I am seeking advice about how to construct a charging circuit for 1.2v 1200mah ni-cad batteries. I have around 60-70 of these batteries and I want to create a bulk charging circuit so I can charge 5 or more (preferably 10 or so) at once while still being able to charge only 1 at a time if that is all that needs to be charged.
I found this schematic:
and a descriptive post here: http://www.electro-tech-online.com/threads/help-me-build-a-simple-nicad-charger.90780/#post-714659
about the math behind the charging for the original posters circumstances, but I am wondering if I can simply parallel the load to multiple batteries to charge many at once. I am sure the LM317 can handle 10 batteries at 120ma charge rate.
Overall question: Is it possible to use that schematic and parallel the load to multiple batteries? Also is this math correct as per the following details:
Battery -> 1.2v 1200mah Charge rate -> 0.1C*1200mah = 120ma Charge time -> (1.4 * 1200mah) / 120ma = 14 hours R1 -> 1.25v / 0.120ma = 10.416Ω DC supply input -> (1.2v * 1cell) + 2v = 3.2v or higher
How many watts should R1 be in this situation? Is it also safe to increase the charge rate from 0.1C to 0.2C or 0.3C? I don't have any way to monitor the batteries temperature. These batteries were manufactured in 2011 so they are pretty new (if it makes a difference).