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06-22-2010 | 02:44 PM

#24

TimBle

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From: Cape Town, SOUTH AFRICA

RE: Battery condition?

i can't be bothered to argue: took this from wiki.

ΔV charging method

According to Panasonic and other NiMH cell manufacturers, the ΔV method is one of the preferred charging methods for charging. The charger measures the rate of change (signified by the symbol Δ) of the voltage of the cell (signified by the letter V). This is illustrated in the "NiMH charge curve" figure. The cell or battery is rapidly charged at a constant current of 1 C/h, where C is the capacity of the battery (the capacity is expressed in ampere hours, or more commonly milliampere hours (mA·h). After the cell is fully charged, and as it begins to overcharge, the voltage polarity of the electrodes inside the battery will begin to reverse, and this will cause the battery voltage to decrease slightly. A ΔV type battery charger ends the charge cycle by switching off the charging current when it senses this drop in voltage. In some cases, a very small "trickle charge" may remain. The "charge curve" graph also shows that the charge voltage will change depending on the charge current (it also changes with temperature and battery age). This generally means that a constant-voltage charging method cannot be used automatically, because it will either be unsafe, or it will not charge batteries reliably and consistently. This is unlike a lead-acid cell for example, which can, in theory, be more easily charged at a suitably chosen constant voltage.[7]<h3>ΔT temperature charging method</h3>

The ΔT temperature change method is similar in principle to the ΔV method. Because the charging voltage is nearly constant, if constant-current charging is used, then a near constant power is entering the cell. When the cell is charging, most of this power will be converted to chemical energy. However, when the cell is fully charged, most of the charging power will then be converted to heat. This results in an increase in the rate of change of temperature, which can be detected by a sensor measuring the battery temperature.<h3>Manual charging</h3><div class="thumb tright"></div>

If a suitable battery charger is not available, constant-voltage or constant-current charging can be done manually, at a moderately high charging rate, if careful attention is given. For proper charging, the voltage and/or current must be set to a suitable charging rate for the particular battery, and a timer should be set. Periodic monitoring is strongly recommended to avoid overcharging (resulting in a voltage drop), or overheating (resulting in an excessive temperature rise and possibly an overpressure condition).[citation needed]

It is safer just to use a C/5 or C/10 charge-rate. [8]<h3>rickle charging</h3>

Some equipment manufacturers consider that NiMH cells can be safely charged in simple fixed, low-current chargers with or without timers, and that permanent overcharging is permissible with currents up to 0.1 C (where C is the current equivalent to the capacity of the battery divided by one hour). According to the Panasonic NiMH charging manual, extensive trickle charging can cause battery deterioration due to overcharging, and it is the least preferred charging method concerning battery performance. If it is used, the trickle charge rate should be limited to between 0.033 C and 0.05 C for a maximum of 20 hours to avoid damaging the batteries.[7]

For a slow charge, or "trickle charge" process, Duracell recommends "a maintenance charge of indefinite duration at 0.0033 C".[9] Some chargers do this after the charge cycle, to offset the natural self-discharge rate of the battery. To maximize battery life, the preferred charge method of NiMH cells uses low duty cycle pulses of high current rather than continuous low current.

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