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Author Topic: LiPo information that may help you  (Read 915 times)

Offline rmfish

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LiPo information that may help you
« on: June 12, 2012, 03:28:11 PM »
Hello everybody, I would like to offer the following to try to pass on some information about LiPoly batteries. There are lots of myths and misinformation out there and since there is the potential for fire/explosion and other nasty things that might happen, what you read here could save you and your loved ones a great deal of hassle and/or pain.

So, who am I? Well I have been involved in the electronics field for about 50 years. I have been on the Electric  Committee of the Model Aircraft Association of Canada, (MAAC) for over 5 years and in that capacity, with the other committee members we try to answer all of the questions and pass on safety information to the MAAC membership. We, the committee have researched the LiPoly battery since it's release to the model users of the world quite a few years ago now.
The following is an absolute rule or law with no if's ands or buts, there can be no discussion,

A LiPoly battery must be charged with a LiPoly Charger, no other charger can be used, end of story.

One thing that rears it's head on a fairly regular basis, (having read your bulletin board you fellows are no exception) is the dreaded ?C? factor. What does a 1 or 2 C charge rate mean? The answer is quite simple really, C is a multiplication factor, if the battery manufacturer states that the 2000MAmpHr battery you just purchased has a C1 charge rate it means that you MUST charge the battery at 2 Amps or less, 2000 Miliamp hours = 2 amps, a 5000MAmpHour battery at 5 Amps or less. If the Manufacturer states that the battery has a charge rate of 2C then the 2Amp battery can be charged at 4Amps or less, the 5Amp battery at 10Amps or less. A further word of caution is in order at this stage, the harder you charge your LiPoly the shorter it's life. The number of charge/discharge cycles that a LiPoly has is not infinite, the higher you charge/discharge the battery, the shorter it's life.  It is far better to have two or three packs charged and ready to go when you go to a track. When you complete your first run, remove that pack and charge it at C1, use your second battery for your next run, charge it at C1 Etc Etc, wash and rinse.
The next thing that is frequently misunderstood  is the Discharge C rating. There are usually two numbers given. For example, the numbers might be,  Discharge at 25C ? 35C for 30 seconds. If this was your 2Amp battery above it would mean that you could apply a load of up to 50Amps continuously with a possible overload, of up to 70Amps for 30 seconds only. This is where most people come to a nasty ending. They think that they can apply a load of 70 Amps most of the time, ultimately, the battery fails, sometimes with spectacular results.
What you need to do is find out how many Amps your motor draws at full throttle. For this example let's say that your motor draws 25 amps wide open. The 25c battery above would be great for this motor, 2AmpsX 25C = 50Amps, your load of 25 amps would not be overloading this battery at all. The next thing you want to be looking at is run duration. Again, using the 2000MiliAmpHr battery above, 2000MiliAmpHr = 2Amp hours. In other words this Battery will provide 2Amps of energy for one hour with a load of 2Amps.
Now we can calculate the approximate run time of your car or truck, if you also fly an airplane this formula works for you too. When I was at RC Pit Stop I purchased a 2 cell LiPoly pack made specifically for cars, it is a 3700Ma battery, that's a 3.7 AmpHour battery. (It fits in my Glider perfectly too). In order to calculate an approximate run time for you car you would need to know the Amp draw at full throttle of your car motor. Lets say it is 15 amps. Now we need the Amp minutes of the battery---3.7Amps X 60 minutes = 222 Amp minutes. 222 Divided by 15 = 14.8. A run time of roughly 15 minutes. This will depend entirely on how accurate your motor current test results are. Of course, you do not run full throttle for the entire time but this would be the approximate run time if you did.
If you have any questions, feel free to ask and I will give you a no nonsense reply.
Robert.  |  In The Pits  |  Battery talk  |  LiPo information that may help you

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