NiMH Rechargeable Batteries


The newer nickel metal hydride (NiMH) power cells are a vast improvement in the ability to do vast amounts or intensive amounts of electrical work as compared with the old-fashioned NiCad (nickel cadmium). They are also a lot more environmentally safe,

Cadmium is a very toxic metal, making for expensive, safe disposal.

The real advantage, however, is power capacity and in some applications NiMH batteries actually out perform one use alkaline batteries.

In digital flash cameras, for example. These use a vast amount of power to light the LCD display, charge up the capacitor for the electronic flash, keep the picture in memory on the card and then operate the various components required to adjust the camera for proper exposure and capture the image.

In recent tests I got nearly four total 8 Mb memory cards full of maximum resolution images with NiMH batteries, but barely two full cards worth with standard NiCad batteries. When I tried a set of fresh Alkaline batteries they wouldnít even give me five full pictures before the warning lights appeared on the Panasonic Lc-20.

I had been using NiCad in my portable walkman for several years now and was surprised just how long NiCads can last, NiMH are said to be just as stable. I was getting about two weeks work of intermittent use out of a set of AAA batteries in that unit. NiMH would probably give three to four weeks, as they do discharged slightly faster than NiCad (which have a storage life of a month).

Some rechargers, such as the Radio Shack 23-406 I got years ago, are capable of handling both NiCad and NiMH, but there is an adjustment switch. If your charger isnít compatible donít put the wrong type batteries into the unit or you could end up exploding the batteries!

The cost of NiMH batteries, are, however, much higher. Upwards to twice the cost unless you wait for a bargain or comparative shop, like I do on a regular basis. I once found a set of 4 NiMH batteries with a slow charging unit for less than the price of just the batteries.

NiCads are about $3 - $4 a pair. NiMH are $6 - 8 a pair. So far Iíve saved more than four times the cost that all my NiCad and NiMH batteries, plus their chargers cost in the years Iíve owned them.

There are, however, some applications that these batteries are not good for. Some music devices that use 9V batteries wonít fit the rechargeables, such as wireless hand-held microphones, which was a drag because those things eat batteries like crazy.

The voltage level is lower than normal flashlight or alkaline batteries, however the constant voltage in a circuit is more stable. Regular flashlight batteries start at 1.5 volts and drop to under 1.2 volts with a load, while rechargeable batteries maintain a 1.25 voltage throughout most of their useful working time.

This may have been part of the reason alkalines petered out on me in the digital camera. The voltage drop after several discharges may have lowered the threshold of power below what the camera needed, as when I put those same batteries into a flashlight they worked quite well.







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