hankster
11-02-2005, 12:42 AM
In most cases when we look at chargers, the first thing that we are concerned about are the features of the charger. Does it have digital display? How about adjustability? How high can it charge? What about discharging? But there are deep secrets within chargers that we should be more concerned about then then just a few features or a pretty face.
http://www.hobbytalk.com/images/articles/chargercurves05.jpg When we think of linear charging, the most common method for charging batteries, we think that a constant charge rate is applied to a battery until it is done charging and then the charger shuts off. But charger manufacturers have a different idea. Many of them have done years of research to try and get their chargers to charge your batteries so they perform better.
The charger manufacturers think that if you perform better at the track, you'll figure it is the charger making it happen and you'll buy their products again. For the most part that is a fallacy on their part. Almost no one thinks about their charger in the equation when looking of better performance. You just buy the best you can afford, or what everyone else is using, and figure its doing it's job. But is there more to battery chargers than what meets the eye?
You bet! The two most common charging methods are linear and pulse. Most RCers think that when a charger is using a pulsed mode, the current supplied to the batteries are pulsed between some lower amp rate to the rate that was set. No one really thinks about how long these pulses are or how low the current drops during the low side of the pulse. Likewise, RCers think that a linear mode is just that, the battery is charged at a constant amp rate until the battery is completely charged. Many charger manufacturers have a different idea!
At this point I won't get into pulsed mode a lot (other then GM's VIS mode) since most RCers don't use it. We will concentrate on linear modes and see just what your charger is doing when it is charging your batteries. I have not tested every brand of charger on the market. The tests I have are for those that are available to me and with help from Tom Englehart for the CE Turbo 30 profiles.
Lets see just what is going on...
Here are some details on what is happening when you are charging your batteries with some of the common chargers that are available. You can see a more detailed graph and download the Excel spreadsheet with all of the data so you can examine the information more closely if you would like. At this point we will not try to determine what charger is best. We will just be pointing out the different methods that some manufacturers use for charging batteries.
http://www.hobbytalk.com/images/articles/chargercurves03.gifCompetition Electronics Turbo 35 The CE Turbo 35 is one of the more common high end chargers you will see in the pits. CE's line of chargers have been around for years and they also manufacture the most common battery matching equipment on the market today. It uses what most of us would consider a straight linear charge profile. The current applied is constant throughout the charge and once the batteries have peaked, the charger shuts off completely.
http://www.hobbytalk.com/images/articles/chargercurves02.jpg Apex Alpha The Alpha is an inexpensive AC/DC charger that I use a lot just because it is small and can be hooked up to an AC or DC power source. The Alpha uses a straight linear charging method although the amp rate can drop off slightly as the voltage of the pack rises. I attribute this more to the inexpensive design then something that was designed into the charger.../images/articles/chargercurvers01.gif Integy 16x5 This is Integy's newest charger. This is where things start to get interesting. During the first 5 minutes or so of the charge cycle, the 16x5 "rests" the current rate a half dozen times. During these short rests, the current rates drops to (or close to) zero amps. After those initial few "rests", it then finishes the charge in a normal linear method. Integy claims this is done to evaluate the pack being charged to eliminate false peaks and to insure that both NiCds and NiMh batteries get a complete charge.
http://www.hobbytalk.com/images/articles/chargercurves04.jpgGM Commander 2000 This is GM's newest charger on the market. I got one because I was interested in their VIS charging method... plus I just like to be different. The most interesting feature of the Commander is the VIS charging method that GM claims increases the voltage in a pack which would be most useful in stock class racing. They also include a Peak mode and a Thermal mode.
GM Commander 2000 - Peak Mode The Peak mode is what would be used if you wanted to charge with a linear method. It does this for the most part... with a twist! During charging, it is a straight linear current rate, much like the Turbo 35. But, when the charger shuts off after the battery is fully charged, the Commander keeps pulsing the battery with short duration current pulses. My guess is this is done to keep the at maximum charge without resorting to a trickle charge.
GM Commander 2000 - VIS Mode The VIS mode is what GM considers their voltage enhancing charging method. This seems to be some variation on a pulse charging method but the current supplied during the pulses vary at what seems like random rates. Although my sampling rate was not fast enough to see actually what is going on during these pulses, it looks like the current is not actually being shut off, but is just being reduced at random rates. The timing of the pulses are consistent, but depth of the pulse is what varies. Like the Peak mode, the batteries are pulsed after the batteries have been charged.
Conclusions So you can see, not all chargers are the same. I have not tried to determine which of these methods are best, I am just pointing out that different manufacturers use different charging methods. If I get access to any other brands of chargers, I will run them through our tests and add them to the list. Be sure to check out the graphs to visually see the charging profiles.
Next on our list is to check out the discharge profiles of those chargers that are capable of discharging batteries. Keep on eye out for this info to come out shortly.
Note: The voltages of all curves has been normalized (factored) to start the charge process at a 0 reference point for the volts to help compare the charge profiles more directly against each other. In these tests, the actual voltage reading is not what is really important, it is what is happening during the charge process that we are comparing.
