Lipo Electric Batteries & Chargers > Important information on Lithium Polymer (LiPo) batteries

Charging/Safety IMPORTANT!

* If you're a type of person that prefers to push the limits of products, or be haphazard about following safety requirements then lithium technology is not for you. Read on to find out why.

When I got my first electric airplane "The FireCat" from Hobby Lobby, I thought that the 5 minute flights it gave me were rather pathetic, so I bought a 2 pack LiPo pack. I love 'em. It took longer to discharge the battery on the FireCat than the transmitter.

I wanted to know more information on these Lithium Batteries; so I started searching and studying more about them. I read all the news alerts of fellow RCer's getting hurt or batteries causing home fires and people getting hurt from lipo batteries. I tried charging them unattended and in series. I got rather worried setting the timer to start the charge before I got home from work so that I could go flying that evening. The charger brought the batteries on charge as programmed to do. But while I was still away from home on my way from work; my daughter almost called the fire department because the batteries blew up and smoked the house up from the basement all the way to upstairs and stunk highly. Boy! What a close call this was. Fortunately my charging area where the batteries were laid out was on a good piece of thick safety-glass and the electrical circuit for high and low voltage was protected to shut down in case of any electrical short or thermal overloads and set off the smoke alarm over the charging area. The alarms in the house were going off as my daughter came in the house. Can you imagine!! After this and think about what had happened and to why the batteries faulted, I decided I am a hard rock gasser. It is lucky that I did not try to charge these batteries while in the airplane or the house could have burned down. You see, when a LiPo battery is at a voltage above 4.2 volts, it will destroy the battery and, if not caught early, it will catch on fire. The problem with charging them in series is that the charger can only measure the sum of the voltages. Therefore if one battery pack is at 4.0 volts and the other is at 4.2, it can only measure the sum of the batteries, 8.2 in this example. When the charger measures 8.2, it will continue charging because 8.4 (the voltage of a fully charged 2 cell LiPo) has not yet been reached. Then if one of the cells reached 4.3 volts, it will catch on fire. At this point you could not predict exactly what would happen so we emailed an engineer of a battery company. (Thunder-Power)

What he basically said is this: While charging LiPo batteries in series is a very popular way to charge multi cell batteries, it is very dangerous. It is safe for the first couple of charges, but because of the manufacturing process, each battery has a slightly different discharge rate, therefore one battery will discharge slightly faster then the other one, and so the differences of the voltages of the two batteries will increase whenever they are used. To solve this problem, you must frequently test the voltages of the individual cells, making sure they are not any more than 30mV (.03 volts) apart. If they are, discharge the battery of the higher voltage with a 10k ohm (10000 ohm) resistor until they are the EXACTLY the same voltage.

I have only charged my pack once, so I'm not too worried, but some of you out there might not know this stuff, so do what the chief engineer of a battery manufacturing company tells you to. The technology that's made this possible is also changing the face of electric modeling at local fields and indoor flying sights across the country. Lithium Polymer batteries are the latest technology and offer several times the capacity/run time of previous generation Nickel Cadmium and Nickel Metal Hydride batteries, with reduced weight and size. Plus the latest generation LiPo (short for Lithium Polymer) cells have a low internal resistance, so they're able to provide high amp draw for powering high-performance and even large-scale models.

Thunder Power is the current performance leader in LiPo batteries. Imagine flying a GWS Tiger Moth or FD stick for over an hour on a single charge. Or imagine an indoor 3-D model that you can hover in a small office for over 15 minutes. With LiPo batteries you no longer have to imagine, as this type of performance is now a reality.

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Analyzing a LiPo Fire    (7 mb)

3 cell LiPo in enclosure    (6 mb)

LiPo Bunker Tests    (14 mb)

Thunder-power Home Page (open in new window)

Thunder Power LiPo Instructions and Guidance Acrobat PDF

More information on LiPo's at RC Hobbies (open in new window)

A very good report on LiPo Batteries (open in new window)

AMA Safety Information about LiPo Batteries Acrobat PDF