JnB Posted April 14, 2016 Share Posted April 14, 2016 Hi I have just ordered a KingSong ks16-A with 840 wh battery (presumably with a fast charger) I would love to protect my new baby as best possible, so I was considering buying the Charger Doctor V2http://hobby16.neowp.fr/2016/02/06/charge-doctor-v2-10a-3/ Could anyone advise if this is a good idea, and potentially about what settings to use for optimal protection? Perhaps even @hobby16 :-) /Jon Link to comment Share on other sites More sharing options...
US69 Posted April 14, 2016 Share Posted April 14, 2016 It is a Very good idea...and Hobby16 described it the best way himself how to set it: http://hobby16.neowp.fr/2016/02/29/what-is-the-recommanded-charge-current/ Link to comment Share on other sites More sharing options...
jbwheel Posted April 14, 2016 Share Posted April 14, 2016 Once you approximately know long you need to charge after some trips, best and cheapest protection is a mechanical timer. You should also not leave charging batteries without surveillance. Link to comment Share on other sites More sharing options...
TwixFix Posted April 14, 2016 Share Posted April 14, 2016 I have the KS14C 840wh w/fast charger I ordered from @Jason McNeil via eWheels.com. I've been using the Charge Doctor V2 and it works great. I have logged the charging curve and consulted @hobby16 and have mine set to cut off at 1.8 amps for ~90% charge assuming the battery is indeed 840wh. I'm currently trying to determine the real capacity of the pack which requires charging the battery when fully discharged, but the pack is so large that it's a pain to use up all the battery. Link to comment Share on other sites More sharing options...
JnB Posted April 14, 2016 Author Share Posted April 14, 2016 Thanks all for your input - and especially @TwixFix for giving me some suggestions for actual values I have ordered the CDv2 nad looking forward to see it in action :-) Link to comment Share on other sites More sharing options...
viti Posted April 15, 2016 Share Posted April 15, 2016 Hi, I think in the following Thread by @Jason McNeil you'll find the exact Voltage data and further info. Why Fast-Charging Rocks Started by Jason McNeil, 6 April Link to comment Share on other sites More sharing options...
hobby16 Posted April 15, 2016 Share Posted April 15, 2016 On 14/4/2016 at 4:52 PM, TwixFix said: I have the KS14C 840wh w/fast charger I ordered from @Jason McNeil via eWheels.com. I've been using the Charge Doctor V2 and it works great. I have logged the charging curve and consulted @hobby16 and have mine set to cut off at 1.8 amps for ~90% charge assuming the battery is indeed 840wh. I'm currently trying to determine the real capacity of the pack which requires charging the battery when fully discharged, but the pack is so large that it's a pain to use up all the battery. Indeed, discharging such a massive battery is not easy, it's called a richman's problem This is an empirical way to determine the battery's capacity without fully discharging it. It's an in-the-ballpark estimate based on the fact that the more capacity, the more time it takes to increase a same amount of voltage for a same charge current. It suppose various simplifying hypothesis : - charge current is constant during sampling period - voltage increase is linear from 0 to 90% capacity Full capacity Wh can then be estimated by "hobby law" Wh = 800 * I * delta t /delta V I : charge current delta t / deta V : sample point data from V(t) graph Example of calculation on a KS 840Wh charging curve, data taken between points A & B (chose an interval of 1h or 2h where voltage is relatively linear and current is constant) I = 3,65A delta t =2h, delta voltage= 65,0V-58,0V = 7V => delta t / delta V= 0,286h/V (meaning it takes about 0.286h = 17 minutes to increase battery voltage by 1V) => capacity = 800*3,65*0,286 = 835 Wh I get my wheels' total capacity with about 5% accuracy using this formula. Try "hobby law" yourself to see if you can get the same result. Link to comment Share on other sites More sharing options...
checho Posted April 15, 2016 Share Posted April 15, 2016 On 4/14/2016 at 8:02 AM, JnB said: Thanks all for your input - and especially @TwixFix for giving me some suggestions for actual values I have ordered the CDv2 nad looking forward to see it in action :-) The recommended voltage to make the batteries last is 64.8v, this represents an 80% charge. The first time you use the charge doctor do not worry about the current cut off monitor the voltage as it goes up, once the voltage reaches 64.9v look at the Amps it is charging, that will be your current cut off point, it will be specific to the charger and battery pack. A better solution is to use a high quality charger like the satiator but the cost will be significantly higher, that way you can program the trickle currents when the battery packs are extremely discharge or near full, the bulk current and the cut off voltage. I highly recomend both the charger doctor and the satiator charger. It is bad to fast charge a lithium battery when the voltage is extremely low, for example anything below 48v would be considered too low, the bms will protect the voltage from being too low, but if the voltage where to be very low it is best to trickle charge and then bulk charge, only a good charger will do that. Link to comment Share on other sites More sharing options...
hobby16 Posted April 16, 2016 Share Posted April 16, 2016 17 hours ago, checho said: The recommended voltage to make the batteries last is 64.8v, this represents an 80% charge. The first time you use the charge doctor do not worry about the current cut off monitor the voltage as it goes up, once the voltage reaches 64.9v look at the Amps it is charging, that will be your current cut off point, it will be specific to the charger and battery pack. Good point. Note that cut off voltage will be dependent of charge current since the Charge Doctor's voltage reading is a value under charge. Ideally, cells' voltage must be measured with no charge current to remove the biais voltage caused by the cells' internal resistance : chargers cut current, sample voltage, then reestablish current to continue charge (that is also how it can determine the cells' internal resistance). But of course, the Charge Doctor can't do that because of the protection diode on the BMS (you can only inject power to the battery through charging port, not seek power, nor measure its voltage). Anyway, once you have the full charge curves and an approximation of the 100% capacity, there is no problem to determine the 80% charge cut-off setpoint. As to 48V, I wouldn't say it's a "too low voltage" battery, it's a dead battery (LiIon batteries) ! On all my wheels, at around 54V, there is a tilt back that force you to climb down. It's impossible to discharge the battery to a lower voltage. I have summarized various voltage thresholds here : http://hobby16.neowp.fr/2015/08/08/how-to-to-care-of-your-unicycles-battery/ Link to comment Share on other sites More sharing options...
JnB Posted May 14, 2016 Author Share Posted May 14, 2016 Thanks for all the tips I still haven't gotten my new wheel, but I have been using the Charge Doctor on my old one. I usually save the logs, so I can review them again later. It is a little troublesome to use use the graph viewer although @hobby16 did a great job to make easier I created a small app, than can help view the files - and figured I would give a little back by supplying it here - the zip file includes source and executable (compiled to .Net 3.5) You enter the path to the kst2 executable and the log file, it then generates a session file (kst) and a batch file to launch it, and does so Attached a couple of screenshots /JnB LogHelper.RENAMETOzip Link to comment Share on other sites More sharing options...
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