Published 31 Mar 2018
Sort Batteries
The proposal is for a machine to help recycle domestic batteries by sorting them into Zinc/Carbon, Alkaline, Lithium, Nicad, Ni-Mh categories and with a theme of sustainability/recycling the machine discharges any cells that have residual charge into the machine to power it.
It could also assess the health of cells to decide whether they were actually near new and should be re-used rather than recycled, especially expensive rechargeable cells.
I am thinking here of A, AA, AAA, B, C, D type cylindrical cells that can all be handled in a similar way. I am envisaging a simple mechanism mechanically that has a feeder/hopper into which cells are dumped, they then roll down a chute one by one, and they are scanned as they rotate, to read their labels. Any unidentified cells go into a separate output bin. Identification could be through OCR and text matching or image pattern matching of the entire label. There would need to be an initial 'training' period.
Implementation notes
- I am thinking of minimal complexity hardware, and all the work done by software. So the mechanism would just be required to release one cell at a time down a chute, in either polarity orientation (ie it wouldn't worry about which end was which). So the rest of the system would handle cells either way around with regard to positive/negative terminals.
- The feeder mechanism can measure the diameter of the cell to assist with scanning the label around the circumference. Probably the easiest way to measure diameter is with a lever arm that the battery passes under.
- There is perhaps no logical start/end to labels apart from the seam
- The scanning could be done with a linear CCD sensor synced to the battery being rotated, like the old document hand scanners that used a roller to clock the scanner as it was moved across a page.
- Voltage/discharge characteristics could be used for identification, but difficult due to the unknown state of the cells.
- Charging characteristics would be dangerous to assess unless the cell was already determined to be rechargeable
- Pre sorting of leaking batteries would be required as wouldn't want leaking battery material throughout the machine. Perhaps liquid or stains on the battery label could be detected.
- To measure battery health, and discharge batteries a connection needs to be made to either end, with some batteries there needs to be significant pressure (eg a spring) pressing the contact onto the battery to ensure the end-caps contact the internal anode/cathodes properly. Might need some sort of battery terminal clamp that is opened momentarily to admit the battery, battery contacts can be automatically centred with a lever that adjust for height (diameter) of the battery.
More musings
Real recycling plants are quite concerned about the purity of their inputs, eg they don't want any non lithium-ion cells mixed into the waste recycling stream or it will contaminate their chemical outputs. It occurs to me that another good distinguishing feature of cell technology is density - probably a bit messy to immerse the cells into liquid to measure displacement, but as these types of cell are all regular shapes (cylinders), it's not too difficult to measure their length, diameter and weight to determine density.
Powering it from the discarded cells would be a fun aspect, but I have no idea of whether the amount of power available would be the right order of magnitude to be feasible. I can imagine the machine being solar powered and doing a sort of bootstrapping operation, where it starts off early in the morning (first light) just using solar energy to slowly sort through cells until it finds enough residual power to start running the machine at full speed. At the other extreme, if there is a lot of “cell waste” power available, the machine can be used for recharging other devices too (eg phones, laptops … electric cars 
). Maybe it would have to flare-off the extra power by powering the locations lighting or even heating/cooling.
To minimise power consumption, we probably want to minimise handling of each cell (ie not move it from station to station for different functions).
We can probably have the system using gravity for most of the movement through the system, to minimise the energy needed.
If we detect rechargeable batteries we can test them with a charge then discharge them back into the system reservoir (need to monitor heating during charging).
This is the sort of project that could be implemented in dozens of different ways, eg a marble-track type arrangement with the cells rolling through the system, stopping at different stations along the way to be processed, then dropped into the appropriate bin, or a series of robot arms to pick up, orientate, and place the cells as appropriate. Maybe it could be a whole Instructables competition category 
.
Links to Useful Resources
- Everything you need to know about batteries Overview of battery types and technologies.
- Joule thief, extracting energy from low voltage sources.