I have a loop based BMS system which will stop the charger if the loop opens so I could rig up a circuit with a relay to open the loop but I prefer to use the configuration in my existing charge controller. Jay Summet
On January 5, 2016 11:07:14 PM EST, Ben Apollonio <[email protected]> wrote: >Hi Jay, > >I think your approach is good. Some chargers (Elcon, at least) let >your BMS throttle charge current with an external voltage signal. If >your charger supports this, you could try wiring up a comparator and a >flip-flop to latch the signal at 0A when you hit your target voltage at >30A. > >Cheers >-Ben > >On Jan 3, 2016, at 9:28 PM, Jay Summet via EV <[email protected]> >wrote: > >> I want to charge at maximum current to 80%, and then shut off. My >thoughts on this subject are listed as text below, or you can follow >this link to see the images of my charging profiles: >> >> >http://www.summet.com/blog/2016/01/03/default-charging-profile-charge-to-80-capacity-quickly/ >> >> I welcome any comments about issues or tricks I may have overlooked. >> >> Thanks, >> Jay >> >> >> >> Because I have a relatively short commute, and rarely anticipate >needing my full 100% pack capacity, I have chosen to charge my truck to >an 80% SOC on a daily basis to maximize battery life. One nice thing >about the 80% level is that most batteries can be charged at a >relatively high rate of speed up to 80%, and then you need to slow down >the charging a bit to prevent them from overheating. (This is why DC >Quick Chargers will quickly bring an empty battery up to 80%, but then >slow down quite a bit after that.) >> >> My first attempt at programming an 80% charging profile was very >simple, just set MaxV to 128.5 and set the TermC (termination current) >to 2 amps. This works well, it gets the pack voltage up to 128.5 volts >and holds it there until the battery stops accepting much current. The >only issue is that it is wasting time, because for a good amount of the >charging period the current flowing into the battery is less than the >maximum 30 amps (4.0 kW) that the chargers can produce. The charging >curve looks like this: >> >> >http://www.summet.com/blog/wp-content/uploads/2015/09/charging_2amp_cutoff.png >> >> >> >> In an effort to speed up my charging, I set the MaxV to a higher >amount ( 128.9 volts) so that at the 128 volt level the battery pack >would still be accepting a higher current, and then set my TermC to the >highest level my EVCC allows (10 amps). This results in a charging >curve that looks like the following: >> >> >http://www.summet.com/blog/wp-content/uploads/2016/01/charging_10amp_cutoff.png >> >> >> As you can see, I spend more time delivering 30 amps before the >current draw from the pack starts to drop off, and the curve reaches >the cutoff point much quicker. My EVCC currently limits the TermC >parameter to 10 amps or less, probably because they have not >anticipated somebody trying to charge only to 80% as quickly as >possible. >> >> If I could set the TermC parameter to 20 or 25 amps it would allow me >to set the MaxV up higher (131?). The goal would be to find a voltage >setting such that the pack would be drawing 20 or 25 amps right when it >hit the 128.5 volt level. So my curve would basically be flat, full on >charging at 30 amps up until the very end when it would start to taper >off and the charging would end at 25 or 20 amps. >> I’m not worried about setting the MaxV higher than the actual voltage >I’m attempting to hit, as it is still much lower than my pack’s actual >max voltage, and if something were to change with the pack chemistry >making it miss the TermC cutoff, the MaxV would still stop the pack >from reaching 100% charged. (and the termination timeout would >eventually hit.) >> >> This is the end of my main thought, but you can continue reading >for….. >> >> Extra Info about my pack, charging to the 80% level, etc… >> >> The 48 modules from my Nissan Leaf battery pack (LMO/LNO chemistry) >are arranged in a series of sixteen sets of 3 parallel cells. This >gives me a 180Ah battery with an absolute maximum voltage of 134.4 (4.2 >volts per cell). In actual use the 4.2 VPC level should never be >reached, if you charge the cells to 4.1 volts per cell they are around >99% charged. As the extra 0.1 volt difference between 4.1 and 4.2 >doesn’t really buy you much extra capacity, most people use 4.1 volts >per cell (131.2 volts) as a safe “full” or 100% capacity on the Leaf >Cells. My Mini-BMS units will start to shunt voltage at 4.1 VPC, and >raise an over-voltage alarm at 4.2 VPC. >> >> However, if you charge the cells to 4.0-4.01 VPC (128-128.5 volts) >that corresponds to about 80% of their maximum possible capacity. To >maximize cell and battery pack life, you want to minimize the time the >cells are fully charged or fully discharged. If you can keep the cells >between a 10%-80% state of charge (SOC) it will maximize their battery >life. >> >> Keeping them above 10% SOC is easy…don’t drive until they are empty. >Keeping them at or below 80% SOC is also easy, simply turn off your >charger when they are only 80% charged. This is why the early Nissan >Leafs had the option to only charge the battery to 80%. (Removed in the >newer Leafs due to EPA regulations on how maximum range is calculated.) >> >> If you want the extra 20% of range that charging to 100% SOC would >give you, it is better to charge to 100% and then immediately discharge >the pack by driving it (as opposed to leaving it sitting at 100% charge >all night). This is one reason why Nissan Leaf’s have a charge timer, >so that you can tell the charger to finish just before you start your >daily drive. (The other reason is so that you can tell it to start >charging only after the low cost nighttime electricity rates start, if >you are on a time of use metering rate plan.) >> >> My 2nd charging profile will be a 4.1 VPC full 100% capacity charge, >for when I feel the need to really go long distances. (or to get the >pack ready for a top balancing equalization charge, my future 3rd >charging profile.) >> >> Jay >> _______________________________________________ >> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >> http://lists.evdl.org/listinfo.cgi/ev-evdl.org >> Read EVAngel's EV News at http://evdl.org/evln/ >> 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/20160106/18c482ac/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
