NiMH Battery Charger

GOALS

  • Ability to charge up to (6) AAA,AA,C,D and (2) 9V Batteries
  • Design biased towards Panasonic’s Eneloop chemistry
  • Charge all capacities in under 6 hours.
  • Full speed charging no matter how many batteries installed at once.

THE WHY

I have a bunch of Panasonic (Sanyo) Eneloop AA/AAA batteries and I love them.  I really like the fact that they hold a charge when sitting on the shelf.  I currently have three charges:  Nitecore Intellicharger i4 (AA/AAA), Thunderbolt Magnum (AA/AAA/C/D/9V) and Duracell Accu Charger (AA/AAA).  I don’t really have any problems charging my AA/AAA batteries, as all three chargers handle that reasonably well.  My problem occurs when trying to charge my 11,000mAh D-cell batteries.  The Thunderbolt Magnum and the Rayovac charger I had before that, would never get the D-cells up to full charge.  They would seem to charge for about 8 hours and then just shut off leaving me with half-dead D-cells.  I think part of the problem is most chargers have an 8-hour safety timer to minimize the risk of overcharging NiMH batteries.  While I believe this is a simple safety solution, the problem is you cannot charge 11,000mAh batteries in 8 hours when your charge rate is only 375mA.

This battery charger project aims to remedy this problem by have all charging channels capable of delivering up to 2.5A.  This should allow us to charge a 13,000mAh battery in under 6 hours.  And since this is one-half the maximum charge rate for high-capacity D-cells, it should be safe.  I also would like to implement the most accurate detection using both dT/dt and dV/dt methods. And since a full charge should take only 6 hours, I”ll even keep an 8 hour safety timer.