![]() If your charger charges at a high charge rate, do a temperature check. If you want to improve battery performance with a low-cost charger, estimate the battery state-of-charge and set the charge time accordingly. ![]() Low-priced consumer chargers are prone to incorrect charging. Many battery users complain about shorter than expected service life and the fault might lie in the charger. In essence, this battery has shrunk to half the size while the fixed timer is programmed to apply a 100 percent charge without regard for battery condition. ![]() The same scenario occurs if the battery has lost capacity and can only hold half the charge. Harmful overcharge can occur when charging partially or fully charged batteries, even if the battery remains cold. At a C rate of 0.1C to 0.3C, the voltage and temperature profiles do not exhibit defined characteristics to trigger full-charge detection, and the charger must depend on a timer. It is difficult, if not impossible, to slow charge a NiMH battery. Modern chargers accommodate both battery systems. A NiMH in a NiCd charger would overheat, but a NiCd in a NiMH charger functions well. The differences in trickle charge current and the need for more sensitive full-charge detection render the original NiCd charger unsuitable for NiMH batteries. NiCd is better at absorbing overcharge and the original NiCd chargers had a trickle charge of 0.1C. NiMH dislikes overcharge, and the trickle charge is set to around 0.05C. Rather than achieving the expected 350–400 service cycles, the aggressive charger might exhaust the pack after 300 cycles. Although a higher capacity is desirable, filling the battery to the brim adds stress and shortens the overall battery life. Known as the “step-differential charge,” this method works well for all nickel-based batteries.Ĭhargers utilizing the step-differential or other aggressive charge methods achieve a capacity gain of about 6 percent over a more basic charger. This scheme continues until the battery is fully charged. The charge continues at a lower current and then applies further current reductions as the charge progresses. When reaching a certain voltage threshold, a rest of a few minutes is added, allowing the battery to cool down. Some advanced chargers apply an initial fast charge of 1C. Many chargers include a 30-minute topping charge of 0.1C to boost the capacity by a few percentage points. These “or-gates” utilize whatever comes first. Well-designed NiMH chargers include NDV, voltage plateau, delta temperature (dT/dt), temperature threshold and time-out timers into the full-charge detection algorithm. This requires electronic filtering to compensate for noise and voltage fluctuations induced by the battery and the charger. NDV in a NiMH charger should respond to a voltage drop of 5mV per cell or less. A mismatched or hot pack reduces the symptoms further. Negative Delta V to detect full charge is faint, especially when charging at less than 0.5C. The charge algorithm for NiMH is similar to NiCd with the exception that NiMH is more complex.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |