FlipBoard

Welcome to our new Magazine format! All new content will now be brought to you in this easy, new format. All our older content can still be found by scrolling below. Simply click the ">" to start the magazine and navigate via your arrow keys.

Monday, May 11, 2009

Batteries Part 2 Nickel-Cadmium

These rechargeable cells have been around for a long time, and were the only rechargeable batteries available in the standard dry cell sizes for many years. They run at a lower voltage than alkaline cells do, having 1.25v fully charged and 1.0v when drained, so voltage-sensitive electronics (like digital cameras) do not work well or at all with them. Ni-Cads also have a lower capacity than alkaline batteries do, they usually only have 5-600mAh, or equivalent to the carbon-zinc cells. Cadmium is a toxic metal similar to lead, so these batteries need proper disposal.
They have advantages as well. Ni-Cads will discharge at very high rates without harm to the cells. A Ni-Cad AA cell can discharge at ten or more times the rate that an alkaline battery can handle. Cordless drills and RC cars almost always use Ni-Cad battery packs for this reason. They can handle as many as a thousand cycles before failing, and their self-discharge rate of 10-20% per month is the lowest of the rechargeable cells. Their efficiency (power in/power out) of 70-80% is very good as well.
To get the best use out of your Ni-Cad cells, it is essential to purchase a ‘smart’ Ni-Cad charger, many of the problems with these batteries are due to cheap constant-voltage chargers. Overcharging Ni-Cads is one of the fastest ways to destroy them, on a constant-voltage charger a fully charged Ni-Cad cell will actually draw more current as it heats up, which makes more heat, which draws more current… Ni-Cads suffer from ‘memory’, where if they are only partially used and then recharged, eventually they only have that much capacity to give. A ‘smart’ Ni-Cad charger has the capability to do a ‘deep-discharge’, which fully drains the Ni-Cad cells, wiping the memory and restoring capacity.
Nickel-cadmium batteries are the ‘workhorses’ of the rechargeable designs, and if treated well, will serve well.