24 Eneloop AA batteries Roomba 581 modification

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Re: 24 Eneloop AA batteries Roomba 581 modification

Postby glnc222 » August 19th, 2016, 1:34 pm

AA cell background info
Interesting data on AA rechargeable battery brands in comparison review, revealing issues, lot of details, tests, charging methods, trade-off between capacity and cycle longevity.
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Re: 24 Eneloop AA batteries Roomba 581 modification

Postby fergambo » October 13th, 2018, 7:30 am

Hi to all, and thanks for this fantastic post full of information

After bad experiences with all batteries I've tried for my Roomba 560, some time ago I could find this post and I've tried to make a similar battery, besides of I'm a lover of Eneloop Batteries (and my old Romba too)
As my main requirement is the possibility of easy refreshing / replacing any individual eneloop, I've used battery boxes to avoid any soldering, so I can only use 12 AA batteries.

My first test has been with normal (1900 mAh) eneloops, in order to change to pro (2500 mAh) if the experiment was acceptable.

I've put the 12 eneloops in 2x6 AA box and the thermistor (measured 10 ohm to 26 ºC, so is OK according to Service Manual) inside the box of my last Li battery, I've done a final charge (eneloops was installed charged previously), and the battery length was 45 min (so 60 min for 2500 mAh Eneloop Pro)

After charging my second test, was very similar, 43 min.

But in my third Test I've only obtained 15 min after a very short time of charging. When Roomba stopped in low battery, almost suddenly changed from green to red, and after testing battery was over 14 v, and any individual AA was over 1 v, but really pack is really hot.

For muy fourth test, the charge time was short too, si I forced a pair of additional charges ereseting Roomba, but the cleaning time was the same, 14 min.

I know charging is stopped by cells temperature, I'm not sure if during cleaning temperature stops too, the only I'm sure the voltage is correct. All this could even have some relation with the failure of my last bought batteries, start well die before one year.

My Roomba base output is fail (2v output) so I always charge Roomba directly by connecting the PSU directly into the charging jack on the side of the Roomba.

Sorry if it's not convenient to post here after two years, but it's the only thread of eneloop battery for roomba I've found

Thanks and regards
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Re: 24 Eneloop AA batteries Roomba 581 modification

Postby glnc222 » Today, 8:02 pm

Experiments were made with AA cells for Neato Botvac batteries used by one owner, maybe not too different from Roomba batteries. Testing equipment constructed showed this size cell cannot support the current drain levels of the robots without severely shortening the battery life. The Neato puts about a 3 amp load on the pack, which may be divided into less per cell depending on parallel construction. There seems to be a reason, though, why larger size cells are used in robots with their power requirements. The AA cells can appear misleading in initially running the bot but wearing out quickly.

Besides testing the cells in a robot, a continuous battery cycling tester was constructed to measure the cycle life of the cells under loads similar to the robot -- run inside a cook pot in case of any damage unattended 24/7. It was surprising to find such short life. In normal load use for that size cell I would expect much longer life. The higher load applied would seem to make the difference. There are different load specs for AA cells, some mentioned as higher load oriented. The Eneloop technology, now adopted by other brands as well, offers the advantage of long shelf life, less self-discharge in storage which was a disadvantage of NiMh cells compared to lithium in the past.

Of course, enough parallel series could reduce the load on AA cells to whatever is needed, but the number of cells and space requirements -- and cost -- could make it impractical for the robot.
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