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BQ2000T charge rate for delta T detection

Phil Bromley
Prodigy 80 points
Other Parts Discussed in Thread: BQ2000T

I am using a circuit based on the one in the BQ2000T data sheet (Figure 11 page 13 rev D). It is charging a 3 cell NiMH battery at about 1 amp. It worked fine when charging a 1.8Ah battery, but now we are switching to a higher capacity battery of 2.4Ah, and I am getting some problems.

What I am seeing is that the batteries are getting a lot hotter when being charged. I have changed the resistor divider on the TS input to allow a higher temperature on the thermistor, but I am still not getting a consistent termination. With some batteries the charger will terminate on high temperature cut-off rather than delta T.

My question is can I reduce the charging current to reduce the heating in the batteries, while still detecting the temperature rise at end of charge? What is the minimum charge rate for reliable delta T detection?

Thanks,

Phil