WThesing
Elite Member
Battery Clinic - Chapter 1
For those of you that use your metal detectors enough to invest in rechargeable batteries, I hope that this little article is helpful. I will try to shed some light on the differences, as well as some of the technology in order for you to make informed decisions. This should save you some frustration as well as money in the long term.
First off, some basics: We are mainly concerned with two types of battery technology. Chemical cells are those which give off a current through chemical reaction, such as lead / acid cells, and the more popular alkaline cells. These are two different chemical technologies, the alkaline being the newest and generally having the longest duration or life expectancy. Both of these types are single use cells with an output of 1.5 Volts per cell. When the chemical reaction slows down due to depletion, the current output also slows, and eventually ceases.
The other type of technology would be the multi-use, or rechargeable cell. They are available in nickel cadmium (Nicad), nickel / metal hydride (Nimh), gel cell, and the newest technology, lithium polymer (Lipo). For our usage we will be concerned with Nicad?s and Nimh. Of the two, THERE IS A DIFFERENCE !!!! Nicad?s are designed to be used in a full charge to full discharge cycle. This means that from full charge they are to be used to what is considered optimum discharge, which is 50 % voltage drop or lower. Both Nicad's and Nimh's have an voltage output of 1.2 Volts per cell, so we are looking at .6V or lower. Incidentally, the difference in voltage output between single use and rechargeable cells will not matter in today?s electronics.
Nimh's are a newer technology than Nicad. The advantage is that they can be recharged at any point in their use cycle without any ill effect. When Nicad's are charged without being fully discharged, they develop what is termed as a "memory". This is a condition which prevents them from reaching a fully charged state. It will eventually shorten the cell life considerably. If either of these types of cells are cared for and maintained properly, they are capable of hundreds of recharge cycles, thus saving the purchase of another set of single use cells.
CAPACITY
The single use cells may provide a slightly longer operational time ON AVERAGE, but not by much. They also have a more gradual voltage drop-off than rechargeables, but this really doesn?t affect performance of the detectors, since their circuitry is designed to operate in millivolts. One of the main terms you should be concerned with is the CAPACITY of the cell, which is its rating in AMP HOURS. For our purposes the cells are rated in Milliamps or Milliamp Hours (Mah). This is similar as to how big a gas tank you have, or the amount of electrical "fuel" stored in the container or cell. That amount of current storage or "CAPACITY" is referred to in battery terms as the value "C". Example: a 2000 Mah capacity cell would have a value where 1C is equal to 2000 Mah, 1/10C = 200 Mah.
Not all rechargeable cells are created equal!!!! When purchasing, be concerned with the cell capacity. The higher the milliamp rating, the longer you will be able to use the cell before needing a charge. Generally speaking, the higher the rating, the more costly the cell. This of course depends on where you buy them. There are also differences in quality of cells. Generally those manufactured by Sanyo and Panasonic are the best. They are marketed under numerous different labels such as Eveready, Ray O Vac, etc.
As of this time, the best AA cells that I have found that are readily available, have a good capacity, and are reasonably priced would be the Eveready 2500 Mah Nimh. They also make a AAA 850 Mah Nimh cell. I have purchased the AA's at about $1.10 per cell in packages of 8.
I will be adding to this article when time permits. Chapter 2 will deal with recharging.
For those of you that use your metal detectors enough to invest in rechargeable batteries, I hope that this little article is helpful. I will try to shed some light on the differences, as well as some of the technology in order for you to make informed decisions. This should save you some frustration as well as money in the long term.
First off, some basics: We are mainly concerned with two types of battery technology. Chemical cells are those which give off a current through chemical reaction, such as lead / acid cells, and the more popular alkaline cells. These are two different chemical technologies, the alkaline being the newest and generally having the longest duration or life expectancy. Both of these types are single use cells with an output of 1.5 Volts per cell. When the chemical reaction slows down due to depletion, the current output also slows, and eventually ceases.
The other type of technology would be the multi-use, or rechargeable cell. They are available in nickel cadmium (Nicad), nickel / metal hydride (Nimh), gel cell, and the newest technology, lithium polymer (Lipo). For our usage we will be concerned with Nicad?s and Nimh. Of the two, THERE IS A DIFFERENCE !!!! Nicad?s are designed to be used in a full charge to full discharge cycle. This means that from full charge they are to be used to what is considered optimum discharge, which is 50 % voltage drop or lower. Both Nicad's and Nimh's have an voltage output of 1.2 Volts per cell, so we are looking at .6V or lower. Incidentally, the difference in voltage output between single use and rechargeable cells will not matter in today?s electronics.
Nimh's are a newer technology than Nicad. The advantage is that they can be recharged at any point in their use cycle without any ill effect. When Nicad's are charged without being fully discharged, they develop what is termed as a "memory". This is a condition which prevents them from reaching a fully charged state. It will eventually shorten the cell life considerably. If either of these types of cells are cared for and maintained properly, they are capable of hundreds of recharge cycles, thus saving the purchase of another set of single use cells.
CAPACITY
The single use cells may provide a slightly longer operational time ON AVERAGE, but not by much. They also have a more gradual voltage drop-off than rechargeables, but this really doesn?t affect performance of the detectors, since their circuitry is designed to operate in millivolts. One of the main terms you should be concerned with is the CAPACITY of the cell, which is its rating in AMP HOURS. For our purposes the cells are rated in Milliamps or Milliamp Hours (Mah). This is similar as to how big a gas tank you have, or the amount of electrical "fuel" stored in the container or cell. That amount of current storage or "CAPACITY" is referred to in battery terms as the value "C". Example: a 2000 Mah capacity cell would have a value where 1C is equal to 2000 Mah, 1/10C = 200 Mah.
Not all rechargeable cells are created equal!!!! When purchasing, be concerned with the cell capacity. The higher the milliamp rating, the longer you will be able to use the cell before needing a charge. Generally speaking, the higher the rating, the more costly the cell. This of course depends on where you buy them. There are also differences in quality of cells. Generally those manufactured by Sanyo and Panasonic are the best. They are marketed under numerous different labels such as Eveready, Ray O Vac, etc.
As of this time, the best AA cells that I have found that are readily available, have a good capacity, and are reasonably priced would be the Eveready 2500 Mah Nimh. They also make a AAA 850 Mah Nimh cell. I have purchased the AA's at about $1.10 per cell in packages of 8.
I will be adding to this article when time permits. Chapter 2 will deal with recharging.
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