William's Workbench

Several years ago I got a good deal on a used Romba Discovery. A good cleaning and an AC adapter from the parts bin later it worked fine. The battery didn’t have much life in it after a few months of use so I bought another on eBay and all was well.

Fast forward a couple of years and the little robot had fallen into disuse but still sat patiently on its charger. Upon trying to start to use it again the battery gave out. After a charge it would give anywhere from 1 to 30 seconds of run time before flashing red and crying pitifully that it needed a charge. Some internet searching and forum reading led to a battery conditioning technique that is recommended by the manufacturer. I also took this opportunity to finally build a serial interface for the Roomba (more bits from the parts bin = $0 cost). Thanks to a few lines of Perl to parse the serial output and gnuplot I have pretty graphs of the battery charging cycle (that is currently 52 hours into the recommended 72 hours).

Click on the graphs to embiggen.

Here is voltage and current for the first 52 hours. You can see that the most interesting stuff happens in the first 17 hours.

 

Here is voltage/current and voltage/temperature for the first 17 hours. Something radical appears to happen around the 3 1/2 hour mark.

 

Hmmm, not sure what that means. Did the battery do something (possibly vent) due to heat? 40C isn’t all that warm but who knows.

After the 72 hours is up I will run the Roomba and see what kind of behavior I get.

 

Update

The battery did not respond to the reconditioning. One new battery from eBay later and the Roomba is back to normal.

This entry was posted on Thursday, February 24th, 2011 at 9:58 pm and is filed under Electronics, Robotics. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.