Motor Selection, Continued:

Watts, Amps, Thrust, Kv ratings, Props, Lipoly Batteries and ESC’s, how do you muddle thru all this?! First, let’s discuss batteries. Then we can pull it all together…

Lipoly Batteries:

Batteries were a real mystery at first, but it isn’t as complex as it first seemed. First, we now recognize that “Lipoly” batteries are the best commercially available power storage devices that we can obtain at affordable prices.

The acronym Lipoly is from Lithium Polymer (aka, Lithium-Ion), and represents a very high-density energy storage technology developed mostly for cellular telephones. The energy density of a Lipoly or “Lipo” is more than twice that of NiMH (Nickel-metal Hydride) which is better than NiCd (Nickel Cadmium) by some significant margin. This translates to batteries that are now far less than half the weight with incredible current delivery capacity.

This advance in battery technology is the single most significant reason for the explosion in popularity of “foamie” aircraft. Coupled with high efficiency brushless motor technology, the power-to-weight ration of electric powered aircraft has finally come to a practical level to make this hobby segment a possibility.

Here are the basics about Lipoly batteries as I understand it now. Terminology is cryptic. Let’s decipher the simple “3S TP1320 12C” that I mentioned before.

3S = 3 cells, and each Lipoly cell is 3.7 VDC, so a 3C is 11.1 VDC.

TP = Thunder Power. Many batteries have grown nick-names.

1320 = milliamp-hour rating, or “mAH” as it is typically noted. This is what it implies; you should be able to draw 1320 milliamps (mA) for one hour (or 1.32 Amps for one hour). It’s not entirely accurate in reality, because you can only safely discharge the battery to a specific minimum level, and beyond that the battery can be damaged. There are also efficiency factors and temperature variables to further influence the battery’s ability to deliver energy, as well as the charge “quality” and topping-off efficiency of the charger.

12C = Current Delivery Rating, which is represented as a multiple of the AMP-Hour (not milliamp hour) rating of the battery. So, the rated “continuous” current draw for this battery is 1.32 x 12 = 15.84 Amps.

This is a tricky little trap for novice electric buyers. We see in the market that the lower the C rating, the cheaper the battery. Not understanding the concept of the “current delivery capacity” and buying a bigger mAH battery with a low C rating can leave you wanting.

My first purchase of a Lipoly battery was a Watt-age 1500 mAH. I figured out later that this battery is only 7C, which calculates to 10.5 Amps. Later, by luck only, I bought Thunder Power 1320 mAH batteries that have a 12C rating… they can deliver 15.8 amps! At first that was mystifying that a 1320 was WAY better than a 1500? Well, it’s all about the quality of the Lipoly cells, and their inherent ability to deliver current. Buyers beware! You need a calculator to buy properly matched batteries!

There are other complications with battery jargon that I don’t see the novice concerned with that has to do with parallel and series gang-wiring of multiple cells for bigger aircraft. Buy the time your ready for that, you’ll already understand all that from your own learning.

Continued…