Basics About Batteries
WHAT ARE LIPO BATTERIES AND WHY ARE THEY SO POPULAR IN THE RC WORLD
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LiPo batteries are a type of rechargeable battery that has taken the electric RC world by storm, especially for planes and helicopters. They are the main reason electric flight is now a very viable option over fuel powered models.
The lithium-polymer differentiates itself from conventional battery systems in the type of electrolyte used. The original design, dating back to the 1970s, uses a dry solid polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows ions exchange (electrically charged atoms or groups of atoms). The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.
Advantages
Very low profile - batteries resembling the profile of a credit card are feasible.
Flexible form factor - manufacturers are not bound by standard cell formats. With high volume, any reasonable size can be produced economically.
Lightweight - gelled electrolytes enable simplified packaging by eliminating the metal shell.
Improved safety - more resistant to overcharge; less chance for electrolyte leakage.
Limitations
RC LiPo batteries are still expensive compared to NiCad and NiMH, but coming down in price all the time.
Although getting better, RC LiPos dont last that long, perhaps only 300-400 charge cycles (much less if not cared for properly). That said, I have heard some people getting over 1000 cycles if all the rules are followed.
Safety issues - because of the volatile electrolyte used in LiPos, they can catch fire or explode.
RC LiPo batteries require unique and proper care if they are going to last for any length of time more so than any other battery technology. Charging, discharging, and storage all affect the lifespan get it wrong and a LiPo is garbage in as little as one mistake.
LIPO BATTERIES RATINGS
These are the three main numbers you will need when going battery shopping
Voltage/Cell Count: How many volts a battery can produce, which is determined by the cell count of a LiPo battery. With LiPo batteries, each cell is equal to 3.7V per cell, and when fully charged, will equal to 4.2V per cell.
MAH: Short for Milliamp Hours, this is the capacity the battery has to offer - the more capacity (mah), the longer the flight time. But, going beyond a specific capacity suggested for your aircraft will cause flight problems due to weight & size, so be sure to stay within recommended limits.
C Rating: This is a term for the discharge rating, or how much power the battery can give in amps. To figure out the amount the battery can give, divide the Mah of the battery by 1,000, and multiply it against the C rating. For a 2200mah battery that has a 25C rating, 2200 divided by 1,000 = 2.2, and multiplied by 25 = 55. This means that the battery can give 55A of power continuously.
Continuous Discharge Rating: This would be the batteries ability to deliver amperage on a continuous level - for instance, a 5000mah battery rated at 25C continuous would be able to continually give out 125A (5000 divided by 1000 = 5 multiplied by 25 = 125). When choosing a battery, be sure that the battery can continually provide the proper amount of amps the motor is drawing; if the motor is drawing more than the battery can give out continuously, the battery will run very hot, puff up and fail.
Max/Burst Discharge Rating: All batteries have an ability to deliver a higher amount of amps for a short period of time - usually double the continuous amps the battery is rated for. This is good when the motor asks for a large amount of power on a very short scale. The max/burst rating should never be relied on to cover the amp draw on a continuous level, because as the name implies, the battery can only "burst" this level of amperage for a very short period of time, usually rated in seconds.
CHARGING SAFETY
Charging LiPos: LiPo batteries have many great advantages over many other batteries on the market, but due to their chemical layup, they require special care. Balancing the voltage of a LiPo batter is very crucial, because if the voltages of the individual cells differ by a modest degree, the cells have the chance of being over charged or drained too low, which will damage them.
Without going to a great degree of detail, LiPo batteries must never be charged over 4.20V per cell, and never be drained past 2.75V per cell. This may seem difficult to manage, but its not. All modern LiPo chargers have built in electronics that will not allow them to be charged over 4.20V per cell, and when flying, the ESC used in the aircraft/vehicle will usually alert the operator that the voltage is closing in on an unsafe level, which allows the user to power down the motor as to not over discharge the battery.
Balancing LiPos: When it comes to charging a LiPo battery, balancing is crucial. Most modern LiPo chargers have a built in balancer that will keep all the cell voltages in line within 0.01V. By properly balancing a battery when charging, the battery will last longer, operate more efficiently, and will be much safer in terms of use.
LiPo Safety: LiPo batteries offer great power & performance, but when not cared for in a proper manner, they can be unstable, and can even lead to a fire. If a LiPo battery is not charged with a dedicated LiPo charger, is charged in an incorrect fashion, or is damaged in any way, the battery may begin to swell and heat up, possibly resulting in a dangerous fire. Some LiPo batteries will begin to swell or puff when they have an internal chemical issue, and if continued to be used, could result in a fire or explosion. In short, proper LiPo maintenance will avoid these issues, and charging in a safe, appropriate manner will avoid any fire risks.
by: Alain.Nguyen
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