Special charger needed for Nickle Metal Hydride?

Thread Starter

Gdrumm

Joined Aug 29, 2008
684
I have an old cordless vacuum with a 14v NiMH battery, but I don't have the charger.

Can I use one of my many wall-warts (same voltage, or slightly more) to charge it?

(I know how to set up tips and polarities, etc.)

Thanks,
Gary
 

bertus

Joined Apr 5, 2008
22,270
Hello,

Here is a quote from the Batteryuniversity :

The nickel-metal-hydride battery

Research on the nickel-metal-hydride system started in the 1970s as a means of storing hydrogen for the nickel hydrogen battery. Today, nickel hydrogen is used mainly for satellite applications. nickel hydrogen batteries are bulky, require high-pressure steel canisters and cost thousands of dollars per cell.

In the early experimental days of nickel-metal hydride, the metal hydride alloys were unstable in the cell environment and the desired performance characteristics could not be achieved. As a result, the development of nickel-metal hydride slowed down. New hydride alloys were developed in the 1980s that were stable enough for use in a cell. Since then, nickel-metal hydride has steadily improved.

The success of nickel-metal hydride has been driven by high energy density and the use of environmentally friendly metals. The modern nickel-metal hydride offers up to 40% higher energy density compared to the standard nickel-cadmium. There is potential for yet higher capacities, but not without some negative side effects.

Nickel-metal hydride is less durable than nickel-cadmium. Cycling under heavy load and storage at high temperature reduces the service life. nickel-metal hydride suffers from high self-discharge, which is higher than that of nickel-cadmium.

Nickel-metal hydride has been replacing nickel-cadmium in markets such as wireless communications and mobile computing. Experts agree that nickel-metal hydride has greatly improved over the years, but limitations remain. Most shortcomings are native to the nickel-based technology and are shared with nickel-cadmium. It is widely accepted that nickel-metal hydride is an interim step to lithium-based battery technology.

Here is a summary of the advantages and limitations of nickel-metal hydride batteries.


Advantages


  • 30-40% higher capacity than standard nickel-cadmium. Nickel-metal-hydride has potential for yet higher energy densities.
  • Less prone to memory than nickel-cadmium - fewer exercise cycles are required.
  • Simple storage and transportation - transport is not subject to regulatory control.
  • Environmentally friendly - contains only mild toxins; profitable for recycling.
Limitations

  • Limited service life - the performance starts to deteriorate after 200-300 cycles if repeatedly deeply cycled.
  • Relatively short storage of three years. Cool temperature and a partial charge slows aging.
  • Limited discharge current - although nickel-metal-hydride is capable of delivering high discharge currents, heavy load reduces the battery's cycle life.
  • More complex charge algorithm needed - nickel-metal-hydride generates more heat during charge and requires slightly longer charge times than nickel-cadmium. Trickle charge settings are critical because the battery cannot absorb overcharge.
  • High self-discharge - typically 50% higher than nickel-cadmium.
  • Performance degrades if stored at elevated temperatures - nickel-metal-hydride should be stored in a cool place at 40% state-of-charge.
  • High maintenance - nickel-metal hydride requires regular full discharge to prevent crystalline formation. nickel-cadmium should be exercised once a month, nickel-metal-hydride once in every 3 months.
They need a special charging device to prevent overcharging.

Bertus
 

marshallf3

Joined Jul 26, 2010
2,358
I have an old cordless vacuum with a 14v NiMH battery, but I don't have the charger.

Can I use one of my many wall-warts (same voltage, or slightly more) to charge it?

(I know how to set up tips and polarities, etc.)

Thanks,
Gary
If it's old the batteries may already be past their useful life. I'd try charging it at slightly higher than the 14V for an hour or so, if it will still charge you could go on to figuring out the amount of time at a specific current you'd need then plug the charger into one of those $4 timers.
 
Top