This is a battery load test for the Karcher RC3000. It is identical to Vic7767's load test for the Roomba battery (see http://www.vic7767.com/how-do-i/
).UPDATED 29 MARCH 2012 - see "CYCLING UPDATE" belowDo not try this yourself unless you're confident in what you're doing - shorting batteries is dangerousBackground to this test
The need for this test arose due to a discussion regarding the impossible length of time Karcher RC3000 batteries seem to last. There are at least 6 members on this forum who have Karchers in excess of 6 years old, that are/were still working on original batteries. My oldest Karcher is between 6-7 years old, and cleans min 80sqm 2-3 times a week. Given that the Karcher returns to base to empty/recharge typically every 20-40 minutes, that's an awful lot of cycles over 6+ years... many, many more than the accepted 500-1000 cycles for a NiMh battery (up to 1200 according to Panasonic).
A member rightly pointed out that, logically, NiMh batteries couldn't possibly last that long... and he's right, in theory at least! So I promised to load-test my 6+ year old ones to see what they were still capable of...Test set-up
The Karcher was fully charged on its own base before the batteries were removed. Karcher uses 2 x 6v NiMh batteries at 1700mAh (10 x 1.2v cells) wired in series to give 12v at 1700mAh total capacity. To make this as accurate as Vic7767's accepted Roomba test, the batteries are wired in series and the load (lamp) is identical to Vic7767's - an MR16 12v lamp drawing 20watts (the Karcher draws 18w, so like the Roomba, its near identical to actual consumption of the robot itself). A digital volt meter is wired in parallel to monitor the voltage. The test cut-off I determined as 10 volts to make the test similar to Vics (although I'd usually cut-off at 0.9v per cell).Test results
At full charge, after 20 minutes rest, the batteries showed a combined total (series) voltage of 14.07v. The test ran until the voltage showed 10.00v. The time elapsed was 43 minutes
. In theory, this means that the Karcher is still capable of running up to 43 minutes on 6+ year old batteries! Well, it impressed the heck out of me since my Karcher normally returns to base within 20-30 minutes, presumably to empty rather than charge! I have no logical explanation as to why these batteries can last that long after all these years, but the test clearly shows that they can (and frequently do).Cycling to (hopefully) improve performance
Samsung quote their Navibot SR8855 battery to have a servicable life of 1 year. After 18 months, my orginal 14.4v/2000mAh Navibot battery was giving a poor 26 minutes maximum run-time. Cycling that battery increased that life to a consistent 67 minutes! So here I'm going to cycle these old Karcher batteries, then repeat Vic7767's load test and update the results - to see if these batteries performance/run-time is/can be improved. As the Karcher would charge these batteries in series, I'm going to cycle them in that manner too although better results would be likely if cycled individually.CYCLING UPDATE 29 March 2012
: Normally when cycling a battery you’d expect to see a progressive increase in the amount of charge being taken into and discharged from the battery pack with each cycle. That didn’t happen here. Over 4 consecutive discharge/charge cycles, these 6+ year old Karcher batteries returned a remarkably consistent 1470-1473mAh over each cycle - quite a high proportion of their original 1700mAh capacity. Repeating vic7767’s load test showed a marginal increase to 51 minutes
(the maximum theoretical run-time of the robot). It’s not the dramatically improved performance you’d normally expect and usually obtained when cycling, for example, the Samsung Navibot battery which showed a more than doubling of run-time.
The Karcher does not drain its batteries once its finished cleaning as other robots do, but neither does it "max out" its batteries on every cleaning cycle. These unexpected cycling results lead me to suspect these batteries are indeed being “hyper-cycled” – a theory first suggested on this forum by Spirit Force. This is a methodology used by electrically assisted cars such as the Toyota Prius - frequent cycling in shorter bursts using just a small percentage of the batteries total capacity to prolong life well beyond the norm. Spirit Force has suggested a method to test/measure this theory which I will try, and update results here when I can: It may hopefully help explain why these batteries last so long! But for now I need my charger back to cycle my work tool pack batteries...