This site maintained by: Curtis L. Olson
|
Battery Chargers - Mark J. Ptaszynski I was recently involved in a conversation at the field regarding the battery chargers that we all use with our R/C equipment. There was some confusion as to the different types of chargers and their intended purpose so I will try and clarify the mystery as best I can. There are four basic types of chargers that we currently use for our NiCd battery packs. The first would be the charger that comes with the radio system. This is a constant current charger and is the safest charger we have. Most of the manufacturers make a dual output 50 milliamp wall unit - one output is for charging the transmitter while the other charges the receiver, or flight pack. It is the safest because it is the slowest charger requiring 12 to 16 hours to fully charge a depleted pack. 50 milliamps is a C10 charge rate or charging at 1/10 of the rated capacity of the pack (a 500 milliamp pack is considered normal size). Keep in mind that 500 milliamps is ½ amp, so 50 milliamps is .05 amps. If you leave this charger on for an extended period of time no real damage will be done to the pack. Actually any over charging of a NiCd pack will generate internal heat that causes the battery to degrade or lose capacity over time but with a C10 charge rate the damage is so minimal that we can barely measure it. If you get into the habit of putting your batteries on charge the night before you go flying with a C10 rate you will have a fully charged pack ready to go in the morning and give you a good days worth of flying. This will give you many years of trouble free batteries. The second type is the constant voltage charger. This unit starts out with a high output current (approximately .8 amps) and as the battery voltage goes up the charging current goes down. This is commonly called a field charger, run off of a 12 volt source such as your field box battery or car battery and is a very reliable type. It can only charge a pack to approximately 60 to 70% of the packs capacity (depending on the brand) making it a very safe non-destructive quick charger that needs no supervision. When the maximum 60 to 70% is reached the charger shuts itself off. This is perfect for getting more flights in when you have been flying for a while. The third type is the delta peak voltage charger. This type has a very high rate of charge at 2 to 4 amps and is also powered by a 12 volt source. As the battery is charged the voltage climbs. When the pack is fully charged the voltage drops slightly (it peaks) it is this slight drop in voltage that the delta peak charger detects and uses to turn itself off. This charger is very popular with the R/C car crowd but most of their cells are specially vented to allow for a very high rate of charge and discharge. To be used with our NiCd packs it would be best if it were equipped with a thermister to detect excessive heat build up thus shutting itself off before any damage is done to the pack. Excessive heat inside the battery can cause thermal runaway and if this happens the delta peak charger can not turn itself off thus damaging a battery pack. The fourth type of charger is a dump-timed impulse type. A high positive charge pulse is given for a certain amount of time, followed by a negative pulse for about 1/3 the time of the positive pulse. This is done to lower the temperature inside the battery during charging and results in higher capacity being returned to the battery in any given amount of time compared to the standard high rate charger. These chargers also use a delta voltage check on either the positive or negative pulse to terminate the charge cycle. But be warned if the device being charged has a protective diode in the circuit the dump-timed impulse charger may fail to terminate the charge cycle. Not a desirable out come. Keep in mind that heat is the worst enemy of your battery, the slower you charge your battery the less heat is produced. If on the other hand charging time is more important to you then use a type that fits your needs but use it wisely. All you want to do is return to the battery what has been used without over charging. Next month I will try and cover trickle charging and cycling of your battery packs. |