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(Real) Intelligent NiMH Chargers?
Anti_Climax asks: "I, like many Slashdot readers, have a lot of battery powered devices. With the large number of cells that are in use at a given time, I have taken to using NiMH rechargeables (Ten 2.0Ah Cells for $10 at the local Fry's Electronics). My current charger is a timed unit that was made when 1.3Ah was the norm. I have accepted the fact that if I want my cells charged properly and quickly, I will need to invest in an intelligent charger. With the dozens of manufacturers in the market right now, the Google results are promising but far too broad. What have been your personal experiences in this area? How many of the supposed Smart Chargers are anything but? Who's offering the best deal for my dollar? While I don't need my cells to charge in 15 minutes, I would like to find an inexpensive Intelligent charger that can charge 4 or more high capacity cells (in pairs or individually) in an hour or less."
This subject was covered a while ago in this ask slashdot. I remember because I bought my charger just after it being published.
My advice is that you just buy whichever one that *clearly* states that is microchip (that is deltaV) controled rather than stopped by timer. Mine is a Hama and it works well.
For the batteries, check this comparison. To sum it up, the more mAh the better, brands are usually not that important.
Rechargeables are not the best idea for low(est) power devices. A common TV remote control operates on two, sometimes three Alkaline cells for two or three years, sometimes even longer. Most, if not all, remote control chips are optimized for this operation mode. True, if you press a button on a remote, it draws a lot of power for the infrared LEDs. One ampere is not unusual. But it sends very short pulses (or else the LEDs would literally burn), and the real power does not come from the battery, but from an electrolyte capacitor contacted in parallel, via a very small resistor, to the battery. It is rapidly discharged by the LEDs, and then charged again by the battery. The battery just has to provide a very small current to recharge the capacitor after each pulse, and an even smaller, permanent current for the controller chip. Alkaline cells have a very low self-discharge factor, so they can work like this for years. The remote control continues to work even if the alkaline cell is nearly dead (1.3 V), but with a reduced range (because of the lower available energy due to the lower voltage) and with a noticeable recovery time. When the voltage is so low that the chip does not work properly, it starts to send nonsense to the TV (and may under certain circumstances crash the microprocessor inside the TV - nobody is perfect).
If you replace the alkaine cells with NiCD or NiMH, this lowers the available voltage by 0.3 volts per cell (NiCD=1.2 V, alkaline=1.5 V), thus reducing the available engergy for the LEDs, thus reducing the range of the remote control. Those rechargable cells discharge themselves, so you need to recharge them often. But at that time, you want to use your remote control as well, so you need two pairs of rechargeable cells, and you need a charger. Probably a good one, so it does not kill your cells while loading them. And after some time, your rechargeables are dead because they had nothing "to do". So you need two new pairs of cells, probably after two years. Just about after the same time that you would have bought the first new pair of alkalines (the first one is usually included).
Just calculate for yourself: Using rechargeables in remote control is nonsense. And if you are concerned about the environmental impact: At least here in Germany, there is a well-working return system for alkaline (and zinc carbon) cells (in fact, you have to return your used cells).
The same is also true for other low(est) power devices, like clocks and calculators with liquid crystal displays (LCDs), and most analog quartz clocks. Radio controlled analog clocks need a little bit more power and a "high" voltage for the receiver, so they can not drain alkaline cells as much as clocks without receiver and remote controls.
My "BRAUN" electical toothbrush uses a single NiCd cell which is permanently charged when it sits in its "docking station". After about one year of permanent "keep alive" charging, the cell is now nearly dead. It still can hold enough energy to work for five minutes, but when it is disconnected from the wall outlet for more than a few hours, it simply does not work and needs two days to recharge. The cell is sealed into the toothbrush, having a predetermined breaking point in the case to take out the cell for disposal, so I can not replace the cell without permanently damaging the toothbrush. A trick I've seen too late on TV: Do not permanently charge the toothbrush, discharge it while using, and connect it only to mains when it is empty. It will need round about a day to charge. This will avoid the memory effect.
About batteries and cells:
A cell consists of two electrodes (the positive anode and the negative cathode), the electrolyte, and a case. Depending on the materials used, a single cell has 1.2V (NiCd and NiMH), 1.4V (zinc air button cells), 1.5V (alkaline and zinc carbon), 1.55V (Silver / Quicksilver button cells), 2V (Pb=lead acid), 3V (Lithium), o
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