does support up to 200AH with it's current sensor...which was important for my project).You may wish to choose one with a 100 AH or lower current sensor if you will be testing at lower currents, as the accuracy of the current sensors is usually a percentage of their max rating. (Also note that a shunt based current sensor is more accurate than these magnetic sensors that you put the wire through, but if you are trying to get a very accurate measure you probably are not buying $30 meters.....)Jay On 3/13/19 10:21 AM, Dan Baker via EV wrote:I have been communicating with a couple sellers now on Aliexpress. Pricesseem quite varied and reviews are mixed on these batteries. I suspectthere isn't a lot of standards or testing on actual claimed capacities. I would like to try a 12v pack or 2 before buying more and perform some tests to verify capacity. Has anyone done this testing before? I assume the ahrating is based on a 1amp draw for x amount of claimed hours. So would I hook up a 12 watt load (LED bulbs?) and watch pack voltage till it drops till below 12v? Or would I measure it till the BMS protection cuts in - (9-10v?). Some reviewers have found packs listed at 100ah capacity to actually have only 30ah cells inside, lots of misinformation. Thank you, DanOn Tue, Mar 12, 2019 at 1:01 PM Jay Summet via EV <ev@lists.evdl.org> wrote:On 3/12/19 9:59 AM, Dan Baker via EV wrote:If I don't charge with my Sevcons and use the included individual 12v chargers, would there still be worry of connecting too many in series?Isit charging,discharging or both the issue when connecting in series?That depends entirely upon the battery model/manufacturer and the specs for that specific battery. If there is an issue, it would most likely be an issue for both charging and discharging. The thing to watch out for is if the batteries have a MOSFET (solidstate switch) that is used to disconnect the battery when charging (donecharging, voltage too high) or when discharging (voltage too low). Inmany cases, the MOSFETS are not rated for super high voltages. It may betwice the working voltage or much higher (24,36 or perhaps 60 volt rated). If your series pack goes above the MOSFET rating, it is likely to fail spectacularly (short closed in the worst case) when it is asked to disconnect the battery.If the batteries use relays or contractors, they may or may not be ratedfor higher series voltages, you need to verify. In short, the electronics that are making these batteries "drop inreplacements" for a 12 volt battery are designed to work at that voltage level...with perhaps a 2x or 4x safety factor (24 to 48 volts), but thesystem was not designed for high voltage (72-144 or higher) to be seen by the battery. The BattleBorn batteries for example use 60V electronics, and are ratedto be used in series up to a 48 volt system (They were designed this wayto be a drop in replacement for 12, 24, 36 and 48 volt solar power systems....but many "auto starter" or RV replacement batteries gave nothought about using more than one in series, or if they did, it was onlyup to a 24 or 48 volt level.) Jay _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at 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/20190313/9f300d12/attachment.html>_______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.orgPlease discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)_______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.orgPlease discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
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