Author: Mark Fadely
Edition: Model Aviation - 2009/06
Page Numbers: 127,128,129
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Radio Control Helicopters

Mark Fadely [[email protected]]

See you at the Extreme Flight Championships

This is my favorite time of year. I love spring and early summer, because you have the whole year of good flying weather to look forward to.

Some lucky pilots live in temperate climates that allow for year-round outdoor flying. I am stuck smack dab in the middle of the Midwest: Indianapolis, Indiana. There are no mountains or oceans here, but we do have one fabulous attraction. The RC highlight of the nation is the AMA Headquarters and International Aeromodeling Center. It is only 45 minutes from where I live.

In a few days, the 2009 Extreme Flight Championships (XFC) will be held at the AMA flying site. It takes place June 12–14. It is the only competition that includes the world's best airplane and helicopter pilots in one spectacular show. Plan to attend this event if you can. It is a jaw-dropping experience.

Let's shift our attention to a concern that many pilots share. Batteries are used in several facets of RC. When you have spent time in the hobby, you start learning about the various types of batteries, along with their chemical makeups.

Batteries are the lifeblood of successful RC flying, so you must know how to handle each kind properly. If you do not follow the rules, you might find yourself in a dangerous situation.

I'm going to highlight the most misunderstood of all batteries: the Li-Poly. They are used in many gadgets, including every cell phone on the planet. If a battery is safely used by so many people, what is the big problem? I asked my good friend, Clint Akins, to write a brief explanation of Li-Poly handling requirements. He is the manager of FlightPower batteries, which makes a full line of Li-Poly cells. He takes these batteries' safety seriously. To help pilots better understand the potential pitfalls of Li-Poly handling, Clint wrote something special for us.

Chargers 101: Taking the Black Magic Out of Li-Poly Batteries

Let me start by saying that Li-Poly (Lithium-Polymer) batteries and Li-Poly chargers have improved greatly over the last few years.

In the beginning the chargers were very crude and often charged in stages. For example, the early chargers were simply set to the desired voltage and charge rate, and they often charged very 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: a damaged pack, or worse, a fire.

Let's stop for a moment and understand why. Li-Poly batteries 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 info 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 it becomes dangerous and can cause a fire.

We do not hear of nearly the problems with charging batteries that we used to. Is it because there are fewer people using Li-Poly 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. As I stated previously, this document is intended to help simplify some things and take the black magic out of Li-Poly charging by explaining a little about the chargers and the batteries.

The basic Li-Poly chargers today are pretty simple, and the user sets the voltage or cell count (nominally 3.7 volts per cell) and the charge rate, which is normally 1C. This brings up the first question: what does 1C mean?

Just to simplify things, 1C means one times the capacity. Packs are usually rated in mAh (milliamp hours), and chargers are set in values of amps. There are 1000 mAh in an amp.

Example:

  1. We will use a 3S, 2100 mAh pack. 3S means three cells, three times the nominal voltage of a cell (3.7 x 3 = 11.1 volts). At full charge it will be 4.2 volts per cell, or 4.2 x 3 = 12.6 volts.
  2. This pack could be called a 2.1 amp pack: by dividing 2100 mAh by 1000 we get 2.1 amps.
  3. 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 like 1C, and we know how to figure charge rate and the voltage we want to charge at, 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 you use a balancer?

A basic balancer equalizes the cell voltages in a pack to within set parameters. This keeps the cells at or close to the same voltage as each other, which allows them to perform at their best and lengthens 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 is an added safety feature that is very affordable and can be used on most chargers.

For example, the FlightPower V-Balancer goes between the charger and the battery and reads information from the battery while it balances the pack. Where is this safety feature? The internal circuitry of the V-Balancer monitors the cells and if there is a problem during the charge the balancer will 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 relink the balancer and continue the charge. Chargers with these features sell for around $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 info from the balance taps of the battery, which can be displayed on the LCD screen of the charger. This feedback is used to slow the charger down when needed and also terminate the charge where 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." Typically balance chargers have internal balancers and work much like the loop systems but only require an external board to hook the balance taps to and an output for the main power wires. Most of these chargers charge through the main power wires and read info 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 usually have the ability to terminate the charge if there is a problem.

This has been a basic overview of different types of Li-Poly chargers and an attempt to help others understand a little 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 Li-Poly sacks and/or Li-Poly bunkers is also recommended, and I personally recommend that you never charge a pack while it is in a model. Never run a pack below 80% of its capacity. As an example, a 2100 mAh pack should never have more than 1680 mAh discharged without recharging. This is not only 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 most popular type of battery. I hope pilots can reduce their risk of accidents by adhering to the guidelines you have laid out.

That is all we have room for this month, so I hope you'll be back here again next time. MA

Sources:

Transcribed from original scans by AI. Minor OCR errors may remain.