Thread Tools
This thread is privately moderated by mike_kelly, who may elect to delete unwanted replies.
Oct 26, 2014, 11:27 AM
Wisconsin
Thread OP
Mini-HowTo

Newbie to Newbie: Battery technology



Radio Control (RC) models have been around for many decades. They started out with fuel-based engines because the battery technology was not available to store enough energy to enable electric flight. With the invention of the Lithium Polymer (LiPo) battery, electric flight blossomed because it was able to not only store a reasonable amount of energy but it was also relatively light weight. But Lithium Polymer battery technology must be understood by the new RC enthusiast because it can be dangerous if not treated properly. LiPo batteries are made up of multiple cells joined together to create a battery of a certain total voltage. Each cell is about 4 volts, thus two cells (2S) equal an 8-volt battery and three cells (3S) (3x4v=12v) equal a 12-volt battery, etc. You will see people refer to batteries as 2S, 3S, 4S, 5S, or 6S; they are all multiples of a single lithium polymer cell joined together to form a higher voltage battery. If you join two batteries or cells in series the voltage increases; if you join two batteries in parallel, the voltage stays the same but the total energy capacity available increases. If you have six single-cell LiPo batteries in series, it is called a 6S battery with a voltage of 6x4v=24v. If
you have two 3S 1000milliamp (ma) (same as 1 amp) batteries wired in parallel, you have what is referred to as a 3S 2P battery (P=parallel) at a voltage of 3x4v=12v and a capacity of 2x1000ma=2000ma, which is the same as 2 amps.
http://www.rclab.info/2012/05/basics...batteries.html

There are important basic electrical relationships that will help you understand your electric-powered aircraft. Voltage is the push, sometimes related roughly to water coming out of a hose. The speed that the water leaves the hose is the equivalent to the voltage of a battery and the diameter of the hose or how much volume comes out is roughly like the current or amperage of a battery. If you multiply Current in amps (I) times Voltage in volts (E) this equals Power in watts (P). For example, if you have a 3(S) (=12v) battery with a capacity of 1800ma (1.8 amps), then that battery stores 12v x 1.8a=21.6 watts. Think about an old fashioned water wheel used to power flour mills in the old days. You need power to move that big wheel around. If you have a tiny but very fast stream of water you can't move the wheel. If you have a large volume but it is moving very slowly you also can't move the wheel. Power is a combination of the "push" or voltage and "volume" or current. You can't separate the two components of power.
If you use a higher voltage battery like a 6s instead of a 3s the voltage is higher and the current is lower but for the same load the power is the same. Lower current does not mean lower power. If you have a 300watt motor and using a 3s battery it pulls 25amps, then you change to a 6s battery and it pulls 12.5 amps, it is NOT using less energy or power. It is the same 12v*25amp=300watts and 24v*12.5amps=300watts.

In order to protect your LiPo, you generally don't want to use more than 80% of its capacity in any flight. In our example you don't want to use more than 1800 x .8=1440 milliamps or 12v x 1.44amps=1728 watts. If you run down your batteries below this level, it can damage the battery. You can get an idea of the battery condition by monitoring the voltage during flight. The voltage will go down as you use energy from the battery. Many flight controllers have built in alarms you can program to notify you when your battery voltage is below a preset point and tell you it is time to land as soon as possible. If lithium batteries are over-charged or damaged, they can burst into flames. One indication of being over-charged is when you see your battery 'puff-up' or change thickness. If handled properly, lithium batteries can be used safely and with long life but if miss-handled they can cause a tragedy.

A special battery charger is needed to charge LiPo batteries. Such a charger is programmed to know the voltage or number of cells in the battery pack and the capacity. It is designed to recharge your LiPo battery with just enough energy to replace what you used and to not over charge. It consists of a main connection to the battery and another connection called the balance connector (http://www.tjinguytech.com/charging-...nce-connectors). This connector has individual connections to the individual LiPo cells that form the battery pack. It is used to make sure each cell is charged uniformly rather than one cell being over-charged and another being under-charged. This connection is used by the charger to balance the charge across the pack. LiPO batteries are best stored in a fire-proof container and not stacked on top of each other. If one were to fail, you don't want it to damage all the other batteries you own. In addition, a larger more dangerous fire might ensue. Fire-proof bags are available for battery storage. Many people use military-surplus metal ammunition boxes or you can build a battery "safe" by using concrete building bricks:
Flite test battery vault
It is best to store your batteries outside your home in a cool dry place, if possible. There is much more to learn about LiPo batteries: knowing how much energy you have used after a flight, when to land before your battery runs out, and the best handling techniques to increase the life-span of these pricey batteries. I hope to cover those details in the future.

Next: Motors and Speed Controllers
Last edited by mike_kelly; Dec 21, 2015 at 11:25 AM.
Sign up now
to remove ads between posts
Sep 14, 2016, 09:46 PM
Embedded system developer
RandallM's Avatar
Great explanation Mike.

In my first electrical engineering class in college, the prof explained voltage and current also in terms of the familiar flow of water as follows: Voltage is analogous to water pressure and has the potential to do work. No work is actually done until water flows. This is your battery current.

The diameter of a water pipe determines its resistance to the flow. This is the resistance of the circuit. The pipe diameter coming out of the main water pump will determine the minimum flow resistance and hence the maximum flow rate. Batteries have internal resistance that determines the max peak current it can produce.

Also its helpful to think of a battery as being a water tank with a fixed amount of water in it (think mAh). You can remove water (or current from the battery) faster or slower but ultimately there is only so much to get.

Its also helpful to understand that a battery with a higher voltage (2S lipo 7.4V) is capable of producing more motor torque than a 1S 3.4V cell.
Nov 04, 2017, 10:46 PM
scared to fly
i came to know from my uncle who works in Texas instrument.....some of his friends has developed a lipo that u can puncture ....can even cut with scissor ........ sky will not fall over your head...if you do that.


Quick Reply
Message:
Thread Tools