The voltage is important in that we can see that the 16x5 voltage drops .15 volts during it's pulses and the drop in voltage during the GM VIS charge varies. The time factor is somewhat important as you can see the pulses in the 16x5 charge happen during the first 360 seconds and that the GM VIS pulsing happens throughout the charge.
http://www.hobbytalk.com/images/articles/chargercurves05.jpg When we think of linear charging, the most common method for charging batteries, we think that a constant charge rate is applied to a battery until it is done charging and then the charger shuts off. But charger manufacturers have a different idea. Many of them have done years of research to try and get their chargers to charge your batteries so they perform better.
The charger manufacturers think that if you perform better at the track, you'll figure it is the charger making it happen and you'll buy their products again. For the most part that is a fallacy on their part. Almost no one thinks about their charger in the equation when looking of better performance. You just buy the best you can afford, or what everyone else is using, and figure its doing it's job. But is there more to battery chargers than what meets the eye?
You bet! The two most common charging methods are linear and pulse. Most RCers think that when a charger is using a pulsed mode, the current supplied to the batteries are pulsed between some lower amp rate to the rate that was set. No one really thinks about how long these pulses are or how low the current drops during the low side of the pulse. Likewise, RCers think that a linear mode is just that, the battery is charged at a constant amp rate until the battery is completely charged. Many charger manufacturers have a different idea!
At this point I won't get into pulsed mode a lot (other then GM's VIS mode) since most RCers don't use it. We will concentrate on linear modes and see just what your charger is doing when it is charging your batteries. I have not tested every brand of charger on the market. The tests I have are for those that are available to me and with help from Tom Englehart for the CE Turbo 30 profiles.
Lets see just what is going on...
Here are some details on what is happening when you are charging your batteries with some of the common chargers that are available. You can see a more detailed graph and download the Excel spreadsheet with all of the data so you can examine the information more closely if you would like. At this point we will not try to determine what charger is best. We will just be pointing out the different methods that some manufacturers use for charging batteries.
http://www.hobbytalk.com/images/articles/chargercurves03.gifCompetition Electronics Turbo 35 The CE Turbo 35 is one of the more common high end chargers you will see in the pits. CE's line of chargers have been around for years and they also manufacture the most common battery matching equipment on the market today. It uses what most of us would consider a straight linear charge profile. The current applied is constant throughout the charge and once the batteries have peaked, the charger shuts off completely.
http://www.hobbytalk.com/images/articles/chargercurves02.jpg Apex Alpha The Alpha is an inexpensive AC/DC charger that I use a lot just because it is small and can be hooked up to an AC or DC power source. The Alpha uses a straight linear charging method although the amp rate can drop off slightly as the voltage of the pack rises. I attribute this more to the inexpensive design then something that was designed into the charger.../images/articles/chargercurvers01.gif Integy 16x5 This is Integy's newest charger. This is where things start to get interesting. During the first 5 minutes or so of the charge cycle, the 16x5 "rests" the current rate a half dozen times. During these short rests, the current rates drops to (or close to) zero amps. After those initial few "rests", it then finishes the charge in a normal linear method. Integy claims this is done to evaluate the pack being charged to eliminate false peaks and to insure that both NiCds and NiMh batteries get a complete charge.
http://www.hobbytalk.com/images/articles/chargercurves04.jpgGM Commander 2000 This is GM's newest charger on the market. I got one because I was interested in their VIS charging method... plus I just like to be different. The most interesting feature of the Commander is the VIS charging method that GM claims increases the voltage in a pack which would be most useful in stock class racing. They also include a Peak mode and a Thermal mode.
GM Commander 2000 - Peak Mode The Peak mode is what would be used if you wanted to charge with a linear method. It does this for the most part... with a twist! During charging, it is a straight linear current rate, much like the Turbo 35. But, when the charger shuts off after the battery is fully charged, the Commander keeps pulsing the battery with short duration current pulses. My guess is this is done to keep the at maximum charge without resorting to a trickle charge.
GM Commander 2000 - VIS Mode The VIS mode is what GM considers their voltage enhancing charging method. This seems to be some variation on a pulse charging method but the current supplied during the pulses vary at what seems like random rates. Although my sampling rate was not fast enough to see actually what is going on during these pulses, it looks like the current is not actually being shut off, but is just being reduced at random rates. The timing of the pulses are consistent, but depth of the pulse is what varies. Like the Peak mode, the batteries are pulsed after the batteries have been charged.
Conclusions So you can see, not all chargers are the same. I have not tried to determine which of these methods are best, I am just pointing out that different manufacturers use different charging methods. If I get access to any other brands of chargers, I will run them through our tests and add them to the list. Be sure to check out the graphs to visually see the charging profiles.
Next on our list is to check out the discharge profiles of those chargers that are capable of discharging batteries. Keep on eye out for this info to come out shortly.
Note: The voltages of all curves has been normalized (factored) to start the charge process at a 0 reference point for the volts to help compare the charge profiles more directly against each other. In these tests, the actual voltage reading is not what is really important, it is what is happening during the charge process that we are comparing.
The voltage is important in that we can see that the 16x5 voltage drops .15 volts during it's pulses and the drop in voltage during the GM VIS charge varies. The time factor is somewhat important as you can see the pulses in the 16x5 charge happen during the first 360 seconds and that the GM VIS pulsing happens throughout the charge.