Jason McNeil Posted September 13, 2015 Share Posted September 13, 2015 Energy regeneration from braking is of mixed benefit: while it is nice that some of the recaptured energy can be recovered back to the battery pack, the information provided from the battery industry is that any slight over-charge to a fully-charged cell will considerable 'stress' it, & dramatically reducing the packs life expectancy. Method: This test was on a fully charged King Song 800W, 680Wh, connected to an EagleTree eLogger with a sample rate of 50Hz. According to manufacturer, the instrument can only record current in a single direction, so instead of the typically configuration, BAT connected to the Battery & ESC to the controller, for this test, the connectors were reversed (Bat-> CB, ESC-> Battery pack), with the expected result that only power from regeneration is captured.Result: fortunately the eLogger is able to record both the power draw during acceleration & recovered energy in braking. In the output graph output, we see that the voltage drops from 67v to below 62v in a couple second & during hard-braking, the voltage immediately springs back, & in some cases, exceeds 72v. Discussion: for those using their eWheel in low-lying flat areas, these transient excesses into the +67v territory shouldn't worry to much about it. However, for owners wishing to use their eWheels on continuous descents, especially with fully charged batteries, it could do a great deal of harm to their eWheel's battery pack. Devices with less cells are more susceptible to degradation, as there is proportionally more stress per/cell (same energy, but cells to soak it up..).In light of this evidence, it is strongly encouraged, that before engaging in any prolonged braking on a full pack, that they either a) the user not fully charge the pack, try to use up some of the pack before heading out.Future work: the issue of degradation on account of regeneration has not been satisfactorily addressed by any of the manufacturers—the exact degree of this problem needs further research & investigation. The ideal solution would be to have the controller rate-limit the voltage/current to the battery-pack within the battery manufacturer's defined limits, dissipating the excessive energy into some sort of thermal resistance with active cooling. These are not trivial solutions, but neither are they insuperable—I believe that many of the premature Wheel failures are primarily a direct result of over-charging during regen. UPDATE:It should be stressed that over-charge phenomenon is not specific to King Song; later on I did similar set of tests with the Ninebot E: fully-charged voltage is around 61v. While testing discovered the cut-out point is 1500W, where the voltage falls through the floor at 47.24v, before cutting out. It's a curious result, because even though the KS 800W only has twice as many cells, the voltage is far more volatile under load. In these tests, my acceleration was about half as much as the KS800 before giving out... Link to comment Share on other sites More sharing options...
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