robca Posted August 26, 2015 Share Posted August 26, 2015 Thanks to an idea in the BMS/shunting thread (http://forum.electricunicycle.org/topic/459-electric-unicycles-bms-problem-and-solution/), I'd like to suggest this mod to monitor the individual cell health of a battery pack.Assuming you don't mind soldering, it's a cheap (~$6 plus a couple of weeks waiting time for shipping) and effective solution that also adds a single cell alarm to warn you of possible ageing problems ahead of time.I use these for my RC models, and they work exceptionally well: http://www.ebay.com/itm/FC-1-8S-Lipo-Li-ion-Fe-Battery-Voltage-2IN1-Tester-Low-Voltage-Buzzer-Alarm-/221849272720 (if the link doesn't work, search for "lipo alarm 8s", picture below). The alarm can be set between 2.7 and 3.9, and the alarm is super-loud. Each cell is monitored independently (i.e. if you set the alarm for 2.8V, as soon as just one cell hits that value, it starts beeping). You will need 2 of them (since one monitors up to 8 cells)Then 2 of these http://www.ebay.com/itm/New-8S-JST-XH-Connector-balance-silicone-wire-CellLog-9-PIN-/181713383731 (if the link doesn't work, search for "jst 8s", picture below). They have nice, super flexible silicone wires, that will simplify positioning things inside the limited space.Finally solder those wires to your battery pack. That's the past where you need to locate each battery terminal, cut a small hole in the heat shrink, and solder a wire where battery meet, following the enclosed schema (see below). There is a point where the GND of one alarm is connected to the 8s terminal of the other (since that alarm is designed to measure a series of batteries). Pay attention to the red wire on each connector (marked on the circuit), and solder wires in order. Insert the alarms into the JST connectors (respecting polarity, red wire to 8s terminal, but they are protected in case you insert them upside down). The alarms will show the exact value of each cell in turn, then the value of their half pack (should show between 25 and 33.6V).If you set the alarm to, say, 2.8-3V, you will get a sharp beep as soon as one of the cells goes that low (with no cutoff or other side effects, if you shunted). If you place the alarms so you can see them, it will tell you which cell is the lowest. If you see that one cell is always the one triggering the alarm, you know you have a cell that is at risk. If different cells trigger the alarm, you have a healthy packWhile in theory this could be replicated for bigger packs (32 and 64 cells), given that those packs are used in parallel, the risk of a overloaded battery is much lower. This seems a good insurance for single pack EUCsPlease note that the alarm draws 13 mA when connected, so you should either add a switch on the GND leg to disconnect it when storing the EUC for a long time (during short trips the impact will be negligible) or remove the alarm from the JST connector when storing it. It will take a super-long time to actually discharge a battery, but I think that its power is always provided by the cell connected between GND and pin 1, so that battery will end up being over-discharged compared to the rest of the pack if you leave it on for more than a week) Link to comment Share on other sites More sharing options...
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