An expert takes the mystery out of LiPos
by Mark Fadely [email protected]
Thank you for stopping by to check out the helicopter column this month. In this month’s column, you will learn about the often misunderstood LiPo batteries and how to properly charge them.
Clint Akins works for Castle Creations and is a longtime heli pilot who is also an expert on electric-power technology. Castle Creations makes a variety of products including many ESCs for helicopters.
I asked Clint to explain some of the important aspects of charging helicopter batteries. This is what he had to say.
“Let me start by saying that LiPo batteries and LiPo chargers have improved greatly over the last few years. In the beginning the chargers were crude and often they charged in stages; the early chargers were simply set to the desired voltage and charge rate and they often charged aggressively in the first stage.
“This usually was fine until we (the end users) made the mistake of putting a battery on a charger that was already charged. The result was almost always the same; yep, a damaged pack or worse, a fire.
“Let’s stop for a moment and understand why. LiPos are typically fully charged at 4.2 volts per cell. The early chargers were programmed to blast a heavy charge to the pack for the first cycle and they never sensed any information from the pack initially as to the charge level. The chargers would push the voltage above 4.3 volts per cell, which can damage not only the cycle life of the pack, but become dangerous and can cause a fire.
“We do not hear of nearly as many problems with charging batteries as we used to. Is it because there are fewer people using LiPo batteries? Is it because the technology of the chargers is much better, and the education of the end-user has improved.
“How do you keep up with it all? While we are fortunate to have technology moving fast, it can also be difficult to keep up with. This document is intended to help simplify some things, and take the black magic out of LiPo charging by explaining a little about the chargers and the batteries.
“The basic LiPo chargers today are pretty simple, and the user sets the voltage or cell count (3.7-volts per cell) and the charge rate, which is normally 1C. This brings up the first question: what does 1C mean? 1C means one times the capacity. Packs are usually rated in mAh (milliampere-hours) and chargers are set in values of amps.
“Let’s just simplify this and make it easy. There are 1,000 mAh in an amp. As an example we will use a 3S 2,100 mAh pack. 3S means we have three cells, three times the nominal voltage of a cell (3.7 x 3 = 11.1 volts). We know that the pack is 11.1 volts at nominal voltage and fully charged it will be 4.2 volts per cell, or 4.2 x 3 = 12.6 volts.
“This pack could be called a 2.1-amp pack. Dividing 2,100 mAh by 1,000 will give us the value of the pack in amps, which is 2.1. If we want to charge this 2.1-amp pack at 1C we would set our charge rate at 2.1 amps.
“Now that we understand terms such as 1C, and we know how to figure charge rate and the voltage at which we want to charge, we will move on. A good tool to use with a basic charger is a balancer. I prefer to take it one step further by using a feed-through balancer.
“What is the difference and why should I use a balancer? A basic balancer equalizes the cell voltage on a pack to within set parameters. This will keep the cells in the pack at or close to the same voltage with each other, which will allow them to perform at their best. It will also lengthen the cell life.
“The difference between the feed-through balancer and the typical balancer is that the feed-through checks each cell as it is charging and maintains the proper levels. It also includes a safety shutoff in case problems are found in one or more cells.
“This added safety feature is very affordable and can be used on most chargers. For example, some balancers go between the charger and the battery and it reads information from the battery while it balances the pack.
“Where is this safety feature? The internal circuitry of the balancer is monitoring the cells. If there is a problem during the charge there are parameters set to cause the balancer to unlink, which breaks the circuit between the charger and the battery.
“To simplify, if you set the charger to the wrong cell count, the balancer will unlink before damaging the pack. This gives you a chance to reset the charger to the correct settings and then re-link the balancer and continue the charge. Chargers with these features sell for approximately $50.
“The next type of balance charger is a loop system or closed circuit. In these systems the charger has an add-on balancer and data cable. The balancer not only balances, but it also reads information from the balance taps of the battery, which can be displayed on the charger’s LCD screen.
“This information that is being fed back to the charger is also used to slow the charger down when needed and terminate the charger when needed, but the balancing is being done outside of the charger.
“The next type of charger I would like to mention is a balance charger. Balance chargers typically have internal balancers and work very much like the loop systems, but they only have an external board to hook the balance taps to and an output for the main power wires.
“Most charge through the main power wires and read the information through the balance taps, as well as balance through the same taps with their internal balancers.
“There are a few chargers that charge through the balance taps usually at 1C. The balance chargers typically ramp the charge rate up and down as needed and have the ability to terminate the charge if there is a problem.
“This is a basic overview of different types of LiPo chargers and an attempt to help others understand a little bit about basic charging and the knowledge needed to do so. Always read the recommendations made by both the battery manufacturers and the charger manufacturers.
“Never charge any battery unattended no matter how much you trust your charger. The use of LiPo sacks and/or LiPo bunkers is also recommended. I recommend never charging a pack while it is in a model.
“Never run a pack below 80% of its capacity—a 2,100 mAh pack should never have more than 1,680 mAh discharged without recharging. This is not only a good safety practice, but it is also recommended to prolong the life of your investment. I hope this has been helpful.”
Thank you, Clint. That is some great information about safe charging practices for the popular battery type. I hope pilots can reduce their risk of accidents by adhering to the guidelines you have presented.
That is all there is room for in this month’s heli column. I hope to see you all back here again next time. ✈
SOURCES: Castle Creations (913) 390-6939 www.castlecreations.com
International Radio Controlled Helicopter Association www.ircha.org
RC Helicopters
Mark Fadely
Transcribed from original scans by AI. Minor OCR errors may remain.
