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I can report back to anyone interested, that this pack is still working great. I still have the original 8 cells, with the two "el cheapo" ebay BMS modules. Tiffany runs around everyday from 7:30AM until almost 11AM. She is exactly the same as she always was, in terms of noise and erratic behavior, but has a lot more stamina! Approx 3.5Hours of runtime. Take note Mr Hoover, install Lithium cells in your robot vac, they're much better.I'm guessing they used brushed motors in her as well, and that will be the next thing to replace :)
Hi Mrygula,The Roomba may have been trying to draw more current than your cells could provide. You may have had one bad LiIon cell, that's what happens with laptop packs, one cell effectively kills the lot. Do you recall if they were hot? Did you use thick enough gauge wire? The 20AWG wire should be good for 11Amps, which is way more than I require.Also, what voltage requirement is the Roomba? Did you match it or get close enough to the original design?
Hi Jeff22,The ebay BMS manages the charge state of the batteries. The internals of the Hoover delivers charging power to the battery pack at about 17V, and the BMS takes over from there. I may revisit the solution if I find that the cells are failing or *gasp* exploding, but in the few weeks it's been operating, all has been fine.The only issue I have noticed since installing is, the "Full Go" option doesn't function, as it doesn't actually get full in it's eyes. A full NiMH pack will "Burp" to let it know it's done 14.4V. The LiION pack should not get overcharged due to it's higher voltage capacity of 16.8V. The most I have seen the pack charge to is 16.1V, which is well below the maximum of the lithium cells.
Getting Started with Electronics
Hoover Tiffany (5240) Robot...View Instructable »
Thanks! It's so frustrating trying to use Putty to get the thing to do anything! I bought a pretty cheap Amica one from Ebay ($4), and have been fiddling for a few hours trying to get the firmware right.Anyway, after that, following your quick tutorial, and changing the "pinMode(16, OUTPUT);" and for the other references to 13, it flashes the onboard blue LED just fine. Now to tinker some more :)h
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