Hi
I've been using the BQ2000 based fast charger (1 A) for a 2S NiMH pack but lately when connecting a pair of Eneloop cells to a transmitter after the first charge, it occurred to me the cells were not fully charged. The transmitter has a power gauge so the difference was immediately apparent for the cells when they were freshly installed vs after 1 charge.
I then used another charger with a slightly faulty termination but it did charge the cells to full capacity. This got me investigating things a little deeper and it seems the -dv of 3.8mv for the IC is much lower than the cell's. Eneloop cells are made to have a -dv of 5mv (as per factory specs) so I guess that's the reason the BQ2000 charger was terminating prematurely.
The faulty termination charger allows me to set the -dv value as it is expected that this rate would increase as the cells age. I have 2 questions here :
a) How can I alter/scale the BQ2000's -dv of 3.8mv externally ? I'm thinking perhaps an external feedback divider circuit that would continue sending the average peak battery voltage until the set -dv was detected, and then send the actual battery voltage to terminate fast charge ? (meaning until the 5mv -dv was detected, it would keep sending the peak avg voltage).
b) Does this -dv value for cells increment with each additional cell in series or is it constant for the entire battery pack regardless of the number of cells ?
Thanks for your inputs
Regards