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08/08/2004 |
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Ansmann Battery Chargers Don Bradbury takes a look at a pair of high performance units to keep your digicam batteries in top condition.
The ubiquitous AA size battery now powers countless devices, the particular interest here being the digital camera. Of these, despite the introduction of dedicated Lithium rechargeables, some can still use Nickel Metal Hydride (NiMH) AA cells as an alternative power source. Rechargeable batteries are the thing these days, not only because they are far more cost effective than Alkaline cells, accepting up to 1000 charge/discharge cycles, but also because Alkalines show poor operational life in digicams. Alkalines simply cannot deliver the current required without sagging the cell’s voltage to such a degree that the camera thinks they are exhausted long before they actually are. NiMH cells are the preferred option for the format, Nickel Cadmium now being ‘old hat’ on technical grounds that we needn’t go into, and Lithium rechargeables being hitherto incompatible with the AA battery format, though they are now beginning to come in. But NiMH cells need some taking care of; they simply will not stand up well to factors such as deep discharge, over-charging, and over-heating. What you need for such cells is a smart battery charger, and German company Ansmann have produced a range. Options We looked at the ‘Energy 4’ and the ‘Digispeed 4’, which came complete with four AA size 2300mAh cells in the former case, and four AA size 2200mAh cells in the latter case.
The ‘Energy 4’ is a microprocessor device that features individual cell control. When rechargeables are inserted it first makes a quick check on capacity, auto-diagnoses the state of each cell and reports any that are faulty, then carries out a refreshing program in which any tired cells are detected, and then uses Delta Peak control for each cell’s recharge. Delta Peak has to do with the control of input voltage and cell temperature, thus minimizing damage to the cell’s chemistry and structural integrity. The ‘Energy 4’ concludes the recharge program with an automatic switch-over to a safe trickle charge that can be used to maintain full charge without over-charging and thus compensate for the NiMH cell’s major inherent weakness, that of self-discharge. Any cell will run down in storage, but the NiMH suffers more than most, hence the need for top-up trickle charging. Status LEDs A range of LEDs show refreshing, charging, ready, and error modes, and users should be prepared for about 15 mins of the former when camera-dead batteries are inserted, before charging proper starts. This worked well. Although the cells got quite warm during charging, the rate of charge is such that temperatures are within safe limits provided the ventilation holes are not covered. Between 4 hours and 4 hours 13 mins was required for all four of these high capacity cells to be reported as fully charged. Coming with a smart range of plug-in adapters, and an auto-voltage sensor, this device can operate in all European countries, the US, Japan, and Australia, so that will satisfy the inveterate traveler. Microprocessor control of charging is indicated by eight flashes of the status indicators each minute, and every aspect of charging is well looked after, including auto-detection of NiMH or NiCd cells. In fact this unit can accept AA cells, AAA cells, or 2 x 9V block cells. It also features a safety timer in case poor quality cells are inserted. Speed charging The ‘Digispeed 4’, in contrast, is a much higher speed, fan-cooled device that can charge AA size NiMH cells in an hour at a current rate of 1.75A. Well, it can if they are 1500mAh capacity. The supplied cells were the more up-to-date 2200mAh type, and here the full charge time was around 90 mins.
The Digispeed can also charge batteries via a supplied 12-18V DC adapter; a noteworthy addition for the traveler, making the unit useable in car, boat, caravan etc, and all with individual cell management. Amazingly, the cells remained quite cool in the Digispeed, and this with a fan that was merely intermittently on. Again microprocessor controlled, damaging heat was all but absent, and there was never any fear that they would suffer heat damage from the high rate of charging this unit can deliver. That said, not all of the cells supplied initially charged at the same rate. Starting with discharged cells, on the first run one cell was reported to be fully charged in 15 mins, another in 16 mins, a third in 20 mins and the last in 50 mins, whereas full charge should not have been reached until 90 mins. After discharging, three were recharged a second time in the full 90 mins, indicating a charge to full capacity, but one cell was still reported as fully charged in only 24 mins. At the third cycle, all the batteries were cut off at essentially the same time, indicating that full charge had been accepted on all four channels. Cycling We were left wondering whether this phenomenon was due to the particular set of cells or the Digispeed’s fast charging routine, but Ansmann said it is normal. “Two or three cycles of charge/discharge should be expected before full capacity is guaranteed with any NiMH cell”, ie avoiding premature cut-off of the charging voltage. “The initial charge is, in fact, completing the manufacturing chemistry of the NiMH cell, and full cell charge is given only when this is carried out by the user.” The Digispeed is again fully automatic, incorporating a full set of status LEDs (though in this case without a refresh function) and was most impressive in the way it handled cell temperature through its Delta Peak technology and reasonably quiet fan. In fact the only drawback of this unit, for those who must have charging completed quickly, was the need to manually select NiMH or NiCd cells before charging. Ansmann told us that despite the superior temperature control with the ‘Digispeed 4’, the longest cell life, ie maximum number of charge/discharge cycles, is still given by the technology of the ‘Energy 4’ - for those who can afford to wait. ‘Digispeed’ technology is for those who cannot afford to wait for a more traditional, lower current charger bringing their AA cells to full charge, and they pay for that in somewhat reduced battery life – perhaps 500 cycles rather than an anticipated 1000. In conclusion While £50 for a battery charger may seem a little steep, you’re paying for superior technology that can avoid reduced life in NiMH cells. Such advances have to be paid for, and the bottom line is that we were impressed by these two Ansmann chargers and their respective high capacity NiMH cells. The life of the latter we cannot, of course, comment upon, but the essence of a good NiMH battery is low internal impedance, an initial capacity as claimed, with minimal capacity decrease in the short term – as you may find with inferior brands.
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