Delta Peak Negative Pulse Chargers By James Goss   This is a real mouthful of technical words for us average RC modelers to swallow, much less understand what they actually mean. These pulse chargers have been out on the market for a few years now and they do seem to work well. I have been using one on my giant scale planes now for about two years and I really do like it. I am going to switch all my chargers over to the negative pulse system because they completely do away with cell memory. With negative pulse charging you will never have to cycle your battery packs again to prevent memory. Your battery packs can be placed on charge at any time and no matter what state of charge they are in the pulse charger will charge them to the peak level. It will then switch to a maintenance mode that will keep them fully charged for any length of time. Pulse chargers may be used with nickel cadmium, nickel metal hydride, and lithium ion batteries. I would still recommend placing a new battery pack on an overnight slow charge before using the peak charger or any other type of fast charger. This is due to the individual cells having different peak charge times. The peak detector senses the average charge of the pack and not the peak on any one cell. If you only fast charge the pack and never slow charge it the lagging cell (the one that is slower to charge) will become under charged more and more as time goes on. A slow charge will allow each cell to become closer to being fully charged so it is wise to use slow charges after every five or six fast charges.      Delta peak negative pulse chargers get their name because the charging current is not a steady dc current flow. Instead the charging current is broken up into one-second pulse intervals. After the one second of current flow there is a rest period for about two milliseconds where nothing happens. A pulse is defined as a sudden change in voltage or current, so you can see where the name “Pulse” comes from in the title. Now to explain the “Peak” part of the title. This is the easy part because peak refers to the battery being fully charged. During the idle state the battery is checked to see if its voltage has increased since the last voltage check. This voltage check is made about every 1.007 seconds. If the microprocessor sees that the voltage has indeed increased in its value, another cycle of charge current will be applied to the battery. Delta is a letter in the Greek alphabet that is normally used to indicate a small change in some variable in an equation. In this case a change in voltage is indicated by the word “Delta”.      How about the “Negative” in the title? This is where the pulse chargers are in a class by themselves. This is the ingenious or creative part of the charger that separates the men from the boys so to speak. After the one-second-charge pulse and the two-millisecond rest period a reverse polarity pulse of about 5 milliseconds is connected across the battery. Actually this reverse polarity is the same as connecting a heave load across the terminals of the battery for that amount of time. This is how the charger removes any memory that may be formed in the battery. Actually memory refers to the formation of gas bubbles on the plates of the cells. These gas bubbles are a normal formation while in the charge cycle and they tend to insulate the plates of the cells from the electrolyte. These insulating bubbles will reduce the chemical activity around the area of the plates and reduce the capacity of the battery. The reverse polarity pulse tends to remove these bubbles and lets the cells work at their maximum capacity.      So the complete charge cycle for a Delta Peak Negative Pulse Charger consists of a one second charge pulse, a two millisecond rest period, a five millisecond negative pulse, another rest period so the microprocessor can check for delta peak, and the charge cycle starts over again if needed. After peak voltage is detected the charger switches over to its maintenance mode where it applies a charge pulse at the rate of one pulse every fifteen to thirty seconds. As a backup to the delta peak voltage sensing circuit most manufacturers will add a timing circuit so that after a given amount of charge time the charger will automatically go into its maintenance mode. So on large capacity packs you may have to charge two or three times to get them to cycle at their full capacity. This is ok because you can charge them as many times as you like because the pulse charger will not over charge the pack.      Remember now that you still need to cycle your battery from time to time in order to check its condition. The pulse charger does not tell you if your battery has its rated capacity or not. The only way to get that information is to cycle your battery and get a reading in milliamp hours. (Read my article “Minutes of Milliamp Hours”) If you didn't already understand what a Delta Peak Negative Pulse Charger was all about maybe this has helped you a little.