Tuesday, August 7th, 2012 10:48 am GMT -6 Tuesday, August 7th, 2012 10:48 am GMT -6Tuesday, August 7th, 2012 10:48 am GMT -6
 
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If you treat your model airplane battery well, it will treat you well.


 

 

 

Nomenclature

Most of us fly our electric model airplanes using lithium-ion polymer (LiPo) battery packs. Almost all battery packs come with their cells wired in series. The most common configuration for a park flyer is 3S, which means three cells in series. Unless you know better, stick with a 3S pack.

Out of the three numbers that identify a battery pack, this one is the most important. The number of cells in the battery pack along with the Kv rating of the motor determine the RPM of the propeller.

The fully charged voltage on a cell is about 4.2 volts. Multiply by the number of cells to get the maximum pack voltage. As it discharges, the average voltage on a LiPo is 3.7 volts.

The capacity of the pack is how much electrical current it can deliver when discharged over an hour. The labels measure this in milliamps. In other words, if the label says “2300“, then the pack can deliver 2.3 amps for an hour.

We are much more likely to fly for something like six minutes instead of an hour. Then you can roughly multiply by ten the current. So for our example battery pack, that would be 23 amps at 11.1 volts (3*3.7) for six minutes.

Note that in practice you cannot get a full 23 amps for six minutes. The faster you discharge a battery pack, the higher the electrical losses and the higher the loss in efficiency.

The C rating is a multiple of the battery pack’s capacity. If the C rating is 30, then in our example 2.3 * 30 = 69 amps. That means that our pack can be discharged at up to 70 amps or so without permanent damage.

Battery Care

If you treat your battery well, it will treat you well. With reasonable care and use, a battery pack should be good for at least three seasons of heavy flying.

Do not discharge the battery pack below 3.2 volts per cell. The setting in your speed control for this will be called something like “cut-off voltage”. You want to make it medium or high.

If you are not going to be using the battery pack for at least a month, put it into a storage charge. This is a 50% charge or about 3.7 volts per cell.

Always use a charger with a balancer. Nowadays there aren’t too many excuses for not doing so.

If you are on the market for a new charger, look for one with a discharge cycle. They cost more, but come in very handy when putting your batteries into a storage mode. I have a Junsi iCharger 306B, and I just press a button for a storage charge. Then it either charges up or discharges the pack safely until it reaches the target voltage. Easy peasy.

Connectors

It can be really tricky soldering a connector onto a battery. Since a battery can never be fully discharged, there is a big danger of shorting out the terminals with your soldering iron. Yes, it has happened to me.

For that reason batteries almost always come with connectors pre-soldered. The problem here is that there are many different connectors on the market. The connector on the battery has to match up with the connector on your speed control.

I used to cut-off the connectors on my new battery packs and solder on my favorite. Because of the problems with shorts and because of the extra work involved, I do not do that anymore. I just keep an assortment of short jumpers that convert from one connector type to another. I’m in this for the flying, not the soldering.

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